Estimating Drainage-Area Pressure with Flow-After-Flow Testing
- C. Shah Kabir (Hess Corp.) | Malek Mohamed Elgmati (Missouri University of Science & Technology) | Zulfiquar Reza (Schlumberger Middle East SA)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 30 October-2 November, Denver, Colorado, USA
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 4.6 Natural Gas, 2.4.5 Gravel pack design & evaluation, 5.8.7 Carbonate Reservoir, 2.4.6 Frac and Pack, 5.6.4 Drillstem/Well Testing
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Estimating the individual wells' average drainage-area pressure or pav is cornerstone to any reservoir-management practice. Yet, conventional methods do not always offer reliable solutions to this vexing problem. This study shows that transient flow-after-flow (FAF) testing offers an excellent opportunity to establish pav in a time-lapse mode, when conducted following operational shut downs. Instrumented wells are natural candidates for FAF testing.
The real-time surveillance offers the opportunity to perform rate-transient analysis that results in drainage volume and, consequently, pav. However, gathering quality rate data commensurate with pressure over a long producing period is fraught with uncertainty, which raises questions about the validity of the pav so obtained. In addition, continuous changes in drainageboundary conditions pose modeling challenges with a given reservoir model. Therefore, the independent estimation of pav cannot be overemphasized. This paper presents a theroretical framework for transient FAF testing and also shows a pragmatic approach to handling pressure/rate data incoherence.
Deliverability testing of gas wells originated from the work of Rawlins and Schellhardt in 1936, based on the conventional flow-after-flow or FAF test. In this approach, each flow period needs to be long enough to attain the drainage radius, thereby making this test unattractive from a practical standpoint. A need for more pragmatic measures spawned developments of isochronal and modified-isochronal tests, which are well documented in the literature. The theoretical basis for both isochronal and modified-isochronal tests were intitially provided by Aziz (1967) for Darcy flow, followed by Mattar and Lin (1981) for non-Darcy flow. Although the modified-isochronal test is quite efficient, further time is saved by conducting a transient FAF test that eliminates the intervening shut-in periods. The SPE Transient Well Testing monograph (2009) makes this point, which also was noted earlier by Kabir (2006).
This study provides a theoretical basis for transient FAF testing and shows its application as a reservoir-management tool. Overall, this study shows development of a pragmatic methodology for FAF testing as a continuous reservoir-management practice by demonstrating its applications in vertical, horizontal, and layered reservoirs. The reservoir-drainage configuration appears important only in vertical wells. Certainly, the proposed approach is an attractive alternative to conventional buildup tests, and competes favorably with transient-PI (Medeiros et al. 2010) solutions. A robust computational algorithm is offered to handle inconsistencies associated with both rates and pressures.
|File Size||1 MB||Number of Pages||19|