An Innovative Manganese Tetroxide/CaCl2 Water-Based Drilling Fluids for HT/HP Wells

摘要

Drilling gas reservoir in Saudi Arabia 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 when drilling 5–7/8”hole,due to the high concentration of CaCO3 required,sticking occurs resulting in expensive 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 is damaging because it does not dissolve in commonly used acids.Fracture stimulation or deep penetration can be done but at high cost. Saudi Aramco developed drilling fluids 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 Mn 3 O4 make it good weighting material to reduce solids loading and settling compared to CaCO3(2.78 g/cm 3 and D50 10 microns)and BaSO4(4.20 g/cm 3 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.