Research On Reservoir Characteristics Of Shahezi Formation In Xujiaweizi Depression

Shahezi formation developed widely in Xujiaweizi depression, drilling shows that this formation has a good prospect in gas exploration. But the distribution of sand gravel body and the definition of favorable zones is unclear, which restricted the exploration. On the basis of stratigraphic classification and sedimentary facies research, integrated regional tectonic characteristics, using the theory of reservoir geology, reservoir characteristics of Shahezi group are studied in this article, and the favorable reservoirs are predicted, too.Through core analysis and thin section identification, we find that the reservoir rock types of interest formation are mainly sandstone, and mudstone followed, which contains a small amount of coal and volcanic rock. For reservoir property, the average porosity is3.7%, the average permeability is0.22mD, which belongs to Ⅲ to Ⅳ reservoir. The porosity and permeability are generally decreasing by depth, abnormal values existing in some certian depth. Reservoir space types are primary intergranular pore, secondary pore and fracture, mainly secondary pores. Diagenesis includes compaction, cementation, metasomatism and dissolution. Reservoir is mainly influenced by diagenesis, sedimentary microfacies and structure.Based on thickness statistics of sandstone, mudstone and coal in single well, according to sequence stratigraphic classification, combining with seismic attributes prediction and plane distribution of sedimentary facies, we mapped the thickness contour map of glutenite, mudstone and coal seam. It shows that sandstone thickness generally increases from west to esat, and well developed in the fault zone, such as Xuxi fracture, Xuzhong fracture and Xudong flower fault. Mudstone developed in lacustrine deposition area in the central basin. Coal seam is mainly distributed in the braided river delta plains.Using seismic attributes prediction and distribution characteristics of sand body, combining with the plane distribution of sedimentary facies belt, according to the distribution of porosity and permeability, The reservoir was divided into three levels namely Ⅲa, Ⅲb and IV, which shows that SQ3,and SQ4is main gas reservoir in the work area. Combining previous research results, intargeted geochemistry, geology, construction and other factors, the hydrocarbon accumulation characteristics was concluded and the interest exploration area was defined.