Interpretation of Tests in Fissured and Multilayered Reservoirs With Double-Porosity Behavior: Theory and Practice
- Alain C. Gringarten (Scientific Software-Intercomp)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- April 1984
- Document Type
- Journal Paper
- 549 - 564
- 1984. Society of Petroleum Engineers
- 5.1.2 Faults and Fracture Characterisation, 4.1.5 Processing Equipment, 5.6.1 Open hole/cased hole log analysis, 5.2 Reservoir Fluid Dynamics, 5.6.3 Pressure Transient Testing, 5.2.1 Phase Behavior and PVT Measurements, 5.1.1 Exploration, Development, Structural Geology, 1.2.3 Rock properties, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 4.1.2 Separation and Treating, 5.8.6 Naturally Fractured Reservoir, 1.6.9 Coring, Fishing, 5.6.4 Drillstem/Well Testing, 3.2.4 Acidising
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Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area,these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering.
This paper summarizes current knowledge of reservoirs with double-porositybehavior. These include both naturally fissured reservoirs and multilayeredreservoirs with high permeability contrast between layers. The first partpresents available solutions to the direct problem (i.e., solutions to thediffusivity equation) that problem (i.e., solutions to the diffusivityequation) that have appeared in the oil and groundwater literature over thepast 20 years. The second part discusses methods for solving the inverseproblem--i.e., identifying a double-porosity behavior and evaluating allcorresponding well and reservoir parameters.
Several field examples demonstrate various aspects of double-porositybehavior and illustrate how additional knowledge of the reservoir (e.g..fissured vs. multilayered, gas saturation. etc.) can be obtained from numericalvalues of the reservoir parameters. Practical considerations for planning testsin Practical considerations for planning tests in double- porosity reservoirsalso are included.
The movement of underground fluids is of interest in many differentengineering fields and, consequently, has been the subject of active researchover the past 40 years.
Interpretation procedures, however, are well established only for porousfluid-bearing reservoirs considered reasonably homogeneous. Fluid-flow behaviorin heterogeneous formations is still the subject of much debate. It is agreedonly that conventional methods primarily developed for homogeneous reservoirsmay be inadequate, and that new specific approaches may be required to providea convincing explanation for some commonly observed flow peculiarities.
There has been no unified approach to the problem, heterogeneous reservoirbehavior in the literature is still considered too complex and too diverse tobe analyzed in a systematic and unique way. The main reason is the generalbelief that an interpretation model must closely approximate the actualcomplexity of the reservoir. The observation of a very large number of welltests in many different formations around the world, however, reveals that thenumber of possible behaviors during a well test is limited; therefore, only alimited number of interpretation models is required for well test analysis.This is because during a well test, the reservoir is acting only as a filterbetween an input signal, the change in flow rate, and an output signal, thechange in pressure, and only high contrasts in physical properties within thereservoir can be highlighted.
In practice, a test reveals only that the reservoir acts as one singlemedium (homogeneous behavior) or as two interconnected media (heterogeneousbehavior). The terms "homogeneous" and "heterogeneous" are related to reservoirbehavior, not to reservoir geology. "Homogeneous" means that the permeabilitymeasured in a test and that measured in a core are the same, although theresulting numbers may be different. "Heterogeneous" means that thesepermeabilities are likely to be different. permeabilities are likely to bedifferent. The Double-Porosity Model
The particular case of heterogeneous behavior where only one of the twoconstitutive media can produce to the well is called "double-porosity"behavior.
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