Applications and Characterization of NMR Relaxation Derived from Sphere‐Capillary Model

Abstract

Regarding all pores in rock as a system consisting of spherical pore and capillary pores, this paper presents a model of Sphere‐Capillary. After all pores are divided into different groups by their radii, the relaxation time of each group can be calculated with the Sphere‐Capillary Model. The transversal relaxation time (T2i), spaced on the Sphere‐Capillary Model, can be utilized to conduct the inversion of NMR relaxation signal. Our research suggests that the T2 distributions from the inversion are relative to special pore structures defined by the Sphere‐Capillary model. Using different Sphere‐Capillary Models to derive different relaxation times, then conduct the inversion relaxation signal with the relaxation time. When a T2 distribution fits the relaxation signal in the least squares, the pore structure defined by the Sphere‐Capillary Model characterizes the pore system in rock best. Data from lab NMR measurements are analyzed with the Sphere‐Capillary Model, and the results are compared with the pressure data from mercury injection. This research shows that the Sphere‐Capillary Model describes properly the relaxation characteristic relative to pore structure. Furthermore, the relaxation characteristic may hold a relationship with pore fluids.

Study of Rock Conductive Mechanism Based on Pore Structure

“…Attributing the changes of pore structure to the ratio variation of cylinder radius and sphere radius (C d in Eq. (4)) [14] , the volume of the sphere-cylinder model serving as porosity keeps the same as in the rock model. In the variations of C d , the radius of the spherical pore According to the different degradations of the sphere-cylinder model, the volume calculated for each degradation of the sphere-cylinder model is also equal to the pore volume, and the equations can be obtained as follows:…”

“…In reality, since rock pore structures are complicated, apart from using experimental analysis, it is still difficult to find out a satisfactory relationship between the conductivity and the pore structure in a complicated reservoir [15] . In this study we apply a sphere-cylinder model to analyze the relationship between pore structure and electrical conductivity [14] . Without loss of generality, we assume the cross-section area of the sphere-cylinder rock sample is 1 and its length is also 1, and the rock sample is within a unit volume (Fig.…”

Theoretical Mechanism and Application of Sphere–Cylinder Model in NMR for Oil–Water Porous Media

“…Þ can then be obtained (CALLAGHAN et al, 2003;NGUYEN and MARDON, 1995). Since pores are still treated as isolated pores, this approach is only valid for isolated spherical pores, cylindrical pores and planar pores separately (LIU et al, 2004).…”

“…These become the main factors to control production of oil, water and wells. In this study, a forward model (SphereCylinder) for NMR is proposed to investigate pore structure based on the mechanism of proton relaxation in specialized spaces (Liu et al, 2004(Liu et al, , 2006. This model also considered the connection for different pores in two-phase porous rocks which are saturated by oil and water.…”

Numerical study of the stress field during crack growth in porous rocks

“…Working with the porous reconstruction model, the relationship between the porous structure and the stress distribution characteristics can be established, and the influence mechanism of the stress field on crack growth can be determined. Recently, researchers have attempted to establish porous rock models by mathematical and numerical methods (Barla 1972;Bryant and Blunt 1992;Lock et al 2002;Jiao et al 2003;Okabe and Blunt 2004;Liu et al 2004;Wang et al 2005;Ju et al 2008;Yang et al 2010;Ju et al 2013). These models provide an effective way to solve a variety of physical and mechanical ''black box'' problems related to porous rock.…”