Study On Prediction Method Of Lost Circulation Fracture Width

During drilling operation,various problems and challenges will be encountered,especially drilling mud loss.Lost circulation is a common problem,which usually leads to interruption of drilling process and reduction of efficiency.In order to solve and deal with the problem of lost circulation,appropriate lost circulation materials are often used to plug the lost circulation layer in engineering to prevent the drilling fluid from continuing to leak to the formation.However,the premise of the correct selection of lost circulation materials is to have a correct understanding of the fracture width of the layer to be plugged.At present,the selection of lost circulation materials mostly depends on field experience,and the plugging efficiency is low.Quantitative analysis of mud losses is a direct method for prediction of fracture width,which offers a criterion for designing lost preventive materials and guides early remedial actions.Therefore,taking the lost circulation fracture width as the research object,this thesis introduces the establishment of drilling fluid leakage model and how to obtain the value of lost circulation fracture width by solving the drilling fluid leakage model.Firstly,the drilling fluid leakage model is simplified,and the drilling fluid leakage dynamic model of Herschel-Bulkley fluid leakage into horizontal fractures is established.Through the dimensionless treatment of the model,the type curve related to the performance parameters of drilling fluid is obtained,and a series of dimensionless invasion coefficients α can be obtained from the actual drilling fluid parameters.Then,by comparing and analyzing the field real-time lost circulation data with the type curve,the value of α corresponding type curve is obtained.Next,for the analysis and processing of the type curve,this thesis solves the fracture width from two aspects: matching the type curve with the field data and matching the regression slope of the field lost circulation data through the processing of the approximate straight line segment of the type curve.Through the analysis of the properties of the type curve,it is found that the drilling fluid propulsion section of the type curve can be treated approximately as a straight line,and the dimensionless coefficient α corresponding to the type curve can be determined by matching the slope through field data processing and linear regression.Through Hough transform,the straight line is transformed into the data point set in the parameter space of geological information,and the classification chart of leakage channel is obtained.The fracture width is calculated by matching the field data with the trend of the type curve,and analyzes the influence of the change of parameters on the fracture width.At the same time,considering the uncertainty of parameters,the uncertainty analysis of leakage model is carried out,and then the distribution interval of fracture width is given from the uncertainty of results.Finally,through the field actual leakage data given by the cases in the literature,the model and its solution proposed in the thesis are verified.The predicted fracture width value,distribution range and classification chart of leakage channel type are in good agreement with those given in the literature,which proves the rationality of the model and its solution.