Anpeng deep strata series are usually buried deeper than 3 000 m,and belong to the lower part of the third member of Hetaoyuan Formation fan delta sedimentary system.The difference of sedimentary environment resulted in serious heterogeneity of the sandstone reservoirs.Core descriptions,conventional thin section,injecting thin sections,SEM observations,X-ray analysis of clay minerals,mercury injection data and pattern analysis of pore structures show that the major rock types are lithic sandstone,feldspathic litharenite and lithic arkose.Also it is found that,in the sandstone,the subaqueous distributary channel sandbodies and the mouth bar sandbodies have the best physical properties.Rapid accumulation,miscellaneous grain size,low maturity of texture and composition are the predetermination condition of low permeability.The main type of pores is the secondary porosity.The reservois are poor in pore throat distribution,complex in structure,small in throat and their evident character is heterogeneity.They are the typical compacted low permeable reservoirs.The diagenesis,especially the compaction and the later carbonate cementation are the key factors affecting the microheterogeneity of the reservoirs and leading the reservoirs to be compacted and low permeable.
