The Jintan giant carbonate gas field in the Central Luconia Province, offshore Sarawak, Malaysia, has been on production for more than 8 years. One of the main challenges currently faced by the subsurface team is the prediction and handling of water breakthrough at the existing producers. To optimise near term well and reservoir management, but equally important to evaluate the remaining potential of the field, an integrated approach and robust understanding of the field is essential. This paper explains how Shell Malaysia with support from their partners are using a combination of 4D seismic technology, reservoir surveillance, and integrated reservoir modelling workflows to achieve this objective.All the producing wells are situated in the northern, crestal area of the field, whereas the southern part of the field extends up to 5 km away from the nearest producer. A reservoir surveillance program has been in place since first gas via a deviated well, dedicated to monitoring fluid contact movements on a yearly basis. To complement this, two time-lapse (4D) seismic surveys have been successfully acquired in 2008 and 2012, which provide a field-wide image of the top-sweep contacts. The 2008 survey was limited to two narrow swaths located around the surface facility platform area to assist in the targeting of two in-fill producers, successfully drilled in 2008 and 2010. In 2012, much larger 4D swaths were acquired which cover the majority of the field. This high-quality data has provided crucial information on sweep, including a very strong indication that gas has been produced from a wide area. This includes the southern part and edges of the field, enabling in a clearer definition of future development plans.Our ability to use 4D time lapse datasets and surveillance data to effectively constrain the static and dynamic models allowed the delineation of the dynamic behavior of different reservoir geobodies (reef margins, karst, faults) through the production lifetime of the field. This has given insights into the controls on water influx and sweep which can be transferred to other carbonate reservoirs and fields with less data, to better understand and predict their likely dynamic behavior. To assure the quality of the models used for this purpose, in-house best practices have been employed, including 3D Close-the-Loop to assure the quality of the static model and 4D Close-the-Loop to assure realistic fluid dynamics of the field. Experimental design has also been used to capture and dynamically model a realistic uncertainty range. This will enable better production forecasting, and thereby help to define, optimize and realize the remaining opportunities.

Pore-pressure prediction in a mature hydrocarbon province with producing fields bears issues different from an exploration or immature basin setting. Appraisal and production activities can introduce anadditional set of complications that needs to be considered to make well-constrained pore-pressurepredictions. Problems for infill drilling can arise from severe changes in rock strength (fracture gradientreduction), caused by depletion of reservoirs through production, or development drilling in neighboringfields, if there is pressure communication via a common aquifer. Increases above initial pressure can be caused by crossflow from overpressured reservoir layers through poor cement bonds or abandonments. Reservoirs can also receive additional pressure through water or gas injection. The Luconia gas province is a mature basin and several stages of successful exploration, appraisal, development and infill-drilling campaigns. Shell, supported by its partners, has successfully overcome the above mentioned issues by thorough and innovative pore-pressure prediction approaches. In addition to the standard bracketing of uncertainties, 3 key process elements are employed:proper framing of the pore-pressure prediction and continued interfaces with all stakeholders anda 'scenario-based'prediction approach, that captures all possible effects caused by appraisal and production of the target reservoir or neighboring fields, and that predicts their impact on the pore pressure of the reservoir to be drilled.Risks identified are captured and mitigated via a 5 point pore-pressure prediction that spans a facilities design range as well as a wider drilling range. The drilling-range end members have a low probability of occurring, but have to be captured to enable hardware selection that ensures safe drilling execution. State of the art technologies are employed to achieve this, including 4D seismic, regional databases, innovative modeling methodologies and full integration in a well-delivery process.

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