Experimental Study of Matrix Permeability of Gas Shale: An Application to CO2-Based Shale Fracturing

Abstract

Because the limitations of water-based fracturing fluids restrict their fracturing efficiency and scope of application, liquid CO 2 is regarded as a promising substitute, owing to its unique characteristics, including its greater environmental friendliness, shorter clean-up time, greater adsorption capacity than CH 4 and less formation damage. Conversely, the disadvantage of high leak-off rate of CO 2 fracturing due to its very low viscosity determines its applicability in gas shales with ultra-low permeability, accurate measurement of shale permeability to CO 2 is therefore crucial to evaluate the appropriate injection rate and total consumption of CO 2. The main purpose of this study is to accurately measure shale permeability to CO 2 flow during hydraulic fracturing, and to compare the leak-off of CO 2 and water fracturing. A series of permeability tests was conducted on cylindrical shale samples 38 mm in diameter and 19 mm long using water, CO 2 in different phases and N 2 considering multiple influencing factors. According to the experimental results, the apparent permeability of shale matrix to gaseous CO 2 or N 2 is greatly overestimated compared with intrinsic permeability or that of liquid CO 2 due to the Klinkenberg effect. This phenomenon explains that the permeability values measured under steady-state conditions are much higher than those under transient conditions. Supercritical CO 2 with higher molecular kinetic energy has slightly higher permeability than liquid CO 2. The leak-off rate of CO 2 is an order of magnitude higher than that of water under the same injection conditions due to its lower viscosity. The significant decrease of shale permeability to gas after water flooding is due to the water block effect, and much longer clean-up time and deep water imbibition depth greatly impede the gas transport from the shale matrix to the created fractures. Therefore, it is necessary to substitute water-based fracturing fluids with liquid or super-critical CO 2 in clay-abundant shale formations.

Numerical Simulation Using Finite-Difference Schemes with Continuous Symmetries for Processes of Gas Flow in Porous Media

“…Let us consider a particular example of Equations (2) with the equation of state for ideal gas with constant temperature ρ = χP and with the Klinkenberg relationship for permeability [10,13], which is given by (4) as follows:…”

“…. s be the difference invariants, which are found from the system of Equations (13). The approximation of differential invariants (10) via difference invariance (13) is the next step for constructing invariant difference schemes, which can be written as…”

Pore Network Modeling Study of Gas Transport Temperature Dependency in Tight Formations

“…Performing experimental work on rock samples at varying temperatures is quite challenging and associated with a high degree of uncertainty due to heating/reheating hysteresis and the length of time it takes to reach the thermal equilibrium. 24 The concept of “digital rocks” or pore network models (PNMs) where pores are interconnected by throats provides an alternative means of performing parametric analysis. Pores are where fluid is stored, while throats or capillaries are the conduits for transport among those pores.…”

Development of Chelating Agent-Based Polymeric Gel System for Hydraulic Fracturing

“…Hydraulic Fracturing is prominent amongst permeability-impaired formations (low permeability reservoirs) i.e., shale-gas and tight-gas [6][7][8][9]. Hydraulic fracturing significantly improves the productivity of the wells and the overall recovery factor [10].…”