engleski

Long-Term Cement Deterioration Under the Severe Sour Gas Conditions (a Case Study)

The study is based on the case history of several wells at one of the largest gas condensate fields in Pannonian basin (Croatia) where the long term cement deterioration was indicated. The research was carried out in order to investigate the possible mechanism of impairment. After almost fifteen years of undisturbed production from naturally fractured carbonates in some cases the plugging across the perforated zone with unidentified debris, accompanied by water cut increase, jeopardized the future well service. The study involves the laboratory evaluation of the actual environmental downhole impact (high reservoir temperature, BHST > 180oC, sour gas: 22% CO2 and 150 ppm H2S) to the well cement as well as debris identification. Experimental results, simulating downhole conditions in laboratory and well logging survey, suggested that well cement, after a long-term exposure could be deteriorated loosing its compressive strength and integrity. The dominant mechanism of cement deterioration is caused by CO2 corrosion process in the form of carbonic acid leaching. The CBL log data verified the cement disintegration behind 7 in. casing after 15 years of well production period.

well cement; sour gas; deterioration mechanism; laboratory tests

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