Detection and Location of Two Parallel Sealing Faults Around a Well

Abstract

A new technique is presented for detecting the existence of and distance to two parallel sealing boundaries surrounding a producing oil or gas well. A log-log plot of time rate of change of well pressure vs. time provides a unique behavior to detect such a condition and allows the use of type-curve matching techniques to determine the khproduct. Introduction The idea of detecting and locating a reservoir boundary from transient pressure-time data first appeared in 1951. In that year Horner1 presented the transient pressure behavior of a constant-rate well located near a linear sealing fault. He also presented a method to calculate the distance to the fault from buidup pressure data. Dolan et al.2 applied the technique to drillstem tests. Davis and Hawkins3 gave an equation to determine the distance to the fault from drawdown pressure data. Gray4 reviewed these methods and discussed their limitations. Bixel et al.5considered a more general problem: a well located close to a linear discontinuity across which hydraulic diffusivity changes. They showed a procedure to determine the distance to such a discontinuity. Evrenos and Rejda6 employed superposition techniques to simulate various combinations of linear boundaries of interest in gas storage systems and showed how a match between the actual test data with various hypothesized model conditions can be used to arrive at a probable configuration of boundary conditions. Overpeck and Holden7 considered the effect of reservoir anisotropy on fault detection and showed that the distance calculated could differ by as much as 20% with those obtained by assuming isotropic medium. They gave a procedure for imaging when the principal permeability axes are at some angle other than 0 or 90° to the fault boundary. Rodgers and McArthur8 employed a minimum in standard deviation between observed pressures and a least-squares straight-line fit to determine boundary configuration. Prasad9presented a procedure to compute transient pressures for a well between two sealing faults intersecting at any angle. Jones10 in 1961 drew attention to the possible use of rate change of well pressure with time in detecting reservoir boundaries. Van Poollen11 presented graphs of time rate of change of well pressure during drawdown for various well locations between faults intersecting at 90 and 36°. Although this approach yields interpretable drawdown behavior, it has not been used widely in the petroleum literature. Witherspoon et al.12 considered the effect of a linear no-flow or flow boundary and presented the dimensionless pressure behavior caused by a constant-rate producing well at an observation well some distance away. They discussed techniques to analyze drawdown test data.

Pressure-Transient Tests and Flow Regimes in Fractured Reservoirs

“…1a). This is the dual-porosity geological model for which Barenblatt et al (1960) and Warren and Root (1963) presented solutions, although their solutions do not contain any explicitly modeled fractures. 2.…”

“…On the other hand, one can treat discontinuous low-conductivity and/or short fractures as an enhancement of matrix permeability, for which one can use locally either a singleporosity model with average properties or the Warren and Root (1963) dual-porosity-type models, while maintaining global heterogeneity, and particularly anisotropy, because even small fractures may have a dominant direction.…”

“…In some cases, we compare these flow regimes with those from field data. We also present two examples of history matching of the pressure-transient data generated by use of the Biryukov and Kuchuk (2012) model for discretely and continuously fractured reservoirs with the Warren and Root (1963) dual-porosity-type models. When we refer to the Warren and Root (1963) dual-porosity-type models, we include all their variations added since the 1960s.…”

From Straight Lines to Deconvolution: The Evolution of the State of the Art in Well Test Analysis

“…Applications to well test analysis first appeared in the late 1970s: A log-log plot of d⌬p/d(⌬t) vs. ⌬t was suggested as an alternative to straight-line analyses for interference tests (Tiab and Kumar 1980a), tests in fractured wells (Tiab and Puthigai 1988), and tests in reservoirs bounded by two parallel faults (Tiab and Kumar 1980b) and by multiple faults (Tiab and Crichlow 1979). The advantage of using a derivative on the basis of the natural log of elapsed time, d(⌬p)/d(log⌬t), which emphasizes radial flow, was also demonstrated for the description of heterogeneous reservoirs (Perez-Rosales 1978).…”

Well Test and PTA for Reservoir Characterization of Key Properties

“…Djebbar and Henry (1979) shows a type curves matching technique for interpretation of the pressure transient behavior of wells located in various Multiple Sealing-fault systems because the presence of a fault in a reservoir is of great importance, considerable numbers of pressure analysis techniques dealing with this situation have been proposed in literature. Djebbar and Anil (1980) presents study on the behavior of a well located between two parallel boundaries. Stehfest (1970) Abramowitz and Stegun (1970) present polynomial approximation to compute the modified Bessel function, Giovanni (1990).…”