Summary

Matrix acidizing of high-temperature gas wells is a difficult task, especially if these wells are sour or if they are completed with high-chrome-content tubulars. These harsh conditions require high loadings of corrosion inhibitors and intensifiers in addition to hydrogen sulfide scavengers and iron control agents. Selection of these chemicals to meet the strict environmental regulations adds to the difficulty in dealing with such wells. Recently, a new environmentally friendly chelating agent, glutamic acid-diacetic acid (GLDA), has been developed and extensively tested for carbonate and sandstone formations. Significant permeability improvements have been shown in previous papers over a wide range of conditions. In this paper, we evaluate the results of the first field application of this chelating agent to acidize a sour, high-temperature, tight gas well completed with high-chrome-content tubulars.

Extensive laboratory studies were conducted before the treatment, including corrosion tests, coreflood experiments, compatibility tests with reservoir fluids, and reaction-rate measurements using a rotating disk apparatus. The treatment started by pumping a preflush of mutual solvent and water-wetting surfactant, followed by the main stage consisting of 20 wt% GLDA with a low concentration of a proper corrosion inhibitor. Following the treatment, the well was put on production, and samples of flowback fluids were collected. The concentrations of various ions were determined using ICP. Various analytical techniques were used to determine the concentration of GLDA and other organic compounds in the flowback samples.

The treatment was applied in the field without encountering any operational problems. A significant increase in gas production that exceeded operator expectations was achieved. Unlike previous treatments where hydrochloric acid (HCl) or other chelates were used, the concentrations of iron, chrome, nickel, and molybdenum in the flowback samples were negligible, confirming low corrosion of well tubulars. Improved productivity and longer-term performance results confirm the effectiveness of the new chelate as a versatile stimulation fluid.

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