Study on organic reefs-type reservoir at Changxing for-mation of east Banqiao area in east-north Sichuan

Changxing formation of east Banqiao area in east- north Sichuan is mainly composed of bioclastic limestone, reef limestone,putty-powder crystal dolomite and fine- medium crystal dolomite,among which medium crystal dolomites are preferential to form good reservoirs.Ac- cording to curves analysis of reef crest,the reef is consid- ered to be superposed through at least three sedimentary cycles.The diagenesis such as cemented filling,dolomiti- zation and dissolution play a crucial part in reservoir for- mation.Through eletro-microscope observation,the ce- mented filling is thought to be three-period with primary porosity mostly filled in,bioclastic limestone is evolved into fine-medium crystal dolomite by mixed water dolo- mitization,while the intercrystalline-dissolved pores,ir- regular dissolution pores and cave generated from dissolu- tion become main reservoir spaces.