Structural Characterization Of High Temperature And High Density Oil-based Drilling Fluid For Fracture Sealing

Natural fractures provide the main seepage channel for the evelopment of oil and gas well.However,they will lead to working fluid loss and induce serious formation damage.During drilling and completion,adding LCM into working fluid and forming a fracture plugging zone is the main way to control the loss.The quality of the fracture plugging zone is determined by its structure,it is of great significance to study the relationship between the structure of fracture plugging zone and its bearing capacity for working fluid loss control and formation damage control.Taking the bashikiqik formation of the sandstone reservoir in kuqa piedmont of tarim basin as the research object.Basing on the fracture development and loss data of reservoir,the relationship between the loss rate and the fracture width was clarified,and the types of drilling fluid loss in the reservoir were revealed.Wedge-shaped fracture rock samples with specific fracture width were selected to carry out the test experiment on the bearing capacity of the fracture plugging zone.The evaluation method system of performance parameters of LCM was established,and the performance evaluation experiment of LCM was carried out.The LCM suitable for the working area is optimized,and the fracture plugging zone with high bearing capacity is formed.The multi-scale structural characterization of high pressure fracture plugging zone was carried out,the structural model of fracture plugging zone was improved,and the optimization method of LCM for ultra-deep well was improved.The following results have been achieved.An overall framework for the structural characterization of fracture plugging zone is proposed.Basing on the structural characteristics of the fracture plugging zone,the multi-scale structural characterization parameters of the fracture plugging zone were defined.Fracture plugging zone is a granular material system composed of LCM.On the micro scale,the particles of LCM were analyzed by measuring the performance parameters of LCM.On the microscopic scale,the particle group of LCM was analyzed by measuring the distribution of LCM in the fracture plugging zone.On the macroscopic scale,it shows the overall structural characteristics of the fracture plugging zone,and the characterization analysis is completed by measuring the framework and pore structure of the fracture plugging zone.The performance of high temperature and high density oil-based drilling LCM was evaluated.The effect of the performance of LCM on the structure of fracture plugging zone is clarified,and the evaluation method system of the performance of LCM is established.The characterization method of micro-scale of fracture plugging zone was defined.The evaluation experiment of LCM was carried out and the key performance parameters such as the compressive and temperature resistance of the LCMl were measured.The optimized LCM is suitable for reservoir loss control.The structural characterization experiment of high pressure fracture plugging zone was carried out by using standard size and full diameter wedge-shaped seam rock samples.The fracture plugging zone with high pressure capacity was extracted,and the multi-scale structural parameter determination method of fracture plugging zone was clarified.The structural analysis of fracture plugging zone was carried out on the mesoscale and macroscopic scales.The experimental results show that,on the microscopic scale,the fracture plugging zone is mainly composed of granular LCM,including a small amount of flake LCM and fibers,and the granular and flake LCM are evenly distributed,and the fibers are mainly distributed in the front of the fracture plugging zone.On the macroscopic scale,the average roundness and the D90 in particle size distribution of the LCM in the fracture plugging zone in the front section is the smallest,and the D90/wf ratio in the middle and back fracture plugging zone is 0.9?1.0.From the front to the back,the face rate of the fracture plugging zone is gradually reduced,and the number of pores at the edge of the large LCM is large and the area is large.Considering the multi-scale structural parameters of the fracture plugging zone,the structural model of the highpressure fracture plugging zone is improved.The mechanism of instability of high temperature aging structure of c fracture plugging zone is clarified.The bottom of ultra-deep well has a high temperature environment,which is easy to cause high temperature aging reaction of the LCM in the fracture plugging zone.After the high temperature aging of the LCM,the pressure resistance is reduced,the particle size is degraded under the action of the comprehensive stress field,and the matching degree with the crack is decreased.At the same time,the friction coefficient of LCM is reduced,and the fracture plugging zone moves toward the crack tip,which induces structural instability of the fracture plugging zone.Considering the high temperature aging performance of LCM and the characterization parameters of fracture plugging zone structure,the plugging formula is optimized,and the selection method of LCM for ultra deep fractured reservoirs is improved.