The Sedimentary Facies Analysis Of Chang-2 And Chang-6 Oil-bearing Formation In Yanhewan Area Of Ansai Oilfield

Ansai Oilfield is located in central Ordos Basin, and it is 20 kilometers to the northwest of Yan’an city, Shaanxi province. This thesis selects Chang-2 and chang-6 oil-bearing formation as studied object. Based on the theories of sedimentary petrology, petroleum geology, reservoir geology and well logging geology. According to the field geological investigation, combined with regional geological data, drilling, logging, thin section identification and other testing data. We try to study the sedimentary facies of chang-2 and chang-6 oil-bearing formation, the main research results and understanding can be listed as follows:1. According to the outcrop observation, the Identification of drilling cores and cuttings.At the same time, we should considering the sedimentary cycle, and using the log interpretation, special maker bed to determine the division and contract of the Chang-6 oil bearing bed. From top to bottom, the Yanchang formation can be divided into 10 oil-bearing beds(from chang-1 to chang-10), and the chang-2 oil bearing bed can also subdivided into chang-21, chang-22, chang-23, the chang-6 oil bearing bed can be subdivided into chang-61, chang-62, chang-63.2. According to the analysis, we consider that the main rock type is feldspathic sandstone in the study area. The Lithic feldspathic sandstone take the second place, the quartz sandstone is the least.3. IN the period of chang-2 deposition, the sedimentary environment was delta plain subfacies, and the micro-facies were the distributary watercourse and the swamp.IN the period of chang-6 deposition, the sedimentary environment was delta front subfacies, and the micro-facies were subaqueous distributary channel and inter-distributary estuary.4. According to the mineral characteristics, clay mineral assemblag, rock structures, tectonic characters and rock porosity, which show that the chang-2 and chang-6 reservoirs mainly distributed in A period of late diagenetic stage. Based on analysis of rock physical properties, sections, cast sections, scanning electron microscope Statistics show that The main pore type of the chang-2 reservoir is inter-granular pore,the main pore type of the chang-6 reservoir is inter-granular pore,the second is laumontite solution pore and feldspar dissolution pore. The physical property of chang-2 reservoir belongs to medium porosity and extra-low permeability, low porosity and low permeability, which means a poor physical property. the physical property of chang-2 reservoir belongs to low porosity and extra-low permeability, which means a extra worse physical property.