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 )
- G.S. Brar (Alberta Energy Resources Conservation Board) | K. Aziz (U. of Calgary)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- February 1978
- Document Type
- Journal Paper
- 297 - 304
- 1978. Society of Petroleum Engineers
- 4.6 Natural Gas, 5.3.2 Multiphase Flow, 4.3.1 Hydrates, 5.8.7 Carbonate Reservoir, 5.1.2 Faults and Fracture Characterisation, 4.2 Pipelines, Flowlines and Risers, 5.5.2 Core Analysis, 5.6.4 Drillstem/Well Testing
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Two new methods (simplified isochronal test [SIT] analyses) to predict the stabilized deliverability potential of gas wells are presented. These techniques use isochronal data from modified isochronal tests and also provide 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).
The most commonly used method to predict the initial stabilized deliverability potential of a gas well is the modified isochronal test that includes an extended flow period to pressure stabilization. Some reservoirs do not period to pressure stabilization. Some reservoirs do not attain stabilization even after 100 or more hours of now and consequently a reliable, extended flow period on such reservoirs can be unreasonably expensive and wasteful. In many instances, new wells are not tied into a pipeline 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 Alberta Energy Resources Conservation Board (AERCB) have imposed limitations (20 MMscf) on the amount of gas that can be flared during most gas well tests. To circumvent this problem, the isochronal portion of a test may be conducted while the extended flow period is delayed until the well is tied into a pipeline. Finally, in many cases where complete, modified iochronal test have been run, extended flow tests simply are not conducted to stabilization and the stabilized deliverability potential must be estimated from just the isochronal flow data.
This paper presents two simple techniques to predict the stabilized deliverability potential, using only the isochronal data from modified isochronal tests. With either of the proposed techniques, which are referred to as "simplified isochronal test (SIT) analyses," it is possible 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 other well and reservoir data to predict the stabilized deliverability potential of gas wells.
These techniques are based on existing theory for the analysis of gas well-test data. The quadratic form of the deliverability equation describes the pressure-flow rate relationship. The transient and stabilized flow coefficients in this equation are calculated using SIT methods.
The isochronal-test method described by Cullender and the modified isochronal-test method proposed by Katz et al. have been used extensively to develop performance curves for gas wells-particularly the performance curves for gas wells-particularly the modified isochronal tests. A requirement of such testing procedures 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 fast stabilization, it is undesirable from a conservation standpoint to flare gas needed to establish stabilized flow.
Consequently, the supposedly stabilized deliverability potential reported in tests usually is not representative of potential reported in tests usually is not representative of the stabilized performance of wells. The methods presented 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 a stabilized flow test.
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