The Reservation Analysis Of Neopaleozoic Shanxi Formation And Lower Shihezi Formation On Yan X Well

Based on the sedimentary characteristics, petrologic features, reservoir property and Pore structure of Shanxi and Lower Shihezi Formation in Yanchuan area, to analyze the factors affecting Reservoir property. Compared with other gas-well in region of interest and combined with regional sedimentary evolution of Ordos Basin, it is thought Shanxi Formation mainly develops The meandering river delta depositional system, Lower Shihezi Formation develops Braided River Delta depositional system. The Underwater distributary channel sand body consist of Upper Paleozoic cheaf gas reservoir. Chemical analysis of rocks of54Reservoir casting slice reveals Lower Shihezi and Shanxi Formation are mainly made up of Lithic quartz sandstone. Mineral component is most of quartz, rock debris are mainly magmatite and metamorphite and sedimentary debris is less. Besides, a small quantity of chert exsits. Matrix include hydromica, kaolinite, greenite, calcite, dolomite and kiesel. Total content is high, but change a lot.The average porosity and permeability of Shanxi Formation are6.42%and0.298x10-3μm2, the average porosity and permeability of Lower Shihezi Formation are6.15%and0.243xlO-3μm2. Compared with Well Yan A (The average porosity and permeability of Shanxi Formation are5.30%and0.439xl0-3μm2, the average porosity and permeability of Lower Shihezi Formation are5.07%and0.184×10-3μm2) and combined with regional Stratum characteristics, we know Shanxi and Lower Shihezi Formation in Yanchuan area are charactered by low porosity and permeability. Shanxi Formation is little better than Low Shihezi Formation. Pore structure types include intergranular pore, intergranular dissolved pore, feldspar solution openings, rock debris dissolution pore, zeolite dissolved pore and intercrystal pore.According to the feature of capillary pressure curves, combined with the propertiesand casting slice information, the reservoirs of Shanxi and Xiashihezi formations in the well were divided into four categories:Reservoir I mainly included the dissolved pore-intergranular pores combination, and the curve was characterized by almost no obvious straight segments, lower inflection point, the longer horizontal length of the curve of mercury, which meant that the largest connected pore throat radius, the maximum feed mercury saturation, the smaller volume of rock’s small pore throat. Pore throat radius distribution histogram showed a single peak, well-sorted, and taking up of9%of such reservoir samples.Reservoir II mainly composed of the dissolved pore-intergranular pores, then minor of the micro-dissolved pore-intergranular pores, and the curve was represented by an obvious straight curve segments, the higher inflection point, the smaller slope, the longer horizontal length of the curve of mercury, which meant that they have larger displacement pressure, lower production capacity, the maximum feed mercury saturation, the smaller volume of rock’s small pore throat. Pore throat radius distribution histogram showed a single peak, better sorted, which accounting for34.1%of such reservoir samples.Reservoir III mainly consists of the micro-dissolved pore-intergranular pores, and the curve has higher inflection point, a large slope, less longer horizontal length of the curve of mercury, which indicated that the largest connected pore throat radius is small, and the maximum feed mercury saturation is greater than50%, the rock’s small pore throat accounted for a large volume. Pore throat radius histogram has lower histogram, poor sorting, peak width, which accounted for52.3%.Reservoir IV is microporous composite reservoir. The curve has high inflection point, a large slope, close to45°, shorter horizontal length of the curve of mercury, the maximum feed mercury saturation is small and the largest connected pore throat radius is also small with poor sorting, which is mainly of small pore in the rock. Pore throat radius histogram has ultra-low histogram, poor-sorted, such reservoir samples (4.6%). It mainly dominated by Reservoirs II and III, which accounted for86.4%.