Nonlinear Transport Properties in Tight Formation

Date

2018-05

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Abstract

Five different plug scale based measurements are modeled, emphasizing the role of nonlinearities. The necessity of using the full nonlinear flow equation for the interpretation of the data is discussed. Our implementation of the transport equation includes the assumption of constant viscosity, rock compressibility, and pressure dependent permeability. Forchheimer terms are assumed negligible due to the low flow rates encountered. The standard techniques (steady state, unsteady state, pulse decay, and sinusoidal pressure) differ from one another due to the addition of reference chambers.

The density effect establishes a nonlinear pressure profile even after the transients have dissipated. This effect leads to the estimation of permeability that is too small compared to the typically assumed linear profile. In contrast, the Klinkenberg effect causes an increased estimate of permeability. It is difficult to separate these two effects, as a result, modeling the full nonlinear behavior of the transport properties is necessary. The different effects of the non-linearities are presented for the modeled measurement protocols. A new technique, the k0-b plot is introduced to separate these two effects.

Unique equipment was developed at University of Houston, which is much simpler and minimize the impact of gas leakage. Prototype equipment was built, and the initial permeability measurement was performed. This equipment allows all the standard technique to be performed. In addition, a new technique (the moving boundary conditions) is possible. The advantages of this technique are discussed.

The modeling indicates that plug scale measurements are practical in terms of the amount of time required, and that grinding of the samples is not necessary. We recommend performing measurements at different mean pore pressure to allow the k0-b plot to be applied.

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Keywords

Nonlinear, Transport, Permeability, Unconventional, Gas

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