Favorable Area Prediction And Evaluation Of Chang6 Reservoir In Dalugou-Liandaowan Region Of Ordos Basin

Ordos Basin is the second largest sedimentary basin in China.The basin is rich in oil and gas resources,it has become a key target area for oil and gas exploration in Changqing Oilfield.After years of exploration and development of oil and gas,it has achieved rich results.The object of this study is the Chang 6 reservoir in the Dalugou-Liandaowan area of the Ordos Basin.The Dalugou-Liandaowan area is located in the middle part of the northern slope of the Ordos Basin.Because the tectonic movement of the basin is characterized by overall uplift and overall settlement,the faults in the basin are not developed,and there is no large basal uplift,the inherited development features are obvious,and the deposition environment maintains long-term sustained stability,which is conducive to the generation and preservation of oil and gas.This study systematically studied the sedimentary system characteristics,sandbody distribution,reservoir characteristics,reservoir controlling factors and distribution characteristics in Dalugou-Liandaowan area of Chang 6 reservoir,provide the direction and basis for the work of the next step in the exploration and development of oil and gas.During the research of the project,the Chang 6 oil reservoir group is divided into three groups that is Chang 6₁,Chang 6₂ and Chang 6₃ from top to bottom.and they are further divided into eight layers,namely,Chang 6₁¹,Chang 6₁²,Chang 6₁³,Chang 6₂¹,Chang 6₂²,Chang 6₂³,Chang 6₃¹,and Chang 6₃².After stratigraphic comparison and analysis,it is considered that each of the Chang 6 oil reservoirs of the Upper Triassic Yanchang Formation Small layer thickness changes little,distribution is stable,and continuity is good.After sedimentary background analysis,it is found that the sedimentary period of the Chang 6 reservoir in the Dalugou-Liandaowan area is a lake basin recession period.In combination with the sedimentary facies symbol and logging curve analysis,the Chang 6 reservoir in the Dalugou-Liandaowan area is identified as a deltaic depositional system.It mainly develops the delta front subfacies,including three types of sedimentary microfacies:underwater distributary channel,channel side margin and inter-branch bay;the underwater distributary channel sand is the reservoir skeleton.The Chang 6 reservoir rock type is mainly feldspar sandstone,The interstitial materials are mainly clays and zeolites,the chlorite and lausonite are the main components.And the detrital grain sortability and roundness are moderate.The particles are mainly point-line contact.The pore types mainly include intergranular pores,feldspar dissolved pores,and zeolite dissolved pores.The average porosity is 11.02%,and the average permeability is 1.49×10^-3?m².The Chang 6 reservoirs in the study area are lithologic reservoirs,and the distribution is controlled by lithologic and sedimentary facies belts.Chang 6 reservoirs are distributed along the underwater distributary channels in the plane in strips,with multiple stages of vertical accumulation and superposition.Finally,combined with the research results in the study area,a prediction is made on the favorable areas for hydrocarbon accumulation in the Chang 6 reservoir group.Two favorable zones of type I,two favorable zones of type II,and one favorable zone of type III are selected.The reserves in the favorable areas have been calculated,and the predicted reserves total 358.2×10⁴t.The oil and gas resources are abundant and have potential for development.