Study On Logging Evaluation Technology Of "Sweet Spot" Fracturing In Shale Oil Horizontal Wells

As shale oil enters the stage of large-scale development,the development mode of horizontal well volume fracturing gradually reveals the problems of low drilling encounter rate,poor fracturing effect and high engineering cost.Therefore,there is an urgent need to carry out the study of "sweet spot" selection for fracturing horizontal wells in shale oil,which can help to find the best exploration and development area and formation,and provide the basis for selecting the best landing point for horizontal wells and optimizing the segment fracturing work.Based on geological,logging,oil test data and core experimental data,this paper briefly introduces the geological characteristics of the study area,conducts research on the four reservoir characteristics and their relationships,establishes a reservoir parameter logging interpretation model,calculates the sandbody structure index,and establishes reservoir quality classification criteria based on the above research results;calculated the brittleness index,in-situ stress,and fracture pressure,and constructs a completion quality logging interpretation model.Based on the idea of analogy method,the reservoir quality and completion quality key parameters are combined,the horizontal well segment grading comprehensive evaluation index is constructed,and the shale oil horizontal well fracturing sweet spot segment grading evaluation criteria in the study area are established,and further classify the horizontal reservoirs into three categories: high quality reservoirs,secondary reservoirs,and poor reservoirs,so as to provide a theoretical basis for the optimal selection of fracturing location and identification of sweet spot.theoretical basis for the optimal selection of fracture locations and identification of sweet spots.The main results and understanding are as follows:(1)Based on the coring and logging data,the four characteristics of the reservoir and the relationship between the four properties are studied,and it is clear that the relationship between lithology,physical properties,oil-bearing properties,and electrical properties in this area is more obvious,and the oil-bearing properties have a certain positive correlation with the physical properties and electrical properties.(2)Based on core description and conventional logging data,the logging response characteristics of different diagenetic sands of shale oil reservoirs were analyzed.The different logging response characteristics and structural indices of different rocks can be effectively identified in single well logging of diagenetic sand bodies.(3)Using the mathematical statistical regression method,a reservoir parameter logging interpretation model is constructed by combining the geological conditions and physical basis of the work area.Based on the research results of reservoir four properties relationship,inductive statistics of the relationship between production capacity and preferred parameters,the classification criteria for reservoir quality evaluation are determined.(4)Based on the programmed logging interpretation model,combine logging and recording data and mathematical models to carry out the calculation of brittleness index,in-situ stress,fracture pressure and comprehensive interpretation of logging data.By calculating the brittleness index,in-situ stress and fracture pressure,the completion quality log interpretation model is constructed and the reservoir quality evaluation classification criteria are determined.(5)Based on the idea of analogy method,analyze the connection between sand structure index,physical parameters,oil content index,brittleness index,stress difference coefficient,fracture pressure and high-quality reservoirs,construct a comprehensive index for horizontal well segment classification evaluation,and combine with dynamic production data to subdivide horizontal segments into three types of reservoirs,so as to accurately determine the "sweet spot" for fracturing.