Abstract

This study presents an analytical method for determining the double-porosity reservoir properties using interference pressure data in an infinite reservoir producing at constant pressure. Wellbore storage and skin effects at the production and observation wells are neglected. The effects of rD, λ, and ω, on interference pressure responses are examined. For dimensionless inter-well distances of 100 or more, the pressure responses are practically collapsed. As a result of this, a general type curve that can be used for any value of rD, is presented. Hence, for a given pressure response and rD the type curve yields unique values of λ and ω. In addition to the log-log type curve, a semi-log type curve that is more useful for pD values greater than 0.1 is presented.

The semi-log derivatives of the interference pressure responses are considered. The pressure derivatives enhance small variations that occur in the pressure response during the flow period affected by the double-porosity nature of the reservoir.

It is observed that using a simple correlation with λ and rD, the derivative curves for rD values greater than 100 can be collapsed. Hence, a semi-log derivative type curve is developed. This type curve has two maxima. The early-time part is influenced by λ. The time separation between the first maximum and the second maximum is a function of ω. The late time behavior is again a function of λ.

Introduction

Well testing has long been a very useful tool to evaluate reservoir properties such as storativity and transmissivity. In an ordinary well test, a variety of well boundary conditions can be used, such as step changes in rate or pressure, or as instantaneous slug removal. In contrast to single well testing, interference testing is limited to the collection of pressure data from an observation well.

Interference testing is a multiple-well test that requires at least one active well and at least one observation well. The active well is either a producer or an injector, and the observation wells are shut-in wells in which pressure effects caused by the active well are measured. This kind of testing has the advantage of investigating reservoir properties where the characteristic length of the system is the interwell distance rather than the wellbore radius.

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