Integration of MPD and Direct Pressure Measurements to Provide Risk informed Pore Pressure Ranges for Process Safety in Challenging Infill Drilling in Differentially Depleted HPHT Formations of N. Kuwait Jurassic Gas

The North Kuwait Jurassic Gas (NKJG) carbonate reservoirs are of middle Jurassic age and comprise six main units (or flow zones) comprising carbonate limestones, dolomites and evaporites. These are HPHT (high pressure, high temperature) and critically sour tight carbonate reservoirs with pervious dolomite and very tight/ impervious limestone matrix and anhydrite vertical flow barriers. These were originally overpressured reservoirs, all the flow zones in these dolomite and limestone units were on a narrow pressure band (11000 to 12000 psi, or 14-15 ppg equivalent mud weight) in the pre production stage. Due to varied depths and productivity, different flow zones were put on development at different places of the field as part of field development strategy. Magnitude of differential pressure across different flow zones is magnified with increased production, resulting in drilling complications leading to stuck pipe, bore hole stability issues. A good understanding of robust uncertainty range of expected formation pressure is critical for safe design of drilling, as well as safe execution of infill drilling which can meet business objectives of desired production levels. This operational excellence was achieved by integrating the indirect pressures (from drilling) with direct pressure measurements and reworking the formation pressure uncertainty range as an input for well and drilling design. Figure 1Location map of North Kuwait Jurassic Gas (NKJG) Fields Pore pressure prediction is crucial in drilling because accurate estimation allows for optimized drilling fluid density and well design, directly preventing catastrophic events like blowouts and wellbore collapse. Without it, there could be immense risks including loss of well control, formation damage, significant non-productive time, and severe damage to equipment and personnel. Precise pore pressure knowledge helps define safe drilling windows, enables effective well completion, and aids in mapping hydrocarbon migration paths. Below schematic shows the workflow for achieving the desired outcome for well delivery. Figure 2Pore pressure prediction and impact on well delivery However, a single point pore pressure prediction is most of the times is impossible as well as can lead to inadequate understanding of possible ranges. In order to fully appreciate the uncertainty range, the best approach is scenario thinking and coming up the full pressure range and corresponding probability of each of the ranges. A customer centric and integrated approach is necessary to make sure there is common understanding and alignment on hoe the pressure ranges have arrived and what scenarios could lead these ranges. Integration of pressure available from different sources (both direct and indirect pressure measurement during drilling operations) and deploying the scenario based pore pressure ranges, helped in achieving a maneuverable drilling window which can lead a successful well delivery with reduced drilling complications. This process safety improvement resulted in operational excellence in challenging infill drilling of NKJG wells and helped in disciplined delivery of field development plan (FDP). Five-point pore pressure prediction was deployed which covers all the potential scenarios leading to different pore pressure outcomes. Therefore, the pore pressure ranges were worked out which included the design range (reasonable low case – reference case -reasonable high case). This range allows for deigning the well and mud weight planning for safe and optimum operations. At the same time Minimum pressure and Maximum pressure are used as safety range to ensure there is adequate response to safely overcome these scenarios in case the ranges have materialized. The full ranges of PPP from 5-point methodology are shown below: