Cost Effective Management of the Impact of Low Quality Barite on Functionality of MWD Tools in Deep Wells

Abstract

Abstract Data from Measurement While Drilling (MWD) tools are critical to successful drilling operations, because they aid real time assessment of down-hole conditions and support critical decision-making. De-risking lithology and pore pressure uncertainties while drilling exploration wells are reliant on these measurements. The reliability of MWD tools is known to be affected by mud properties, such as concentration of low- and high-gravity solids, mud viscosity and gel strength. The high mud density required for deep well drilling operations requires an unavoidable increase in solids content, which can lead to tool failure if the fluid design or quality of constituents is suboptimal. The upper part of the 8 ½" section of the BGG-S1 HPHT well was drilled with mud weight of 16 lb/gal. The mud weight was increased to 16.3 lb/gal because of the higher pore pressure prognosis across the deeper reservoirs. The increase in mud weight resulted into higher solids content as a result of addition of more weighting agent to the fluid. After the mud weight was increased, multiple BHA runs were made because the power module of the MWD tool was not responsive. Further investigation of the repeated failures identified the root cause as solids drop-out when flowing mud through the MWD tool. The poor quality of locally sourced barite used in the operation contributed to the poor performance of drilling fluid, because it resulted in higher solids content in the mud. The solids deposition challenge was resolved by conditioning the mud to an emulsification specification that is higher than conventional industry practice. The well was eventually drilled successfully to TD after the treatment, using a single BHA run with continuous MWD data acquisition and transmission. This paper reports the impact on the mud system associated with the quality of barite, the failure mode of the MWD power module, and the treatment of the mud to ensure technical success of the drilling operations on BGG-S1.