Sedimentary Reservoir Of Cambrian,Hechuan Area Of Central Sichuan Basin

The marine strata in the Sichuan Basin are rich in natural gas resources.The large Anyue gas field in central Sichuan has confirmed the development of high-quality reservoirs and huge resource potential in the Sinian Cambrian system,and has recently achieved good exploration results in the Cambrian Xixiangchi Group.This article takes the Cambrian Longwangmiao Formation and Xixiangchi Group in the Hechuan area of central Sichuan as the target layers,and based on core,drilling,seismic,and analytical data,conducts sedimentary analysis to clarify the characteristics of favorable reservoir facies zones,and obtains the following understanding:(1)The Cambrian Longwangmiao Formation and Xixiangchi Group are both carbonate platform sediments.The lithology of the Longwangmiao Formation and the Xixiangchi Group is very similar,mainly consisting of granular dolomite,crystalline dolomite,argillaceous micrite dolomite,and micrite dolomite.Three types of sedimentary subfacies have been identified: the Tainei shoal subfacies are mainly composed of sandy clastic dolomite and oolitic dolomite,with high development of dissolution pores.The storm shoal subfacies are mainly composed of irregular interlayers of muddy grain dolomite and muddy grain dolomite,with sedimentary structures such as grain sequence bedding and underdeveloped dissolution pores;The intertidal marine subfacies are mainly composed of dark gray to gray argillaceous mudstone and mudstone,with undeveloped pores.(2)The logging and seismic facies characteristics of the Longwangmiao Formation and Xixiangchi Group are very similar to those of the intra platform beach and inter beach sea subfacies combination.In terms of logging facies,it is mainly characterized by a relatively high degree of serration,with a funnel-shaped shape.In terms of seismic facies,the shoal within the station has a medium amplitude intermittent reflection feature,and the reflection layer is irregular.(3)It is proposed that the inner beach of the Longwangmiao Formation is overlaid layer by layer from east to west,and the thickness of the inner beach shows a significant thinning trend towards east.The cumulative thickness is 20-40 m,and the beach to land ratio is 0.2-0.4.The inner beach development thickness is the highest in the Gaoshi 16 and Gaoshi 21 well areas in the western part of the work area.There is no obvious migration pattern in the Xixiangchi group beach body.The lower beach area has a ratio range of 0.1 to 0.2,a cumulative thickness range of 4-16 m,and the upper beach area has a ratio range of 0.16 to 0.31.The cumulative thickness of the beach body is 9-18 m.The Gaoshi 21 well area has a high degree of development and a larger thickness of the beach within the platform.(4)The formation and development of high-quality reservoirs in the Longwangmiao Formation and Xixiangchi Group are clearly controlled by sedimentation,with the best storage performance in high-energy platform shoals and underdeveloped storage space in storm shoals.