Authors' Reply to Discussion of Interrelationship of Temperature and Wettability on the Relative Permeability of Heavy Oil in Diatomaceous Rocks
- A.R. Kovscek (Stanford University) | J.M. Schembre (Chevron) | G.-Q. Tang (Chevron)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- June 2008
- Document Type
- Journal Paper
- 437 - 438
- 2008. Society of Petroleum Engineers
- 4.3.4 Scale, 5.2.1 Phase Behavior and PVT Measurements, 5.4.6 Thermal Methods, 5.5.8 History Matching, 5.4.10 Microbial Methods, 5.5 Reservoir Simulation, 5.3.4 Integration of geomechanics in models
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This paper is the authors' reply to the discussion of SPE-93831-PA.
Dietrich's discussion is wide ranging. We agree that oil recovery from diatomite rocks is influenced by a variety of mechanisms, that compaction plays a role, and that more work in the area of recovery mechanisms and their representation within a reservoir simulator is warranted. His critique of our work, however, incorrectly summarizes our experimental procedures and it misrepresents the importance that we attribute to hot-water imbibition in relation to the other mechanisms that contribute to thermal oil recovery. His discussion of the simulation of field-scale recovery processes does not appear to acknowledge the need for upscaling or the inherent nonuniqueness present in history-match results. Our work highlights the role of fines detachment as well as silica and mineral dissolution combined with compressive stress (Schembre et al. 2006; Ikeda et al. 2007; Ross et al. 2008). We have found that rock wettability evolves favorably to a more water-wet state with
elevated temperature. This change in wettability contributes positively to recovery.
Laboratory Procedures and Measurements
We study imbibition processes for steam-based thermal-recovery processes because field experiments and simulations have made
clear that steam injection into diatomite is accompanied by significant condensation, among other effects (Kovscek at al. 1996a, 1996b; Hoffman and Kovscek 2004). Mechanisms that aid water imbibition into the rock matrix in a field setting clearly improve recovery by both spontaneous and forced imbibition. Considerable disagreement remains about the magnitude of pressure drops achievable during field-recovery operations and diatomite relative permeability endpoints are rate dependent (Kamath et al. 1995). Accordingly, we have studied spontaneous countercurrent and cocurrent, as well as forced imbibition. We have given particular weight to spontaneous countercurrent tests of diatomite at elevated temperature and pressure because such tests provide an unambiguous baseline. Given the relevance of factors such as thermal expansion, oil viscosity reduction, forced imbibition, and steam displacement, we have not stated nor implied that spontaneous countercurrent imbibition is the dominating mechanism at field scale.
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