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# From Straight Lines to Deconvolution: The Evolution of the State of the Art in Well Test Analysis

- Authors
- Alain C. Gringarten (Imperial College)
- DOI
- http://dx.doi.org/10.2118/102079-PA
- Document ID
- SPE-102079-PA
- Publisher
- Society of Petroleum Engineers
- Source
- SPE Reservoir Evaluation & Engineering
- Volume
- 11
- Issue
- 01
- Publication Date
- February 2008

- Document Type
- Journal Paper
- Pages
- 41 - 62
- Language
- English
- ISSN
- 1094-6470
- Copyright
- 2008. Society of Petroleum Engineers
- Disciplines
- 5.8.6 Naturally Fractured Reservoir, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 4.3.4 Scale, 4.6 Natural Gas, 6.5.3 Waste Management, 3.3.1 Production Logging, 3.3.6 Integrated Modeling, 5.8.8 Gas-condensate reservoirs, 5.8.7 Carbonate Reservoir, 3.3 Well & Reservoir Surveillance and Monitoring, 5.1.2 Faults and Fracture Characterisation, 7.5.3 Professional Registration/Cetification, 5.1 Reservoir Characterisation, 2.4.3 Sand/Solids Control, 5.2.1 Phase Behavior and PVT Measurements, 7.5.4 University Curricula, 5.6.3 Pressure Transient Testing, 5.3.2 Multiphase Flow, 5.2.2 Fluid Modeling, Equations of State, 5.6.1 Open hole/cased hole log analysis, 5.5 Reservoir Simulation, 5.6.11 Reservoir monitoring with permanent sensors, 5.1.1 Exploration, Development, Structural Geology, 2 Well Completion, 5.6.4 Drillstem/Well Testing
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### Summary

Well test analysis has been used for many years to assess well condition and obtain reservoir parameters. Early interpretation methods (by use of straight lines or log-log pressure plots) were limited to the estimation of well performance. With the introduction of pressure-derivative analysis in 1983 and the development of complex interpretation models that are able to account for detailed geological features, well test analysis has become a very powerful tool for reservoir characterization. A new milestone has been reached recently with the introduction of deconvolution. Deconvolution is a process that converts pressure data at variable rate into a single drawdown at constant rate, thus making more data available for interpretation than in the original data set, in which only periods at constant rate can be analyzed. Consequently, it is possible to see boundaries in deconvolved data, a considerable advantage compared with conventional analysis, in which boundaries often are not seen and must be inferred. This has a significant impact on the ability to certify reserves.

This paper reviews the evolution of well test analysis techniques during the past half century and shows how improvements have come in a series of step changes 20 years apart. Each one has increased the ability to discriminate among potential interpretation models and to verify the consistency of the analysis. This has increased drastically the amount of information that one can extract from well test data and, more importantly, the confidence in that information.

### Introduction

Results that can be obtained from well testing are a function of the range and the quality of the pressure and rate data available and of the approach used for their analysis. Consequently, at any given time, the extent and quality of an analysis (and therefore what can be expected from well test interpretation) are limited by the state-of-the-art techniques in both data acquisition and analysis. As data improve and better interpretation methods are developed, more and more useful information can be extracted from well test data.

Early well test analysis techniques were developed independently from one another and often gave widely different results for the same tests (Ramey 1992). This has had several consequences:

• An analysis was never complete because there always was an alternative analysis method that had not been tried.

• Interpreters had no basis on which to agree on analysis results.

• The general opinion was that well testing was useless given the wide range of possible results.

Significant progress was achieved in the late 1970s and early 1980s with the development of an integrated methodology on the basis of signal theory and the subsequent introduction of derivatives. It was found that, although reservoirs are all different in terms of depth, pressure, fluid composition, geology, etc., their behaviors in well tests were made of a few basic components that were always the same. Well test analysis was about finding these components, which could be achieved in a systematic way, following a well-defined process. The outcome was a well test interpretation model, which defined how much and what kind of knowledge could be extracted from the data. The interpretation model also determined which of the various published analysis methods were applicable and when they were applicable. Importantly, the integrated methodology made well test analysis repeatable and easy to learn. The evolution of the state-of-the-art techniques in well test analysis throughout these years can be followed from review papers that have appeared at regular intervals in the petroleum literature (Ramey 1980, 1982, 1992; Gringarten 1986; Ehlig-Economides et al. 1990).

**File Size**5 MB

**Number of Pages**22

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