Predicting the Fracture System in Shah Structure in Onshore Abu Dhabi Using Analogue Modeling Approach

Abstract The aim of this study is to demonstrate the value of a fully integrated ensemble-based modeling approach for an onshore field in Abu Dhabi. Model uncertainties are included in both static and dynamic domains and valuable insights are achieved in record time of nine-weeks with very promising results. Workflows are established to honor the recommended static and dynamic modeling processes suited to the complexity of the field. Realistic sedimentological, structural and dynamic reservoir parameter uncertainties are identified and propagated to obtain realistic variability in the reservoir simulator response. These integrated workflows are used to generate an ensemble of equi-probable reservoir models. All realizations in the ensemble are then history-matched simultaneously before carrying out the production predictions using the entire ensemble. Analysis of the updates made during the history-matching process demonstrates valuable insights to the reservoir such as the presence of enhanced permeability streaks. These represent a challenge in the explicit modeling process due to the complex responses on the well log profiles. However, results analysis of the history matched ensemble shows that the location of high permeability updates generated by the history matching process is consistent with geological observations of enhanced permeability streaks in cores and the sequence stratigraphic framework. Additionally, post processing of available PLT data as a blind test show trends of fluid flow along horizontal wells are well captured, increasing confidence in the geologic consistency of the ensemble of models. This modeling approach provides an ensemble of history- matched reservoir models having an excellent match for both field and individual wells’ observed field production data. Furthermore, with the recommended modeling workflows, the generated models are geologically consistent and honor inherent correlations in the input data. Forecast of this ensemble of models enables realistic uncertainties in dynamic responses to be quantified, providing insights for informed reservoir management decisions and risk mitigation. Analysis of forecasted ensemble dynamic responses help evaluating performance of existing infill targets and delineate new infill targets while understanding the associated risks under both static and dynamic uncertainty. Repeatable workflows allow incorporation of new data in a robust manner and accelerates time from model building to decision making.

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Drilling Through Fractured Gas Bearing Formation to Access Previously Inaccessible Parts of an Offshore Reservoir in Abu Dhabi Using Pressurized Mud Cap Drilling - Case Study

10.2118/207759-ms ◽

2021 ◽

Author(s):

Omar Nazih Jadallah ◽

Mujahed Saleh ◽

Mohamed Rebbou Benberber ◽

Upadhyay Arvind ◽

Zhanibek Diltaiyev ◽

...

Keyword(s):

Sea Water ◽

Drilling Fluid ◽

Abu Dhabi ◽

Fracture System ◽

Well Control ◽

Oil Reserves ◽

Challenging Tasks ◽

Control Response ◽

Hydrocarbon Gas ◽

Gas Bearing

Abstract Drilling through fractured gas bearing formations to access the oil reserves underneath has been one of the most challenging tasks for the drilling Team due to the embedded risks such as; total circulation losses, Gas migration, well control issues, hole instability, cutting beds accumulation and stuck pipe. This paper explains an approach in drilling fractured gas bearing formations that was performed for the first time in offshore Abu Dhabi field-A, Pressurized Mud Cap Drilling (PMCD). Drilling through fractured Gas bearing formation causes the loss of the mud column and the consequent intrusion of hydrocarbon gas to the wellbore, thus initiating well control response, which adds to the flat time and might cause cutting slippage, stuck pipe and eventually loss of well objective. PMCD is best suited to deal with such situation, as it allows drilling to continue under the mentioned circumstances by filling the well with sacrificial fluid while the well is closed, fractures take seawater, cuttings and the formations pressure lefts the underbalanced annular fluid to reduce losses volume. Two wells were drilled successfully using the PMCD technique in Field A where the anticipated fracture gas bearing formations system was encountered shortly below the 9-5/8″ casing shoe. The performance increased substantially in the second well as lessons learnt were implemented to avoid any time loss. Drilling the 8-1/2″ Hole section started in well #2 conventionally with required 200 psi overbalance mud weight, the drilling fluid system is directly changed to sacrificial fluid (Sea water) once the fracture system is hit and total losses observed. A light Annular mud (Seawater) is pumped in the well's annulus. After having stable PMCD parameters, drilling continued at an ROP of 100-150 FPH. TQ & Drag real-time monitoring & intermittent pumping of 3 × 50 bbls weighted HVP to clean bit & BHA from cuttings were essential to avoid getting the pipe mechanically stuck. The 6,710 ft section was drilled successfully, Striped BHA Out of hole, Ran 7,160 ft of 7″ Liner, perform cement Job & achieved isolation. Comparing with offset wells drilling conventionally in field-A through the gas bearing fractured zone, PMCD saved +/− 44 days of the well time, cost and achieved the target. and greatly improved the operational safety by providing closed-loop drilling. The PMCD application on the two wells is the first of its type in offshore Abu Dhabi, it allowed accessing parts of the reservoir that have been inaccessible due to the fracture system. Additionally, it increased safety of operation & saved rig days that would have been spent in treating losses and well control operation. Pressurized Mud Cap Drilling application in field-A provides a solution for a wider implementation in developing fractured gas cap resources in future.

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