Study On Reservoir Characteristics And Controlling Factors Of Shaximiao Formation In Southern

The gas reservoirs of the Jurassic Shaximiao Formation in the south region of West Sichuan basin are the typical tight sandstone secondary gas pools with low porosity and low permeability. It is one of the most important areas of exploration shallow gas of the Jurassic in the western area. Through many years of exploration, many of gas reservoirs have been discovered, such as Su-matou, Bai-mamiao, Guan-yinsi and so on, It shows good exploration prospects of the Shaximiao Formation in the south of western Sichuan. Therefore, study the characteristics and controlling factors of reservoir is of great significance. This paper combines the results of previous studies, applied the theories and methods of Sedimentology, Mineral petrology, Reservoir geology, etc, analyzing the provenance characteristics, distribution of sand body, reservoir characteristics and the controlling factors of reservoir development.This paper shows that the deposition of Shaximiao Formation is affected by two provenance in the south of western Sichuan. Primarily including the Northwest provenance from Middle and southern sections of the Longmen mountains and the Northern provenance with difference rock types which effected by the Micangn-Daba mountains and Longmen mountains. The main depositional environments of Shaximiao Formation in this area are river and delta. The type of delta is the distributary channel-type shallow water delta, which is mainly made of distributary channel. The reservoir lithology is mainly fine and medium-grained Feldspar sandstone and Lithic feldspar sandstone, its properties showed the characteristics of low porosity and permeability. The main types of reservoir space are residual intergranular pore and feldspar dissolution pore. The development of reservoir is controlled by many factors, the impact of sedimentation on reservoir performance from the differences of provenance and sedimentary microfacies. Reservoir is more developed in the sandstones with high feldspar or in the thick sandstones developed in distributary channel. Compaction and carbonates cementation are two important reasons to make the sandstone densification, and the sandstone with dissolution or chlorite rims cemented have many dissolution pores or residual intergranular pores, Tectonic have important significance of improving the porosity and permeability of reservoir and the formation of the second gas pools.We have understand the distribution of reservoir of Shaximiao Formation from many information, such as drilling, oil test results and log interpretation results, and so on. Reservoirs are mainly distributed in the section Ⅱ,ⅢandⅣ of Shaximiao Formation on the longitudinal, Horizontal distribution of reservoir affected by provenance and sedimentary microfacies, and distributed mainly in the distributary channel sand in the eastern part of the Su-matou,Yan-jingou where affected by the northern source.In recognition of reservoir characteristics, reservoir development controlling factors and the distribution of reservoir, proposed the selection principle of selection the favorable distribution area of the reservoir. Combined with the drilling and logs, selecting the favorable distribution area of the reservoir of the Shaximiao focus interval-the Ⅱ and Ⅲ segments.