Reservoir Description Of Chang-6 Oil-bearing Layer Of Triassic Yanchang Formation In Beita Zone Of Zhidan Oilfield, Ordos Basin

Based on the research results of Triassic Yanchang Formation in Ordos Basin, the use of petroleum geology, sedimentology, sequence stratigraphic theory, in accordance with the principles of marker bed, standard floor, cycle contrast, formation thickness, fine classification and correlation of strata is completed. Chang 6 oil-bearing layer is subdivided into Chang61,Chang62, Chang63, and Chang64 oil-bearing sublayers. And Chang61 is subdivided into Chang61-1, Chang61-2, Chang62 into Chang62-1,Chang62"2, Chang62-3, Chang63 into Chang63-1, Chang63-2.On this basis, the structural characteristics of Chang 6 oil-bearing layer is studied, a gentle west-dipping monoclinic, nose slightly structures locally developing, bottom-up with a clear succession, controlling the oil and gas accumulation.By observing the core, sedimentary facies sign recognition, logging facies analysis, combined with regional sedimentary background, Chang 6 oil-bearing layer mainly develops delta front depositional model, and identified underwater distributary channel, distributary bay, underwater distributary channel flank, mouth bar, sheet sand and so on five kinds of sedimentary microfacies and sedimentary facies and sand body in general showed NE-SW trending banded distribution, split between the river is split between the Gulf of separation. Chang 6 oil-bearing layer is mainly feldspathic sandstone, detrital mainly feldspar, quartz, with a low compositional maturity, a low-especially low porosity, extremely low low permeability reservoirs, pore types Reap between dissolved pore, intergranular pores, followed by throat types are mainly fine throat, larynx times for fine and micro-jets, is a small hole-fine throat. Integrated reservoir rock types, sedimentary facies, diagenesis, reservoir properties, sand thickness, microscopic pore structure characteristics, capillary pressure curves, etc., the Chang6 classified as Ⅲa～Ⅳb categories, including good reservoir Ⅲa class layer, Ⅲb classes for better reservoir, Ⅳa class medium reservoir, Ⅳb class of poor reservoir. Chang6 lower limit of reservoir lithology fine sandstone level, oil level lower limit for the oil patch, the lower limit is 9.0% physical properties (porosity) and 0.2×10-3μm2 (permeability), the lower limit of the electrical oil saturation≥40%,4.0 resistance>18Ω·m and acoustictime≥218μs/m. Calculated using the volume of Chang6 petroleum geological reserves of 1061.42×104t, oil-bearing area 18.80km2.