Abstract
Ying-Qiong Basin in the west of South China Sea contains plenty of abnormal high-pressure gas reservoirs, whose stress sensitivity is crucial for well productivity. To explore the influence of stress sensitivity on production, the variable outlet back pressure stress sensitivity experiments were applied to test core sample permeability under different burden pressure and obtain the relational expression of power function of core stress sensitivity. Afterwards, new productivity equation is deduced in consideration of reservoir stress sensitivity, and the affection of stress sensitivity on production is analyzed. The result demonstrates close link between stress sensitivity and productivity, since single well production decreases dramatically when reservoir stress sensitivity has been taken into account. This research is constructive for well-testing data interpretation in stress sensitive gas reservoirs.
Highlights
Stress sensitivity refers to the phenomenon that permeability changes along with the effective stress in the production process of oil or gas pay
Ying-Qiong Basin in the west of South China Sea contains plenty of abnormal high-pressure gas reservoirs, whose stress sensitivity is crucial for well productivity
To explore the influence of stress sensitivity on production, the variable outlet back pressure stress sensitivity experiments were applied to test core sample permeability under different burden pressure and obtain the relational expression of power function of core stress sensitivity
Summary
Stress sensitivity refers to the phenomenon that permeability changes along with the effective stress in the production process of oil or gas pay. Abundant experiments showed that high-pressure gas reservoirs, especially those of low-permeability have stress sensitivity [1] [2] [3] [4]. Middle-deep layers of Ying-Qiong Basin in the west of South China Sea contain abnormal high-pressure (formation pressure coefficient is larger than 1.8) gas reservoirs, most of which present intense stress sensitivity during depletion development. Liang been done abroad on stress sensitivity and productivity of this type of gas reservoir. They confound the concept of effective stress with producing pressure drop when they establish the productivity equation. Based on former studies, this research discussed the influence of stress sensitivity on reservoir physical properties and gas well production through experiments and productivity test analysis, deduced the productivity equation that takes stress sensitivity into consideration, on the basis of revised stress sensitivity equation and gas reservoir seepage feature, and eventually applied this equation for productivity analysis of gas reservoirs in Ying-Qiong Basin
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