A Three-Parameter Dual Porosity Model for Naturally Fractured Reservoirs

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A Three-Parameter Dual Porosity Model for Naturally Fractured Reservoirs

Abstract

This studypresents a new model to analyze the behavior of naturally fractured reservoirs(NFRs). The model considers the geomechanical behavior of the fracturedreservoirs and the corresponding effects on the fracture aperture, which may bean important parameter for stress-sensitive NFRs. It includes the elasticityparameters, such as Poisson’s ratio and Young’s modulus.

Pressure depletionin an NFR, inherent to production, can result in effective stress change that,in turn, may change fracture permeability in NFRs. This may influence thebehavior of NFRs, which has been studied thoroughly in the literature; however,not analytically but only numerically. A rigorous mathematical model isdeveloped in this study which couples geomechanical and fluid flow aspects forcharacterizing a stress-sensitive NFR. In the model, we consider asemi-infinite radial flow with flux boundary conditions at the wellbore(Neumann condition) and constant pressure at infinity (Dirichlet condition). Itis also assumed that the external forces acting to the reservoir are constant,that there is interaction between the two regions, i.e. matrix and fracturesystem, via the change of pore pressure and effective stress.

Since the changein effective stress induced by reservoir compaction may affect the pressurebuildup curves in NFRs,new equations on buildup interpretation are developed tobetter understand this effect, and to precisely evaluate the reservoirproperties. An iterative algorithm is also developed which enables us not onlyto interpret the buildup data to compute the fracture parameters, namelyfracture porosity, fracture permeability, fracture storage capacity, and the elasticityparameter, but also to evaluate them more accurately. Such a new techniqueimproves NFR characterization through the inclusion of the fourth dimension,time, into buildup interpretation. This new well test interpretation method isa dynamic reservoir characterization, which is usually the mission oftime-lapse (4-D) multicomponent seismology.

From this study,we found that knowing three parameters is sufficient to both distinguish areservoir with dual porosity from that of a homogenous one and to characterizea dual porosity reservoir. Two of the parameters represent the fracture storagecapacity and matrix-fracture interaction. A third one reflects the effect ofboth matrix geomechanics and fracture aperture decline on the behavior of NFRsas time progresses. These parameters can be obtained by precisely interpretingdrawdown or buildup tests. This solution is applicable to any reservoircontaining dual porosity rocks.

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Hadi Jabbari, SPE, and Zhengwen Zeng, SPE, University of North Dakota

admin

谢谢楼主的宝贵资料！

葛布斯

admin 发表于 2017-11-4 18:33
谢谢楼主的宝贵资料！