The Research Of Logging Recognition Method Of Effective Reservoir On Special Low Permeability Reservoirs For Yanchang Formation In Huanjiang Area

Huanjiang area is located in the western of Ordos Basin, the main oil-bearing bed is the Triassic yanchang formation and Jurassic yan’an formation. Huanjiang oilfield is typical of the low permeability tight sandstone reservoirs, reservoir property is bad, anisotropy is strong and the relationship between oil and water is complicate of the reservoir. The difference of diagenesis and pore configuration seriously impacted the ability which takes well logging data to accurately identify and evaluate reservoir. We research the Chang6reservoir of Huanjiang area in the Ordos Basin from the complex pore structure of low permeability reservoir, the electrical and lithology characteristics, logging interpretation model, low permeability formation with rapid identification and logging, capacity prediction and other aspects. The main conclusions are as follows:(1)The depositional system of the Chang6reservoir in Huanjiang area belongs to the delta front and turbidite fan depositional environment coexist, main microfacies types are underwater distributary channel and turbidite channels. The main rock types are lithic arkose, feldspathic lithic sandstone, the content of feldspar and quartz are higher, debris is lower, and mainly metamorphic rock debris. The average porosity of Chang6reservoir is9.6%, average permeability is0.3×10-3μm2, reservoir property is bad, the characteristics perform low porosity, ultra-low permeability.(2) The pore types of Chang6reservoir in Huanjiang area are mainly intergranular pores, followed by feldspar dissolution porosity and other pore types are relatively small.The average displacement pressure is1.78Mpa, median pressure6MPa, median throat radius is0.15μm, Chang6reservoir develops small pore and it’s pore structure is not good.(3) Diagenesis is the main factor to control reservoir developing, our study area has a strong diagenesis, complex type, compaction plays a major role in the destruction of primary porosity, while developing the cementation; Metasomatism and dissolution play a major role to form secondary porosity, and play a very important role to improve the reservoir properties of the area.(4) On the basis of fine interpretation model of reservoir parameters and the lower limit of reservoir properties, the paper established reservoir parameter limit value method, invasive characteristics analysis method, acoustic time overlap with the resistivity diagram method, lithology-electrical crossplot method, differential analysis method, horizontal contrast method and other comprehensive technologies for judging oil-water bed quantitative and qualitative to improve the coincidence rate.(5) On the basis of logging reservoir classification, comprehensive utilize of logging, oil testing dynamic information, the main factors of impacting reservoir capacity are the effective thickness of reservoir, oil saturation, porosity and permeability, to get the lower limit of different productivity levels of various parameters, and identify the oil-water bed qualitative. Dividing reservoir capacity into a hierarchy according to per meter of Nissan fuel to establish the quantitative evaluation model of capacity respectively, it has greater accuracy and good effect of geological applications.