Fly ash as an additive for controlling sagging tendency in ilmenite densified water-based mud for a highly inclined high temperature well

Abstract

Sagging has a detrimental outturn on the drilling effectuation and increases the drilling risks. Drilling deviated wells and wells with high pressures and temperatures has a greater impact on the sagging occurrence. It is desirable for a drilling operator to ensure stability and maintain the suspension of weight material in the fluid throughout the drilling operation. Optimum drilling fluid design for the drilling industry aids in the effective removal of cuttings and suspension of cuttings to avoid expensive complications and maintain the stability of the well particularly for drilling highly deviated wells and wells in high-temperature harsh formations. Drilling fluid physio-chemical behavior changes because of the weighing agent separating from the liquid phase and settling down, which is referred to as sagging and is more prevalent in highly inclined wells and wells with high temperatures. Few studies are geared toward understanding and possibly mitigating the occurrence of solid sagging to improve the drilling performance, particularly in highly deviated wells and wells in high-temperature harsh formations. This study evaluates the effectiveness of fly ash buffered with an industrial standard polymer to eliminate ilmenite sag encountered with water-based drilling fluids at high-pressure high-temperature (HPHT)environments when accessing geothermal wells, extended-reach wells, and high-inclined wells. Four laboratory barrels of water-based drilling fluids were formulated for this study. Fly ash of 130 μm particle size was added to mud samples at 0, 1, 2, and 3 lb./bbl ratio. Each industrial standard polymer of 1lb./bbl was added to all four samples prepared. The influence of fly ash on drilling fluids properties was thoroughly evaluated by measuring static and dynamic sagging at vertical and inclined (300, 450, 600, 700, 800, and 900) conditions over a range of temperatures (2500F, 3000F, 3500F, and 4000F). It was observed that the inclusion of fly ash improves the sagging phenomena and the rheological behavior of the water-based mud samples to satisfy the industrial API standard value.