High-temperature aging property evaluation of lost circulation materials in deep and ultra-deep well drilling

Drilling fluid losses always occur in deep and ultra-deep well drilling of fractured reservoirs, which will cause serious formation damage and significant economic losses. Drilling fluid losses often reoccur in the drilling of reservoir section, indicating the evaluation indexes of acid dissolution rate, particle size distribution and etc. for the conventional lost circulation material (LCM)are unable to meet the needs of lost circulation control. The walnut shells and millimeter-scale calcium carbonates often used in Kat gas reservoirs located in Tarim Basin are studied to conduct a high temperature aging experiment on LCM. Experimental evaluation indicates that the walnut shells stay at 180℃ diesel for 24 h, and their color change from yellow to black with the quality, friction coefficient and compressive strength reduced by 25.16%, 28.24% and 21.21% respectively. As the millimeter-calcium carbonates stay at 180℃ diesel for 24 h, their color changes from white to light yellow with the quality and friction coefficient reduced by 2.47% and 1.33% respectively, while their compressive strength is almost unchanged; The bearing capacity of the plugged zone formed by high temperature aged walnut shells and millimeter-scale calcium carbonates is reduced by 48.84%. The analysis demonstrates that the high temperature aging failure of LCM is an important factor for the structure destruction of fractured plugging zone and reoccurring losses in deep and ultra-deep well. © 2019, Editorial Office of ACTA PETROLEI SINICA. All right reserved.