Reservoir Characteristics Of Xujiahe Formation In The Puguang Area

The continental strata made a good progress in the Puguang area. Because of the rich gas resources and active recoverable reserves, it is always be key area about exploration and development. But because of formation compaction and poor reservoir property, it is difficult to explore the nature gas in this area. In this paper, under the guidance of sedimentology, analytical data and the well logging data, I study the reservoir characteristics of Xujiahe formation to provide theoretical references for the next exploration and development.Study shows that Xujiahe group can be further divided into six members. Sedimentary’s type complex which mainly include the delta, alluvial fan, alluvial plain and lake sedimentary system. Alluvial fan sedimentary system developed in T3X4, alluvial plain developed in T3X5and the lacustrine depositional system exists in the T3X3, T3X5and T3X6. Delta is widely developed which mainly developed in all the sections.The lithology of Xujiahe formation is mainly aphanites and medium grained lithe sandstone; secondly, it’s the feldspathic lithe sandstone. The matrix consists of miscellanea and cement, which include siliceous and carbonate cement; The sandstone’s grain is mainly mesograin, the next is aphanites and moor rock. The contact way is mainly point to liner, the psephicity is subangular, the sizing is well to middle, sustaining way is mainly about particle sustaining.The reservoir space is remaining intergranular pore、intergranular pore-. intragranular dissolved pore、intercrystal pore and microcrack which communicate each other with turning bottleneck checking bottleneck and flaky bottleneck. The porosity is mainly areola and micro-vuggy, the style of bottleneck mainly include slender and micro. The arraying style of pore throat mainly consists of areola-slender bottleneck and micro porous micro bottleneck. The curve of CP divide Ⅰ、Ⅱ、Ⅲ、Ⅳ types, the one belongs the best reservoir, the next is the Ⅱ, the Ⅲ includes the poor reservoir, the IV is the no reservoir. According to mercury intrusion method, the mean radius of bottleneck is small, which presents high drainage pressure、low ejection efficiency and big mercurial instauration volume, and heavy heterogeneous medium in plane view.The study area of Xujiahe formation is a low-porosity to extra low-porosity、low to extra low-permeability. The porosity is between0.1%and7.8%, and the mean is1.9%; the variation range of permeability is big, which is0.004md to15.852md, the mean is0.0855md. The contact exists in porosity and permeability, and the developing splits improve some pores; the physical property of reservoir presents improving tendency from T3X6to T3X2in longitude view.The diagenesis’s style in Xujiahe formation is rich, including compaction、 pressolution、cemetation、denudation、metasomasis、cataclasis and packing action, which denudation and cataclasis fall into constructional diagenesis and compaction and cemetation reside destructive diagenesis. The diagenetic stage of Xujiahe formation achieves late time, and the degree of diagentic evolution is high.The main elements of controlling the reservoir’s development are the deposit、the diagen and tectonoclastic effect. The best deposit controlling physical property is anastomosed stream and the best depositional microfacies is the distributary channel. The development of diagen reforms the growing of reservoir, the constructional diagen improves the physical property of reservoir; the destructive diagen hinders it; the splits made up of tectonoclastic effect positively improve the reservoir. The reservoir of Xujiahe formation divided into four types, which the main are Ⅱ type and Ⅲtype. According to the lower limit of effective porosity, it is2.5%, the areal distribution feature is researched. The developmental area of reservoir in Xujiahe formation centralizes in PG4-PG2-HZ1well and PL1well. The developmental area of reservoir in T3X2centralizes in PG2well、PL1well and HZ1well. The developmental area of reservoir in T3X4centralizes in PG2-HZ1well and LJ1well. The developmental area of reservoir in T3X6centralizes in PL1-LJ1well.