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Adaptation of Combined Dual Gradient & Pressure Mud-Cap Drilling Techniques to a HPHT Well- Field Xavier


 This paper identifies the potential and limitations of using Dual Gradient Drilling (DGD) combined with Pressure Mud-Cap Drilling (PMCD) in an onshore field where narrow and unpredictable mud weight window was encountered. Some of the world's largest conventional oil fields are located in deep High Pressure, High Temperature formations beyond the earth surface. As the industry engages in these highly productive and promising deep fields, major obstacles are encountered during drilling which leads to high amounts of costly Non-Productive Time (NPT) due to kick or other drilling related problems. With unique challenges such as kick, lost circulation, and narrow drilling windows, there is a need for innovative techniques to develop these fields in a more effective manner.
 DGD combined with PMCD is presented as a favorable solution to overcome the challenge of kick associated with a HPHT well in a certain field; Field Xavier, in the Niger Delta. Being able to control the bottomhole pressure profile throughout the wellbore and react to pressure fluctuations, allows drilling to proceed uninterrupted, while keeping the operational problems to a bare minimum. To achieve this, the mud SGs estimated to be used as the heavier mud, ranged from 2.4 SG to 3.7 SG, which will require andinvolve costs in weighting up mud with the use of weighting agents, which are quite expensive, and advanced technology to pump the heavily weighted mud downhole, without mud losses and risks of differential sticking.
 For this case study, which was conducted for the Field Xavier onshore production well in the Niger Delta, based on prior measured pore and fracture pressure gradients, the drilling mud program was designed for the two MPD variants; Dual Gradient Drilling (DGD) and Pressure Mud Cap Drilling (PMCD). The onshore well, which has a depleted formation, above a higher pressured formation, is to be drilled with the planned drilling mud program, with 0.319 psi/ft to 0.439 psi/ft for the depleted formation and 0.75 psi/ft to 0.89 psi/ft for the high pressured formation.
 This method can be applied in deviated, horizontal and vertical wells, although change in mud volume will have to be accounted for.