Development and Field Trial of New Acid Soluble Drilling Fluids

Abstract Stuck pipe, historically, has presented huge challenges to the worldwide oil industry. Stuck pipe has resulted in a great amount of nonproductive time, thereby causing huge monetary losses to the oil industry. A new drilling fluid has been designed, which employs a combination of two different weighting agents viz. barite and manganese tetroxide (Mn3O4) to overcome the problems linked with stuck pipe. Drilling fluids formulated with a combination of manganese tetroxide and barite as weighting agents are expected to have the following advantages: a) Better sag resistance, b) lower equivalent circulating density (ECD), c) lower fluid cost, and d) stuck pipe mitigation due to acid solubility of manganese tetroxide. This paper describes the formulation of 100 pcf and 150 pcf drilling fluids formulated with a combination of barite and Mn3O4 as weighting materials and hot rolled at 270°F and 300°F, respectively. The experimental work involves measuring rheological properties and high temperature, high pressure (HTHP) fluid loss at the specified temperature. Barite sag measurements were also performed on 150 pcf drilling fluids to determine the sag resistance of the fluid. The paper describes results of using different organic acid based filter-cake breaker fluids for the partial dissolution of Mn3O4 based filter cake. The paper also describes the data obtained from the field trial of 100 pcf and 155 pcf fluids formulated with barite and Mn3O4 for wells with a BHST of 290°F. The paper discusses the advantage of using such drilling fluids 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 barite as weighting agent. The 100 pcf and 150 pcf fluids showed superior rheology, thin filter cake and better sag resistance as compared to fluids formulated with only barite as the weighting agent. Different organic acids were able to partially dissolve the filter cake of drilling fluids formulated with barite and manganese tetroxide as weighting agents. 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.