Optimized design of mud level of deepwater CML dual gradient drilling

A mud level optimization model of CML dual gradient drilling was established in order to optimize the wellbore pressure profile and improve the drilling depth. In this model, the mud level is optimized by taking the minimization of bottom hole pressure difference as the optimization objective under the constraint of formation pressure window. In addition, the influences of drilling fluid density, pump rate and safety margin on optimization results were analyzed based on case analysis. It is indicated that compared with pump rate, drilling fluid density has more influence on maximum drilling depth, bottom hole pressure difference and optimal mud level. If safety margin is taken into consideration, wellbore pressure will be within the pressure window more safely, but maximum drilling depth is reduced greatly. What’s more, the optimized mud level can not only improve drilling depth, but also decrease bottom hole pressure difference while realizing reservoir protection.