Publications

BD formation has characteristics of 305 °F and 8100 psi, with 5000 ppm of H2S and 55000 ppm CO2 content. In these wells, manganese tetraoxide (Mn3O4) was used as the drilling mud weighting material because it is less damaging to environment and formation than other muds. Coiled Tubing (CT) was proposed to perform Mn3O4 mud cake removal by spotting an acid solution in the open hole section. The use of strong acid in a high temperature well will result in a corrosive environment as well as a fast reaction, giving less time for CT to spot the acid. In addition, hazardous chlorine gas is produced. Therefore, slow reacting organic acid was preferred. The reaction of 15 % weight acetic acid and 50 % volume chelating agent with Mn3O4 at temperature of 305 °F was studied. A corrosion test was performed to see the effect of the acid and 4,600 ppm H2S on the CT string and completion tubing. A volume of 155 ppb Mn3O4 mud was mixed in a laboratory scale and tested using a viscometer and a densitometer to represent actual drilling mud in the well. Filter cake was made using HPHT filter press and 10 micron alloxite disc to represent formation permeability. After 6 hours reaction time, 100% solubility of filter cake was achieved. Using 0.6 % volume organic acid inhibitor and 0.6 % volume H2S inhibitor, the corrosion rate on HS-90 CT metal after 16 hours in contact with 5000 ppm H2S and 15 % weight acetic acid was acceptable. This solution was used in two different BD wells. With 6200 psi wellhead pressure and presence of H2S and CO2, this filter cake removal method has been proven to increase reservoir production up to 1.6 MMcfd, decrease formation pressure drawdown up to 341 psi, and improve cost efficiency by using CT to accurately place the right amount of acid solution across the open-hole section. Keywords: filter cake removal, coiled tubing stimulation, acid wash, HPHT stimulation, H2S corrosion