A New Model for Pressure Transient Analysis in Stress Sensitive Naturally Fractured Reservoirs

Abstract

In this paper, based on our analytical model, we analyze the transient pressure response of a naturally fractured reservoir with pressure dependent rock properties. ABSTRACTThe most commonly used methods to describe the transient flow behavior in porous media are based on the assumption of constant rock properties. Nevertheless, these methods are not strictly applicable to reservoirs that undergo changes in the rock properties due to variation in pore pressure. A frequent characteristic of fractured reservoirs is sensitivity of permeability and porosity to effective stress. This paper presents a new analytical model, for interpreting pressure transient test. The model considers the flow in a naturally fractured stress sensitive reservoir, that is to say, the dependency of rock properties on pressure is established (dependency of permeability on pore pressure is measured by the permeability modulus parameter), and makes that the flow equation be strongly non linear. Likewise, the theory is developed under unsteady-state or pseudosteady-state conditions, and considers that: the fracture is uniformly distributed, matrix geometry is the so called stratum and flow contribution from the matrix to the fracture is described by the term source proposed by De Swaan.The problem stated is solved through an analytical approach for different boundary conditions and different permeability modulus values, thus obtaining type curves that can be used for the analysis of pressure buildup and drawdown tests.

Pressure-Dependent Natural-Fracture Permeability in Shale and Its Effect on Shale-Gas Well Production

“…Reference Rutqvist et al (2002) 3 k f ¼ k fi e Àdf 3 Dp Raghavan and Chin (2002) Raghavan and Chin (2002) Rock Type III Raghavan and Chin (2002) and Celis et al (1994) 7 Raghavan and Chin (2002) and Rutqvist et al (2002) 8 Raghavan and Chin (2002) and Minkoff et al (2003) 9…”

“…Although the effect of stress on matrix (primary) permeability and hydraulic-fracture conductivity has been studied in more detail in the literature (e.g., Pedrosa 1986;Celis et al 1994;Best 1995;Gutierrez et al 2000;Chin et al 2000a, b;Kwon et al 2004;Raghavan and Chin 2002;Tao et al 2010), information on the effect of decreasing natural-fracture (secondary) permeability when the fluid pressure declines is limited. Existing studies in this area fundamentally focus on characterizing fractures and their stress dependency independently of their impact on the production performance.…”

“…The permeability-modulus concept assumed an exponential variation of permeability with pressure, which was simplified with the Taylor expansion of the diffusivity and the permeability moduli. Celis et al (1994) used the permeability-modulus concept to analytically model unsteady-and pseudosteady-state flow of oil in naturally fractured, stress-sensitive reservoirs. Best (1995), however, focused specifically on shale permeability and noted that there was no agreement on whether the permeability/pressure relationship in shale could be represented by a single mathematical expression.…”

A New Method for Research on Unsteady Pressure Dynamics and Productivity of Ultralow-Permeability Reservoirs

“…The seepage mechanism of low-permeability reservoirs is very complex. Due to the stress sensitivity effect and threshold pressure gradient in low-permeability reservoirs [1][2][3], the current research on the theory and application of seepage flow in offshore low-permeability oil reservoirs has limitation, including two common features: (i) as the two variables, stress sensitivity effect and threshold pressure gradient, both have big influences on seepage, most models only consider one of them as factor; (ii) in order to prevent the blowout, using of the mud with high density in offshore drilling and mud pollution caused by this method is not taken into consideration in most models.…”

Pressure transient analysis of a vertical well with multiple etched fractures in carbonate reservoirs

“…On the other hand, the other dual-porosity model was widely used on the basis of the assumption of a transient exchange term between matrix and fracture. Several researchers have presented different geometric shapes of matrix blocks, such as slab, cylindrical and spherical matrix blocks, to describe the unsteady state exchange (de SWAAN, 1976;Kucuk andSawyer 1980, Cinco-Ley andSamaniego 1982;Olarewaju and Lee 1986;Celis et al, 1994;Hassanzadeh et al, 2009;Babak and Azaiez 2014;Wang et al, 2015). The biggest difference between the pseudosteady state and nonsteady state flow is that the pressure derivative curve of the former has a deeper trough like a bell-shape than the latter one being relatively flat at the transition flow period.…”