Sedimentary Reservoir Of Permian,Hechuan Area Of Central Sichuan Basin

The marine strata in Sichuan Basin are rich in natural gas resources.After obtaining the prospecting right of Hechuan block in the middle of the basin,Daqing Oilfield Branch has carried out a series of natural gas exploration and evaluation work,and has made great discoveries in the Permian Qixia-Maokou Formation,showing good resource prospects.In this paper,the three strata of Permian Qixia Formation,Maokou Formation and Changxing Formation in Hechuan area of central Sichuan are taken as the main target strata.Based on core,drilling,seismic and analytical test data,the sedimentary analysis is carried out to clarify the characteristics of favorable reservoir facies belt.The following understandings are obtained :1.The Qixia-Maokou Formation mainly develops bioclastic limestone,micritic bioclastic limestone,argillaceous micritic bioclastic limestone and residual bioclastic dolomite.It is an open carbonate platform sedimentary environment,which can further identify the inner beach subfacies and platform depression subfacies.The Changxing Formation develops bioclastic limestone and micrite bioclastic limestone related to micrite,which are bioclastic beach and inter-beach sea subfacies deposits.Some wells develop in-situ growth reef limestone / dolomite as intra-platform reef subfacies.2.The natural gamma curve corresponding to the combination of Qixia-Maokou Formation platform depression and platform beach subfacies is a toothed low amplitude-high amplitude logging combination,mostly with loophole rhythm,and the seismic facies characteristics are not obvious,which is a good continuous medium-strong seismic facies.The natural gamma curve corresponding to the combination of the intra-platform depression and intra-platform beach subfacies of the Changxing Formation is a dentate low-high amplitude logging combination,mostly a loophole rhythm,and the reef is a high-amplitude micro-dentate logging response.The seismic profile of the reef in the platform is a mound seismic reflection,and the thickness of the reef in the platform is obviously thinner in the direction of the depression in the platform.3.The Qixia-Maokou Formation is the sedimentary environment of open platform facies carbonate platform.The platform endogenous debris beach of Qixia Formation mainly develops in the upper part of Qixia Formation,and develops in a large area as a whole.The cumulative thickness of the beach body is more than 10 meters.The ratio of the upper beach of Qixia Formation is 0.2-0.5,and the change of the thickness of the beach body is not obvious.The thickness of the bioclastic beach is the largest in Gaoshi16 and Gaoshi 113 well areas in the west of the work area.The Maokou Formation hardly develops bioclastic shoals in the work area,which is a deep-water open platform deposit.The sedimentary pattern of the Changxing Formation is relatively complex,and the whole is an open carbonate platform.However,the platform depression deposits are developed in the north-southwest-east direction of the work area,and the platform reefs are scattered on the edge of the depression.4.The main reservoir type of Permian in Hechuan area is dissolved pore dolomite reservoir,which is concentrated in the upper part of Qixia Formation and the upper part of Changxing Formation.The high-energy beach and reef are the basis for the development of high-quality reservoirs,and hydrothermal dolomitization is the key.