Research On Comprehensive Logging Evaluation Method For Shale Oil Reservoirs Of Fengcheng Formation In Mahu Sag

With the development of oil and gas resources exploration,continental shale oil reservoirs have gradually become the focus of scientific researchers.Continental shale oil reservoirs are characterized by diverse mineral types,well-developed sedimentary structures,frequent lithofacies changes,and strong vertical heterogeneity.Therefore,it is impossible to identify reservoir lithofacies only by using conventional logging data,and it is difficult to achieve the evaluation accuracy requirements of relevant characteristic parameters.In this paper,taking Fengcheng Formation shale oil reservoir in Mahu Sag as an example,on the basis of core slice and core XRD analysis experiment,a classification scheme of rock type,sedimentary structure and lithofacies of Fengcheng Formation shale oil reservoir is established.In this paper,the logging evaluation model of Well Maye 1 is calibrated under the constraints of physical property analysis experiment,rock mechanics experiment,differential strain in-situ stress experiment,and CT scanning experiment after core pressure.Therefore,the relationship between lithofacies,reservoir quality and engineering quality is summarized,and the vertical distribution law of dominant reservoirs is explored.The research results show that the shale oil reservoirs of Fengcheng Formation are mainly composed of quartz,feldspar minerals,dolomite and calcite,with less clay minerals,and occasionally alkaline minerals and pyrite.At the same time,there are a large number of sedimentary structures with different thicknesses in the reservoir.According to the relative specific gravity of minerals and the thickness of sedimentary structures,the rock types are divided into 5 types,and the sedimentary structures are divided into 3 types,and then 15 types of "rock type + sedimentary structure" lithofacies are obtained.According to Litho Scanner lithology scanning logging and FMI microresistivity imaging logging button electrode,it can realize the continuous identification of single well lithology and sedimentary structure,and then complete the lithofacies division of the whole well section.The classification results show that the shale oil reservoirs are mainly composed of thin-layered felsic shale,lamellar dolomitic shale and massive mixed shale.According to CMR-NG two-dimensional nuclear magnetic resonance logging,the total porosity and water saturation of the reservoir can be characterized,and the reservoir quality classification scheme is established based on the formation resistivity,and three types of reservoirs are divided.A logging characterization model of shale oil reservoir rock mechanical parameters,brittleness index,magnitude and direction of current horizontal in-situ stress and natural fractures was established using conventional logging and Sonic Scanner logging as the main technologies.To sum up,the engineering quality classification scheme was formulated based on the brittleness index,the two-dimensional stress difference and the intensity of natural fractures,and three types of reservoirs were also obtained.According to statistics,both the engineering quality class I sweet spots and the reservoir quality class I reservoirs mainly develop two types of lithofacies: thin-layered felsic mud shale and laminated dolomitic mud shale.However,when the relative proportion of massive mixed shale increases,the reservoir quality and engineering quality deteriorate significantly.Comparing production capacity,it is found that the dominant intervals in the Fengcheng Formation shale oil reservoir are4575m～4698m and 4745m～4864m.