A Critical Review for Proper Use of Water/Oil/Gas Transfer Functions in Dual-Porosity Naturally Fractured Reservoirs: Part I

Abstract

Summary Accurate calculation of multiphase-fluid transfer between the fracture and matrix in naturally fractured reservoirs is a crucial issue. In this paper, we will present the viability of the use of simple transfer functions to account accurately for fluid exchange resulting from capillary, gravity, and diffusion mass transfer for immiscible flow between fracture and matrix in dual-porosity numerical models. The transfer functions are designed for sugar-cube or match-stick idealizations of matrix blocks. The study relies on numerical experiments involving fine-grid simulation of oil recovery from a typical matrix block by water or gas in an adjacent fracture. The fine-grid results for water/oil and gas/oil systems were compared with results obtained with transfer functions. In both water and gas injection, the simulations emphasize the interaction of capillary and gravity forces to produce oil, depending on the wettability of the matrix. In gas injection, the thermodynamic phase equilibrium, aided by gravity/capillary interaction and, to a lesser extent, by molecular diffusion, is a major contributor to interphase mass transfer. For miscible flow, the fracture/matrix mass transfer is less complicated because there are no capillary forces associated with solvent and oil; nevertheless, gravity contrast between solvent in the fracture and oil in the matrix creates convective mass transfer and drainage of oil. Using the transfer functions presented in this paper, fracture- and matrix-flow calculations can be decoupled and solved sequentially--reducing the complexity of the computation. Furthermore, the transfer-function equations can be used independently to calculate oil recovery from a matrix block.

Application of the two-stage Markov chain Monte Carlo method for characterization of fractured reservoirs using a surrogate flow model

“…We employ the dual-porosity, dual-permeability model for single-phase flow through a fractured porous medium, denoted by . This type of model first appeared in the sixties (see, e.g., [5,29]) and has continuously evolved since its initial introduction [1,4,19,25].…”

“…Nevertheless, in the interest of focusing our effort on developing the general MCMC framework for fractured reservoirs we will use the more traditional models in [1,4,19,25]. We expect that as our level of understanding matures, exchange of these models in achievable.…”

“…We note that shape factors and applicable shape factor coefficients are a topic in the previous research, and we refer the interested reader to [1,4,19,25,29] for details of extensive discussion on the proper use of transfer terms. We remark that more sophisticated flow scenarios require increasingly difficult transfer functions.…”

Analytical Estimation of Water-Oil Relative Permeabilities through Fractures

“…This process is called imbibition when the displacing fluid is water, and gravity drainage when the displacing fluid is water. Depending on the flowing phases present in the fractured reservoir, either the capillary or the gravity force becomes dominant [3]. These forces can work in tandem or can oppose each other [4].…”

Shock-Induced Borehole Waves and Fracture Effects

“…Fractured reservoir is ubiquitous in hydrocarbon reservoir engineering (Chilingarian et al 1992;Naimi-Tajdar et al 2007;Ramirez et al 2009). The Stoneley wave (St) has been used for the detection and characterization of fracture zones (Hornby et al 1989;Kostek et al 1998;Qobi et al 2001;Saito et al 2004).…”