Mechanism of Permeability Evolution for Reservoir Sandstone with Different Physical Properties

Abstract

Permeability of sandstones with different properties taken from Chongqing reservoirs has been measured and deeply discussed under increasing deviatoric stress. Corresponding to the distinct features in the stress-strain behaviors, the permeability of sandstones is found to evolve with a clear permeability decrease in the initial closure region, a constant permeability value in the elastic region, a permeability increase in the crack initiation and propagation region, a sharp permeability increase in the crack growth region, and a decrease permeability in the residual stage. The results also show that the variation patterns of permeability are similar for two reservoir sandstones under combination of confining pressure and water pressure; however, the strength and permeability are smaller for the sandstone with mud than that without mud, deeply indicating that mud-like materials have a relatively great impact on the mechanical properties and permeability, so mud components cannot be ignored for prediction of reservoir permeability. Furthermore, a statistical damage constitutive model considering hydraulic-mechanical coupling process is presented to calculate the damage variable , illustrating that larger water pressure will result in a relatively smaller damage variables and corresponding maximum, which explains that the permeability increases more rapidly and is larger for the sandstone without mud than that with mud, and sandstone damage related to corresponding circumferential crack strain and permeability has been investigated, also implying the evolution mechanism of permeability for two sandstones with different physical properties. Therefore, it is worth pointing out that rock physical properties have a great influence on the reservoir permeability under complex extraction conditions and cannot be ignored, which is necessary to improve the recovery ratio and productivity.

Blasting-Induced Permeability Enhancement of Ore Deposits Associated with Low-Permeability Weakly Weathered Granites Based on the Split Hopkinson Pressure Bar

“…The initial permeability coefficient was positively correlated with porosity [19], but this relationship was not always true. This demonstrated that the porosity of rocks affected permeability, and the permeability coefficient depended on the number of seepage channels formed by internal defects in rocks and the content of clay minerals [18,42,43]. After cyclic impacts, the permeability coefficient increased and the increment rose with the increment in porosity.…”

“…Using the steady-state method, the permeability test was performed on weakly weathered granite samples before and after impacts, that is, the osmotic pressure difference formed in the two ends of the rock samples, to record the inflow volume V of seepage water, lateral confining pressure, and osmotic pressure difference. The expression is [18,32]…”

“…In the seepage test, the influence of burial depth on permeability coefficients was large and therefore could not be ignored, so 0.25 MPa of the axial load was applied. Specific operations of the seepage tests are given in the literature [18,32], and installation of the samples is shown in Figure 5 3. Results and Discussion…”

“…Through uniaxial cyclic impact loading on granites by carrying out SHPB, Zhu et al [17] revealed the damage laws and mechanisms of multiple blasting on rock masses in engineering construction. Based on a triaxial seepage test, Liu et al [18] investigated the evolution of permeability in sandstones with and without mud under different loading conditions and analyzed the factors influencing permeability changes. Based on studies on the permeability of ionadsorbed rare earth ores by combining with hydrodynamics, Tian et al [19] obtained that porosity is positively correlated with permeability.…”

Investigation on Nonlinear Flow Behavior through Rock Rough Fractures Based on Experiments and Proposed 3-Dimensional Numerical Simulation

“…In addition, when fluid is injected into a fracture intersection, the flow pressure and flow rate distribution are affected by many factors such as fluid properties [23], fracture intersection angle [24,25], fracture surface roughness [23], and pressure gradient [26]. The fluid flow behavior derived for a single fracture [27][28][29] is not applicable to the case of fracture 3 Geofluids intersections, especially when the nonlinear flow regime is considered. Numerical simulations have been performed by Liu et al [30] and Xiong et al [31] to estimate the effects of fracture intersections on the nonlinear flow behaviors in crossing fractures.…”