Research On Drilling Fluid Plugging Technology In Changling Area Of Jilin Oilfield

Lost circulation is a common phenomenon in the drilling process and will increase the risk of drilling construction and cause reservoir damage,which is a major technical problem in the drilling construction process.The Changling area is located in the middle of the fault depression in the southern part of the Songliao Basin.The formation is a volcanic rock formation with well-developed fractures,which is very prone to leakage.Therefore,this paper analyzes the leakage situation in the Changling area,and forms a leak prevention and plugging technology for this block,which meets the drilling requirements of this area.In this paper,the reservoir space types of formations in Changling area are studied,and the results show that formation fractures are well developed,mainly structural fractures,and90% of the fracture widths are below 50 μm.The core analysis,reservoir sensitivity evaluation,etc.were carried out.On this basis,the damage mechanism analysis and leakage mechanism analysis were carried out,and the main damage modes of the reservoir were clarified as solid phase damage,water phase trap and stress sensitive damage.In view of the large fractures with unknown width existing in the Changling area,comprehensively considering factors such as wall leakage and fracture deformation,a mathematical model for the radial leakage of Bingham plastic fluid and Herschel-Bulkley fluid drilling fluid in one-dimensional fractures was established.Simulations were carried out to analyze the factors affecting loss,including drilling fluid properties and fracture characteristics.The results showed that fracture width,fluid loss coefficient,fracture stiffness,dynamic shear force,and fluidity index had a greater impact on drilling fluid loss,the plastic viscosity and the consistency coefficient had a smaller impact on drilling fluid loss.The leakage data collected from the well histories of the two wells were analyzed for an example,and the simulated leakage curve was compared with the actual leakage curve to obtain the predicted average fracture width,which provided a certain basis for the selection of plugging materials and the formulation of plugging schemes.According to the above damage mechanism analysis and model application examples,the plugging materials are optimized and the formula of LWD plugging agent is designed.According to the simulated loss test,sand bed intrusion test,API fluid loss test and other experimental results,the best formulation of plugging agent while drilling is optimized.Comparative experiments,compatibility evaluation and reservoir protection evaluation were carried out,and the results showed that the preferred formulation of LWD plugging agent has excellent performance,is compatible with the field drilling fluid system,and has good reservoir protection ability.Based on the research in this paper,the model can be used to quantitatively predict the width of fractures in time,providing a basis for the subsequent selection of plugging materials and formulation of plugging plans;the optimal plugging agent while drilling can effectively plug the micro-fractures existing in the Changling area,improve the success rate of one block.