Extended-Reach Well in Shale Formation: What is the Maximum Measured Depth while Coiled Tubing Drilling

Abstract

Abstract The extended-reach well (ERW) and coiled tubing drilling (CTD) have been widely used in the development of shale gas. Although there are numerous advantages of CTD, the extension ability of CTD is restricted since the coiled tubing (CT) cannot rotate in the borehole during drilling process. Generally, the longer horizontal section of the horizontal ERW corresponds to the higher shale gas production. Therefore, we need to predict the ERW's maximum measured depth (MMD) while CTD and evaluate whether the predicted MMD can meet the requirements of shale gas development or not. In this study, a prediction model of MMD for horizontal ERW while CTD in shale formation is presented. The model is established based on the dynamic pressure balance of the bottom hole and the mud weight window of the drilled formation. Three processes of drilling, tripping in and tripping out are considered. The study shows that the buckling of the CT and the decreased pitch length result in a decrease in annular pressure losses, and all of them are conducive to the greater MMD of horizontal ERW while CTD. Moreover, drilling along the direction of minimum horizontal principal stress has a greater MMD in shale formation. In addition, the MMD decreases with the increase in tripping velocity. The annular size also has great effects on the extension ability of CTD. This work provides a practical tool for determining the ERW's MMD while CTD in order to meet the requirements of shale gas development and obtain good economic benefits. The study is significant to the development of shale gas.