Effect of Stress and Pressure on Gas Flow Through Natural Fractures

Abstract

Gas conductivities of narrow natural fractures in sandstone and chalk were measured under varying stress and pore pressure conditions and showed a decrease in conductivity with increasing net stress. Natural fractures in mudstones exhibited continuously decreasing conductivity upon application of stress, so that correlatable conductivity data could not be obtained. Effectivestress-law behavior for the sandstone and chalk fractures were examined, giving a values in the range of 0.8-1.06, where a is the parameter in the effective-stress law, u -aP. The value of a for the fracture in chalk was nearly constant, but the values for the fracture in sandstone tended to decrease with increasing stress. Transition Reynold's numbers and turbulence factors for flow through the chalk and sandstone fractures were determined, yielding turbulence factors ranging from 6.0-20xl0 6 ft-l (2.0-6.6xlO-5 cm-l ) for differently stressed fractures. The entire flow behavior of these natural fractures, including conductivity, effective-stress law, and turbulence, is controlled by stress and pore pressure. As a result, pressure depletion during production will significantly change the productivity of a reservoir with similar natural fractures.

Principal Permeability Determination from Multiple Horizontal Well Tests

“…At least qualitative relationships between the principal horizontal permeability axes and magnitudes and those of stresses have been postulated or field tested by Walsh 9 , Warpinski 10 , Warpinski et al 11 and Buchsteiner et al 12 These results provide a mechanism to know when permeability anisotropy may be significant and to know its direction, which are the major factors in optimizing the well trajectory orientation.…”

Analyzing Well Performance in Hydraulically Fractured Gas Wells: Non-Ideal Cases

“…Warpinski et al evaluated this effect in the Mesaverde formation at the Multi-well Test site in the Piceance Basin of Colorado. 25 A graph of permeability ratio (k ÷ k 0 ) versus effective horizontal stress was produced from this work, shown in Figure 18. 26 Effective stress is the net stress acting on the rock framework and is the difference between total stress and reservoir fluid pressure.…”

Advanced reservoir characterization and evaluation of CO2 gravity drainage in the naturally fractured Spraberry Trend Area. Annual report, September 1, 1996--August 31, 1997

“…The average molecular weight of the oil is 219. 39. The oil sample was tested at 100 "F and 1000 psig.…”