Acid Soluble Drilling Fluids: Development and Field Trial

Abstract

Abstract Stuck pipe can not only significantly increase the cost of drilling but also has the potential to decrease the chances of successfully drilling a well within the stipulated time. A number of techniques and tools have been developed to solve the stuck pipe problem after they occur. However, the real objective should be to avoid the problem of stuck pipe to begin with and if and when they occur, the choice of treatment to release a stuck pipe should be such that it is not only cost effective but also quick. Such an objective prompted us to develop a new drilling fluid formulated with a combination of two different weighting agents, viz. barite and manganese tetroxide (Mn3O4). This paper describes the formulation of medium and high-density drilling fluids viz. 120 pcf and 150 pcf density fluids. These drilling fluids have been formulated with a combination of barite and Mn3O4 as weighting materials and hot rolled at 250°F and 300°F, respectively. After hot rolling these fluids at the specified temperatures, rheological properties and high temperature, high pressure (HTHP) fluid loss were measured. Sag resistance of the drilling fluids was estimated by perfoming static aging experiments in which the fluids were aged in inclined and vertical positions. To evaluate the filter-cake breaking potential of these mangansese tetroxide based drilling fluids, different breaker fluids were tested on the new 100pcf drilling fluid so as to calculate the % filter-cake removal efficiency. The paper also describes the data obtained from the field trial of 100 pcf and 145 pcf fluids formulated with barite and Mn3O4 for wells with a BHST of 290°F. The paper discusses the benefits of using drilling fluids formulated with barite and manganese tetroxide in mitigating stuck pipe issues and highlights their benefits in terms of better barite sag resistance and lower equivalent circulating density as compared to conventional drilling fluids formulated with 100% barite as weighting agent. The 120 pcf fluid when static agend showed superior rheology, thin filter cake and better sag resistance as compared to the 120pcf fluid formulated with only barite as the weighting agent. Different filter-cake breaker fluids have been showon to partially dissolve the filter cake of drilling fluids formulated with the acid-soluble manganese tetroxide as a weighting agent. This partial dissolution of filter cake is sufficient to free the pipe in the case of any stuck pipe event in the wellbore. The drilling fluids formulated with a combination of barite and manganese tetroxide showed good rheology, barite-sag resistance and resulted in successful drilling of wells having a BHST of 290°F.