Thursday, November 23, 2017

Matrix Acidizing chapter 1

The simple aim of matrix acidizing is to improve production - reduce skin in reservoir engineer parlance -by dissolving formation damage or creating new pathways within several inches to a foot or two around the borehole. This is done by pumping treatment fluid at relatively low pressure to avoid fracturing the formation. Compared with high-pressure fracturing, matrix acidizing, is a low-volume, low-budget operation.

Matrix acidizing is almost as old as oil-well drilling itself. A Standard Oil patent for acidizing limestone with hydrochloric acid (HCL) dates from 1896, and the technique was first used a year earlier by the Ohio Oil Company. Reportedly, oil wells increased in production three times, ad gas wells four times. Unfortunately there was a snag - the acid severely corroded the well casing. The technique declined in popularity and lay dormant for about 30 years.

Then 1n 1931 , Dr. John Grebe of the Dow Chemical Company discovered that arsenic inhibited the action of HCl on metal. The following year, the Michigan-based Pure Oil Company requested assistance from Dow Chemical Company to pump 500 gallons of HCl into a limestone producer using arsenic as an inhibitor. The previouslnya dead well produced 16 barrels of oil per day, and interest in acidizing was reborn. Dow formed a subsidiary later called Dowell to handle the new business. Three years later, Halliburton Oil Well Cementing Co. also began providing a commercial acidizing service.

 Sandstone acidizing with hydrofloric acid (HF) - hydrochloric acid does not react with silicate minerals - was patented by Standard Oil company in 1933, but experiments in Texas the same year by an indepedent discover of the technique caused plugging of a permeable formation. Commercial use of HF had to wait until 1940, when Dowell hit on the idea of combining it with HCL to reduce the possibility of reaction products precipitating out of solution and plugging the formation. The mixture, called mud acid, was first applied in the Gulf Coast to remove mudcake damage.



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