An Improved Triple-Porosity Model for Evaluation of Naturally Fractured Reservoirs
- Ali Al-Ghamdi (University of Calgary) | Bo Chen (Yangtze University) | Hamish Behmanesh (Petroleum University of Technology) | Farhad Qanbari (Petroleum University of Technology) | Roberto Aguilera (University of Calgary)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- August 2011
- Document Type
- Journal Paper
- 377 - 384
- 2011. Society of Petroleum Engineers
- 5.7.5 Economic Evaluations, 1.14 Casing and Cementing, 5.7 Reserves Evaluation, 5.6.1 Open hole/cased hole log analysis, 4.3.4 Scale, 5.8.6 Naturally Fractured Reservoir
- Vugs, Petrophysics, Carbonates, Natural fractures, Triple porosity
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Many naturally fractured reservoirs are composed of matrix, fractures, and nontouching vugs (there can also be any other type of nonconnected porosity that can occur; for example, in intragranular, moldic, and/or fenestral porosity). An improved triple-porosity model is presented that takes these different types of porosities into account. The model can be used continuously throughout a reservoir with segments composed of solely matrix porosity, solely matrix/fractures, solely fractures/vugs, or the complete triple-porosity system.
The model improves a previous triple-porosity algorithm by handling rigorously the scale associated with each: matrix, fractures, and vugs. This permits determining more-realistic values of the cementation or porosity exponent, m, for the composite system and consequently improved values of water saturation and reserves evaluations. The values of m for the triple-porosity reservoir can be smaller than, equal to, or larger than the porosity exponent of only the matrix blocks, mb, depending on the relative contribution of the vugs and fractures to the total porosity system.
It is concluded that not taking into account the contribution of matrix, fractures, and vugs in the petrophysical evaluation of triple-porosity systems can lead to significant errors in the determination of m, and consequently in the calculation of water saturation, hydrocarbons in place, and recoveries, and ultimately can lead to poor economic evaluations--either too pessimistic or too optimistic. This is illustrated with two examples from Middle East carbonates.
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