Mega-extended-reach wells (MERWs) can be drilled from one platform to develop the remote surrounding satellite oil & gas reservoirs in deepwater. Though the platform is located in shallow water, some MERWs can be targeted the reservoirs in deepwater. In mega-extended-reach drilling (MERD) 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 (SMWW) and a limited well depth for MERD operation. In this work, considering the pressure balance of bottom hole including the thermal and seepage effects, a method for predicting the maximum allowable well depth (MAMD) of MERD to deepwater target is presented. Meanwhile the factors affecting the MAMD of MERD to deepwater target are also investigated. The study shows that seepage significantly affects the MAMD of MERD to deepwater target while the thermal's effect is not very obvious, 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 of MERD turns out to be obvious anisotropy, drilling in the direction of minimum horizontal in-situ stress in the formation is prone to attain a wider SMWW and a longer MAMD than other directions. Moreover, for a given target zone, the MERD with a horizontal bottom hole has a much longer MAMD than that of MERD with an inclined bottom hole, and the MAMD can also be effectively increased by reducing the annular pressure loss. This work provides a practical tool for enhancing the design of MERWs to develop the remote satellite oil & gas reservoirs in deepwater.