App Chap 5

AFPC Drilling Operations Manual Chapter 5 - Appendices

Chapter 5 - General Drilling Practices Appendices Topic

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See Page

Appendix A - Large/Small Scheme Well Lithology, and Problems

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Appendix B - Field Experiences

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AFPC Drilling Operations Manual Chapter 5 - Appendices

Appendix A Large/Small Scheme Well Lithology, and Problems

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AFPC Drilling Operations Manual Chapter 5 - Appendices

Large/Small Scheme Well Lithology, and Problems

Lithology Fars Graup

Large Scheme Wells

Small Scheme Wells

Average Depth m TVD BDF 0

Average Depth m TVD BDF

Jeribe, Dhiban, Euphrates

+/-1100

+/-800

Chilou Jaddala Aaliji, Shiranish

+/-1400

+/-1100

+/-2300

+/-1800

Erek

+/-3400

+/-2600

R'mah

+/-3500

+/-2700

Derro

+/-3600

+/-2900 NP

Judea Carbonate Rutbah Mulussa

+/-3700 +/-3800 +/-4000

+/-3100 NP +/-2900 +/-3000

+/-42100

+/-3200

Well TD

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Generalised Problems • • • • • • • • • • • • • • • • • • • • • • •

Severe losses Formation washouts Drillstring failure Stuck pipe Stuck pipe Potential H2S Losses Soft sticky formations Stuck pipe Chert Soft sticky formations Potential H2S Losses Shiranish gas Potential gas filled formations Losses Unstable formations Hole collapse Losses Unstable formations Hole collapse Losses Losses

• Abrasive formation, differential sticking • Differential sticking • Unstable formation

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Appendix B Field Experiences

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Field Experiences 1 - General Fars

There have been instances of the well flowing when water has been pumped prior to cementing the surface casing. Exploration wells drilled on the banks of the Euphrates River experience top hole and location collapse due toe the very shallow aquifers which cause the well to slough. Driven conductors have to be used in this case.

Lower Fars Salt/TZC

The Lower Fars Salt, just above the Lower Fars transition zone carbonates (TZC), will washout and increase the chlorides in the mud and the mudweight rapidly. Attempts have been made to drill the intermediate section with salt saturated mud resulting in losses. Dilute and dump is the most economical procedure, (see Large Scheme Wells 2, 17.1/2in Hole Section and Small Scheme Wells 3, 12.1/4in Hole Section - Procedure). Current trends are to avoid dilution and allow mudweight to creep up to 10ppg.

Miocene Sequence

All AFPC's fields contain the Miocene sequence which is usually cased off by the intermediate casing. The Chilou and Euphrates formations can be hydrocarbon bearing and can contain H2S. Oil staining and fluorescence are usual in the Jeribe. In the Thayyem, An Nishan and Ash Shola fields there are wells (beam pumps) which are producing from these formations. The significant thing is that AFPC normally drills through these formations, in large and small scheme wells without BOP’s fitted (see AFPC’s Shallow Hydrocarbons Policy). Losses (up to 30 bbl/hr) can occur while drilling the Miocene sequence. Generally these cure themselves while drilling ahead. Spot LCM pills if this is not the case.

Jaddala

The Jaddala is used as the intermediate casing seat (and is competent, although LOT results vary) and generally contains chert towards the base. The usual approach is to get through the chert (which can be up to 30%), or at least until the percentage of chert reduces, before running casing. The LOT results are variable even within a field. Usually require 12.5 ppg (small scheme wells) or 14.5 ppg (large scheme wells).

Aaliji

The Aaliji is normally stated in the well proposal as the shallowest hydrocarbon bearing formation based on observations on other wells. There has not been a recorded case of any significant gas readings while drilling the Aaliji in recent years. This may change with the annulus pressures (Shiranish gas) seen in some fields which could charge the Aaliji. Continued on next page

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Field Experiences 1 - General, Continued Shiranish

All wells have Shiranish usually consisting of Upper and Lower although some old Drilling Programmes specify an 'Intra' version (this may be what is now called the Upper). The problems associated with the Shiranish vary from field to field (see following sections).

Erek

The Erek is the production casing seat in large scheme wells. In a Large Scheme, the casing seat is 10m below bottom Shiranish to allow drill ahead with reduced mudweight. It can be missing completely on some wells and have gas filled fractures (Omar North/North East) in other wells. The Erek can be a good seismic marker.

Derro and R'mah

The Derro and R'mah formations may or may not exist in wells within a field. They are both unstable shale formations and usually contain chert. There are serious concerns on the stability of these formations if drilled with water based mud. Both the Derro and R'mah can contain sands which may be hydrocarbon bearing and at initial pressures. The quality of the sands are poor relative to the Rutbah. In Maleh and Galban some wells have been produced on Derro sands. The Al Kharrata field produces from fractures in the R’mah.

Post Judea Sandstone (PJS).

Like the Rutbah, normally seen in the small scheme well fields such as Maleh.

Judea Carbonates (JC)

Below the PJS - can have losses due to being fractured. Top of the JC is a good seismic marker.

Rutbah

The Rutbah generally has an Upper and Lower section with the Upper section mainly claystone. The main Lower Rutbah is predominantly sand with high permeability. The Rutbah can be (totally or partially) eroded in both large and small scheme wells. The sandstone is abrasive to highly abrasive and varies between fields and within a field. Typically the Rutbah in the large scheme wells is the most abrasive. Small scheme wells are not so abrasive but El Isba and Sijan are fairly abrasive. Continued on next page

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Field Experiences 1 - General, Continued Mulussa

The Mulussa is made up of stringers of sandstone/siltstone/claystone and is as abrasive as the Rutbah. Penetration rates are generally less than the Rutbah especially in the non-sand lithologies. The Mulussa comprises different sections (‘Fl .x’, ‘F2.x’, ‘E, etc.) and has many claystone/siltstone seals. The risk of penetrating a stringer at initial pressure, or having a high pressure differential between sand beds, is quite high. TPG generally want to see the ‘K3’ marker for seismic control. When drilled with water based mud tends to have large washout which cause some drilling problems and compromise electric log data acquisition.

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Field Experiences 2 - Reservoir Section - General Fractures

Reservoir sections can have fractures (any formation) but these are mainly seen in small scheme wells. A re-entry sidetrack from Maleh 103 hit a fracture, not seen in the original hole, although the well path was only 15m from the original wellbore. Fractures have proven difficult to seal even after pumping many cement plugs/LCM. Although it may be possible to cure the losses with cement, when the plug is drilled the losses could start again.

H2S

Most reservoirs have some H2S after they have been in production, however it is normally only seen on workovers. Miocene reservoirs contain H2S in Al Kharrata, Thayyem, Ash Shola and An Nishan fields. However, H2S is not observed when drilling a large/small scheme well through the Miocene in Thayyem.

Normally Occurring Radioactive Material (NORM)

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NORM exists in some producing wells and contaminates the wellhead and tubing. NORM is present in the sludge/corrosion associated with production. Lagoons of formation water can also contain NORM.

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Field Experiences 3 - Omar Area Introduction

Only large scheme wells are drilled in the Greater Omar area which covers the Omar, Omar North, Omar North East, Saban, Al Ayya, Jazieh, Jarnof and Shahel Fields. The Omar Area and specifically the Omar field (and the 'sub' Omar fields) are noted for features described in the following section.

Drillstring Failures in the 17.1/2in and 12.1/4in Hole Sections

Not yet fully understood but factors involved are/maybe drillstring dynamics, sulphates in the mud, formation washouts and torque. See Appendix C

Shiranish Gas Kicks

Thought to be high pressure but low volume gas in fractures. Usually get light crude in the mud but the gas may be more a condensate which turns to gas near surface. The flow seen is possibly the gas just rapidly expanding at surface which usually will overflow the bell nipple. There appears to be little correlation between gas readings and the observed gas and it may contain C02. Turns mud to an emulsion 'chocolate mousse' - Should be treated with demulsifier prior to entering the gas 'zone'. Initially seen in the last 60m before the Erek (9.5/8in casing seat) but has been found in the Upper Shiranish on recent wells. Omar 153 had a water kick in the Shiranish. (See reference DOM Chapter 9 – Water Based Muds 2 - Emulsification and DOM Chapter 13 - Well Control - Potential Problems 2 - Shiranish Gas) The closed in pressures can be unusual with a higher Pdp than Pann and can vary dramatically while bringing the well under control. Typically the LOT at the 13.3/8in shoe will leak off before the required 14.5 ppg therefore limiting the mudweight. In most cases where the mud weight was raised above 13.5 ppg, losses occurred. Attempts should be made to deplete the gas by circulation before raising the mud weight. As standard drilling programmes specify the mud weight to be brought to 12.5 ppg, 200m prior to the top of the lower Shiranish (attempting to reduce initial closed-in pressures) in case of a Shiranish kick, depletion should be tried first (could be several days). Raising the mud weight should be the last resort and only after instruction by Drilling Management. Production tests have been carried out on the Shiranish but the production dropped rapidly. Continued on next page

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Field Experiences 3 - Omar Area, Continued Annulus Pressures Between 13.3/8in and 9.5/8in Casings

Resulting from the Shiranish. Can be gas or oil.

Slow Penetration Rates In The Reservoir

Varies but 1 - 2 m/hr is standard (can be as low as 0.2m/hr or as high as 5m/hr). Metres drilled by each bit can vary between 10 -120m. Gauge wear is the main problem and in which case roller reamers should be run (near bit).

Deviation Natural Drift Tendency

Although not consistent even within the Omar field the general tendency is north +/20o with drifts up to 140m. Some parts of the field produce almost vertical wells.

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AFPC Drilling Operations Manual Chapter 5 - Appendices Reservoir Pressures

The Omar field is geologically complex with many faults/fractures forming compartments. Several wells have been drilled which unexpectedly entered compartments which were charged by water injectors (while expecting depleted pressures). The Mulussa can have stringers of sands at both initial and depleted pressures. The overbalance (+/- 2 000 psi) on depleted reservoirs does not generally result in significant losses but manifests itself in very low ROP. Problems associated with the large scheme well design are: • casing wear • liner problems.

Casing Wear Wear in the 13.3/8in casing is a major problem. Probably due to drillstring harmonics in conjunction with the type and condition of drillpipe hardbanding. It is essential that casing wear is monitored daily and reported, (see Casing Wear 1 Causes and Effects). Liner Problems There have been many problems setting mechanical liner hangers, not being able to rotate sufficiently to set the slips, which have contributed to, or been the cause of cementing failures. AFPC now use hydraulically set hangers which has resulted in less problems. Losses while cementing liners is a concern and when losses are observed while drilling it is acceptable practice to pump excess cement and leave it on top of the liner to compensate for losses while the cement sets. When no losses occur, an integral packer can be included and when sufficient rise around the liner is observed (∆P) the packer will be closed. The Mulussa shales in general are unstable; thought to be caused by hoop stresses. While drilling with OBM the hole might stay in caliper, but running the liner and cementing same, surges in several cases caused the hole to collapse, packing off the hole. Also the water flushes are thought to invade the shales causing it to collapse. Inhibition of flushes, avoidance of surges and uninterrupted circulation during cementing is essential. Relatively poor liner cement bonds are common.

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Field Experiences 4 -Small Scheme Well Fields Introduction

If Shiranish problems are encountered in small scheme wells it is generally a kick, followed by total losses (up to 400 bbls), followed by gains (up to 500 bbls). Typically the mud weight is increased for the kick and then losses occur with the new mud weight. Usually after trying LCM, etc. drilling continues with a lighter mud weight than prior to the kick with losses while circulating and flowing on connections. i.e. circulating out the kick by the drillers method and allowing it to deplete should be the preferred option. Problematic volcanics are more often encountered in the small scheme wells. These can wipe out bits and roller reamers in a very short time with the section being reamed many times. To date attempts to cement them off have been successful in a few cases, although in some instances perseverance with reaming can lead to getting past them as well.

Sijan

The reservoir is abrasive and volcanics have been encountered causing significant problems.

El Isba

The reservoir is abrasive. Shiranish problems encountered for the first time on well ISB 121 (thought to be fractured through to the Rutbah). There can be significant amounts of chert in the Derro/R'mah formations. Extensive volcanics have been encountered in the reservoir without too many problems while on other wells a few metres have caused major problems. The El Isba field has a gas cap and water injection, both these drive the production. A fracture (in the gas cap) was encountered in El Isba 123, causing total losses followed by a kick.

Maleh

Usually small scheme but several modified large scheme wells (large scheme sizes set at small scheme depths - without the liner) which enable ESP’s to be used. Horizontal wells use this scheme (with barefoot completion). Severe (or total) losses have regularly been encountered in the Maleh reservoir generally because of fractures.

Tanak

Generally easy drilling but has the most problems with running and cementing 7in casing due to the instability of the Mulussa shales (see Alert on running and cementing 7in production casings).

Ghawari

In recent memory the biggest problem with Shiranish was encountered on GHW 104. There have been no problems on the latest wells.

Thayyem

H2S in present in the Miocene wells but not encountered when drilling small scheme wells.

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