A Petrophysical Dual-Porosity Model for Evaluation of Secondary Mineralization and Tortuosity in Naturally Fractured Reservoirs
- Jaime Piedrahita (University of Calgary) | Roberto Aguilera (University of Calgary)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- May 2017
- Document Type
- Journal Paper
- 304 - 316
- 2017.Society of Petroleum Engineers
- Naturally Fractured Reservoirs, Tight Gas, Tortuosity, Secondary Mineralization, Fracture Compressibility
- 8 in the last 30 days
- 444 since 2007
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Quantification of secondary mineralization or cementation within natural fractures has not been considered in previous petrophysical dual-porosity models. This is, however, of paramount importance because morphology of the fractures indicates that they can be open or partially or completely mineralized.
If cementation with secondary minerals is complete, the recovery of hydrocarbons will be generally very small because hydrocarbons will not have any way to move from matrix to natural fracture and then to the wellbore. However, if secondary mineralization is partial, production rates and recoveries could be quite significant because the secondary minerals would play the role of natural proppant agents helping to maintain the fractures open as the reservoir is depleted. If the fractures are initially open, production rates and recoveries could be large or small depending on the relative orientation of the natural fractures with respect to in-situ stresses.
These observations lead to the key objective of this paper: to develop an analytical dual-porosity model using resistance networks for quantifying petrophysical fracture parameters such as degree of cementation (ß), formation factor (F), dual-porosity exponent (m), and tortuosity (t) for different degrees of mineralization (cementation) within the fractures. The method further allows estimating matrix and fracture porosities and fracture compressibility on the basis of the amount of secondary mineralization.
Use of the new dual-porosity model is explained with two core data sets drawn from tight gas formations in the United States and Canada. A comparison is made with results of current dual-porosity models that do not take into account secondary mineralization within the natural fractures and tortuosity.
The conclusion is reached that the proposed dual-porosity model provides a valuable new quantitative tool for petrophysical and reservoir-engineering evaluations of naturally fractured reservoirs. This is illustrated with two numerical examples that show determination of original petroleum in place and recovery. One example is volumetric, and the other one is based on the material-balance calculations.
|File Size||1 MB||Number of Pages||13|
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