Reservoir Main Controlling Factors Of The Forth Leikoupo Formation In Chuanxi Gasfield

This paper takes carbonate reservoir of the forth Leikoupo formation in Chuanxi Gasfield as research object.Based on the material derived from Pengzhou 1,well Yashen 1 and Yangshen 1,the author identificated the slice and observed the drilling core systematically.For that,by studying the petrology characters,the type and intensity of the reservoir space,the diagenesis,the author obtained the scientific basic data.The author used the logging,geochemical and other methods,from sedimentation reservoir character and diagenesis aspect,to analyze the reservoir and type of the forth Leikoupo formation,to summarize the main controlling factors and to predict the favorable zones distribution.Based on the study of microscopic characteristics of reservoirs,the author clarified that,the Leikoupo Formation develop dolomite pore reservoir of tidal flat in Chuanxi Gasfield,with widely distributed,thick,and gas-bearing characteristic.The reservoir can be divided into upper and lower sections in the vertical: the lower reservoir section is generally medium-low porosity and low-permeability type II-III dolomite reservoirs,with multiple sets of thin-layer high-porosity type I reservoirs.The upper reservoir section is mainly a type III pore-fracture limestone reservoir with a type II pore type dolomite reservoir.The author refined process of the diagenesis and pore evolution of the forth Leikoupo Formation.It is clear that dolomite,quasi-homogeneous dissolution,burial dissolution and late rupture are the main driving forces for the formation and preservation of high-quality reservoir pores.It is pointed out that the reservoir pore evolution has gone through three stages: the primary pore shrinkage in the early stage of seabed-shallow burial-early pore formation,the shallow burial late-epoch-epoch-re-burial early pore filling stage and the late burial latent dissolution.At last,the author established the high-quality reservoirs formation model of the forth Leikoupo Formation,the dolomite + pen contemporaneous dissolution + buried deep erosion.Among them,the regional distribution of dolomite has laid an important foundation for the stable and wide distribution of reservoirs;the different degree of dolomitization is the root cause of the difference in reservoir development between the upper and lower reservoirs.the quasi-synchronous dissolution has formed a large number of early pores dissolution,which plays an important role in controlling the distribution of high-quality reservoirs;burial dissolution further enhances the quality of reservoirs.