Analysis of Modified Isochronal Tests To Predict The Stabilized Deliverability Potential of Gas Wells Without Using Stabilized Flow Data (includes associated papers 12933, 16320 and 16391 )
Authors: Brar G.S. , Aziz K. 
Published: December 2007

Two new methods (simplified isochronal test [SIT] analyses) to predict thestabilized deliverability potential of gas wells are presented. Thesetechniques use isochronal data from modified isochronal tests and alsoprovide reasonable values of permeability-thickness (kh), skin factor (s), provide reasonable values of permeability-thickness (kh), skin factor (s), and inertial-turbulent flow factor (D).

Introduction

The most commonly used method to predict the initialstabilized deliverability potential of a gas well is themodified isochronal test that includes an extended flowperiod to pressure stabilization. Some reservoirs do not period to pressure stabilization. Some reservoirs do not attain stabilization even after 100 or more hours of nowand consequently a reliable, extended flow period onsuch reservoirs can be unreasonably expensive andwasteful. In many instances, new wells are not tied into apipeline before testing, in which cases gas must be flared pipeline before testing, in which cases gas must be flared during a test. Regulatory agencies such as the AlbertaEnergy Resources Conservation Board (AERCB) haveimposed limitations (20 MMscf) on the amount of gasthat can be flared during most gas well tests. Tocircumvent this problem, the isochronal portion of a test may beconducted while the extended flow period is delayed untilthe well is tied into a pipeline. Finally, in many caseswhere complete, modified iochronal test have beenrun, extended flow tests simply are not conducted tostabilization and the stabilized deliverability potentialmust be estimated from just the isochronal flow data.

This paper presents two simple techniques to predictthe stabilized deliverability potential, using only theisochronal data from modified isochronal tests. With eitherof the proposed techniques, which are referred to as"simplified isochronal test (SIT) analyses," it ispossible to obtain reasonable values of permeability-thickness possible to obtain reasonable values of permeability-thickness (kh), skin factor (s), and inertial-turbulent flow factor(D). These reservoir parameters may be used with otherwell and reservoir data to predict the stabilizeddeliverability potential of gas wells.

These techniques are based on existing theory for theanalysis of gas well-test data. The quadratic form of thedeliverability equation describes the pressure-flow raterelationship. The transient and stabilized flowcoefficients in this equation are calculated using SIT methods.

The isochronal-test method described by Cullenderand the modified isochronal-test method proposed byKatz et al. have been used extensively to developperformance curves for gas wells-particularly the performance curves for gas wells-particularly the modified isochronal tests. A requirement of such testingprocedures is a flow period to pressure stabilization, procedures is a flow period to pressure stabilization, or stabilized flow. This requirement is not found often, particularly in low-permeability reservoirs. Even in particularly in low-permeability reservoirs. Even in reservoirs with good producing characteristics and faststabilization, it is undesirable from a conservation standpointto flare gas needed to establish stabilized flow.

Consequently, the supposedly stabilized deliverabilitypotential reported in tests usually is not representative of potential reported in tests usually is not representative of the stabilized performance of wells. The methodspresented here overcome this deficiency and are valuable in presented here overcome this deficiency and are valuable in certain situations where it is impossible to conduct astabilized flow test.

JPT

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