Experimental Study of the Effect of Stress on Permeability for the Naturally Fractured Tight Gas Reservoir

Abstract

This paper presents laboratory studies of the stress dependent permeability in the ultra-deep naturally fractured tight gas reservoir in Tarim basin, China and its impact on the long-term gas recovery. Permeability of these samples was measured using pulse decay test technique under a wide range of combinations of effective stress and temperature up to 6500psi and 70° C, respectively through loading and unloading process. Moreover, the effects of morphology and filling condition of natural fractures and effective stress were studied. Due to the existence of natural fractures in tight reservoir, the stress dependency and hysteresis of permeability is larger. In addition, the morphology, distribution and filling condition of the natural fractures have a great impact on the permeability evolution with effective stress. Specifically, the hysteresis of stress dependent permeability is the largest if the nature fracture is through the whole sample and vertical to the end faces while the magnitude of the permeability decline is the smallest if there are multiple or reticular fractures. Moreover, the permeability declines by 10% more as the effective stress reaches 3000psi if the natural fracture is partially filled compared to that of the samples with fully filled natural fractures.