Selection Of Favorable Areas And Evaluation Of Tight Sandstone Reservoir Of Chang 8₁ In Xifeng Area

The Xifeng area is located in the southwest of the Ordos Basin.The Upper Triassic Yanchang Formation Chang 8₁ sub-oil layer is one of the main exploration strata in this area.This layer with thicker sand bodies and favorable oil accumulation conditions is in direct contact with the top Chang 7 source rock.But,due to the tightness of the whole reservoir and strong heterogeneity,the main controlling factors for favorable reservoir development are unclear,and the exploration effect is not ideal,and breakthrough has not been achieved.Therefore,it is currently the main problem facing exploration to clarify the control factors and distribution rules of favorable reservoirs and guide the selection of favorable exploration targets.In response to the above problems,this article takes sedimentology,petrology,sequence stratigraphy,petroleum geology,and logging as guidance,through field analysis,core observation,drilling,logging data,and a variety of experimental testing methods to comprehensively analyze storage sedimentary,petrology,physical properties and oil-bearing properties,diagenesis and microscopic pore structure characteristics.Last,this paper reveals the main controlling factors for favorable reservoir development,establishs comprehensive reservoir evaluation standards,and optimizes favorable production areas.There are some of the main results:?1?According to the marker layer and sedimentary cycle,the Chang 8₁ linoleum group is divided into three small layers from bottom to top.The study is more detailed.?2?The Chang 8₁ sub-oil layer is deposited in the front edge of shallow water delta.The sand bodies overlap frequently in the vertical direction,and the multi-stage superimposed underwater distributary channel is the main reservoir.On the plane,the river sand bodies are continuously distributed in the form of strips in the southwest and northeast directions.?3?Reservoir lithology is mainly detrital feldspar sandstone and feldspar detrital sandstone,the pore type is mainly residual intergranular pores,and the throat type is mainly pore-reducing type,constricting type and flaky and curved flaky.The content of voids is high,the structure of pore throat is complex,and the physical properties are poor.?4?Early compaction,mid-late chlorite cementation and iron calcite cementation are the main causes of porosity loss,and feldspar dissolution is the main way to increase porosity.?5?Chang 8₁ reservoir can be divided into three categories.Class ? reservoirs have the best quality,class ? reservoirs have the best quality,and class ? reservoirs have the worst quality.?6?Combined with reservoir evaluation and reservoircharacteristics,the favorable area selection criteria were established.A total of 19 type ?favorable areas,19 type ? advantageous areas and 11 type ? favorable areas were predicted,with a total area of 853.24km².The research results provide some technical support for the subsequent exploration and development of the oil field.