Research On Fluvial Sand Deposition And Heterogeneity To H8 In The East Region Adjacent To Sulige Gas Field

The member 8 of Xiashihezi formation(H8) in east region adjacent to Sulige gas field is a kind of lithological gas reservoir, which is classified as fluvial facies with characteristics of low porosity, low permeability, and low abundance. As for the reservoir, the buried depth is very deep, the thickness is thin, the interlayers are existent, the thickness of gas is much thin, the lateral variation changes greatly, the vertical connectivity is bad, the effective reservoir is hardly identified, and the determination of well locations is difficult. In order to delineate the distribution of gas reservoir with high porosity and permeability, the sedimentary model and heterogeneity of fluvial sandstone was research.By using the data of log, drilling, test, and outcrop, this paper created the sedimentary facies of the research area after research of the log facies and the lithofacies. Then, considering the distribution of sand bodies, the characteristics of profile, the ratio of sand body and stratum, and the parameters of palaeo-hydrology,this paper created the relevant evolution model after research of the spatio-temporal evolution characteristics of fluvial facies. Further, considering the sedimentary facies,diageneses, pore types, and reservoir physical properties, this paper researched the reservoir heterogeneity, in which the quantitative mathematical model for heterogeneity identification was researched based on the BP artificial neuron network and the Logistic regression.The conclusions can be drawn as follows.(1) The lithofacies can be classified into 16 types in terms of the granularity,lithology, rock morphology and the relationship, and sedimentary structure type. And the sedimentary facies of H8 is fluvial facies, in which the main facies is braided river deposit, second is meandering river deposit, and the third is anastomosed river deposit.(2) The evolution rule and model of fluvial facies of the research area are revealed.In order to achieve this, the sand spatial distribution regularity was researched combined with cause analysis, the river conversion characteristics were researched combined with controlling factors, and the vertical evolution sequence was researchedcombined with sedimentary forms in different areas. The evolution model indicated the river types of H8 had changed in time and space. From west to east, the braided river changed to the meandering river, in which there existed mutual containing.Vertically, the braided river changed to the meandering river, and then changed to the anastomosed river.(3) Low porosity and low permeability is the main reservoir type to H8 in the research area. The relatively high yield reservoirs are distributed in coarse facies with high energy watercourse deposition. The reservoir heterogeneity is much more remarkable, to which the macroscopic heterogeneity is controlled by sedimentary facies; the microcosmic heterogeneity is controlled by lithology, diagenesis, and porosity evolution.(4) The pore development situation is significantly different in different rock types and different strata. The reservoir performance is also different. The quartz sandstone,lithic quartz sandstone, and lithic sandstone all develop residual primary intergranular pores, secondary pores, and kaolinite intercrystalline pores, to which the development is reduced from the quartz sandstone to the lithic sandstone.(5) The mercury injection characteristics are different to different sandstone of H8.The pore throat of quartz sandstone is relatively thick, but its distribution is uneven.While the pore throat of lithic quartz sandstone and lithic sandstone is relatively thin,its distribution is even. The curves are much more similar between the pore types and the mercury injections of sandstone of H8 as a whole, which reflects the similar pore structure characteristics. The pore structures can be classified into four: complex,microporous, dissolved-intergranular, and intergranular.(6) Nine diagenetic facies are identified based on the characteristics of diagenesis,porosity, permeability, and mercury injection. The nine facies are: quartz overgrowth cement mixed with porosity, kaolinite-quartz overgrowth cementation weak soluble phase, pressolution dense phase, authigenic kaolinite intercrystalline pore phase,tuffaceous pore filling phase, clay mineral matrix filling dissolution, hydromica cemented account microporous phase, mechanical compaction dense phase, and calcareous cementation accountable dense phase.(7) A combined method was proposed for reservoir heterogeneity evaluation based on the BP artificial neuron network and Logistic regression using a group of evaluation factors. And two evaluation maps of H8 l and H8 u were presented. The research results show that the BP artificial neuron network and the Logistic regression can be used to evaluate the reservoir heterogeneity and have characteristics of clarity,simple process, less time-consuming and rapid mapping. By contrast, the evaluation result given by the combined method is much more applicable.