Interference Test Analysis In Limited Reservoirs Using The Pressure Derivative Approach Field Example
Authors: Foster G.A. , Wong D.W. , Asgarpour S.A. , Cinco Ley H. 
Published: March 2010

Abstract
Application of type curves to interference testing has usually provided poor results due to match non-uniqueness. In this paper, we present three new sets of type curves using the dimensionless pressure groups PD and the associated derivative vs. time function (equation available in full paper) for the case of an observation well in a rectangular reservoir. These three sets of type curves are generated for the case of the producing well at the comer, end or middle of the rectangular reservoir. The character of this set of type curves, similar to Bourdet et al. type curves, provides a great improvement in obtaining a unique type curve match. This study then explains the use of this new set of type curves for an interference test in a limited reservoir using the Bourdet et al. pressure derivative approach. A field example is included to demonstrate the application of this method to actual test data and how cartesian methods are used to verify the match. Flow regimes covered in the analysis include infinite acting pressure response with wellbore storage and skin at both the active and observation wells, as well as linear flow and pseudo-steady state flow.

Introduction
Modem interference testing has its origins in the water well testing literature(l). Here several shallow observation points at various radii from the pumping well can be easily and inexpensively drilled. Actual water levels are measured directly in the observation wells during drawdown testing. Conversely, interference tests in petroleum reservoirs are almost always conducted at considerably greater depths with non-ideal fluids, non-ideal observation well locations and other complications such as wellbore storage effects and wellbore skin. Currently, it is the practice in the oil industry to use bottom hole pressure gauges in the most convenient observation well measuring pressure disturbances created by a production or injection well (henceforth called the active well).
The infinite acting pressure response of the active well(2,3) and observation well(4–6) both with wellbore storage and skin has been investigated. These results, as will be seen later, are very important to the analysis of finite reservoir behaviour. From the analysis of an interference test in an infinite system, the reservoir permeability, storativity and heterogeneity can be estimated.
Interference testing in closed reservoir systems has also been investigated by Earlougher and Ramey(7). However type curve analysis was difficult due to match non-uniqueness. The present study will demonstrate the use of a new type curve for interference testing in limited reservoirs using the useful Bourdet et al.(8) pressure derivative approach. The addition of the derivative curve combined with the selection of a suitable dimensionless time equation improves the match uniqueness compared with the previous method. A preceding complementary study(9) used the same approach and it will be shown that its results are one case in the present study, namely, both wells at the same location.
This study will also present limits on the location of observation wells in different configurations of rectangular reservoirs.