Oil And Gas Exploration Potential Evaluation Of Dengying Formation In Northern Margin Of Deyang-Anyue Rift Trough

With the development of exploration technology,natural gas exploration in the Sichuan Basin has continued to be expand to deep and ultra-deep layers,and the latest exploration results have also demonstrated the huge oil and gas exploration potential of ultra-deep ancient marine carbonate rocks.The Upper Sinian Dengying Formation on the northern slope of the central Sichuan paleo-uplift has good prospects for exploration and is called upon to become another important breakthrough in the exploration of ultra-deep ancient marine oil and gas.Founded on drilling,logging,cores,microscopic thin slices and 3D seismic data,the paper compares the Gaoshiti-Moxi block and comprehensively analyzes the fourth member of the Upper Sinian Dengying Formation in the northern margin of the Deyang-Anyue rift trough Sedimentary reservoir characteristics.Combined with hydrocarbon source conditions,to discuss the natural gas accumulation conditions of the Upper Sinian Dengying Formation on the northern margin of the Deyang-Anyue rift trough,and propose wells.The main results are as following:(1)Based on JT1 well,It is clear that the depth of the cold bottom is 7421m,and the Dengying Group drilling is 345m,and the drilling is completed within the fourth member of the Dengying Group.Comprehensive lithology,electrical properties,and seismic reflection,combined with the identification of cuttings slices,clarified the top and bottom characteristics of the Deng 4 Member in Well Jiaotan 1.The top is marked by siliceous dolomite and algae dolomite,and the bottom is dominated by algae dolomite and silt dolomite.The main lithology of the Dengying Formation encountered in Well Jiaotan 1 is algae dolomite,sandy dolomite,and mud-silt dolomite,and siliceous is considered in some well sections.The composite record corresponds well with the peaks and valleys of the entire seismic trace,and the cold bottom boundary is a medium continuous-medium amplitude peak.The Deng 4Member of Well Jiaotan 1 has good comparability with the Gaomo area.Its thickness is vast and it cannot penetrate the Deng 4 Member.(2)Based on the identification of cuttings slices and the regional depositional background,the study concluded that the fourth member of the northern slope belongs to the carbonate platform sedimentation,mainly developed mound-shoal complexes,limited lagoons between beaches,among which mound-shoal complexes are favorable for oil and gas storage.The sedimentary facies belt in the middle and lower parts of the Deng 4 in the vertical direction is the most favorable interval for the development of mound-shoal bodies,and the platform margin belt on the plane is the most favorable facies belt for the development of mound-shoal bodies.The mound-sand complex of the fourth member of the Dengquan Member of Well Jiaotan 1 is arrives at 300m thick,and the lithology is dominated by algal dolomite.On the plane,the hills and beaches of the north slope are circulated in an elongated shape in the direction of E-W,and there are many hills and beaches developed inside,stacked laterally,with clear boundaries.The total area of the hills and beaches on the north slope is as high as 1400km~2.(3)Based on Well Jiaotan 1,high-quality reservoirs in the fourth member of Dengying Formation are developed,with a total thickness of 172.9m.The reservoir rocks of Well Jiaotan 1 are mainly algae dolomite,sandy dolomite,and mud-silt dolomite.The storage space is mainly intergranular dissolved pores,cavity dissolved pores,intragranular dissolved pores,intercrystalline dissolved pores,Five types of intercrystalline pores.The reservoir type of Well Jiaotan 1 is mainly of hole type.The high-quality reservoirs are thick and mainly developed in the middle and lower parts.The high-quality reservoirs of the fourth member of the Dengdian Member of the Gaomotai Margin are generally developed within 100m below the top.The short-bottom boundary of the high-quality reservoir in Well Jiaotan 1 is about 200m from the top.The mound and beach provide the material basis for the development of the reservoir,and the karstification provides further dissolution space for the reservoir.(4)The hills and beaches on the north slope have good reservoir forming conditions.During the Qiongzhusi deposition period,high-quality source rocks of the Lower Cambrian Qiongzhusi Formation developed over the rift trough and slope.The mound-shoal body of the north slope is thicker and wider in the higher grinding area.The mound-shoal body described by the instantaneous seismic plane attributes has at least three zones.The north slope is monoclinic as a whole,the height of the gas column in Well Jiaotan 1 is greater than the local closure,and the gas reservoir is a structural-lithological trap gas reservoir.During the oil and gas accumulation period,the northern slope was in the relatively high part of the ancient structure,which was conducive to oil and gas accumulation.The caprock is mainly directly covered and laterally sealed by high-quality source rocks of the Qiongzhusi Formation,which have good preservation conditions.