Research On Sedimentary Facies And Reservoir Features Of Chang 4+5 Of Yanchang Formation In Ansai Oil Field

This paper lucubrates about the sedimentary system development and distributing feature and sandbody distributing features of Chang 4+5 oil formation in Ansai Oilfield, finds hydrocarbon condition at large, analyses and estimates hydrocarbon-bearing characteristics in different stratum and favorable exploration area, finds out petroleum scale and exploration prospects on the basis of gripping investigation areal geological data and digestion and absorption of previous research results. This conclusion is directed by sedimentary theory and methods integrating with theories of technical , stratum, reservoir geology , geochemistry , basin analysis and data of outcrop , drilling , well logging. Meanwhile, the study gets the general geology, analysis assay, well logging and test data, predicts the relation of sedimentary facies and petroleum distribution and the distribution of favorable reservoir of Chang 4+5 oil formation.The study area mainly includes lake and delta sedimentary model, most areas are delta front deposits, and sandbody all show NE-SW banding distribution. The northeast part of study region is deltaplain deposits , shallow lake of Chang 4+5₂ has large scale , only in northeast part there are a spot of deltaplain, while the deltaplain acreage in same part of Chang 4+5₂ is slightly larger. In this part, channel sandbars, deltaic front subaqueous distributary channel and deltaic plain distributary channel are main reservoir bodies.The rock types of Chang 4+5 in this region are mostly arkose or lithic arkose sandstone. Cement types are complicated and various, which are mainly chlorite and calcite. Reservoir sandstone of Chang 4+5 in Ansai oilfield has features as low maturity of mineral and high textural maturity. Dissolve pores of feldspar and so on have high ratio of total pore amount and become relative high quality reservoir of Chang 4+5. Diagenetic minerals are mainly thin film shaped chlorite and increasing shaped quartz minerals. There are autogenous apatites, filled silicious and carbonate minerals as well.Chang 4+5 oil formation in Ansai oilfield is mainly lithology and structure-lithology combination reservoir, in which lithology reservoir is the main part. Chang 4+5₂ formation is mostly composed of lithology reservoir which mainly composed by sandstone undig finely barrier and updig pinch. The distribution of reservoir is controlled by sedimentary processes, source-reservoir-cap favorable assemblage, oil-generating center, favorable reservoif phase, and nose structure and updig direction favorable occlusion. Chang 4+5₂ in the region is main oil-bearing horizon of Chang 4+5 formation, favorable area mainly distributes around Xinghe, Pingqiao, Ansai Yanhewan , where electrical measurement and physical properties are better and have certain reservoir forming conditions, thus , become next exploration target of Chang 4+5₂ . Xihekou-Gaoqiao region is the minor favorable area; Oiliness of Chang 4+5₁ formation in the region is poor as a whole , the area that oil-gas has better show is limited , Sai 80 well field is the more favorable area of Chang 4+5₁ formation, Tanjiaying, Pingqiao, Xinghe, Xihekou-Gaoqiao region are minor favorable area. In general, Chang 4+5₂ oil-gas show is better than Chang 4+5₁.