Flow Modeling of Well Test Analysis for Porous–Vug

Authors: YingLan Jia XiangYu Fan RenShi Nie QuanHua Huang YongLu Jia

Publish Date: 2013/01/15

Volume: 97, Issue: 2, Pages: 253-279

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Abstract

Porous–vuggy carbonate reservoirs consist of both matrix and vug systems This paper represents the first study of flow issues within a porous–vuggy carbonate reservoir that does not introduce a fracture system The physical properties of matrix and vug systems are quite different in that vugs are dispersed throughout a reservoir Assuming spherical vugs symmetrically distributed pressure centrifugal flow of fluids and considering media that is directly connected with wellbore as the matrix system we established and solved a model of well testing and rate decline analysis for porous–vuggy carbonate reservoirs which consists of a dual porosity flow behavior Standard log–log type curves are drawn up by numerical simulation and the characteristics of type curves are analyzed thoroughly Numerical simulations showed that concave type curves are dominated by interporosity flow factor external boundary conditions and are the typical response of porous–vuggy carbonate reservoirs Field data interpretation from Tahe oilfield of China were successfully made and some useful reservoir parameters eg permeability and interporosity flow factor are obtained from well test interpretationCarbonate reservoirs have complex structures and have generated great scientific interest and significant challenges Rawnsley et al 2007 Sarma and Aziz 2006 Bahrami et al 2008 Popov et al 2009 Gua and Chalaturnyk 2010 Carbonate reservoirs can be composed of matrix and fracture systems while others are composed of matrix fracture and vug systems Owing to the existence of fractures and vugs reservoirs have multiple porosity properties Reservoirs composed of matrix and fracture systems are called “matrix–fracture dual porosity reservoirs” Warren and Root 1963 AlGhamdi and Ershaghi 1996 Reservoirs composed of matrix fracture and vug systems are called “matrix–fracture–vug triple porosity reservoirs” Liu et al 2003 CamachoVelázquez et al 2006 Matrix–fracture dual–porosity and matrix–fracture–vug tripleporosity reservoirs are the most commonly studied Lai et al 1983 Rasmussen and Civan 2003 Wu et al 2004 2007 Wu et al 2011 CamachoVelázquez et al 2006 Corbett et al 2010 for example However reservoirs mainly composed of matrix and vug systems like porous–vuggy carbonate reservoirs in Tahe oilfield of China do exist This paper seeks to model matrix–vug dualporosity reservoirs without introducing a fracture systemThe flow problem of oil in porous media reservoirs is a complicated inverse problem in carbonate reservoirs because of their elusive flow behaviors Corbett et al 2010 2012 Fracture and vug development differs across reservoirs Abdassah and Ershaghi 1986 Mai and Kantzas 2007 each reservoir has a distinct set of fluid transport behaviors Well testing analysis is the “eye” for discerning the elusive flow behavior in invisible reservoirs Therefore a vital research task is to establish well test models that evaluate reservoir propertiesThe 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 AlGhamdi 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 CamachoVelázquez et al 2006 Nie et al 2011 2012a Pulido et al 2006 Veling 2002 Wu et al 2004 2007 Wu 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 Pseudosteady interporosity flow characteristics were commonly assumed by considering arbitrarily shaped matrix blocks and vugs CamachoVelázquez et al 2006 Wu et al 2004 2007 Wu et al 2011 Unsteady interporosity manner was assumed by considering spherical shaped matrix blocks and vugs Nie et al 2011 2012a It is hard to distinguish the difference between separate vug and connected vug systems by using well test analysis Hence vug dispersal in carbonate rock was assumed in the flow model In this study we will adopt these assumptions for the convenient mathematical description of fluid flow in vugs The objective of this study is to investigate a flow model of pressure and ratetransient analysis for porous–vuggy carbonate reservoirs Only singlephase flow behavior will be considered in the model because a semianalytical method can adopt to solve the mathematical model Multiphase flow models are hard to solve by using semianalytical methods and are usually solved by using numerical methods The singlephase flow model researched in this study is in theory suitable for oilsaturated reservoirs It can also be applied to water producing oil reservoirs in engineering practices Nie et al 2012b discussed the applicability of a singlephase flow to waterproducing reservoirs in detail and therefore are not discussed here The paper is structured as follows Sect 2 introduces model assumptions on physical properties Sect 3 establishs and solves the mathematical model Sect 4 plots the type curves and analyzes the pressure and ratetransient characteristics Sect 5 discusses the relationship and comparability with earlier numerical studies and Sect 6 validates the provided model using real field data The standard type curves and successful well test interpretation in this article demonstrate that the model can be used for real case studies

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