Abstract
The Hechuan gas field is one of the tight gas reservoirs with the highest formation water salinity in China. The content of metal ions, such as calcium, magnesium, iron, and barium, is as high as 20 g/L. Severe scales in near-wellbore reservoir blocks the gas and liquid flow paths, affecting the normal production of gas wells. The analysis of scale samples shows that the scale compositions in the Hechuan gas field are complex, which are composed of calcium carbonate, calcium sulfate, barium sulfate, iron salt, silicate, and other inorganic scales. To dissolve these scales, 14 kinds of laboratory self-made chelating acids named AST-01 to AST-14, sequentially, were evaluated by the descaling rate, in which the chelating acid AST-01 was selected with a dissolution rate of 77.7%. Meanwhile, the optimal concentration and reaction time of AST-01 were investigated, and the concentrations of the corrosion inhibitor, the iron ion stabilizer, and surfactants were also optimized. Then, a chelating acid descaling formula was obtained, which was 15~20% of AST-01 chelating acid + 1.5~2.0% of corrosion inhibitor + 2.5% of iron ion stabilizer + 0.3% of drainage aid. A pilot field trial of this descaling formula was applied in a Hechuan X1 well. A remarkable result was obtained in that the shut-in tubing pressure recovery rate was increased by 14 times, the gas production was increased by 10 times, and the gas well resumed to produce continuously again.
Highlights
Published: 29 November 2021The Hechuan Gas Field is located in the central part of the Sichuan Basin
A series of chelating acid detergents with both corrosion and chelating ability was selected, and the performance of the detergent was evaluated by laboratory experiments
Through the Energy Dispersive X-ray Spectroscopy (EDS) spectroscopy analysis of scale samples from six wells, it can be inferred that the main inorganic scales in the Hechuan Gas Field are calcium carbonate, calcium sulfate, barium sulfate, formation sands, and iron salts
Summary
The Hechuan Gas Field is located in the central part of the Sichuan Basin. The main development stratum is the Xujiahe formation, and the reservoir permeability is generally less than 0.05 mD, which belongs to tight sandstone reservoirs [1]. Almost all gas wells in the Hechuan gas field produce high salinity formation water, which is on average. The main cations and anions of formation water are K+ , Na+ , Ca2+ , Mg2+ , Ba2+ , Fe2+ , Fe3+ , Al3+ , and Zn2+ , and S2− , Cl− , SO4 2− , and CO3 2−. The total content of calcium, magnesium, barium, iron, and other metal ions is more than 20 g/L, which provides a sufficient source for gas well scaling [3]. Due to the changes in temperature and pressure conditions when gas and water flow through perforation borehole, downhole choke valves, gas nozzles, and other downhole tools, the scales are prone to settle and become thicker and thicker around these flow channels [4,5,6]
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