The geologically complex Algyo field, discovered in 1965, is the largest hydrocarbon occurrence in Hungary, consisting of more than 40 oil-and-gas-bearing layers. The Ap-13, is one of the biggest reservoirs and encompasses a myriad of challenges: it is a depleted (180 bars reservoir pressure at 2400 m) layered dirty sandstone reservoir with a low permeability of approximately 15 mD, containing saturated oil. The 122°C temperature, complex mineralogy, poor consolidation, and a wide range of sources of potential formation damage make any stimulation a challenging and detailed process.

Water injection is one the most commonly used exploitation method because of its favorable results. Sustained injection rate with delimited surface pressure is necessary to maintain the operational and economical advantages; however, formation damage severely impacts the injection trend.

Conventional stimulation systems such as acid outside-phase emulsion and regular mud acids have been used in the past on Algyo injector wells to improve injectivity by targeting the possible sources of damage such as iron compounds, calcite, hydrocarbons, clays, and sand; however, the effectiveness of these treatments has had a limited effective time frame of a few months, with suspected rock disintegration in the near-wellbore area.

Through virtual geochemical simulation and laboratory testing, a novel chelating system was identified as the most suitable technology to efficiently stimulate the Ap-13 reservoir and overcome the inherent extreme conditions.

Three injector wells were treated with this technology, and now, two years later, stable injection rates at optimum surface pressures are still maintained. These favorable results have widened the potential application of the technology to oil and gas wells, and laboratory testing has been optimized through virtual geochemical simulation. Furthermore, the operational risk of stimulation treatment is reduced where no cores are available, such as old wells, or when timing is a constraint, as in exploration wells.

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