Jinhong Chen

Unconventional Spontaneous Imbibition into Shale Matrix: Theory and a Methodology to Determine Relevant Parameters

Spontaneous imbibition of fracturing fluids into a shale formation has many practical applications for shale gas recovery. Because of the strong solid–liquid interaction in low-permeability media, Darcy law is not always adequate for describing liquid flow process in a shale formation. This unconventional (non-Darcian) flow behavior, however, has not been given enough attention in the shale gas community. The current study develops a systematic methodology to address this important issue. We first review related studies in the literature on relationship between liquid flux and hydraulic (or pressure) gradient in low-permeability media; the unconventional flow behavior is characterized by nonlinearity of the relationship. Then, we propose a phenomenological model for liquid flow in shale (in which liquid flux is a power function of pressure gradient) and develop an analytical solution to a one-dimensional spontaneous imbibition problem that obeys the model. The validity of our model is verified by satisfactory comparisons of theoretical and observed relationships between cumulative imbibition and time. The potential mechanisms of the unconventional flow are discussed. Furthermore, based on the developed analytical solution, we propose a laboratory test methodology to estimate parameters for the phenomenological model from spontaneous imbibition tests.

Correction of source-rock permeability measurements owing to slip flow and Knudsen diffusion: a method and its evaluation

Source-rock permeability is a key parameter that controls the gas production rate from unconventional reservoirs. Measured source-rock permeability in the laboratory, however, is not an intrinsic property of a rock sample, but depends on pore pressure and temperature as a result of the relative importance of slip flow and diffusion in gas flow in low-permeability media. To estimate the intrinsic permeability which is required to determine effective permeability values for the reservoir conditions, this study presents a simple approach to correct the laboratory permeability measurements based on the theory of gas flow in a micro/nano-tube that includes effects of viscous flow, slip flow and Knudsen diffusion under different pore pressure and temperature conditions. The approach has been verified using published shale laboratory data. The “corrected” (or intrinsic) permeability is considerably smaller than the measured permeability. A larger measured permeability generally corresponds to a smaller relative difference between measured and corrected permeability values. A plot based on our approach is presented to describe the relationships between measured and corrected permeability for typical Gas Research Institute permeability test conditions. The developed approach also allows estimating the effective permeability in reservoir conditions from a laboratory permeability measurement.

A Non-Invasive Method to Directly Quantify Surface Heterogeneity of Porous Materials

It is extremely challenging to measure the variation of pore surface properties in complex porous systems even though many porous materials have widely differing pore surface properties at microscopic levels. The surface heterogeneity results in different adsorption/desorption behaviors and storage capacity of guest molecules in pores. Built upon the conventional Porod’s law scattering theory applicable mainly to porous materials with relatively homogeneous matrices, here we develop a generalized Porod’s scattering law method (GPSLM) to study heterogeneous porous materials and directly obtain the variation of scattering length density (SLD) of pore surfaces. As SLD is a function of the chemical formula and density of the matrix, the non-invasive GPSLM provides a way to probe surface compositional heterogeneity, and can be applied to a wide range of heterogeneous materials especially, but not limited to, porous media and colloids, using either neutron or X-ray scattering techniques.Surface heterogeneity significantly influences the properties of porous materials, but remains extremely difficult to characterize. Here, the authors extend Porod’s scattering law from homogeneous to heterogeneous porous materials, allowing for surface variation to be non-invasively probed.

Assessing Tensile Strength of Unconventional Tight Rocks Using Microwaving

The URTeC Technical Program Committee accepted this presentation on the basis of information contained in an abstract submitted by the author(s). The contents of this paper have not been reviewed by URTeC and URTeC does not warrant the accuracy, reliability, or timeliness of any information herein. All information is the responsibility of, and, is subject to corrections by the author(s). Any person or entity that relies on any information obtained from this paper does so at their own risk. The information herein does not necessarily reflect any position of URTeC. Any reproduction, distribution, or storage of any part of this paper without the written consent of URTeC is prohibited.