Development of a New Reservoir-Friendly Drilling Fluid for Higher Gas Production

Abstract

Drilling gas reservoir requires high mud density to balance the reservoir pressure. To formulate such fluids, calcium carbonate (CaCO3) was used because of its high acid solubility. However, due to the high concentration of CaCO3 required for high density drilling fluid, sticking might occur which might result in fishing and/or sidetracks operations. To minimize sticking problems, barite (BaSO4) is added with CaCO3 to reduce the amount of solids needed to formulate the drilling fluid. However, barite can cause potential damage because it does not dissolve in commonly used acids. Drilling fluids were developed at a wide range of densities using CaCl2 salt with Manganese Tetroxide (Mn3O4). No similar formulations were developed before to the best of the authors’ knowledge. The properties of small particle size (D50=1 microns), spherical shape and high specific gravity (4.9 g/cm3) of Mn3O4 make it good weighting material to reduce solids loading and settling compared to CaCO3 (2.78 g/cm3 and D50=10 microns) and BaSO4 (4.20 g/cm3 and D50=20 microns). The objective of this study is to show the lab work involved in designing water-based drilling fluids using CaCl2 / Mn3O4. The experimental work in this paper involved rheological properties, thermal stability, API and HT/HP filtration. The data generated from this study showed that Lignite and Vinyl amide/vinyl sulfonate copolymer are recommended to provide good rheological stability and filtration control for CaCl2/Mn3O4 drilling fluid. Polyanionic cellulose polymer and starch can used to formulate KCl/Mn3O4 drilling fluid with good properties at 300 °F.