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FAMILIARIZATION OF WELL SITE GEOLOGY, DRILLING ACTIVITIES & REGIONAL GEO SCIENCE LABORATORY OF KRISHNA .GODAVARI BASIN A PROJECT REPORT Submitted by

JIFFIN P MATHEW

211915219030

KRIPA N VENU

211915219040

MADHAV SAI R

211915219043

In partial fulfilment for the award of the degree of BACHELOR OF TECHNOLOGY in PETROLEUM ENGINEERING RAJIV GANDHI COLLEGE OF ENGINEERING, SRIPERUMBUDUR

ANNA UNIVERSITY: CHENNAI 600025 APRIL 2019 1

DECLARATION

I declare that this dissertation work is an original report of my research, has been written by me and my colleague (mentioned in acknowledgement) and has not been submitted for any previous degree. The analysis and interpretation work is almost entirely my own work; the collaborative contributions have been indicated clearly and acknowledged. Due references have been provided on all supporting literatures and resources JIFFIN P MATHEW (211915219030) KRIPA N VENU

(211915219040)

MADHAV SAI R

(211915219043)

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CERTIFICATE

This is to certify that the dissertation report entitled FAMILIARISATION OF WELL SITE GEOLOGY,DRILLING ACTIVITIES AND REGIONAL GEOSCIENCE LABORATORY OF KRISHNA GODAVARI BASIN, submitted to the Department of PETROLUEM ENIGEERING, RAJIV GANDHI COLLEGE OF ENIGEERING , ANNA UNIVERSITY, in partial fulfilment for the award of the degree of Bachelor of technology in Petroleum Engineering, is a record of bona fide work carried out by Ms.Kripa n venu(Roll No. 211915219040), Mr.Jiffin p Mathew(211915219030) and Mr. Madhav sai r (211915219043) under my supervision and guidance All help received by her from various sources have been duly acknowledged. No part of this report has been submitted elsewhere for award of any other degree.

Mr. V. Siva Kumar DGM (Geology)

Dr. antony bertie morais HOD (PEROLEUM DEPARTMENT) RAJIV GANDHI COLLEGE OF ENGINEERING

Shri Rajkumar Koka DGM (Drilling activities)

Shri Pradeep M Durge Sr.Geologist (RGL)

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ACKNOWLEDGMENT The success and outcome of this project required a lot of guidance and assistance from various people and we are extremely privileged to have this all along completion of our project. All that we have done is only due to such supervision and assistance and we would not forget to thank them. First, we thank our Institution, RAJIV GANDHI COLLEGE OF ENGINEERRING for encouraging us to do this project and there were so many who shared valuable information that helped in successful completion of this project. We thank our Principal Dr. arokya raju, Our Head of Department Mrs. shema.b.sp, Mr. antony bertie morais and our project coordinator/ internal guide Dr. antony bertie morais (HOD – Petroleum Department) for helping us to gain an opportunity to work with highly esteemed organization like ONGC Limited. I respect and thank Mr. T vijay kumaran (Head Forward Base) ,Mr. B P Ram prasad (Head forward base) , for providing me an opportunity to do the project work in (Forward base, ONGC Rajahmundry) and giving us all support and guidance which made me complete the dissertation duly. I am extremely thankful to Staff Training Institute for providing me with the needed help and administrative support without which I would not have had this opportunity of Dissertation work in ONGC. I owe my deep gratitude to our project guide Mr. V. Siva Kumar (DGM, Geology) ,Mr. Rajkumar koka (DGM, Drilling activities) , Mr . Pradeep. M .Durge( Sr.Geologist) who took keen interest on our project work and guided us all along, till the completion of our project work by providing all the necessary information for developing a good system. I would not forget to remember B N . Mondal (CG), R.S Koijam (SG) , Mr. V. Venkanna (Mgr. (Programming),T . R Nanda (Dy .SG) ,M . Bhanu (Dy .SG(S)) Mr. Aneel Baireddy (Dy. SG) , A.K. jain ( GM (chemistry Dept)) ,K .V.V.Ram (DGM(chemistry Dept)) for their encouragement and more over for their timely support and guidance till the completion of our project work. I am thankful to and fortunate enough to get constant encouragement, support and guidance from all personnel’s of Geology and Geophysics Department (Core House, Forward Base, ONGC Rajahmundry) ,Planning–(Drilling Service) Department (ONGC) and Regional geosciences laboratory department (ONGC),which helped us in successfully completing our dissertation work.

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TABLE OF CONTENTS Chapter 1 . WELL SITE GEOLOGY 1.1 K G Basin 1.2 K G Basin evolution 1.3 Tectonic Elements of KG basin 1.4 Generalized Stratigraphy 1.5 Depositional Environment 1.6 Petroleum System 1.7 Geotechinal order (GTO) 1.8 Logging 1.8.1 Mud logging 1.8.2 Sampling logging 1.9 Mater log 1.10 Coring 1.10.1 Side wall coring 1.11 Field visit Chapter 2. DRILLING ACTIVITES 2.1 Drilling 2.2 Method of drilling 2.3 Drilling Rig 2.4 Drilling fluid 2.5 Casing and Cementation 2.5.1 Casing 2.5.2 Types of casing 2.5.3 Cementation 2.6 Well completion 2.6.1 Factors affecting well completion design 2.6.2 Method of well completion 2.7 Well stimulation 2.7.1 Introdution 2.7.2 hydralic Fraturing 5

2.7.3 Matrix acidizing Chapter 3. REGIONAL GEOSCIENCE LABORATORY 3.1 Geology lab 3.2 core lab Chapter 4. REFERENCES

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LIST OF FIGURES No Fig 1

Title Geographic location of K G Basin

Fig 2

Tectonic evolution of K G Basin

Fig 3

Horst & graben sequence in KG Basin

Fig 4

Geology of KG Basin

Fig 5

Stratigraphy of KG Basin

Fig 6 Fig 7

Principal depositional element from shelf staging area to basin Petroleum system of K G Basin

Fig 8

GTO of an exploratory step ot wall in K G Basin

Fig 9

A typical well log with data plotted against depth

Fig 10

Sample drilling cutting under a 10* microscope

Fig 11 Fig 12

An example of master log depicting drilling , mud , gas,& geological A sample core

Fig 13

A typical side wall coring setup

Fig 14

On shore rig model

Fig 15

Top drive system

Fig 16

PDC Drill Bit

Fig 17

Illustration of types of drilling profiles

Fig 18

Casing policy

Fig 19

Method of well completion

Fig 20

Well completion based on tubular configuration

Fig 21

Core sample

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Chapter 1 WELL SITE GEOLOGY 1.1 KG Basin: The Krishna- Godavari basin, a Pericratonic basin, is located along the East Coast of the Indian peninsula. It includes the deltaic plains of the Krishna and Godavari rivers and the interdeltaic regions. Geographically, the basin lies between Vishakhapatnam in the NE and Ongole in the SW. It spreads eastwards in an arc to the area of Archaean outcrop of the Eastern Ghat Complex, at Vijayawada and Guntur, to the deep water of the Bay of Bengal in southeast covering an area of 70,000 sq. km, (28,000 km onshore and 42,000 km offshore). Initially, its eastward limit was believed to coincide with the 200 m isobaths, however the basin edge is now defined as the edge of the continental shelf, close to the 2,000 m isobaths. The basin is about 60 km wide and 100 km long. It is believed to contain over 7 km of sediments, of which 3 km are Palaeozoic and Mesozoic and 4 km are Tertiary, though the basin fill may be nearer 10 km thick towards its eastern margin.

Fig 1: Geographic Location of Krishna-Godavari Basin

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1.2 KG BASIN EVOLUTION: India was part of the Gondwana Super-continent until the Mesozoic when it began tobreak up. The earliest sediments deposited, were possibly part of an early pre-rift sag phase, or part of the initial rift itself. Terrestrial sediments of Draksharama and Talchir formations were deposited during the Carboniferous, on the basement system, which was composed of gneisses and granites with a predominantly EWstructural trend (Eastern Ghat Trend). The initial onset of extension occurred during the Late Carboniferous, directed NE-SW, and resulted in the development of the NE-SW trending Pranhita-Godavari (PG) Graben. This filled with fluvial successions, typically composed of coal rich floodplain fines and sandstone channel systems, including the Barkar and Chintalapudi formations (and equivalents). The main rifting phase began in the Middle Jurassic, in response to the onset of break-up of the Gondwana Supercontinent. Extension directions were oriented NWSE, creating a NE-SW trough, parallel to the structural fabric of the Eastern Ghat Trend within the basement. This trough developed orthogonal to the PG Graben. The SE extent of the PG Graben was involved in the development of the younger rift, exerting some control on its structural configuration and development, and gradually becoming buried by the sediments of the true Krishna- Godavari Basin. The earliest feature to develop was the West Godavari Sub-basin, which was eventually divided at the end of the Jurassic by a central horst structure, the Kaza Ridge. The developing troughs filled with a Middle Jurassic to Barremian succession composed of fluvial, lacustrine and deltaic sediments (including the Golapalli Sandstone, Bapatla Formation, Krishna Formation and Kanukollu Sandstone), which due to the developing arrangement of troughs and highs, have complex lateral and vertical relationships. Marginal marine and possibly open marine conditions became increasingly common towards the end of this rift phase. The final break-up of Gondwana and the initiation of sea floor spreading in the Bay ofBengal occurred towards the end of the Neocomian. Active rifting and extension in the Krishna-Godavari Basin ceased in the Barremian, the basin then became subject to thermal and gravitational induced subsidence (Post Rift 1), as it began to develop into a passive margin basin within a pericratonic setting. This onset of thermal/gravity subsidence, coupled with tilting from the west (possibly as a result of mantle plume activity in Western India), resulted in peneplanation and subsequent drowning of the basin by a major marine transgression during the Aptian-Albian, which in filled the remnant rift topography. The shales deposited during this event, the Raghavapuram Shale, represent the first significant (widespread) marine incursion into the basin. Following this, a regressive phase began to develop, represented by fluvial to deltaic/marginal marine deposition (e.g. Tirupati Formation), passing out in deeper water conditions (Kaikalur Claystone). Utilizing NW to SE lines of weakness related 9

to the early rifting phase, the proto-Krishna and Godavari River systems (along with three minor systems) began to feed sediments into the basin toward the Late Cretaceous. A series of deltas became firmly established along the western margin of the basin (e.g. Bantumilli Formation), which shifted laterally as well as building out into the basin. These deltaic passed out into shelf and basinal depositional systems (e.g. Chintalapalli Formation), the deep water components of which were becoming more common and established. Tilting and continuing subsidence lead to ongoing structural development/reorganization of the basin, with (normal and strike-slip) faulting and movement of fault blocks very common. The end of the Cretaceous, and the beginning of the second post-rift phase (Postrift2) was marked by the basin wide extrusion of submarine basalts (Razole VolcanicFormation). Consisting of three major flow events, these interdigitated with the ongoing marginal to open marine sedimentation. Throughout the Tertiary, the deltaic to deep water deposition continued, with deep water deposition becoming very significant during the Neogene. Input from the developing major river systems during the Tertiary resulted in high sedimentation rates. Subsidence of the basin almost kept pace with this, but deltas were able to prograde rapidly eastwards, significantly narrowing the shelf. Shelf edge deltas developed as a result, overloading the shelf edge. This differential loading and instability induced gravitational collapse, resulting in the development of growth features such as listric faults and rollover anticlines, along with toe thrusts and shale diapirism in the deeper basin. The narrow shelf and collapse features resulted in rapid facies changes across the basin. Relative sea-level changes and minor reorganizations of the basin geometry resulted in several unconformities, the most significant of which, during the Middle Miocene, resulted in significant erosion across the basin. During the Paleogene, the developing sedimentary wedge included the Vadali Sandstone (fluvio-deltaics), Pasarlapudi Formation (shallow shelf) and the Palakollu Shale and Vadaparru Formation (outer shelf to deep marine). Towards the end of the Paleogene, calcareous sedimentation towards the edge of the shelf became important (Bhiminapalli Formation) consisting of argillaceous limestones and calcarenite shoals. During the Late Oligocene and Neogene, clastic dominated delatic to deep marine sedimentation became firmly established. Within this depositional system, the Krishna and Godavari Rivers effectively built out two major sedimentary lobes at their respective mouths (furthering the differential loading). The Ravva Formation developed during the Miocene, but was subject to significant erosion during the Late Miocene. The Rajahmundry Sandstone and Godavari Formation were deposited upon this erosional surface during the Plio-Pleistocene.Within these Neogene depositional systems, deep water turbidite deposition was particularly important, resulting in the significant development of distributary channels and basin floor fans. During the drift phase of the evolution of the Krishna-Godavari Basin, the basin 10

drifted northwards from a position close to 25 degrees south in the Middle Cretaceous to 25 degrees North in the Eocene-Oligocene.

Volcanic activity: Upper Development Cretaceous of unidirectional Lower Paleocene Regression & tilt: Cretaceous

Emergence of basin with seaward progradation: Paleocene to Recent

Breakup into Rift valleys: Lower Formation of Gondwana Cratonic basin: Perios Carboniferous Permian Fig 2: Tectonic Evolution of KG Basin

1.3 TECTONIC ELEMENTS OF KG BASIN: The five major tectonic elements of basin are:  Krishna Graben  Bapatla Horst  West Godavari Sub basin  Tanuku Horst  East Godavari sub basin

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Fig 3: Horst & Graben sequence in KG Basin

Fig 4: Geology of KG Basin

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1.4 GENERALISED STRATIGRAPHY: The basin contains thick sequences of sediments with several cycles of deposition ranging in age fromLate Carboniferous to Holocene. A major delta with a thick, argillaceous facies that has prograded seaward since the Late Cretaceous is a hydrocarbon exploration target. Magnetic and gravity data predicted the basin architecture, which was subsequently confirmed by a multichannel seismic survey. The basin is divided into sub basins by fault-controlled ridges. Sediments accumulated in sub basins more than 5 km thick. Above the basement ridges, thin sediments are found. Until the Jurassic period, sediments were deposited in the rift valley and in topographic lows. This sequence is completely overlain by a Lower Cretaceous, transgressive sedimentary wedge. Later, continued delta progradation characterized basin sedimentation (Godavari clay).

Fig 5: KG Basin Stratigraphy

Fig 5: Stratigraphy of KG Basin

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1.5 DEPOSITIONAL ENVIRONMENT: The depositional environment of early Cretaceous formation is of fluvio-deltaic setting with good sands development in channels and delta distributaries. The late Cretaceous formations are of shallow marine setting with sand developments mostly in tidal channels, bars and sandy flats. The gamma ray and resistivity logs are called typical lithology indicative logs for sililiclastic environments. The log shapes in gamma ray with resistivity are related to sediment character and depositional environment. Four distinct depositional systems have been recognized in Krishna Godavari basin. These are: Godavari delta system, Masulipatnam shelf slope system and Nizampatinam shelf –slope system and Krishna delta system. The maximum thickness of the sediments in Krishna Godavari basin is around 5000 m. controlling factor of the thick pile of sediments is presence of long linear Gondwana rift valley. Paleontological evidences suggest a period of slow sedimentation and subsidence but changes in water depth during deposition.

Fig 6: Principal Depositional Elements from Shelf Staging area to Basin plain

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1.6 PETROLEUM SYSTEM A petroleum system can be summarized as an independent stratigraphic compartment within which the three primary requisites for hydrocarbon accumulation that is, source, and reservoir and cap rocks can occur. The source rocks are mainly argillaceous sequences deposited in reducing environment and contain marineplant organic matter which can be converted to hydrocarbons under certain pressure and temperature conditions which is termed as maturation. In the basin, source facies are known in Carboniferous shalesBarakars, Lower Cretaceous Raghavapuram shale, Paleocene shales and lower Miocene argillaceous sections in different parts of the basin. The reservoir rocks are porous and permeable rocks which not only host the hydrocarbons and allow them to flow within it for a commercial accumulation. On the other hand, the impervious rocks like shales,basalt, carbonates act as cap rocks to arrest the movement of hydrocarbons in the reservoirs both vertically and laterally to form a commercial accumulation. The entrapment styles include – low amplitude structural closures, fault closures, wedge-outs, unconformity controlled structures and permeability barriers in different reservoirs. The major petroleum occurrences include Mandapeta gas field from a Permian sandstone, KaikaluruLingala oil fields from a lower Cretaceous clastics, Tatipaka-Pasarlapudi gas field and Mori oil field from lower Eocene sandstones, Ravva oil field in Miocene clastics off Amlapuram coast. However, the pre-Cretaceous and Cretaceous hydrocarbon fields are more stratigraphically controlled and hence bear relatively less potential, whereas fields in Tertiary sequences are of strati-structural in nature and hence have higher potential. Krishna-Godavari basin is a proven petroliferous basin with commercial hydrocarbon accumulations in the oldest Permo-Triassic Mandapeta Sandstone onland to the youngest Pleistocene channel levee complexes in deep water offshore. The basin has been endowed with four petroleum systems, which can be classified broadly into two categories viz. Pre-Trappean and Post-Trappean in view of their distinct tectonic and sedimentary characteristics. Seismic imaging of Pre-Trappean section poses problems in terms of data quality.

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PETROLEUM SYSTEM

PRE TRAPPEAN

Kommugudem Mandapeta-Red Bed Petroleum system

RaghavapuramGollapalli- TirupatiRazole Petroleum system

POST TRAPPEAN

Palakollu- Pasarlapudi Ptroleum system

Vadaparru Shale Matsyapuri/ Ravva Formation- Godavari clay petroleum system

Fig 7: Petroleum System of KG Basin

1.7 GEO TECHNICAL ORDER (GTO) The programming of a well which covers all geological and technical data and guides the course of the well, is termed as Geotechnical order (GTO) and is jointly prepared by Geologist, Driller and Chemist. The GTO furnishes the guide to everyone connected with the drilling of the well. It provides a guide line and work plan and can be modified if and when required. The geological part of the GTO, incorporates the expected lithological sequence & stratigraphy, proposed coring intervals, geophysical surveys (logging, RFT etc), policy on collection of drilling cuttings, zones of probable caving and mud loss, expected oil and gas shows, formation temperature and pressure. It also includes the recommended mud program showing details of mud parameters to be maintained at different intervals. The casing policy depending upon the geological nature of the rocks, depth of the well and technical problems likely to be faced, is decided accordingly. The drilling related data of the GTO is prepared by drilling engineers, specifies the drilling policy, under appropriate head. A forecast of drilling time is also added as a curve, taking into consideration all the operations proposed to be carried out in the well.

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Fig 8: GTO of an Exploratory Step-out well in KG Basin

1.8. LOGGING: Wire-line logging or Electro logging is the practice of making a detailed record of geophysical measurements of the geological formations penetrated using various instruments housed in a tool conveyed to bottom by a wire-line. These can be recorded in either open hole or cased hole. These tools can be divided into lithological, porosity and special logs. Electro logs give vital information on hydrocarbon bearing zones, lithology, thickness and depth of the potential reservoirs, formation boundaries, and geological co-relations.

There are different types of logs:

i. Gamma ray log: Itis a method of measuring naturally occurring gamma radiation to characterize the rock or sediment in a borehole. Different types of rocks emit different amounts and different spectra of natural gamma radiation. In particular, shales usually emit more gamma rays than other sedimentary rocks, such as sandstone, gypsum, salt, coal, dolomite, or limestone because radioactive potassium is a common component in their clay content, and because the cation exchange capacity of clay causes them to adsorb uranium and thorium. Gamma radiation is 17

usually recorded in API units, a measurement originated by the petroleum industry. Gamma logs are affected by the diameter of the borehole and the properties of the fluid filling the borehole. A common gamma-ray log records the total radiation, and cannot distinguish between the radioactive elements, while a spectral gamma ray log can. An advantage of the gamma log over some other types of well logs is that it works through the steel and cement walls of cased boreholes. It is also used for correlations in cased holes and for depth control along with CCL for perforations.

ii. Spectral logging is a specialized gamma radiation logging to distinguish the three component decay chains (potassium, uranium, and thorium) by the wavelengths of their characteristic gamma emissions. The characteristic gamma ray line that is associated with each component: 

Potassium : Gamma ray energy 1.46 MeV



Thorium series: Gamma ray energy 2.62 MeV



Uranium-Radium series: Gamma ray energy 1.76 MeV

iii. Spontaneous Potential log (Self-potential log or SP log): It works by measuring electric potential difference (measured in millivolts) between electrode at the bottom of the borehole and a grounded electrode at the surface. It is generally run along with the gamma ray.

Clays and shales will generate one charge and permeable formations such as sandstone will generate an opposite one. This build-up of charge is, in turn, caused by differences in the salt content of the well bore fluid (drilling mud) and the formation water (connate water). The potential opposite shales are called the baseline, and typically shifts only slowly over the depth of the borehole. The salt content of the connate water will determine the SP curve to deflect either +ve or –ve against a permeable formation.

If the salinity of the mud is similar to the formation water then the SP curve may give little or no response opposite a permeable formation; if the mud is more saline, then the curve has a positive voltage with respect to the baseline opposite permeable formations; if it is less, the voltage deflection is negative. Mud invasion into the permeable formation can cause the deflections in the SP curve to be rounded off and 18

to reduce the amplitude of thin beds. SP data can be used to locate the permeable formations; the boundaries of these formations; and to determine the values for the formation-water resistivities.

iv. Calliper log: It is a set of measurements of the size and shape of a bore hole commonly made when drilling oil and gas wells. This can be an important indicator of cavings or shale swelling in the bore hole & presence of the mud cake. It is constructed with two or more articulated arms that push against the borehole wall to take measurements. The calliper log is printed as a continuous series of values of hole diameter with depth against the drilled bit size.

v. Resistivity log: It is a method of logging that works by characterizing the rock or sediment in a borehole through measuring its electrical resistivity by sending current into formation. Resistivity is the ability to impede the flow of current through a rock and is expressed as ohm-meter/meter or ohm. Resistivity logs are either later log or Induction type. The laterolog tools use electrodes to inject a current on the formation and to measures voltages at different points in the tool. The induction tools use coils and magnetic fields to develop currents in the formation whose intensity is proportional to the conductivity of the formation. The intensity of these currents is measured on receiver coils in the tool. Most rock materials are essentially insulators, while their enclosed fluids (saline water) are conductors. Hydrocarbon fluids are an exception, because they are almost infinitely resistive. High resistivity values may indicate a hydrocarbon bearing formation. vi. Sonic log: It shows a formation’s interval transit time, designated as ‘dt’. It is a measure of a formation’s capacity to transmit sound (compressional) waves and is expressed in microseconds per foot. Geologically, this capacity varies with lithology and rock textures, notably porosity. The sonic tool is only capable of measuring travel time. It is proportional to the compaction trend of sediment with depth. Quantitatively, the sonic log is used to evaluate porosity in liquid filled pores.

vii.Density log: It determines rock bulk density along a wellbore. This is the overall density of a rock including solid matrix and the fluid enclosed in pores. A radioactive source in the tool continuously emits medium energy gamma rays, which collide with 19

electrons in the nuclei of the formation. With each collision, gamma rays lose some energy due to Compton scattering and reach detector, which in turn counts them with a sufficient energy levels. The n of Compton scattering collisions is related directly to the no. of electrons present in the formation, and hence the bulk density of the formation (no. of electrons per cubic cm of the formation). Geologically, bulk density is a function of the density of the minerals forming a rock (i.e. matrix) and the enclosed volume of free fluids (porosity).

viii. Neutron log: Itemploys a neutron source to measure the hydrogen index in a reservoir, which is directly related to porosity. The Hydrogen Index (HI) of a material is defined as the ratio of the concentration of hydrogen atoms per cm3 in the material, to that of pure water at 75oF. The source mounted in Sonde emits high energy neutrons, which collide with formation nuclei. With each collision, neutrons lose energy and are scattered, while some are captured by other nuclei like Hydrogen. The energy loss is greater when collision takes place with nucleus of equal mass such as Hydrogen. Detector in the Sonde detects the slowed down scattered neutrons.

As hydrogen atoms are present in both water and oil filled

reservoirs, measurement of the amount allows estimation of the amount of liquidfilled porosity. A cross-over between Density and Neutron (plotted in reverse scale) reading in a LDL-CNL Log indicates the presence of possible hydrocarbons in the formation.

ix. Cement Bond Log: Acoustic logging is used for determination of cement bond in cased wells. This type of log is most often referred to as a Cement Bond Log (CBL). Acoustic signals propagated in steel casing are observed to have large amplitude in free (un-cemented) casing. The reason is because much of the energy is retained in the casing. The opposite effect is found in casing that is in contact with a solid such as cement. The casing signal is much smaller in cemented casing because the energy is coupled into the surrounding cement and formation.

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. Fig 9: A typical well log with data plotted against depth.

1.8.1 APPLICATION OF LOGGING:

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1.

Their traditional use in exploration for stratigraphic correlation of formations

and to assist with structure and iso-pach mapping. 2.

To define physical characteristics of rocks such as lithology, porosity, pore

geometry, permeability, and other petro physical parameters. 3.

To identify productive zones, to determine depth and thickness of zones, to

distinguish between oil, gas, or water in reservoir, and to estimate reserves.

1.8.2. MUD LOGGING: Mud Logging is a continuous monitoring system of the various parameters during drilling of exploratory/ development wells for the detection of hydrocarbon bearing zones. Besides this, various studies for detecting/predicting of over pressured horizons are also simultaneously carried out using various instruments housed in mud logging unit. The geo-logging on a well is carried out by geologists who keep record of various parameters on a log sheet called Master log and Geo pressure logs which depict a graphical presentation of various operations, as well as record the pore pressure during drilling of well. At a drill-site, a Mud Logging Unit (MLU) for the real-time monitoring of several parameters will assist Geologist. MLU acquires both online and offline data acquisition by deploying several sensors at different places in rig. Online data acquisition includes real time monitoring of around 24 parameters under three broad categories viz., drilling, mud and gas parameters.

Mud logs are well logs prepared by describing rock or soil cuttings brought to the surface by mud circulating in the borehole. In the oil industry, they are usually prepared by a mud logging company contracted by the operating company. One parameter a typical mud log display is the formation gas (gas units or ppm). “The gas recorder usually is scaled in terms of arbitrary gas units, which are defined differently by the various gas detector manufactures, in practice, significance is placed only on relative changes in the gas concentration detected. “The current oil industry standard mud log normally includes real-time drilling parameters such as rate of penetration (ROP), lithology, gas hydrocarbons, flow line temperature (temperature of the drilling fluid) and chloride but may also include mud weight, estimated pore pressure and corrected d-exponent (corrected drilling exponent) for a pressure pack log. Other information that is normally notated on a mud log include directional data (deviation 22

surveys), weight on bit, rotary speed, pump pressure, pump rate, viscosity, drill bit info, casing shoe depth, formation tops, mud pump information.

MUD PARAMETER: The mud loggers monitor different mud parameters. These mud parameters will help in giving information about the formation that is being drilled or that has been already drilled. The mud parameters that are studied are:

i. Mud weight: It is a differential pressure sensor located in active mud tank and ditch possum belly to measure mud specific gravity in going and out coming. A drop in out coming mud weight could be due to gas influx/kick or due to addition of water or chemicals at surface. A rise in out coming mud weight could be due to addition of barites at surface or due to excess water loss to formation which may lead to stuck pipe later.

ii. Mud Temperature: It is a resistivity-temperature detector mountedin active mud tank and ditch possum belly to measure mud temperature in going and out coming. Sudden rise in temperature out may indicate water influx and a sudden drop can be result of gas influx.

iii. Mud Conductivity: It is mounted on suction pit and ditch possum belly and it measures the changes in mud resistivity depending upon changes in mud salinity.Salt water influx may raise Conductivity out and fresh water/oil/gas influx may show a drop in mud conductivity. But these changes can also be due to addition of water/chemicals at surface into the mud. iv. Mud Flow Rate or Returns (%): It’s a paddle type sensor fitted in flow-line to monitor the % of return flow from well. Flow ingoing is measured by SPM.

v. Pit Levels: They are proximity ultrasonic sensors or floater type mounted in all mud pits, which in turn gives the total pit volume. Any gain or loss can be effectively monitored with these sensors.

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1.8.3 SAMPLING LOGGING: Sample collection and logging is the backbone of all subsequent geological interpretation. It consists of (i) collection of cuttings at regular intervals (e.g. every 5m) & processing; (ii) fluorescence & cut study; (iii) sample description.

Fig 10: sample drill cutting under a 10-x microscope.

The purpose of sample logging is to:

i)

Evaluate the formations penetrated and the hydrocarbon shows encountered.

ii)

Determination of sub-surface contacts, for using data in sub-surface mapping.

iii)

Determination of physical characteristics of sediments.

The cutting samples are collected at the shale shaker at the interval decided by the company as per lag time. The sample is properly washed to remove mud and sieved with proper mesh to remove the caving’s. Two sets of samples are collected among which one is used for laboratory analysis. The samples are washed and dried and are subjected to fluorescence/cut/microscopic studies. The collected washed sample should be studied properly under binocular microscope.

The suggested order for the sample description is as follows:

1) Rock type (Sand/Sandstone, limestone, shale, etc.) with percentage. 24

2) Colour. 3) Hardness. 4) Texture including grain size, roundness and sorting. 5) Cement and/or matrix. 6) Fossils. 7) Accessory constituents. 8) Sedimentary structures. 9) Apparent Porosity. 10) Oil and gas shows.

The samples are then checked for the presence of any oil under Ultra-Violet rays using Fluoroscope. The fluorescence, if any, is noted for intensity, colour and distribution. Normally the gas bearing horizons do not give any fluorescence. The colour of fluorescence under UV light varies from brown, blue, dark green, gold, yellow to white for various hydrocarbon-bearing cuttings. In most cases, the heavier oils have dark brown stains, while light oils tend towards colourless to white. In other words, type of fluorescence is dependent on Specific gravity of crude oil.

It may be noted that fluorescence in the sample does not necessarily indicate the presence of hydrocarbon straight away. The calcareous rock units like limestone and dolomites will give the mineral fluorescence. Various reagents like chloroform, nHexane, acetone, etc. are used to cut/cut fluorescence studies to distinguish the mineral fluorescence from hydrocarbon shows. The calcareous units do not show any cut with solvents; but the hydrocarbons will dissolve in solvent and will stain the solvent with positive cut fluorescence. In oil well terminology, terms positive cut and negative cut are used for reporting the fluorescence of hydrocarbons from that of non-hydrocarbon bearing substance.

1.9. MASTER LOG: Master Logging is the practice of making a detailed record (a well log) of the geologic formations penetrated by a borehole. The log may be based either on visual inspection of samples brought to the surface (geological/logs) or on physical measurements made by instruments lowered into the hole (geophysical logs). Some

25

types of geophysical well logs can be done during any phase of a well’s history: drilling, completing, producing, or abandoning. Well logging is performed in boreholes drilling for the oil and gas, groundwater, mineral and geothermal exploration, as well as part environmental and geotechnical studies. In the oil industry, the well and mud logs are usually transferred in ‘real time’ to the operating company, which uses these logs to make operational decisions about the well, to correlate formation depth with surrounding wells, and to make interpretations about the quantity and quality of hydrocarbons present. Specialists involved in well log interpretation are called log analysts.

Fig 11: An example of Master-log depicting drilling, mud, gas & geological parameters.

1.10. CORING: Coring is used in order to obtain a sample of rock from a borehole that can be seen, smelled, felt and mechanically and chemically examined and analyzed. The primary objective for coring is to determine if a certain reservoir contains oil and gas in commercial quantities. In addition to evaluating the oil and gas content, the 26

determination of the lithology and mineral constituents. In complicated provinces, the cores areused to determine the dip and strike of the rock. In exploratory wells, the analysis of cores is a major source of data for petroleum engineering studies. Porosity, permeability and other engineering, petro physical parameters can be accurately quantified in the lab.

Fig 12: A sample core

Small samples of the core need to be checked under ultraviolet light for any fluorescence and solvent cut studies. The depth interval, recovery of the core, lithology, macroscopic observations such as colour, structures, sorting, hydrocarbon shows observed etc.

Once the core has been described and wrapped, it is placed back in its respective boxes. Individual pieces should be marked with top arrow and number. Arrangements are made such that the core does not shift within the box during transport. The outsides of the boxes should be marked with information that can be used to identify the formation, depth and well.

1.10.1. SIDE WALL CORING: Sidewall cores (SWC) are small cores (usually 1” diameter x 2.5” long) taken from the walls of formation from a well after the formation has been drilled. Their position is chosen after studying electro-logs, cuttings and hydrocarbon shows during drilling. In a single run, around 30-48 SWCs (depending type of gun) can be collected from a bullet type or percussion SWC guns connected to the sonde via wires (Fig. 13 ). It is a cost-effective and time saving technique compared to conventional coring. SWCs 27

provide excellent information on reservoirs, where conventional cores are missed. They give direct inputs on rock type, texture, presence of hydrocarbons, porosity, permeability, rock mechanics, etc.

Fig 13: A typical side wall Coring Setup

1.11 FIELD VISIT: The well that was being drilled was a development well. It was an ‘L profile’ well. The previous development well that were drilled were ‘S profile’. All the crew of the well carries out drilling according to the GTO of the well. If need be, the well site geologist will deviate from the GTO as per the conditions of the well. He is provided with all the drilling, mud parameters in real time whilst the drilling is happening, to take decisions about what should be done next. The data includes Depth, Bit Depth, TVD (for deviated wells), ROP, WOB, RPM, Rotary Torque, Mud weight in, Mud Weight out, Mud weight temperature, Mud viscosity, etc.

The chemist in the well crew helps in maintaining the mud properties as per the geological conditions that may occur during the drilling. The property that affects the mud most is the mud density. It is increased by adding weighting materials like barites. If the mud weight should be decreased, it is diluted with water.

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Fig 14: Onshore Rig Model

The rig used TDS (Top Drive System) which is the advanced version of travelling block without Kelly. A top drive is a mechanical device on a drilling rig that provides clockwise torque to the drill string to drill a borehole. It is an alternative to the rotary table and Kelly drive. It is located at the swivel's place below the traveling block and moves vertically up and down the derrick.

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Fig 15: Top Drive System

During drilling, logging was difficult and hence TLC (Tough Logging Conditions) was used. The TLC (Tough Logging Conditions) system is a pipe-conveyed method that uses special equipment to connect logging tools to drill pipe. This system is used to log wells with difficult borehole conditions such as high deviation angle, multiple doglegs or washouts. The system can then log downwards by adding drill pipe.

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Fig 16: PDC Drill Bit

The Mud Logging unit analyses the mud that is being circulated in and out the well. It maintains the parameters required to drill the well. The mud circulates the cuttings from the borehole to the surface. These cuttings are separated from the mud in the shale shaker and are analysed by the geologist. The mud is filtered and recycled by using solid control equipment like desanders, desilters and degasser. The gas that is obtained during drilling is collected by the MLU and is analysed by the mud loggers. Different C1, C2, C3, C4, H2S, CO2 concentrations are measured.

H2S is a harmful gas. If H2S is present in small concentrations, it can be detected, by odour but encountered in large quantities, is hard to detect by odour. If it is encountered while drilling, the drilling is immediately stopped and measures are taken to counter the presence of H2S. The well chemist adds absorbing and adsorbing agents that help in removing the H2S.

One should always wear a helmet and gas mask whilst in a well. Safety is given importance while drilling. Reservoir sections explained the various parameters to analyse the properties of a reservoir. The tools can be majorly classified in two types:

31

i) Mechanical Tools: As the name suggests, the working principle of the tool is mechanical. These can be used to analyse the pressure of a reservoir. The drawback of the mechanical tools is that they are limited to one parameter. For the measurement of pressure in a reservoir, the mechanical tool consists of a spring which contracts with the increase in pressure and the reading is logged.

ii) Electronic Tools: These tools utilize modern technology to measure various parameters as once. For the measurement of pressure, piezoelectric materials like Quartz are used. These are much more accurate than the Mechanical tools.

Oil and gas companies in the development of new fields use reservoir simulation models. In addition, models are used in developed field where production forecast is required to help make investment decisions. The process is carried out in mainly three steps:

1. Seismic equation derived from the reflected seismic waves collected. 2. Processing of the seismic equation. 3. Interpretation of the developed data.

Seismic sources are generated by various materials such as explosives, vibratos, etc. these sources are generated from the surface into the land which would reflect back at various refractions & these reflected waves are collected by geophones (Onland) or hydrophones (Offshore).

The system used is of high configuration consisting of multiple monitors operating Unix Operating System. The software used to develop and interpret the collected data is Landmark Software or Petrel Software.

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Chapter.2

DRILLING ACTIVITIES

2.1 Drilling: As the saying goes ‘oil is where you find it’, the ultimate tool to find out the new source of the petroleum is drilling of an exploratory well. Once the proposed area is narrowed down through geological, seismic and other studies, the exploration starts with a wild cat well. Once the oil/gas pool is delineated by several test wells and step-out wells, the area will be taken up for systematic exploitation by drilling development wells. Drilling in hydrocarbon exploration is a cutting process that uses a drill bit to cut a hole into the Earth’s substructures to find the oil and/or gas deposits.

The drill bit cuts the subsurface formations by applying pressure and

rotation. The drilled cuttings at the bottom are lifted with a circulating fluid (mostly water based bentonite mud with barite).

2.2 Methods of Drilling: A. Cable Tool Drilling: The earliest known method, where drilling tool is attached to a rocker beam, which creates an oscillatory movement so that the bit falls rapidly and creates successive blows at bottom. The first hole was drilled by this method on 27th August, 1859, by Colonel Drake in Pennsylvania. B. Rotary Drilling: Drilling by the hydraulic rotary technique is widely in use. The mechanisms of rotary drilling are: i) a string of drill-pipe with a cutting bit is rotated, ii) the bit is lowered as the formation drills out under the bit, and iii) the bit is cooled and lubricated with drilling fluid, which also brings the debris to surface so that the bit can drill further. All the drilling equipment comprises a ‘drilling rig’ and are powered with diesel engines . A vertical derrick or mast holds the traveling block assembly, which holds the drill pipe and is in turn, held by the rotary line feeding over the crown block from the draw works. Another component is the mud system which is activated by the slush pumps. The pump sucks drilling fluid from the pits and pumps the fluid through

33

the rotary hose, swivel, Kelly, drill pipe, drill, collars, and finally the bit. The fluid passes through the bit with a jetting action which assists the bit in cutting the hole. C. Dyna Drilling: A down hole drilling motor driven by drilling mud/ air/ gas/ water that imparts rotary motion to the bit connected to the tool, thus eliminating the need to turn the entire drill stem to make the hole. D.Directional Drilling: Conventional wells are drilled vertically from the surface straight down to the pay zone. Directional drilling is the science of directing a wellbore along a predetermined course to a target located at a given distance from the vertical. Measurement While Drilling (MWD) is a real-time system developed to perform drilling related measurements (viz., azimuth and inclination) downhole and transmit information to the surface while drilling a well using a downhole mud motor & other tools. Directional drilling can be inclined/slant or horizontal . i) Inclined/ Slant Drilling: Drilling at an angle from perpendicular (commonly 30° to 45°).

This approach

minimizes surface environmental disturbance. For example, oil reserves under a lake/ shallow sea can be tapped by a slant hole drilled from on shore. Multi-lateral wells can be drilled in this method such as four, six, even eight slant wells are drilled from one "pad" (i.e. well-site). Thus, production of valuable oil reserves is effectively harmonized with conserving the environment. Different borehole patterns in inclined drilling are L-type, S-type and J-type. ii) Horizontal Drilling: Using technologies such as RSS (Rotary Steerable System), drillers are able to execute a sharp turn and drill horizontally along a thin pay zone.

It allows

considerable increase in the recoverable petroleum and in turn production rates in whole field. It avoids water/gas coning and draw-down related problems and environment sensitive issues. This technology is now widely in use in Shale gas & CBM exploration, SAGD (Steam Assisted Gravity Drainage) for heavy oil production.

34

Fig. 17: Illustrations of types of Drilling profiles: (A) from left to right- Vertical, Slant & Horizontal drilling. (B) Types of Slant/ inclined drilling: L, S & J types. 2.3 DRILLING RIG (Fig 18)

1. 35

2. Mud tank 3. Shale shakers 4. Suction line (mud pump) 5. Mud pump 6. Motor or power source 7. Vibrating hose 8. Draw-works 9. Standpipe 10. Kelly hose 11. Goose-neck 12. Traveling block

15. Monkey board 16. Stand (of drill pipe) 17. Pipe rack (floor) 18. Swivel (On newer rigs this may be replaced by a top drive) 19. Kelly drive 20. Rotary table 21. Drill floor 22. Bell nipple 23. Blowout preventer (BOP) Annular type 24. Blowout preventer (BOP) Pipe ram & blind ram 25. Drill string 26. Drill bit 27. Casing head or Wellhead

13. Drill line 14. Crown block 15. Derrick

2.4 Drilling Fluid: Drilling fluid is used while drilling oil and natural gas wells and also used for much simpler boreholes, such as water wells. Liquid drilling fluid is often called drilling mud. The three main categories of drilling fluids are water-based muds (which can be dispersed and non-dispersed), non-aqueous muds (oil-based mud), and gaseous drilling fluid, in which a wide range of gases can be used. The various types of fluid generally fall into a few broad categories: A.

Water-Based Mud (WBM): A most basic water-based mud system begins with water, then clays and other chemicals are incorporated into the water to create a homogenous blend. The most common clay used is bentonite, frequently referred to in the oilfield as "gel". Many other chemicals (e.g. K- formate) are added to a WBM system to achieve various effects, including viscosity control,

36

shale stability, enhance drilling rate of penetration, cooling and lubricating of equipment. WBM can be either simple clay muds or polymer muds. B.

Oil-Based Mud (OBM): Oil-based mud can be a mud where the base fluid is a petroleum product such as diesel fuel. Oil-based muds are used for many reasons, some being increased lubricity, enhanced shale inhibition, and greater cleaning abilities with less viscosity. Oil-based muds also withstand greater heat without breaking down. They also have cost and environmental constraints.

C.

Synthetic Oil based fluid (SOBM): Synthetic-based fluid is a mud where the base fluid is synthetic oil. This is most often used on offshore rigs because it has the properties of an oil-based mud, but the toxicity of the fluid fumes are much less than an oil-based fluid.

Functions of a drilling fluid: Remove cuttings from well; suspend and release cuttings; control formation pressures; seal permeable formations; maintain well-bore stability; minimizing formation damage; cool, lubricate, and support the bit and drilling assembly; transmit hydraulic energy to tools and bit; ensure adequate formation evaluation; control corrosion (in acceptable level); and facilitate cementing and completion. 2.5 Casing and Cementation: The idea of landing the casing, in the wells being drilled for exploration/ exploitation of hydrocarbons, is for supporting the walls of the wells, prevent caving tendencies of unconsolidated formation, and to exclude fluids in other intervals than that from which it is desired to be produced. Gas and oil must be confined within the well casing so that they may not escape into overlying formations. The main purpose of casing & cementation is to achieve the effective zonal isolation and pressure control.

2.5.1. Casing policy: Casing policy (3 or 4 or 5 casing) will be designed based on the target depth, formation pressures, temperatures and other geological & testing factors. Standard casing sizes are given below: Bit size

Casing size

Conductor casing

30”

37

26”

20”

18 ½”

13 3/8”

12 ¼”

9 5/8”

8 ½”

7”

6” or 5 7/8”

5”

2.5.2. Types of Casing i. Conductor Casings: The well is usually spuded with a bigger diameter of hole (26”). If drilling begins in soft formation, a false conductor casing which is the largest diameter casing in the well is normally lowered to a depth of about 500ft depending upon the local condition. ii. Surface casing String (20”):Surface casing is the first string of casing set in a well and is lowered for the purpose of supporting the walls of the hole in unconsolidated surface formations, shutting off surface water or shallow fresh water zones, and as an anchor string for blowout preventer equipment. iii. Intermediate Casing String: After 20” casing is set, the hole is deepened to certain desired depth, which is dependent upon the area and projected depth of the well. The idea of lowering the intermediate string of casing is to case the caving formations, upper gas or oil sands. The most common intermediate casing sizes are 9 5/8”, 10 ¾” and 13 3/8”. iv. Production Casing :When the oil and /or gas producing horizon is approached or after it has been drilled, it is then necessary to set the string of casing into which the oil and/or gas from the formation will flow. The common sizes are 4 ½ “, 5 1/2”, 7” and 9 5/8”. This can be either liner casing or total casing .

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Fig. 19: (a) 3 phase casing policy, (b) 4 phase casing policy

2.5.3. Cementation After running in the casing string to the desired depth, it is cemented in place. Thus the wall of hard solid cement is formed between the outside of the casing and the wall of the hole to shut off high pressure zones, water bearing formations, mud loss zones, etc. The cement further serves to keep the hole from caving which might collapse the casing and to make the casing secure in the hole. Basically the cement used in cementing wells is ordinary Portland construction cement. Control of the fineness of grind and the addition of certain chemicals may be used to accelerate or delay the hardening time, the latter of which can be of great importance in deep and in high temperature wells. The initial casing in a well is cemented to the surface while the inner casings are normally cemented upto a level slightly above the shoe of the outer casing. Before cementation, it is necessary to calculate the volume of cement slurry needed for the job.

i. Primary Cementation: Primary cementation is carried out after lowering the casing. A good primary cementation is always preferable since it saves time and money and prevents formation damage due to excessive secondary squeeze jobs.

39

ii. Secondary Cementing Methods (Re-cementing or squeeze job): Squeeze cementing is carried out to improve the primary cementation, to strengthen casing shoe, liner hangers, to prevent annular leakages and to complete the water shut off jobs. 2.6 Well Completion: Well completion is the interface between reservoir and surface production. Well completion aims at providing conduit from the subsurface reservoir to the surface through which fluids can be produced safely & efficiently.

2.6.1. Factors affecting Well Completion design 

The ideal well completion minimizes initial and operating costs while providing the most effective path to the surface for reservoir fluid.



Reservoir parameters such as formation pressures, rate of production, presence of various fluids, reservoir drive, GOR/ OWR, etc.



Competent

or

loose

formation,

reservoir

characteristics,

Multiple

reservoirs/zones 

Well trajectory & inclination



Surface production facilities and operating requirements



Environmental/ safety concerns, regulations of Government

2.6.2. Methods of Well completion i. Open Hole Completion It is the simplest and cheapest method of well completion where the casing is set at the top of producing horizontal. No perforation is required in this method and producing interval is left without any mechanical supported.

ii. Cased & Perforated Completion It is the conventional method where production casing is cemented through the producing interval and communication is established by perforating the casing. It permits multiple completions & selective stimulation/work-over jobs.

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iii. Liner Completion In this method, casing is run upto the top of pay zone and a liner (slotted) is set across the producing formation. It is used main to control sand incursion.

Fig. 20: Methods of Well Completion. (A) Open hole, (B) Cased hole & perforated, (C) Liner completion.

Based on tubular configuration, completion methods are classified into iv. Tubing less Completion It is the simplest completion practice, where there is no need for large casing through producing interval. However, loading of paraffin & corrosive fluids is a problem. v. Casing with suspended Tubing Completion It is the conventional method where tubing is suspended in the well-bore from a surface control equipment (X-MAS tree). It permits all work-over jobs, artificial lift and controlled flow path for the producing fluid.

vi. Tubing& Packer Completion Tubing & Packer completion provides a number of testing configurations for the completion in complex settings such as multiple reservoirs. Packers are used in the completion system to provide extra safety in the borehole by isolation high

41

pressures, for zonal isolation, easier wireline&downhole operations, and selective stimulation. a) Single string- Single Packer Completion: One pay zone is flowed through tubing and other pay zone through annulus. b) Commingled Completion: when two or more formations are perforated and being produced simultaneously through a common well casing or a single tubing string. c) Multiple String Completion: It is a dual completion method (two packers and two tubings) where selective production from multiple zones is possible.

Fig. 21: Well completion types based on tubular configuration. (A) Tubingless, (B) Single string- single packer and (C) Dual string- dual packer completion.

Once the production testing confirms the presence and potential of hydrocarbons, the well will be connected to surface facilities to X-mas tree for further transportation. If no hydrocarbon shows are encountered, the well is plugged and abandoned. Various cement plugs are put to shut off the well and well mouth is capped. Sometimes, lower strings of casing are cut and recovered for further use. Also, some dry wells may be used for effluent disposal in order to maintain reservoir pressures based on reservoir plan and environmental regulations. 42

2.7 WELL STIMULATION 2.7.1 Introduction Well stimulation is a well intervention performed on an oil or gas well to increase production by improving the flow of hydrocarbons from the drainage area into the wellbore. Stimulation is the opening of new channels in the rock for oil and gas to flow through easily. Well stimulation is also known as Enhanced Oil Recovery. Stimulation treatments fall into two main groups, hydraulic fracturing treatments and matrix treatments Fracturing treatments are performed above the fracture pressure of the reservoir formation and create a highly conductive flow path between the reservoir and the wellbore. Matrix treatments are performed below the reservoir fracture pressure and generally are designed to restore the natural permeability of the reservoir following damage to the near-wellbore area. Stimulation in shale gas reservoirs typically takes the form of hydraulic fracturing treatments.

2.7.1.1 Hydraulic fracturing Fracturing treatments are performed above the fracture pressure of the reservoir formation and create a highly conductive flow path between the reservoir and the wellbore. Matrix treatments are performed below the reservoir fracture pressure and generally are designed to restore the natural permeability of the reservoir following damage to the near-wellbore area. Stimulation in shale gas reservoirs typically takes the form of hydraulic fracturing treatment A propant is a solid material typically sand (treated sand) or manmade ceramic materials designed to keep an induced fracture open during or following a fracture treatment. 2.7.1.2 Matrix acidizing Matrix acidizing refers to one of two stimulation processes in which acid is injected into the well penetrating the rock pores at pressures below fracture pressure. Acidizing is used to either stimulate a well to improve flow or to remove damage. During matrix acidizing the acids dissolve the sediments and mud solids within the 43

pores that are inhibiting the permeability of the rock. This process enlarges the natural pores of the reservoir which stimulates the flow of hydrocarbons. Effective acidizing is guided by practical limits in volumes and types of acid and procedures so as to achieve an optimum removal of the formation damage around the wellbore.

Basically, there are two types of acid treatment Matrix Acidizing- Injection rates resulting in pressures below fracture pressure are termed "matrix acidizing," Acid Fracturing- Injection rate above fracture pressure are termed fracture acidizing.

Matrix acidization in sandstone The goal of sandstone matrix acidizing is to remove siliceous particles such as formation clay, feldspar, and quartz fines that are blocking or bridging pore throats. This is accomplished by injecting acid formulations containing hydrofluoric (HF) acid or its precursors, as HF is the only common acid that dissolves siliceous particles sufficiently.

The main aim of matrix acidizing is to improve production and reduce skin by: 44

Dissolving formation damageCreating new pathways around the wellboreSandstone acidizing is performed for two primary purposes: Perforation breakdown (The fracturing of a perforation tunnel It is sometimes necessary to break down perforations by temporarily pumping acid above fracturing pressure to initiate production or injection of a subsequent treatment, such as hydraulic fracturing. Typically, HCl is used in concentrations ranging from 5% to 20%, with 15% HCl being standard. Near-wellbore formation damage removal : The primary purpose of matrix acidizing in sandstones is to remove formation damage caused by clay and other siliceous fine particles plugging near-wellbore permeability.

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Chapter .3

REGIONAL GEOSCIENCE LABOLATORY (RGL)

Regional Geoscience laboratory provides analyatic support for ;

 Expolration act of K G – P G Basin  Development and production of RJY , EOA, and HPHT asset

RGL STRUCTURE

CHEMISTRY LAB

GEOLOGY LAB



source



sedimentolgy



oil



palynology



water



Core library



cement



Well repository



Drilling fluid



Microbial



Environment



Qualitycontrol

46

3.1 GEOLOGY LAB

It includes :

 Confirmation of lithology and age dating during drilling  Workout any unknown geologic situations for operational need

 G &G Project for regional correlation fine tuning with seismic data in generating new prospects  Liaison with other R&D Institution For Regional Project interms of reservoir characterization

 Age dating , identify missing section , hiatuses etc…..

3.2 CORE LAB

 Core from K G Basin are arranged accordingly to the field wise and area wise for easier indication  In Well Cutting Repository , where the dry well cutting from exploratory wells and development wells of K G Basin are labeled , stacked accordingly to the area wise and field wise and are preserved for future requirement for G&G analysis .

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Fig 22: Core Sample

4.REFERENCE 48

 RAO, G. N. Petroleum Geology: Krishna-Godavari Basin. Geological Society of India, [S.l.], p. 705-706, Dec. 2002. ISSN 0974-6889.  Wikipedia  DGH (Directorate of General Hydrocarbons)  Petrowiki  “Petroleum

Systems

Basin, Handout

Sequences

Stratigraphy”of

KG-PG

of KDMIPE

 Un published Well Completion reports of Exploratory wells of KG Basin, ONGC, Rajahmundry  BagwanSahay ,et al, “Formation and Well site Geological Techniques”, ONGC, Bombay, 1983 .

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51

52

53

54

55

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