库车坳陷东部YN5井下侏罗统致密储层特征及主控因素

Tight Reservoir Beds and Control Factors of Lower Jurassic System in Well YN5,Eastern Kuqa Depression

库车坳陷东部YN5井位于依奇克里克构造带中部，其下侏罗统阿合组发育一套浅色辫状河三角洲相砂岩、砾岩组合，阳霞组为湖泊相夹三角洲平原相的大段泥岩夹砂岩和煤层。通过岩石薄片观察，结合岩石物性测试发现，下侏罗统储层岩石类型主要为岩屑砂岩，岩屑以变质岩岩屑为主；阳霞组以铁泥质和钙质胶结为主，阿合组以硅质和钙质胶结为主。储层孔隙度均小于12％，多介于2％～8％之间，渗透率多介于0.1×10-3～5.0×10-3μm2，平均孔喉半径主要介于0.2～0.6μm之间，阿合组储层物性好于阳霞组。受到原始岩石组分及压实作用的综合控制，阳霞组和阿合组储层物性呈现出两段式自上而下逐渐变差的特征。储层岩石孔隙类型以粒内溶孔和微孔隙为主，是由长石、岩屑以及碳酸盐胶结物等可溶物质遭受溶蚀作用形成，阿合组粒度相对较粗，长石、岩屑等可溶组分含量相对较高，其溶蚀作用较阳霞组更发育。此外，构造作用产生的裂隙是改善储层物性的另一重要因素。

The Well YN5 is located in the Yiqikelike structural belt in the eastern Kuqa Depression.The Yang-xia Formation develops sandstone and conglomerate of braided river delta,while the Ahe Formation develops thick lacustrine mudstone with the interlayer of sandstone and coal seam.Based on the thin section observation and physical property test of the sample,it is revealed that in the rock types of the Lower Jurassic reservoir,the litharenite is predominant with relatively more detritus of igneous rock.The ferruginous and argillaceous cements are dominated in the Yangxia Formation,while the siliceous and calcareous cements are the major cements in the Ahe Formation.The porosity of the Lower Jurassic reservoir is smaller than 12%,mostly between 2% and 8%,the permeability is largely between 0.1 ×10 -3μm2 and 5.0 ×10 -3μm2 ,and the average pore throat radius varies from 0.2 μm to 0.6 μm.Generally,the reservoir physical properties of the Ahe Formation are better than those of the Yangxia Formation.The porosity and permeability of Yangxia Formation and Ahe Formation both display characteristics of two sections varying to worse along the increasing depth,due to the compaction and original materials.There are superior intragranular pores and micropores in the Lower Jurassic reservoir owing to the dissolution of the soluble constituent such as feldspar and detritus.Relatively,the reservoir of Ahe Forma-tion develops more vuggy porosities because of its coarse grains and more feldspar and detritus.The fractures by the tectonic stress play an important role to improve the reservoir physical properties.