Longest Lateral Section Drilled in Pakistan with the Underbalanced Drilling Methodology in a Challenging ERD Well in a Naturally Fractured Reservoir Structure – A Novel Approach Toward Innovative Drilling Techniques

Abstract The X Field, located in Sindh on the right bank of the Indus River, contains a shallow carbonate reservoir structure that is present at a depth of about 650m TVDSS. After continual production from the reservoir, the reservoir pressure has been depleted to sub-normal at ~0.6 SG equivalent mud weight (EMW). While drilling with a conventional mud system encountered total losses and resorted to heavy lost-circulation material (LCM) pills to cure them. All bridging materials pumped in the hole to cure losses invaded the reservoir formation. As a result, the completed well required excessive cleanup operations to bring it into production. Therefore, faced additional costs of loss curing materials, damage to the reservoir formation, and a substantial amount of time for drilling and cleanup operations. It was planned to look for a solution to not only reduce the costs associated with drilling this highly depleted reservoir formation, but also mitigate invasion damage that inevitably affects overall production. Although underbalanced drilling had been used in similar situations, but the challenges associated with this well were quite enormous. The horizontal well design contained a lateral of about 778m. Challenges to account for while drilling the horizontal leg included designing appropriate directional drilling equipment for use with a multiphase fluid, cleaning the hole in the horizontal leg, maintaining underbalanced wellbore pressures in the presence of high annular pressure loss. For this reservoir pressure of 0.6 SG EMW, a nitrified foam system was designed to achieve an equivalent circulating density (ECD) below 0.6 SG EMW. This foam system was designed using a formulated polymer system to yield a high foam quality for suspension and cutting carrying capacity. Geosteering was also performed using RSS, EM-MWD and LWD tools in multiphase fluid system to optimize well placement. In addition, a downhole deployment valve (DDV) deployed inside the casing string enabled isolating the live well while tripping. Applying all these innovative methods the drilling of this cumbersome section was completed in just 4.5 days having an avg ROP of 26 m/hr. Most importantly this methodology helped us to achieve zero skin drilling hence resulting in unprecedented production enhancement from this well. The paper outlines the planning and design of this unorthodox well, its execution, and the results achieved.