Basic Research On Prediction & Control Of Maximum Measured Depth Of Open Hole In Horizontal Extended-reach Drilling

Directional drilling technology for horizontal well or horizontal extended-reach well(ERW)are one of the leading technologies in the current oil & gas engineering.The quantitative prediction and optimization control of maximum measured depth of open hole in horizontal ERW have attracted much attention.The maximum measured depth of open hole is also called the open hole extended-reach limit,which means the well's maximum measured depth while maintaining the wellbore stability of open hole during all drilling processes.Based on the dynamic balance of bottom hole pressure,both the hydraulic parameters of the whole horizontal ERW and the wellbore stability are analyzed.A set of theoretical models of the prediction and control of open hole extended-reach limit is established,which can provide the scientific guidance for risk control and optimization design of horizontal ERW.The annular pressure losses gradient is introduced to replace the annular pressure losses equivalent density of unit length in the original model.The subjective and objective constraint conditions of the extended-reach limit are mainly studied,the extended-reach limit prediction models based on annular single-phase flow,two-phase flow,various working conditions and leakage pressure are established,improving the model's prediction accuracy.In addition,considering the effects of shale hydration stress and offshore dual-gradient drilling on the horizontal ERW's open hole extended-reach limit,the above established prediction model is applied to the shale formation and the offshore horizontal ERW,extending the application scope of the prediction model.The parameters in the prediction model of horizontal ERW's open hole extended-reach limit are analyzed.Based on the above prediction model,further considering the effects of drilling pump and hole cleaning conditions,the mud weight window and the drilling fluid flow rate window are modified,the constraint conditions and calculation model of the maximum rate of penetration of the horizontal ERW's horizontal section are also proposed.In order to improve the horizontal ERW's open hole extended-reach limit,the optimization design principle and control method aiming at the subjective and objective constraint conditions of the prediction model of horizontal ERW's open hole extended-reach limit are proposed,which mainly include the methods of determining the optimal drilling fluid density,optimal drilling fluid flow rate,and the well trajectory optimization design based on the horizontal well's effective extended-reach limit in shale gas formation.Case studies of Jiaoye 2-5HF horizontal well in Fuling shale gas field and Z-42 ERW in Sakhalin Island are analyzed by using the established prediction model of horizontal ERW's open hole extended-reach limit.