EFFECT OF LCM FIBERS ON THE RATE OF THF-WATER CLATHRATE HYDRATE GROWTH IN WATER-BASED DRILLING FLUIDS

摘要

This study investigates how different sized fibers used commonly as Lost Circulation Material (LCM) change the time required for induction and agglomeration of natural gas hydrates in drilling fluids using laboratory experimentally obtained data. Three different sizes of LCM fibers, fine, medium and coarse, were studied to observe how the size of each type of fiber affects the rate of hydrates growth. THF-Water clathrate hydrates were used as a model for hydrate growth at standard pressure conditions using a 20:80 molar ratio of THF to water. The concentrations of LCM fibers tested varied between 1-3% by weight. Each type of fiber was tested individually at -6 °C, -3 °C, and 0 °C and monitored for changes in hydrate induction and agglomeration rates. Tests were repeated using water-based drilling fluids using bentonite as the primary viscosifier and barite as a weighting agent to test 10, 12, and 14 ppg fluids. Fibers were tested under static conditions to identify changes in the nucleation and agglomeration rates for each. The rates of hydrate nucleation between samples of THF-Water and LCM fibers and each sample of water-based drilling fluid with LCM fibers was found to be consistent with no statistically significant change in rate being observed due to the fibers present. However, we observed a significant change in the rate of agglomeration that was dependent on the size and concentration of the fiber particles. We identified that fine fibers provided the most significant increase in the rate of agglomeration followed by medium and coarse fibers, respectively, with increasing LCM fiber concentrations. Compared to control samples, using fibers produced initial hydrate agglomeration around the freely suspended fibers. Due to their proximity to other fibers with hydrates developing around them, the hydrates were able to form very large free moving crystals in the solution before completely agglomerating and forming a solid plug. The results and conclusions provide new insights and guidance in drilling fluids and LCM design for offshore deep-water drilling. Gas hydrates can potentially develop and agglomerate along in the BOP and kill/choke lines during a well control event, as what is suspected as what happened in Macondo blowout where a considerable amount LCMs were used during drilling and as a spacer during a negative pressure test.