Www.eni.it Integrated Drilling and Logging Program Approach in HPHT Environment: Successful Drilling of Deepwater Oberan Field, Nigeria, ENI Deepest Well.

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Integrated Drilling and Logging Program Approach in HPHT Environment: Successful Drilling of Deepwater Oberan Field, Nigeria, ENI Deepest Well in Deep Offshore Nigeria


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Field LocationDesign RequirementsApproach

Lean Casing Profile Application Pore Pressure Prediction Well Verticality Formation Evaluation

Execution Pore Pressure Prediction and Mud Weight Management using

LWD Sonic and Resistivity while drilling Well Verticality Integrated Formation Evaluation

Conclusions

Outline


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High Pressure and High Temperature Field

High Pressure (~ 10,800 psia) High Temperature (~157 degC

extrapolated SBHT @ TD)

Oberan-2 Exploration/Appraisal Well 80 km

from coastline in 674m water depth

Test and characterize deep section of anticline structure in equivalent Miocene Bonga Clastic sequence

Planned TD to 4,479 mMD with lean casing profile

Oberan Field LocationNeed a picture of Oberan Field


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1. Each section should be drilled to maximum possible depth

Pore Pressure Prediction and Well Verticality

2. Casing seat point should be set in sand based on criteria of maximum kick tolerance

Lean Casing Profile Application Mud Weight Management

3. Detailed evaluation of all geological targets should be done.

Gas, clays, radioactive minerals and complex lithology

Design Requirements


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Closed loop system to help drill and case well at reduced time and cost

Consolidated technology keeping the same production casing and reducing diameters of surface and intermediate casings

Better rate of penetration due to smaller hole diameter

Reduced cutting volumes, improved hole cleaning and controlled annular pressure losses

Reduction of annular clearances requires closer monitoring of all aspects of operation

Lean Casing Profile Application


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Combined with LWD annular pressure tool ensured effective pore pressure and shock management

Each well section was drilled to maximum depth allowing real time decision in setting casing points. Each section should be drilled to maximum possible depth

Eni patented Circulating Device was used to effectively manage mud weight within narrow margin between fracture gradient and pore pressure.

Eni - Circulating Device


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Help increase and optimize borehole stability

Failure to maintain mud weight within hydraulic operating range can compromise setting deeper casing points

LWD sonic data was primary in under compaction model because less affected by temperature and salinity

LWD Resistivity data was used in hole sections where sonic data was unavailable

Pore Pressure Prediction


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Pre-Drill Model was created using interval velocity from surface seismic and offset well data of Oberan-1

High quality real-time sonic and resistivity data enabler for pore pressure prediction model update. Model was calibrated using data from Wireline formation tester for the section completed to have revised model for next section

Leak off test at the start of each section provided critical calibration point



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Robust real-time communication and workflow was established

All data was shared using real-time data transmission system to make timely and efficient decisions



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Maintaining well verticality helps reduce departure

Less total drilling length helps reduce risks and costs in high pressure high temperature environment

Automated Vertical Rotary Steerable System (RSS) was used to maintain verticality

RSS helps in mud weight management and borehole quality through continuous rotating

Well Verticality

Well Name Average ROP Maximum Inclination

Total Depth

Oberan – 2 38 m/hr 0.26 4,479 mMD

Oberan – 1 5 m/hr 2.61 4,340 mMD


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Comprehensive Wireline Logging Program in 13.5” and 10.625” open hole well section

13.5” Section: High Resolution platform

express and LWD resistivity for fast and robust results

Dipole Shear Imager tool was run for compressional and shear acquisition

Formation Evaluation


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10.625” Section: Accelerator Porosity tool was run

to acquired epithermal neutron measurement for lithology evaluation and gas detection

High Resolution Gamma Ray Spectral Measurement assisted in clay typing and volume indications

Petrophysical information collected was key for MDT operations

Formation Evaluation


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Modular Dynamic Formation Tester was run in 3 well sections

141 pretest acquired and 85 reliable pressure points

Several downhole fluid analysis and sampling stations were performed

Fully characterize hydrocarbon bearing zones and aquifers

Formation Pressure and Sampling


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Some sampling stations used focused technique (Quick Silver Probe)

Allows to capture contaminated fluid and discharge into wellbore and direct clean fluid to fluid analyzers and sampling bottles

Formation Pressure and Sampling

Mud contaminated

fluid

Pure form

ation fluid


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Well PerformanceOberan-2 was drilled to target TD without having to use last planned casing string

Total Depth – 4,479 mMD Maximum Pressure

Recorded - 10,800 psi Maximum Temperature

Recorded – 153.3 ˚C Maximum Deviation – 1.18

˚


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ConclusionsDrilling performance on Oberan-2 was optimized using:

Intelligent fit for purpose new technologies Risks and challenges were assessed in planning stage to safely achieve

well targets

Drilling technologies including automated rotary steerable system, lean profile application, eni circulating device and real-time pore pressure helped:

To set deeper casing points To maintain well verticality To increase ROP by drilling close to balance and no sliding To ensure safer drilling practices

Www.eni.it Integrated Drilling and Logging Program Approach in HPHT Environment: Successful Drilling of Deepwater Oberan Field, Nigeria, ENI Deepest Well.

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