A Semi-Analytical Method for Modeling Two-Phase Flow Behavior in Fractured Carbonate Oil Reservoirs

Abstract

It is quite common for oil/gas two-phase flow in developing fractured carbonate oil reservoirs. Many analytical models proposed for black oil wells in fractured carbonate reservoirs are limited to single-phase flow cases and conventional methods have been the use of numerical simulations for this problem. In this approach, a novel semi-analytical method is proposed to integrate the complexities of phase change, pressure-dependent pressure-volume-temperature (PVT) properties, two-phase flow behavior, and stress-dependent fracture permeability characteristics. A dual-porosity, black oil model considering the phase change and two-phase flow is applied to model the fractured carbonate reservoirs. To linearize the model, only flow equations of oil phase are used to develop the mathematical model. Nonlinear parameters and producing gas–oil ratio (GOR) are updated with coupled flowing material balance equations, followed by a novel proposed procedure for history matching of field production data and making forecasts. The semi-analytical method is validated with a commercial simulator Eclipse. The results show that both of the production rate curves of oil and gas phase using the proposed model coincide with the numerical simulator. The results also show that the effects of pressure-dependent fracture permeability, fracture porosity, and exterior boundary on production rate are significant. Stress sensitivity influences production rate during the whole process, reducing the cumulative production. Fracture porosity influences production rate during the intermediate flow periods. The exterior boundary affects production rate mainly in the early and intermediate production periods. Finally, a field example from the eastern Pre-Caspian basin is used to demonstrate the practicability of the method. Acceptable history match is achieved and the interpreted parameters are all reasonable.

Novel Approach for Rate Transient Analysis of Fractured Wells from Carbonate Reservoirs with Heterogeneous Natural Fractures

“…A common challenge for fractured carbonate reservoir evaluation is the characterization of natural fractures and their heterogeneities. Geologic research results show that the fractures are small in size and large in number in this kind of reservoir. , Because it is hard to describe the fractures precisely, the dual-porosity and multi-porosity models are often used to capture the flow behavior. − Many studies have been conducted to investigate the transient flow behavior of fractured carbonate reservoirs based on theoretical models. Well-test interpretation is a valuable method to obtain the critical parameters for wells in fractured carbonate reservoirs.…”

Transient Pressure Behavior of a Horizontal Well in a Naturally Fractured Gas Reservoir with Dual-Permeability Flow and Stress Sensitivity Effect

“…Besides, the pseudosteady-state interporosity flow is firstly adopted to simulate mass transfer between fracture and matrix systems. After that, Kazemi et al [6], de Swaan [7], Raghavan and Ohaeri [8], Serra et al [9], Jalali and Ershaghi [10], Wu and Pruess [11], Bui et al [12], Wu et al [13], Kuchuk et al [14], Jia et al [2], and Wang et al [15] proposed their own dual-media model for naturally fractured reservoirs with the consideration of transient interporosity flow behavior. These models assume that the fracture system is the only flow pathway directly connected with wellbore by ignoring the flow from the matrix system to the wellbore.…”

“…However, most of the models ignored the effect of the stressdependent fracture permeability on transient pressure response. Although a great deal of work has been done on theoretical models of naturally fractured gas wells considering stress sensitivity of fracture permeability, most of them are restricted to the dual-porosity and single-permeability flow problem [3,15,[19][20][21].…”