The Effect of Stress Arching on the Permeability Sensitive Experiment in the Su Lige Gas Field

Comparing with the high permeability reservoir, low permeability reservoir was more sensitive to the effective stress and current stress sensitive experiment assumed that the overburden pressure unchanged during the production. In fact, the overburden pressure reduced during the production due to the stress arching effect and it is easy to form an arch in the overburden when the reservoir was small and softer than the surrounding rock. Based on the theory of stress arch, Arching ratios and overburden pressures in the Su Lige gas field were calculated and this theory was the first time to be applied in the stress sensitive experiments. The experiments considered the shapes of the reservoirs. The shapes of the reservoirs in the Su Lige gas field were classified as the Penny shape and the Elliptic cylinder reservoirs. The arching ratios were 0.12 and 0.28, respectively, for the Elliptic cylinder reservoirs and the Penny shape reservoirs. The permeabilities with stress arch were much larger than those obtained from the routine experiments. The increase proportions of the permeability were related to the arching ratios. The permeabilities increased by 23% and 50%, respectively, for the Elliptic cylinder reservoir and the Penny- shape reservoir with the pressure drop of 25Mpa. The routine sensitive experiments exaggerated the degree of permeability stress sensitivity.