The Research On Reservoir Characteristics To Tight Sandstone Reservoir Of Xujiahe Formation In Puguang Area

Puguang gas field is located in the northeastern sichuan basin, adjacent to north of frontal nappe tectonic belt of dabashan mountain, an area of 1116 square kilometers.The main body of continental in Puguang gas field is in the east of fault-fold belt in sichuan basin which located in the northern end of north east to tectonic belt of Puguang-ShuangShi temple in Huang Jingkou structure belt, between the frontal nappe belt of fault fold belt in dabashan mountain and the gentle fold belt in centre of sichuan basin.The Continental strata in this area is similar with the sichuan basin. Years of exploration and development practice shows that in addition to the Marine carbonate strata in the area,the continental strata developmented at Triassic also has a good potential of exploration.This paper is aiming at researching Xujiahe Formation which is the continental strata of puguang area. The research analysis of many factors,such as the structure, sedimentary facies, reservoir characteristics and so on, in order to profiling the potential of oil and gas exploration in the continental strata of the area deeply.To figure out the distribution characteristics of potential area has important significance of exploration in continental strata.In detailed research and analysis of core, logging data and seismic data, combining with the results of previous research in this area we get several main achievements are as follows:1. In the sedimentary period of Xujiahe Formation, the massive terrigenous clastic from dabashan orogenic belt which located in the northeast of work area is the main source of sediment in work area.2. In the sedimentary period of Xujiahe Formation, the work area is relatively flat slope, mainly developed braid river delta. The plain subfacies is the most developed subfacies in the sedimentary period, the area of the plain subfacies is the most widely, as well the thickness. According to classification and statistics, the Xujiahe Formation in work area developed three types of sedimentary subfacies, a total of eight kinds of microfacies.3.By detailed stratigraphic correlation and characterization of sedimentary facies, the sedimentary thickness of T3X2, T3X4, T3X6 are largest, which sand ratio is higher. The sedimentary thickness of T3X2, T3X4 are thinner, the formation gives priority to with argillaceous sedimentary, the thickness ratio of Sand body and formation is low. In every stratum of Xujiahe Formation, the sand body of T3X2 is the most developed, the connection of sand body come from folded channel is of good degree, T3X4, T3X6 is of lower degree.4.Data analysis shows that sandstone reservoir in work area has good degree in grinding roundness and separation, the maturity structure is relatively high, but the compositional maturity is lower. The content of the feldspar and lithic are slightly high. The triangular diagram of sandstone type shows that the feldspar detritus quartz sandstone is the major developmental sandstone type, the secondly is the feldspthic lithic sandstone. The size of Clastic particle are mainly fine grained and silt, some of them is medium grain and coarse grained sandstone. The typical variegation conglomerate of channel fill deposit appears at the bottom of the T3X4 Formation.5.The analysis assay shows that the sandstone reservoirs of Xujiahe Formation suffered a strong and complex diagenesis. One of the most typical and strong diagenesis is compaction/pressure solution, cementation, fracturing, dissolution and so on. The primary pores of the reservoir has been greatly compressed because of the compaction/pressure solution and cementation, so that the pores disappear. Both are related with each other. They decreased the original joint of reservoir sandstone in the study area.They are the main reason of formation of tight sandstone. The latter two are constructive diagenesis. Both of them can improve the reservoir properties, contact each other, provide the conditions for the development of high quality reservoir in tight sandstone. Rupture caused widely distribution of cracks. It is the most characteristic constructive diagenesis in the study area.The fracturing crack is the most extensive reservoir space. It becomes the channel of dissolution which can promote the occurrence and expansion of the dissolution. It has important meaning for the the formation of dissolution pores and seams. So the dissolution is associated with disruption. Metasomatism is occured with the solution. They generally performed as the reaction of the clay minerals to feldspar or quartz. The result of the reaction is the formation of intergranular pore.6. After careful study we found that the characteristics of the sample in the Xujiahe Formation in strict accordance with the characteristics of the meddle B diagenetic stage to late diagenetic stage. Combined with the previous theories of the Xujiahe formation,we know that it has reached the diagenetic stage of middle diagenetic stage B, or even to the late diagenetic stage.7. The types of the diagenetic facies in the reservoir can be divided into the feldspar dissolution+rupture, siliceous cementation facies, illite-calcite cementation. The siliceous cementation facies, illite-calcite cementation facies is poorly developed in the work area. The feldspar dissolution+rupture is the favorable diagenetic facies. Its location can become the focus of the oil and gas exploration.8. The reservoir in work area is tight. The index of physical property shows that the reservoir belongs to the tight sandstone reservoir. Reservoir space is mainly consist of secondary pore and micro fractures, secondly is micro. There is a great influence of cracks on the tight sandstone reservoir, The development of secondary dissolution pore and crack is closely related to the cracks. The porosity and permeability of the area which the fracture developed are of high value.The area is the favorable areas for the development of gas reservoir. The cracks are mainly developed in thick sandstone of the T3X2, T3X4. So that the two layer is the mostly potential area where gas reservoir developed in Xujiahe Formation.