Variable Flow Rate Reservoir Limit Testing (includes associated paper 4262 )
- Robert C. Earlougher Jr. (Scientific Software Corp.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- December 1972
- Document Type
- Journal Paper
- 1,423 - 1,430
- 1972. Society of Petroleum Engineers
- 0 in the last 30 days
- 185 since 2007
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With this technique, reservoir size can be estimated from pressure data taken from either production or injection wells operating on a cyclic rate schedule. So long as the requirement is satisfied that the flow rate vary cyclically rather than increasing or decreasing montonically, reservoir limit testing is quite simple and an engineer can accomplish it without computer aid.
The conventional reservoir limit test1-4can be used to estimate reservoir size if the test well operates at a constant flow rate during the test. Unfortunately, it is not always feasible to perform a test at a constant rate, at least for more than a few hours. This is particularly true when flow rate varies cyclically as in oil wells that are pumped cylically, water supply wells, and waste-disposal wells.
This paper shows how to estimate reservoir size from pressure data in wells operating with a cyclic rate schedule. The method applies to both injection and production wells. The important requirement is the cyclic rate: rate must oscillate about a mean value within some relatively regular period. When this condition is satisfied, reservoir limit testing is fairly simple. This requirement can be relaxed, in which case there will be a corresponding reduction in the accuracy of the calculated result. This is an important consideration when the engineer has no control over the quality of data - for instance, when the engineer has several years of historical data from a well. If he knows only rate and pressure at several points in time, he cannot apply a very accurate, sophisticated analysis technique. The method of this paper allows him to estimate reservoir size from such data, although the accuracy may be less than desired. This method should not be used if a better approach is available. Its value lies in providing reasonable engineering estimates when conditions prevent testing and analysis under more ideal conditions.
We shall present here a theoretically sound reservoir limit testing procedure for a cyclic two-flow-rate situation. Simulated pressure-time data for more complicated rate schedules experimentally extend the analysis technique to more realistic situations. The analysis techniques and suggestions for its use are presented, and an example using data from an existing industrial waste-disposal well, is included for illustration.
Reservoir Limit Test Analysis
The familiar reservoir limit test1-4 requires that a well be operated at constant rate until pseudosteady-state-flow conditions have existed for some time. Then, reservoir size can be calculated from
where: q=flow rate for the well, STB/D
q>0 for production, q<0 for injection
m*=slope of the linear portion of the pressure vs flowing-time plot, psi/hr
The slope, m*, is the constant rate of pressure change during pseudosteady-state flow; m* is negative for production, positive for injection.
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