Accumulation Controlling Factors Of CH8 Reservoir In A Area In The Middle Of North Shaanxi Slope

The oil field of A area in the middle of the north Shaanxi slope is located in the middle of the north Shaanxi slope of the Ordos Basin,and the region spans from Wuqi to Jingbian to Zhidan.The main oil bearing layers are Triassic Yanchang Formation CH6,CH4+5 and CH2,followed by Jurassic Yan 'an Formation Y10 and Y9.The overall development of Block A has gone through four stages.The first stage is the pilot development trial stage(1996-1997).The CH6 reservoir in Block A has been developed from the initial stage to improve the development efficiency.Actively carry out field development and test,open up water injection,gas injection,gas-water cross injection,rectangular well pattern and large sand volume fracturing,horizontal well development test areas;The second stage is the large-scale construction stage(1997-2003).Since 1997 has built the five li bay,Huolong Mao block,screen out CH6 rich area,and after two years of large-scale production inspection,later rolling expansion,built 840,000 tons of capacity.By the end of 2006,1143 oil Wells had been drilled in Area A,with A daily oil level of 3873 t.The third stage is the stage of development adjustment and small-scale rolling edge expansion(2003-2009).After large-scale construction and production stage,the injection and production well pattern in the block has been basically perfected.However,because the injection-production relationship is not reasonable after the new area is put into production,the reasonable development technology policy of the oilfield needs to be improved in the dynamic adjustment continuously,so that the production level of the oilfield has a large and fast decline range,and some well points even have the problem of water cut rising.Since 2003,in addition to continuing production construction and local rolling edge expansion in the developed blocks,the injection-production relationship adjustment has been implemented in the developed blocks.After several large-scale injection-production adjustments,the water flooding condition of the oilfield is stable,the injection-production relationship tends to be reasonable,the production level rises steadily,and the decline range of the oilfield is small.The fourth stage is the development of tight oil(2010-present),through exploration and technical reserves,the initial formation of tight oil development technology.In recent years,deep exploration and evaluation efforts have been intensified in Block A.High-yielding industrial oil flows have been obtained from CH7-CH8 in Shun 98,Shun 111,Xin 352,etc.,and large scale reservoirs have been found in Block A CH7,High A CH8,Huolangmou CH7,CH81,and CH82,making A great breakthrough in exploration and evaluation.It is predicted that the oil bearing area is 389.8 square kilometers and the reserves are 11.694 million tons,among which CH81 and CH82 have a larger area.The CH8 reservoir in the study area has a good potential for reservoir increase,construction and production,but it is limited by the unclear understanding of reservoir control factors,the unfulfilled scale of the hyperpermeability enrichment zone,and the poor overall physical property of CH8.The direction and scale of deep reservoir increase in A area have been difficult to be confirmed.In this study,the CH8 reservoir in Block A was studied on the sedimentary microfacies and the plane distribution characteristics of sand body,and the comprehensive reservoir evaluation was carried out to clarify the main controlling factors of oil and gas accumulation and enrichment rules,thus providing strong support for the direction of reservoir increase and the deployment of exploration and evaluation in the later period.In this paper,combining with the research in 7 of the well logging,mud logging,coring,oil test,test data and comprehensive logging geology and sedimentology theory method,has conducted A study of CH8 reservoir sedimentary characteristics,reservoir characteristics of micro and macro research and comprehensive evaluation,four fine CH8 reservoir study,to recognize the reservoir plane distribution characteristics,Summarize the main factors that affect the oil-bearing property,and study the controlling factors of accumulation and enrichment rule of CH8 reservoir.In this study,it is found that CH8 in Area A is the delta front,and the main sedimentary microfacies type is underwater distributary channel.The reservoir is dominated by fine sand and contains A small amount of medium sand,silt and mud.By dividing the fine stratigraphic correlation,the porosity model is established by dividing the small layers,and the fine isochronous stratigraphic correlation skeleton section is established.It is revealed that the distribution of source rock has a certain control effect on the reservoir forming range,and the high quality reservoir with high porosity,high permeability and high oil saturation is the main factor controlling the oil production.The comprehensive study shows that the accumulation in A area is characterized by "continuous accumulation near source,differential pressure of driving source and reservoir,and multiple primary and secondary hydrocarbon supply".