Study On Leakage Mechanism Of Fractured Formation

At present,the economic loss of fractured leakage accounts for 90 % of all leakage costs.It is very important to study the leakage law of fractured formation and find out the factors affecting leakage.There are micro cracks and closed cracks in the target formation,which are very sensitive to pressure and easy to expand,resulting in leakage loss.The plugging technology in this area has no scientific guidance and relies heavily on field experience.At the same time,multiple plugging is required to succeed.In order to quantitatively describe and simulate the well leakage problem in fractured formations,it is necessary to use the drilling fluid leakage mechanism combined with fluid model,leakage flow characteristics,fracture parameters and other characteristics to establish a leakage model that belongs to the leakage problem of fractured formations.It provides strong technical support for the prevention and plugging of well leakage in this area.This paper mainly carried out the following research:(1)Comprehensive classification of leakage,combined with the causes of leakage and the causes of drilling fluid leakage dynamics to explain,summarize and analyze the causes of leakage in an oilfield.(2)The fracture parameters are described.The fractal dimension is used to characterize the fracture.The fracture occurrence and fracture size are quantitatively analyzed and calculated,and the fracture channel parameters of the target formation are obtained.Different leakage pressure models are compared.Finally,the leakage pressure in the area is calculated,and the leakage pressure profile is obtained.After the model comparison,the error meets the requirements.Furthermore,the safe drilling fluid density window was calculated to provide accurate data for subsequent research.(3)On the basis of fluid mechanics,the radial leakage model is improved by using the Heba flow type drilling fluid with high calculation accuracy,considering the drilling fluid performance parameters,fracture characteristic parameters,pressure difference between wellbore and formation and radial extension length of drilling fluid.The advantage of the model is that the absolute stable backward Euler difference scheme is used to solve the model,and the results are obtained by MATLAB programming.The model is verified by examples,and the model has certain guiding significance for the leakage prevention of fractured strata in the target block.Understanding the leakage mechanism of fractured formations is of great significance for leakage prevention and plugging.The refinement of the safe drilling fluid density window also plays an important role in reducing leakage and wellbore stability.In terms of controlling the degree of leakage,the two parameters of pressure difference and fracture opening are mainly controlled,which has important guiding significance for field adjustment of drilling fluid density and prediction of leakage.The solution method of the model in this paper has certain reference value for the solution of other models in the future.The research conclusions can provide reference for future numerical simulation,laboratory test and field application.