Improvement Drilling Efficiency by Using Mud Motor and Agitator Bha in 6 1/8-in. Hole: Gulf of Thailand

Abstract

In the Gulf of Thailand (GOT), deep directional drilling wells are planned with two runs using motor and adjustable-gage-stabilizer (AGS) bottom hole assembly (BHA) in the 6-1/8-in. hole section or the rotary-steerable-system (RSS) BHA. However, the cost of the RSS is not economical for some wells. The paper discusses the challenges of drilling in the high temperature environment and explains the engineering and analysis that resulted in a one run hole section with a motor BHA. The extreme temperature elastomer (XT) motor was paired with an agitator system to facilitate the transfer of BHA weight for effective weight-on-bit (WOB) while sliding in long tangent or curve for great depths and temperature more than 150 degree Celsius (⁰C) well. Exhaustive BHA analysis, namely hydraulics, drill-string torque-drag and various sensitivity studies were performed for optimal placement of the agitator and shock sub in the BHA for the best friction reduction and least damaging vibration effect on BHA components. The simulation capabilities were enhanced by trail runs, analyzing historical performance and empirical data to implement step change improvements in the next BHA. The XT motor with agitator-system BHA enabled smooth sliding and fast rate of penetration (ROP) across the entirely true vertical depth (TVD) range of the 6-1/8-in. hole. There was no BHA hanging up when sliding in deep sections of the well, demonstrating stable tool-face control while sliding, which translated to an overall efficient penetration rate. The 6-1/8-in. hole sections drilled with the XT motor and agitator-system BHA demonstrated 30 percent (%) faster ROP than similar TVD sections drilled with a motor without an agitator-system BHA. For example, a 6-1/8-in. hole with 1360-meter (m) drilled in long tangent at 41degree (°) inclination was successfully drilled in one run from shoe to 2584m MD of the well TD in 27 hours, with an average on bottom ROP of 51 meter per hour(m/hr).