Abstract
Stress influence on permeability has been extensively studied by various authors, as the stress can significantly affect reservoir’s productivity. This paper displays the features of permeability stress sensitivity in tight gas sandstone in Kirthar fold belt lower Indus Basin, Sindh, Pakistan. The experiments performed under a range of pore pressure and confining stress, and the results were analyzed by integrating with microstructural observations. The results obtained were used, to explore the combined effects of changing pore pressure on slippage and absolute permeability. The results revealed that the stress sensitivity increases as the permeability decreases; this is because of existence of microfractures and the presence of larger pore throat radius. In addition, the effective pore size was calculated from the gas slip parameter, and at low confining stress levels, this value was in the same order of magnitude as the microfracture width. Moreover, the pore size calculated from gas slip parameters was reduced at higher stress levels, which indicated grain boundary fractures closures.
Highlights
Gas flow in tight rocks has remained interest of many researchers and is extensively investigated because it plays a major role in gas reservoir engineering
The effective pore size was calculated from the gas slip parameter, and at low confining stress levels, this value was in the same order of magnitude as the microfracture width
The absolute permeability falls as the net stress is increased as shown in Figs. 2 and 3, where net stress is given by r0 = rc - nkPp with nk = 1
Summary
Gas flow in tight rocks has remained interest of many researchers and is extensively investigated because it plays a major role in gas reservoir engineering. Low-permeability rocks such as tight sandstone are becoming important source of natural gas, as the production from conventional hydrocarbon reserves is declining, whereas the demand is rising. Developing such low-permeability reservoirs is very challenging as the gas is held in very tight formations having poor pore connectivity. For performance prediction of these reservoirs, laboratory measurements are routinely conducted to characterize these low-permeability rocks. These measurements are made at different stresses, pore pressures and temperatures than are found in the subsurface. Such corrections are complicated by several processes as the stress and pore pressure sensitivity of permeability as well as core damage
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