Study on modified maximum extension length prediction model for horizontal wells considering differential sticking

Abstract

Maximum extension length prediction model for horizontal wells can be used to evaluate the horizontal well's extension capability and predict its maximum measured depth, which is of great significance to the production and economic benefits of horizontal wells. However, the differential sticking is not considered in previous prediction model. To overcome this shortcoming, a modified model considering differential sticking is established based on constraints of wellbore stability, differential pressure, and filtration loss simultaneously during the drilling, tripping processes and static state. Then a horizontal well is analyzed and its maximum extension length is predicted. Results show that within the conventional mud weight window, three ranges of drilling fluid density can be determined, including the first range, the second range and the reasonable range of drilling fluid density. However, only the reasonable range of drilling fluid density can satisfy all constraints of the modified prediction model, including the wellbore stability, differential pressure, and filtration loss simultaneously. Compared with the original model, the predicted well's maximum extension length decreases when the differential sticking is considered. However, it is more accurate, avoiding drilling hazards in actual drilling operation due to the excessive designed measured depth and unreasonable drilling parameters. Moreover, the maximum speeds of casing running down/pulling out are also determined and added to the modified model. Therefore, the modified model with reasonable drilling fluid density and adjusted running down/pulling out speed is the optimal modified model to predict maximum extension length and avoid differential sticking, which can also ensure that the horizontal well's designed measured depth can be successfully achieved. This study is of great significance to improve the prediction accuracy of horizontal well's maximum extension length and avoid drilling hazards, especially the differential sticking. Moreover, it also plays a guiding role in the selection of reasonable drilling fluid density during horizontal drilling.