Evaluation And Prediction Of Fracability Of Shale Reservoirs In Longmaxi Formation In Weiyuan, Sichuan Basin

Fracability refers to the possibility or difficulty of forming a complex fracture network of volume fracturing in a shale reservoir to effectively increase production,which is an important geological basis for whether shale gas fracturing can increase SRV（modified volume）to achieve increased production.The content of brittle minerals in rocks in various shale gas blocks in Southern Sichuan has little difference,but the effect of fracturing is significantly different.Based on the current production,doing research on the influencing factors of the fracability evaluation of the principal research area of Weiyuan,and vertically demarcated the“sweet spot”of both engineering and geological conditions.Combinating with well seismic,geophysical means such as well logging curve,seismic inversion,Petrel modeling and other means.Applying analytic hierarchy process to determine the weight of each influencing parameter in the prediction of fracability.After normalization of each index,the model building and prediction partition of shale fracability were conducted.Compared with the actual fracturing situation of existing horizontal wells,the paper aimed to verified and evaluated the shale gas engineering dessert in this area,and guided the optimization fracturing section selection of horizontal well in the region.Providing reference for the research methods in areas with similar geological conditions.The main achievements are as follows:（1）Based on the field survey and collected data,the regional geological situation,structural characteristics,geochemical characteristics of shale gas beds,sedimentary characteristics,fracture development characteristics,gas bearing characteristics and other conditions in the study area were analyzed in detail.Based on the fracturing precision requirements of horizontal well development of shale gas,the layers with relatively good geological conditions in the first section of wufeng-longmaxi formation,the main target layers,was further divided into 7 layers（4,3³,3²,3¹,2,1¹ and 1²）for subsequent research on fracability.（2）The application of index named E/λin seismic inversion has an obvious advantage in distinguishing fragility,which is applied to the subsequent model construction.According to the investigation and actual situation of the comprehensive method,brittle mineral content,brittleness index,E/λand the coefficient of horizontal stress difference are selected as the main evaluation factors of fracability.（3）Through method of Analytic Hierarchy Process（AHP）and Range Transform,and on the basis of rock mechanics experimental analysis,well log data analysis and seismic inversion,the comprehensive evaluation method of fracability is established.The quantitative evaluation formula of compressibility index FI is:FI（28）0.15S_BI1（10）0.15S_BI2（10）0.63S_E/?（10）0.07S_Kh.（4）Based on Petrel,the establishment of a geological model of the fracability,shows that the western part is better than the eastern part.Fracability of shale reservoir in the intermediate region of well W2,W1 and W3 has the best predicted values.The layers of 2,3¹ and 3³ have the best evaluation results.While 2-3¹ are the“desserts”for engineering and geological sides.The model is consistent with the actual fracturing verification trend,which is more reliable.The model can be used to guide the subsequent development of local well platform and layout.