This paper deals with a study where integration of 3D-seismic survey and reservoir simulation has aided in reservoir characterization which in turn have led to better and effective implementation of reservoir development schemes. Shalmari, one of the major oilfields in Assam-Arakan geological province of North-East India was discovered in 1986 and the initial field development was carried out on the basis of then available 2D-seismic data. During the course of initial field development, the area of major concern was the rapid decline of reservoir pressure. A detailed simulation study was carried out in 1994 for assessment of the pressure maintenance requirements and field development. A 3D-seismic survey was carried out in 1994 in this area to obtain additional information on the reservoir geometry and structural configuration. The processing and interpretation of 3D-seismic data resulted in identification of additional faults thus bringing about a change in the structural configuration of the reservoir. The presence of identified faults was corroborated by pressure transient surveys. This necessitated in carrying out of another detailed reservoir simulation study by building up a geological model based on 3D-seismic data. The basic objective of the study was to carry out a more accurate and reliable reservoir characterization apart from identifying the prominent direction of aquifer support and re-assessment of the hitherto planned reservoir development scheme including ongoing pressure maintenance scheme. The results of the study carried out in 1997 also indicated possible increase in gross ultimate recovery as a result of water flooding. The financial analysis of the development schemes envisaged in this study was also found to be attractive. Cross-discipline integration of data expertise and study has helped in accurate mapping of the minor faults and has provided a better insight into fault transmissibilities in the fluid flow simulation. Introduction Shalmari, a major oil producing field of Oil India Limited situated in the North-Eastern India was discovered in 1986. The initial field development and exploitation of reserves was carried out on the basis of then available 2D-Seimic data (acquired in 1984–85). Based on results of 2D-seismic interpretation and subsequent drilling of wells, the field is subdivided into three major fault blocks viz. Northern, Southern and Well #19 Block reservoirs. The areal extent of the structure is 5.8 sq. km. Till date a total of 30 wells have been drilled in this area at approximately 40 acre well spacing with current production rate of around 690 m3/day from Oligocene sandstone reservoirs. The area of study in this case will be confined to Northern Block reservoir which has 11 wells of which 6 are producing at the rate of 485 m3/day. The Northern Block reservoir has an estimated oil-in-place of 6.4859 MM m3 and recovery till date has been 28% of OOIP. Preliminary material balance and reservoir engineering studies indicated that the Northern Block reservoir was in immediate need of pressure maintenance possibly due to higher productivity of the wells and limited water influx from the aquifer(s). A detailed simulation study using a geological model based on 2D-seismic data was carried out in 1994 to assess the pressure maintenance requirement and to formulate an optimum field development plan. Based on the results of the study, few locations were identified for drilling as injectors and producers as infill/extension wells for adequate drainage of the reservoir (refer Figure 1(a)).

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