The Next Generation of Sakhalin Extended-Reach Drilling

Abstract

Abstract Six of the ten longest reach wells in the world have been drilled in Chayvo field on Sakhalin Island. Significant learnings have been gained from these wells and have been applied to the remaining wells to reduce cost and improve well performance. The learnings are discussed in this paper. The most significant improvement in the Chayvo wells involved redesigning the completion. Initial completions were cased, cemented and perforated on coiled tubing to achieve a low-skin completion with zonal isolation. Alternative completion methods were evaluated after experiencing problems with production liner cementing and coiled tubing perforating. The revised completions incorporate stand-alone screens (SAS), predrilled liners and swell packers to achieve a low damage, sand free completion with zonal isolation. Initial wells required extensive backreaming to make connections and trips. Bit designs, bottom hole assembly (BHA) configurations and operations practices were modified to minimize the amount of backreaming, improve overall rate of penetration (ROP) and achieve a "One-Pass Trippable Hole". Implementation of ExxonMobil's Fast Drill Process1 (FDP) was incorporated to achieve additional improvements in ROP. Another learning was the importance of rotary steerable system (RSS) reliability since eliminating trips to replace the tools were a primary driver in overall performance. Rotary steerable systems were improved by evaluating failures, redesigning downhole components and implementing an incentive contract based on run time. Understanding and managing the causes of vibration using surface and downhole vibration measurement tools also contributed to increased rotary steerable life and higher overall ROP. The evolution of Sakhalin bit designs was driven by a variety of factors. Initial bit design focused on steerability and instantaneous ROP. Second generation bit features were designed to reduce overall drill string torque by reducing micro-tortuosity and bit reactive torque in the 8-1/2 in. hole section. The most recent generation of bit designs have experimented with extra long gauge lengths to reduce bit darting and excessive vibrations in hard stringers while maintaining high ROP capability. The first generation of casing installation employed full or partial flotation to run the 13-5/8 in. casing, 9-5/8 in. casing and 7 in. liners. On site engineering surveillance and calibration of torque and drag models enabled the use of conventional mud-filled casing runs on the subsequent 13-5/8 in. casing and 7 in. liners. Running conventional mud-filled strings reduces the risk of casing collapse and decreases running costs.