Abstract

This paper concentrates on pressure transient tests in triple porosity naturally reservoirs (NFR) with pseudo steady state flow regime using direct synthesis technique.

Thedirect synthesis technique couples the characteristic points and lines from a log-log plot of pressure and pressure derivative data resulting in simple equations to solve for the desired reservoir parameters. Parametric analysis in dimensionless space illustrates the behavior desired reservoir parameters and provides the basis for newly empirical correlations relating these parameters to the field data. Applicability of the empirical correlations corresponding to the characteristic points developed as a result of this work is demonstrated by successfully analyzing simulated pressure transient tests. The direct synthesis method is proposed to overcome problems for the case where there is no guarantee on existence of an early-time unit slope line and /or the late-time infinite acting radial flow line has not been seen due to inner and outer boundaries, lack of points and severe noise problem. Both the effect of wellbore storage and skin are included in the analysis. As a result of this work, direct synthesis simplifies evaluation of pressure transient tests in triple porosity naturally fractured reservoirs (NFR) with pseudo steady state flow regime, eliminates the type curve matching or regression analysis. Before this paper, only one paper was published for well test analysis of triple porosity naturally fractured reservoirs with unsteady state behavior using direct synthesis technique. But in that paper, the effect of wellbore storage and skin in the analysis was not considered and also several interrelated constants were included in the equations used for estimating the reservoir parameters which makes the estimation complicated and erroneous.

Background

During the past 45 years, pressure transient behavior in naturally fractured reservoir has been extensively studied. Barenblatt, et al1assumed pseudo-steady state interporosity flow in a model made of the orthogonal, equally spaced fractures. Warren and Root2used the Barenblatt, et al1 theory and concluded that a conventional semilog plot of a pressure versus time should result in two parallel straight lines with transition zone in between them.

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