Pressure-Transient and Decline-Curve Behavior in Naturally Fractured Vuggy Carbonate Reservoirs

Abstract

This study presents a new way to model high secondary porosity, mainly vuggy porosity, in naturally fractured reservoirs. New solutions are presented for two cases, one in which there is no primary flow through the vugs (which is an extension of the Warren and Root model) and one in which the dissolution process of pore throats has created an interconnected system of vugs and caves. In both cases, there is an interaction between matrix, vug, and fracture systems. New insights are provided.Both pressure and production responses during transient and boundary-dominated flow periods are explored. In transient well tests, for the case in which there is no primary flow through the vugs, a change of slope could be present during the transition period. Thus, this study shows that slope ratios of 2:1 of an earlyor late-time segment vs. a transition segment do not necessarily imply transient interaction between matrix and fractures. It is also shown that the presence of vugs and caves may have a definitive influence on decline-curve and cumulative production behaviors; therefore, it is necessary to incorporate vuggy porosity in the process of type-curve match.Finally, the use of the methodology obtained in this work is illustrated with synthetic and field examples.

Dual permeability flow behavior for modeling horizontal well production in fractured-vuggy carbonate reservoirs

“…Bourdet and Gringarten (1980) used type curves analysis to determine fissure volume and block size in fractured reservoirs. Camacho-Velázquez et al (2005) wrote on oil transient flow modeling in naturally fractured vuggy carbonate reservoirs and analyzed its pressure transient and decline curve behaviors. Corbett et al (2010) studied the numerical well test modeling of fractured carbonate rocks, and discovered that numerical well testing has its limitations, especially when simulating disperse vugs.…”

“…In Pulido et al (2006) and Nie et al (2011), the pathway connected to the wellbore was a fracture system where flow from the matrix system to the wellbore was ignored and the fracture system was treated as the main pathway, thus considering inter-porosity flows from the matrix and vug systems to the fracture system; (2) triple porosity and dual permeability models for vertical well production in fractured-vuggy reservoirs. Camacho-Velázquez et al (2005) considered the vug system as a continuum medium. Thus fracture system and vug system were treated as pathways directly connected to the wellbore and inter-porosity flows between matrix, fracture and vug systems were considered; (3) flow models of horizontal well production in homogeneous reservoirs (Duan et al, 1998;Ozkan and Raghavan, 1991a,b); and (4) dual porosity and single permeability flow models of horizontal well production in naturally fractured reservoirs.…”

Flow Modeling of Well Test Analysis for Porous–Vuggy Carbonate Reservoirs

“…Reservoirs composed of matrix and fracture systems are called "matrix-fracture dual porosity reservoirs" (Warren and Root 1963;Al-Ghamdi and Ershaghi 1996). Reservoirs composed of matrix, fracture, and vug systems are called "matrix-fracture-vug triple porosity reservoirs" (Liu et al 2003;Camacho-Velázquez et al 2006). Matrix-fracture dual-porosity and matrix-fracture-vug triple-porosity reservoirs are the most commonly studied (Lai et al 1983;Rasmussen and Civan 2003;Wu et al 2004Wu et al , 2007Wu et al , 2011Camacho-Velázquez et al 2006;Corbett et al 2010, for example).…”

“…The flow problem in carbonate reservoirs has been well researched: (i) theory and applications on dual porosity flow model for well test analysis of fractured reservoirs (Al-Ghamdi and Ershaghi 1996;Bourdet and Gringarten 1980;Braester 1984;Bui et al 2000;Izadi and Yildiz 2007;Lai et al 1983;Liu et al 2003;Jalali and Ershaghi 1987;Rasmussen and Civan 2003;Wijesinghe and Culham 1984;Wijesinghe and Kececioglu 1985) and (ii) theory and applications on triple porosity flow model for well test analysis of fractured-vuggy reservoirs (Bai and Roegiers 1997;Camacho-Velázquez et al 2006;Nie et al 2011Nie et al , 2012aPulido et al 2006;Veling 2002;Wu et al 2004Wu et al , 2007Wu et al , 2011. Both the medium connected to the wellbore and the interporosity of fluid from the matrix or vug systems into the fracture system were considered as the fracture system.…”

“…Both the medium connected to the wellbore and the interporosity of fluid from the matrix or vug systems into the fracture system were considered as the fracture system. Pseudo-steady interporosity flow characteristics were commonly assumed by considering arbitrarily shaped matrix blocks and vugs (Camacho-Velázquez et al 2006;Wu et al 2004Wu et al , 2007Wu et al , 2011. Unsteady interporosity manner was assumed by considering spherical shaped matrix blocks and vugs (Nie et al 2011(Nie et al , 2012a.…”