Reservoir Characteristics And Controlling Factors Of Hydrocarbon Accumulation In Chang 8 Of Yanchang Formation In The Honghe Oilfield,Ordos Basin

The Chang 8 reservoir group in the Honghe Oilfield in the southern Ordos Basin is a typical low-permeability sandstone reservoir with poor reservoir physical properties and strong planar and vertical heterogeneity.The reservoir characteristics,fracture characteristics,fracture formation mechanism and main controlling factors of the Chang 8 Formation of the Yanchang Formation in Honghe Oilfield were studied,and the internal control factors of the 8 hydrocarbon accumulation in the Chang 8 Formation in the area were analyzed to form a regular understanding of the Honghe Oilfield Science.Reasonably developing and providing geological theoretical basis has important guiding significance for the production capacity of Honghe Oilfield.Based on previous research results,this paper analyzes and studies the basic geological characteristics,reservoir characteristics,fracture characteristics,crack formation mechanism and main control factors,and the main controlling factors of oil and gas enrichment.The stratigraphic structure of the Chang 8 reservoir in the study area is a monoclinic structure with high in the southeast and low in the northwest,and there are uplift belts and faults in some areas;the sedimentary system is the sedimentary subfacies of the braided river delta front,underwater distributary channel and diversion Inter Bay is its main type of sedimentary microfacies;sedimentary facies belt directly controls the distribution of reservoir sand bodies,develops along the main channel and has good connectivity,gradually thinning to the edge of the river.Gray,dark gray,argillaceous feldspar cuttings and lithic arkoses are the main types of sandstone in the reservoir.The average porosity of reservoir sandstone is 10.8%,and the effective permeability is 0.4×10-3?m.The porosity is linearly related to the permeability.The pore structure is mainly composed of small pore-micro throat.Rock diagenesis mainly includes: compaction and pressure dissolution,cementation and dissolution.The physical properties of the reservoir become better with the increase of the content of quartz and debris in the detrital grains,and become worse as the content of mica and feldspar increases.With the increase of clay minerals,the porosity of the reservoir changes little and the permeability changes.Significantly reduced;dissolution in diagenesis and the presence of chlorite films are conducive to better reservoir properties,the presence of kaolinite often also implies the presence of dissolved pores,compaction and cementation are long 8 reservoir low porosity The main reason for low permeability.The types of fractures are mainly structural fractures and diagenetic fractures.High-angle shear fractures are the main types of fractures.The northeast-facing,northwest-facing,north-south-facing,and near-west-to-west-fault fractures are mainly developed.The northwest-western cracks and the east-western cracks are mainly formed under the shear stress of the left-handed shear stress during the Yanshanian period.The north-south and northeast cracks are mainly in the Himalayas.Under the effect of right-handed shear-tensile stress,the main trend of effective fractures is northeast-east direction.The main factors affecting the development of fractures are tectonic stress field,reservoir properties,and micro-sedimentation.The effective deployment of medium-scale oil-rich faults,oil sources and networked rivers controls the high production of Chang 8 reservoirs in the study area.Medium-sized faults of type II,because of the fault distance between 10~35m,spliced Zhangjiatan oil shale and Chang-8 reservoir,creating a double-effects diversion system for vertical and vertical fractures,corresponding reservoirs.The oil-bearing property is good;while the faults of Class I and III are single vertical systems of cracks and faults,and the oil-bearing property is relatively poor.