Acidizing High-Temperature Carbonate Formations Using Methanesulfonic Acid

Hydrochloric acid (HCl) is the most commonly used stimulation fluid for high-temperature wells drilled in carbonate reservoirs due to its high dissolving power and low cost. However, the high corrosion rate of HCl on well tubulars could make its use in deep wells non-viable. The current study introduces the novel application of methanesulfonic acid (MSA), a strong organic acid, to increase the permeability of carbonate formations, specifically at temperatures above 200?F. The objective of the experimental study is to evaluate the performance of MSA as stand-alone stimulation fluid for high-temperature limestone and dolomite formations.

Coreflood studies were conducted at temperature up to 320?F using limestone and dolomite cores and diluted MSA aqueous solutions. A constant injection rate, ranging from 1 to 25 cm3/min, was maintained during the coreflood tests and the differential pressure through the core was measured until acid breakthrough. Samples of the effluent fluids were collected and analyzed using Inductively Coupled Plasma (ICP) to measure the calcium and magnesium concentrations, and a computed tomography (CT) scan of each core was performed after the acid injection to study the characteristics of the generated wormholes.

MSA was found effective in creating wormholes in carbonate cores at the temperatures tested. At low injection rates, face dissolution and conical channels were observed in the cores. At intermediate injection rates, the tendency was to create a few dominant wormholes. At high injection rates, ramified wormhole structures were found, with increased branching for increased flow rates. For each condition tested, an optimum flow rate was identified. Additionally, analysis of the coreflood effluent samples showed no sign of methanesulfonate salts precipitation.

Demonstration of the effectiveness of MSA in propagating wormholes in carbonate cores will offer the petroleum industry with another alternative strong acid to HCl for stimulating high-temperature carbonate formations. MSA?s high acidity, solubility of its salts, and thermal stability, along with its readily biodegradable composition provide a beneficial use for MSA as a stimulation fluid in carbonate acidizing techniques. MSA also has a more favorable corrosion profile on metals, such as high chromium alloys, than usual mineral acids employed in well stimulation.