Calibration of NMR porosity to estimate permeability in carbonate reservoirs
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Considering the performance of carbon dioxide (CO2) stored in geologic reservoirs requires some knowledge of the subsurface heterogeneity, where the most reliable data is extracted from wellbore measurements. This benefit is especially true for carbonate reservoirs were reactions between supercritical CO2, the reservoir brine, and carbonate minerals create new storage capacity and enhanced permeability. Techniques like NMR well logging hold promise for estimating subsurface permeability, because the total porosity and pore size can be calculated from response of 1H NMR signal. Resulting depth profiles of porosity and permeability from downhole logs are useful input for reservoir simulations and can be used to design injection protocols and estimate storage capacity.
We conducted a detailed characterization study to quantify the NMR response to matrix pore space, the connectivity to larger vugs and fractures, and the resulting permeability of core samples from distinct carbonate formations. The cores used in study span 5 orders in permeability, 4 orders in mean T2, and 2%–42% in porosity. The goal of the study was to use independent measures of pore volumes, surface relaxivity, fluid-accessible surface areas, and permeability to develop carbonate permeability models.
It was not possible to develop a single model that reproduced permeability for different carbonate formations, because phenomena specific to the reservoirs could not be extracted even with the state-of-the-art characterization techniques used in this study. Estimates of permeability require calibration. Best calculations for a given formation were achieved by using a simple form of the Kozeny equation (Eq. 6):
κ=Α’θ3*n,
and calibrating A’ and n with laboratory measurements made on the formation cores. Empirical calibrations can then be used to map the vertical heterogeneity of the storage complex to better understand the physical movement CO2 and brine in the subsurface and the positive feedback between mineral dissolution and the development of flow pathways.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA); USDOE Office of Fossil Energy (FE); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
- Grant/Contract Number:
- AC02-05CH11231; AC52-07NA27344
- OSTI ID:
- 1557046
- Report Number(s):
- LLNL-JRNL--764360; 954404
- Journal Information:
- International Journal of Greenhouse Gas Control, Journal Name: International Journal of Greenhouse Gas Control Vol. 87; ISSN 1750-5836
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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