Abstract

This paper discusses a method of determining observation well [ocations, toenable acquisition of infinite-acting radial flow data from a two-wellinserfere1]?e rest, in a rectangular reservoir. Using the dimensionlesspressure derivative responses, this paper investigates observation welllocations generating a minimum of one-half log cycle of infinite-acting radialflow data. The one-half log cycle of semi-log data included data pointsdeviaring from infinite-acting radial flow behaviour by 5%.

Using the exponential-integral solutions for a line-source well, an analyticalsolutiion was obtained following the method of superposition in space to studyinterference resting in rectangular reservoirs. For any outer boundarry, ano-low or a constant-pressure condition can be specified. Dimensionlesspressure derivative responses were computed for various combinations ofreservoir outer boundary conditions, reservoir shapes, and active andobservation well locations.

Results were obtained for 1:1, 2:1,4:1, and 10:1 rectangular Reservoirs. Theinteractions of the well locations in the reservoir and boundary conditions onthe interference test responses have been studied. Results are presented ascontours indicating the limits of observation well locations for interferencetests t/lm would yield at least one-half log cycle of infinire-acting radialflow data. Observation well location consours are also presented for the timeto deviation from infinite-acting behaviour for given active and observationwell locations. These contours should aid in the design of interferencetests.

Introduction

Interference testing is used w learn about communicarion between two wells anddetermine reservoir properties. For homogeneous and isotropic reservoirs aninterference test can determine the transmissivity, or mobility-thicknessproduct, kh/ µ, and the storativity, or compressibility-thickness product,Fc,h. The most common method of interference test analysis is the type-curvemarching method using the exponential-integral solution1 plotted asa log-log graph of Po vs. tr JrD'. In this study, the exponential-integralsolution is used along with the method of superposition in space to generateinterference responses for wells located in rectangular reservoirs. As pressurederivatives can enhance pressure signals and may be more sensitive todisturbances in reservoir conditions,(2–4) this study concentrateson dimensionless pressure derivative responses for wells located in rectangularreservoirs. Tiab and Kumar(5) have previously discussed the use ofdimensionless pressure derivatives in analyzing interference data for wellslocated in an infinite, homogeneous reservoir. Wellbore Storage and skineffects on interference res[S are not considered in this study. In the past, however, several studies(6–9) have been published regarding wellborestorage and skin effects on interference tests for wells located in aninfinite, homogeneous reservoir.

Gobran et al.(10) investigated the determination of infinite-actingflow periods for interference tests in rectangular reservours, using thedimensionless pressure responses. The end of the infinite-acting period wasdetermined to be the rime when the dimensionless pressure drop due to the imagewells was 5% of that of the active well Using a similar criterion the end ofthe infinite-acting period is estimated in this study based on thedimensionless pressure derivative responses.

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