Acidizing Treatments Improve Oil Production 10 Fold
Operators of several wells in Southeast Asia needed to repair damage using an acidizing treatment. But they were worried about the treatment causing precipitation problems. So they carefully analyzed the minerals and fluids in the formation and determined the right formula for success. The result: a tenfold increase in the number of barrels per day, and no precipitation problems.
Using acidizing treatments is an easy way to dissolve solids plugging wells; however, using acid without creating new solids that damage the well is more difficult. But with a thorough analysis of the formation and the right acid combination, it can be done successfully.
Why Choosing the Correct Acidizing Treatment is Critical
Sandstone formations and hydrofluoric acid can be incompatible. When the acid is used at the wrong concentration, it can plug pore throats and further reduce productivity.
In one case, a gas well had been producing 4 MMft3/D from a sandstone reservoir. Operators wanted to improve production, so they used an acidizing treatment. After the treatment, the well’s production fell—down to 2 MMft3/D. Spent-acid precipitates and acid-released fines had damaged the formation. If operators don’t thoroughly understand the formation before acidizing, they can cause more harm than good.
If operators can predict formation response, through formation analysis, they can prevent acidizing damage. There are three formation properties that are important to fully understand pre-acidizing treatment: formation fluid, formation matrix, and formation mineralogy. Analyzing the formation fluid will help operators choose the right displacement fluids to isolate liquids that aren’t compatible with the acid or spent acid products. The formation matrix will help identify problems with acid treatments. And studying the formation mineralogy will help determine the best acid and concentration. Once the formation is thoroughly analyzed, operators can choose the right acid.
A Recipe for Success
Once you’ve got a handle on the formation’s characteristics, choosing the right acid and dose isn’t as difficult. For example, if you’ve got sodium feldspar, it will precipitate fluoride compounds if you use more than 3 percent HF acid. But if you’ve got potassium fluosilicate, it will precipitate if you use more than 1.5 percent HF. If you have clay-containing sandstone, HF acid causes hydrous silica precipitates. And sandstone with high carbonate content will produce large solid precipitates. The right concentration of acid will repair damage without causing more problems.
A flush before the acidizing treatment and a post-treatment flush also will help prevent precipitation problems. Preflush with a solution of 5-15 percent hydrochloric acid or 5-10 percent acetic acid. Those will both dissolve carbonate and prevent calcium fluoride precipitation. A large overflush with 3 percent ammonium chloride, or weak acid will dilute and disperse precipitates away from the wellbore. Doing pre and post treatments will increase the success of an acidizing treatment.
Before You Start, Consult the Experts
Acidizing treatments can damage wells if operators aren’t using the right acid and concentration for the formation. Before using an acidizing treatment, well operators must determine whether the formation solids and fluids are compatible with the treatment. The experts at ATS ChemFlo will help get your formation back to optimal health.