Permo-Triassic reservoirs of the Saigak Field, in the eastern part of the Precaspian Basin of Kazakhstan, produced oil at cumulative rates exceeding 3600 BOPD. This confirms the attractiveness of the post-salt play in this part of the basin. Core studies show that cross-bedded sandstones in braided fluvial channels, alluvial and delta plain deposits are the best reservoirs. Integration of topographic and geomorphological features with satellite and seismic data led to the identification of inter-dome depressions with present-day active subsidence and sedimentation. These depressions are analogues to Permo-Triassic mini-basins. In the wells, reservoirs deteriorate quickly as soon as depositional environments become evaporitic. Seismic inversion was applied on a small 3D data-set covering the Saigak Field. The reduction of porosity with depth correlates well with increasing acoustic impedance values. In the inverted volume, reservoirs were characterized in terms of porosity and connected bodies, an essential input into static and dynamic reservoir modelling.

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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.