The Maximum-Allowable Well Depth While Performing Ultra-Extended-Reach Drilling From Shallow Water to Deepwater Target

Abstract

Summary Ultra-extended-reach wells can be drilled from one platform to develop the remote surrounding satellite oil and gas reservoirs in deepwater. Although the platform is in shallow water, some ultra-extended-reach wells can target the reservoirs in deep water. In ultra-extended-reach drilling from shallow water to deepwater target, some challenges that may be faced are the presence of low temperature, typically weak overburden sediments, unconsolidated formations, and a small sedimentary coverage above the reservoir. This results in a narrow safe-mud-weight window and a limited well depth for ultra-extended-reach drilling operation. In this work, considering the pressure balance of bottom hole including the specific thermal and seepage effects, a method for predicting the well's maximum-allowable measured depth (MD) (MAMD) while performing ultra-extended-reach drilling from shallow water to deepwater target is presented. Meanwhile the factors affecting the MAMD are also investigated. The study shows that seepage significantly affects the MAMD while performing ultra-extended-reach drilling from shallow water to deepwater target: seepage turns out to significantly decrease the MAMD whereas heating the formation is found to be helpful in extending the MAMD. It also shows that the predicted MAMD turns out to be obvious anisotropy; for a normal regime depositional environment, drilling in the direction of minimum horizontal in-situ stress in the formation is prone to attain a wider safe-mud-weight window and a longer MAMD than other directions. Moreover, for a given target zone, the ultra-extended-reach drilling with a horizontal bottom hole has a much longer MAMD than that of ultra-extended-reach drilling with an inclined bottom hole, and the MAMD can also be effectively increased by reducing the annular friction-pressure loss. This work provides a practical tool for enhancing the design of ultra-extended-reach wells to develop the remote satellite oil and gas reservoirs in deep water.