To effectively drain the reservoir formations in a Caspian Sea field from a single offshore ice-proof stationary platform (MLSP), the operator wanted to geosteer extended reach 8½-in (215.9 mm) lateral wellbores at maximum ROP and TD in one run. Development of Korchagina field would require several ERD horizontal wells with step-outs up to 8,000 m. The shallow true vertical depth (TVD) of the reservoir combined with low formation strength of the reactive shale requires high mud weight for stability creating a narrow equivalent circulating density (ECD) window. The hydrocarbons are trapped in an anticlinal feature with 70 m of natural gas cap rimmed by 20 m of viscous oil. To avoid early gas production that would lead to catastrophic water break-through, it is critical to keep the horizontal borehole in a narrow vertical corridor of 4–5 meters TVD to ensure maximum oil recovery. To accomplish the objectives would require the latest methods/technologies and would have to adhere to stringent environmental regulations.

Using an FEA-based design platform, a BHA solution was developed that contained a 716 type PDC bit fitted with premium 16mm cutters followed by a rotary steerable system (RSS) with an 8 3/8-in (212.7 mm) integral blade stabilizer and 6 3/4-in (171.4 mm) flex collar to enhance directional control. A new oil-based mud would be used to reduce friction factor/wiper trips and stabilize the reactive shale stringers that caused problems when rotating/sliding in offset wells drilled with water-based mud.

To fully exploit the integrated BHA’s technological advantage would require establishing a defined set of best practices. In extended reach drilling it is important to monitor torque and drag trends to continuously analyze hole conditions to optimize connections and reduce trip time. Engineers determined that using relatively high pipe rotation (120–180 RPM) would maximize ROP and also enhance removal of drilled cuttings from the low side of the lateral hole section. The drilling team also recognized that reducing connection time is just as important as maximizing ROP because it can account for up to 40% of total drilling hours. To ensure efficient tool make-up, the number of pipe reciprocations was based on modeled torque/drag values enabling engineers to evaluate each stand to effectively manage circulating time prior to setting the slips.

Applying the integrated BHA solution and best practices on well P-116 drilled the lateral hole section at 55m/hr, a 62% increase compared to the best offset ROP of 34m/hr, setting a new 24-hr project drilling record of 691m/day. The reliable 6¾-in RSS operated flawlessly for 154 hrs exceeding operator expectations. The 8½-in 716 PDC bit displayed good directional control and came out of the hole in acceptable dull condition. The use of oil-based mud successfully stabilized the problematic reactive shale formations and enabled the operator to drill a long open-hole section of 3,770 m in one run setting a new Russian 8½-in horizontal length record. The combination of technologies and expertise completed the well 29 days ahead of schedule. With a spread rig rate of $340,000 cost savings was calculated at approximately $10 million USD.

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