The Sirikit West Oil Field lies within the Phitsanulok Basin of Central Thailand. It is a satellite of the main Sirikit accumulation. Within the field, the Lan Krabu Formation represents the main reservoir interval. It is interpreted as fluvio-lacustrine in origin. The three major reservoir sub-members (D, K1 and K2) are subdivided into 10 to 15 m thick parasequences bounded vertically by minor flooding surfaces. Each parasequence represents a progradational phase of mouthbar development which is terminated by a flooding event. A typical parasequence consists of facies progressing from open lacustrine claystone to delta front including mouthbars and channel sands, to floodplain sands and shales. Compared to the Main Sirikit Field, the same stratigraphic intervals in Sirikit West are up to three times thicker. This indicates a strong element of differential subsidence across the major bounding fault between the two fields.

The depositional and sequence stratigraphic models for the area were used as a basis for generating 3-D geological and property models. 3-D modelling was undertaken to determine reservoir architecture and reservoir property trends prior to a new phase of field development. The Shell proprietary correlation software package GEOLOGIX and 3D modelling package MONARCH were utilised to enable rapid evaluation of a range of geological and petrophysical scenarios. For example, differing correlation scenarios reflecting geological uncertainties such as reservoir continuity were generated using GEOLOGIX and rapidly screened in MONARCH. The 3-D models were used for volumetric calculations, well planning, static connectivity analyses of proposed wells and as the input for dynamic flow modelling.

Upscaling of the 3-D geological models was undertaken using REDUCE and dynamic reservoir simulation was performed using the MoReS simulator. History matching of the two geological models carried forward to the simulator suggested that the high reservoir continuity scenario is the most readily matched. The dynamic model is being used as a general reservoir management tool for forecasting, well planning, and for analysing further development options. Results indicate potential for further development and appraisal drilling of up to ten new wells to fully develop the field and achieve optimal oil recovery.

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