Hydrocarbon Exploration

HYDROCARBON EXPLORATION

Sedimentary Basin

Sedimentary basin refers to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification.

Sedimentary rock types

SANDSTONE

BRECCIA

CONGLOMERATE

SHALE FOSSILIFEROUS

ROCK SALT

GYPSUM

COAL LIMESTONE

Relative thicknesses of laminations, beds and strata

Sedimentary rock characteristics

Sphericity of grains

Texture

Waterlain beds

Sorting

Fabrics

Mass flow

Finding oil and gas Geology

Geophysics

Seismic

Well Logging

By studying these sedimentary beds in outcrops and other surface features, geologists can infer where the underground porous reservoirs and impermeable traps might lie Understanding of the shapes of the sedimentary rock layers. Early geophysical methods involved gravity-magnetic mapping, measuring the earth's gravity and magnetic responses at a number of points and plotting the results on a map Geophysicists interpret these results to gain an understanding of the shapes sizes and orientation of rock layers, - stratigraphy and tectonics. To evaluate what kinds of rock are at which depths, how porous the rocks are, and whether there is oil and gas or water in the pore spaces.

Exploration Techniques

™ GEOLOGICAL ™GEOPHYSICAL GRAVITY MAGNETIC SEISMIC

™GEOCHEMICAL SNIFFER

What we look for :

‰ GEOLOGIC SETTING ‰A SIGNIFICANT SEDIMENTARY THICKNESS ‰ FAVOURABLE STRUCTURAL FEATURE ‰ PETROLEUM SYSTEM

Geological surveys

Structural elements Lithology Paleontological study Environment of deposition Stratigraphy Evolutionary sequence of structure

Geological field studies

Gravity Magnetic Studies Relative surface variation of Earth's gravitational acceleration over geologic structures

AEROMAGNETIC RECONNAISSANCE SURVEY

Onland – Seismic surveys (Vibrosis)

Animation courtesy of Elf Aquitaine.

Marine seismic data acquisition

The seismic trace Depth & Time Shot

Surface

Receivers 0 Layer-1

Arrival time

Layer-2 Layer-3

Seismic Section (Land)

Seismic section – Deep Water

Seismic imaging

Coarse Grid (reconnaitory) Semi‐detailed Detailed 3D High resolution‐3D

Xl in e

Se ct io

Inline Section

n

Viewing 3D data in many ways

Time Slice Chair Display

Seabed Logging •

All geological media have some sort of electrical conductivity.

•

Difference in conductivity between shale & sandstone is relatively small when they’re water saturated.

•

The conductivity falls markedly when the sandstone is filled with oil. Resistivity Profile

Seabed Logging

H22O

HC

Water-Filled Reservoir = Low Resistivity

Hydrocarbon-Filled Reservoir = High Resistivity

Less Refraction of Waves to the Receivers

Refraction of Waves to the Receivers

From Seismic to map

Trap A trap is a geologic or a stratigraphic feature capable of retaining hydrocarbons. Hydrocarbon traps that result from changes in rock type or pinch-outs, unconformities, or other sedimentary features such as reefs or buildups are called stratigraphic traps. Hydrocarbon traps that form in Geologic structures such as folds and faults are called structural traps

Petroleum System The key components of PETROLEUM SYSTEM (S) are (1) source rocks, (2) timing of generation, (3) migration (4) trap, and (5) seal

Drilling …..

Drilling…

™MUD LOGGING ™DITCH SAMPLING ™SUBSURFACE PRESSURE MONITORING ™HC SHOW ™TEMP MONITORING ™BLOW OUT PREVENTION ™CORING ™LWD ™MWD

Well Profiles ¾VERTICAL ¾INCLINED ¾HORIZONTAL ¾EXTENDED REACH WELL

RIG

SAKHALIN-1 WELL HORIZONTAL DISTANCE 10 KM.

Open hole logging – Formation Evaluation DIRECT INFORMATION -ROCK FRAGMENTS & FLUIDS Dill cuttings, mud shows Sidewall samples, Cores or core slices, Production tests, Formation wireline samplers, Dill-stem tests INDIRECT INFORMATION -WIRELINE LOGS PHYSICAL PHENOMENON

MEASURED PARAMETER

acoustic -waves

sonic velocities acoustic impedance

gamma / gamma scattering

electron density photoelectric cross section

thermal neutron density

hydrogen density

thermal neutron decay

thermal neutron cross section

neutron activation

elemental concentrations

natural gamma radiation

API

spontaneous potential

membrane potential

electromagnetic waves

electric resistivity / conductivity

Formation Evaluation

Objectives of a Petrophysical Interpretation LOCATE: DETECT: EVALUATE:

reservoir fluid content fluid type : gas / oil / water lithology mechanical properties gross / net reservoir thickness porosity permeability capillary properties salinity of the water original hydrocarbon saturation residual hydrocarbon saturation percent oil/gas/water reservoir pressure

Wire line logs - Open Hole

¾RESISTI VITY ¾DENSITY ¾POROSITY ¾RADIOCATIVITY SPECTRUM ¾TRANSIT TIME

Well completion

Perforation of reservoir

Reserves Reserves are those quantities of petroleum which are anticipated to be commercially recovered from known accumulations from a given date forward. All reserve estimates involve some degree of uncertainty

UNPROVED

PROVED

PROBABLE

POSSIBLE

Volumetrics

OIIP = Area x thickness x porosity x saturation FVF GIIP = Area x thickness x porosity x saturation x Bg

Recoverable Reserves: IIP x Recovery Factor

Production 1. Primary recovery • Reservoir pressure causes OIL to flow to the surface •The simplest way of maintaining production flow rates is to use downhole pumps. (15-20%)

2. Secondary recovery •Secondary recovery methods were developed to improve the recovery factor. The most common method involves flooding the reservoir with water. This involves injecting water into the reservoir to artificially increase the reservoir pressure and press the oil into the production wells (30-40%)

3. Tertiary recovery (EOR = enhanced oil recovery) •The following methods can be used to improve the crude's flow qualities: - Injecting steam into a reservoir heats up the crude and reduces its viscosity. - The same effect can be achieved by pumping in solvents. •Upto 50 % of the original oil in place can be exploited by means of tertiary recovery

Production

Injection Well

Production Well

Injection Well 1. Water 2. Polymer

Classification of crude oil

Classification of crude oil is often by its relative weight or viscosity ("light", "intermediate" or "heavy"); Refiners may also refer to it as "sweet", which means it contains relatively little sulfur, or as "sour", which means it contains substantial amounts of sulfur and requires more refining in order to meet current product specifications

The world reference oils : Brent Crude comprising 15 oils from fields in the Brent and Ninian systems in the East Shetland Basin of the North Sea . Oil production from Europe, Africa and Middle Eastern oil flowing West tends to be priced off the price of this oil, which forms a benchmark. •West Texas intermidiate (WTI) for North American oil. •Dubai used as benchmark for the Asia - Pacific region for Middle East Oil •Tapis (from Malaysia, used as a reference for light Far East oil) •Minas (from Indonesia, used as a reference for heavy Far East oil)