Sedimentary Facies And Reservoir Evaluation Of The 8th Member Of The Permian Shihezi Formation In Sulige Gas Field

Sulige gas field is a typical low-efficiency tight sandstone gas field,and which is one of the largest gas fields of China,there is a large fluvial delta sandstone lithologic trap reservoir in the Shihezi formation of the Permian,importantly the 8th section of Shihezi formation is one of the main gas producing layers.This part of sand formation has great exploration potential depending on its stabilization and good gas bearing.In order to make a detailed analysis of sedimentary facies and reservoir characteristics of this special formation,we used sedimentology,reservoir geology,geophysics and other multidisciplinary theories,combined with geology,logging and other data,make full use of the core and its test analysis,finally we picked out favorable development regions which has high permeablity.In this paper,the 8th section of Shihezi formation is divided into two subsections:H8s and H8x,and four layers:H8s1,H8s2,H8×1and H8x2.The 8th section of Shihezi formation is mainly defined as the braided delta sedimentary environment which firstly divides into 2 phases:braided delta plain?braided delta front,and secondly divides into 8 microfacies:batture bar?channel?flood plain?overflow mud?underwater distributary channel at the leading edge?underwater flood plain?underwater distributary bay?estuary dam.H8x is dominated by delta front edge,the underwater distributary channel is developed.H8s is dominated by delta plain and develops channel and batture bar.The gas content of H8x is better than H8s,the permeability of the channel and estuary dam is better,it is a favorable reservoir face which is mainly distributed in the eastern north part of the study area,and extends southward and gradually decreases.The type of reservoir is difined as low porosity and low permneability.The particle size is between medium to coarse,the pore is mainly intergranular dissolved pores,and the average throat is small.The porosity decreases from the northeast to the south eara,and the permeability decreases from the northwest and the central to the south eara,the change of reservoir physical property is mainly affected by compaction,cementation and dissolution,the high permeability reservoir in the area is mainly formed by medium coarse sandstone with low feldspar and formed by the dissolution of strong organic acid solution and weak carbonate cementation.We optimize 9 evaluation parameters(effective thickness?buried depth?sedimentary facies?porosity?permeability?gross ratio?effective thickness?gas saturation?impedance contrast)to establish comprehensive weighing quantitative evaluation method which is suitable for multi-parameter reservoir in this area.The reservoir evaluation is carried out with sedimentary facies as the main factor,and the favorable reservoirs in the subsection of Hsx are mainly distributed in the eastern and the northeastern of the work area.The distribution of favorable reservoirs in the H8s subsection is slightly shifted from the middle east to the middle west.The favorable reservoir in the H8 section is mainly distributed in the north part of the work area,especially in the northeast corner around sull2-shan 387-shan 372.The reservoir evaluation is carried out by taking effective thickness as the main factor.The effective thickness of the H8x subsection is mainly concentrated in the northwestern corner of the work area,and widely distributed;comparing with H8x,the effective thickness of subsection of H8s is less continuous,and the concentration area of high value shifts to the west;on the whole,the effective thickness of the H8 section has good continuity in the middle and north part,and the high value area is mainly distributed in the north,middle,east and west of the source.Finally,it is concluded that the favorable region of the subsection of H8x is mainly concentrated in the northern area such as su264-su202-su114,and in the northeast area such as su352,shan358,shan362-shan348-shan372;H8s subsection is mainly located in the northwestern area such as su336-sul82-sull3 and the northeastern area such as su265-su272-su270,shan51,and shan 366-shan351-shan348;the potential regions of H8 concentrate in the north of the section and extend to the north east with good continuity such as su236-su210-su112,su342,sul4-64,su352,su336-sul82-su113.