Oil-Viscosity Predictions From Low-Field NMR Measurements
- J. Bryan (U. of Calgary/Tomographic Imaging and Porous Media Laboratory) | A. Kantzas (U. of Calgary/Tomographic Imaging and Porous Media Laboratory) | C. Bellehumeur (U. of Calgary)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- February 2005
- Document Type
- Journal Paper
- 44 - 52
- 2005. Society of Petroleum Engineers
- 5.4.6 Thermal Methods, 5.2 Reservoir Fluid Dynamics, 4.2 Pipelines, Flowlines and Risers, 5.6.1 Open hole/cased hole log analysis, 4.3.4 Scale, 4.3.3 Aspaltenes, 5.8.5 Oil Sand, Oil Shale, Bitumen
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Canada contains vast reserves of heavy oil and bitumen. Viscositydetermination is key to the successful recovery of this oil, and low-fieldnuclear magnetic resonance (NMR) shows great potential as a tool for estimatingthis property. An NMR viscosity correlation previously had been developed thatis valid for order-of-magnitude estimates over a wide range of viscosities andtemperatures. This correlation was built phenomenologically, using experimentsrelating NMR spectra to viscosity. The present work details a more thoroughinvestigation into oil viscosity and NMR, thus providing a theoreticaljustification for the proposed correlation. A novel tuning procedure is alsopresented, whereby the correlation is fitted using the Arrhenius relationshipto improve the NMR viscosity estimates for single oils at multipletemperatures. Tuning allows for NMR to be potentially used in observation wellsto monitor thermal enhanced oil recovery (EOR) projects or online to monitorthe viscosity of produced-fluid streams as they cool.
With approximately 400 million m3 of oil in place, the Canadian deposits ofheavy oil and bitumen are some of the most vast oil resources in the world.1Heavy oil and bitumen are characterized by high densities and viscosities,which is a major obstacle to their recovery. The waning of conventional-oilreserves in Canada, coupled with increasing worldwide demand for oil, hasforced the industry focus to shift rapidly to the exploitation of theseheavy-oil and bitumen reserves.
The most important physical property of heavy oil that affects its recoveryis its viscosity.1 This parameter dictates both the economics and the technicalchance of success for any chosen recovery scheme. As a result, oil viscosity isoften directly related to recoverable reserves estimates.2 Unfortunately,laboratory measurements of oil viscosity become progressively more difficult toobtain as viscosity increases.3 The oil that has been removed from the corealso may have been physically altered during sampling and transport. Thus, theviscosity at reservoir conditions may be different from the value obtainedlater from the laboratory.2 In light of the shortcomings of conventionalviscosity measurements, low-field NMR is considered as an alternative forestimating heavy-oil and bitumen viscosity.
The main appeal of NMR as a tool for assessing reservoir-fluid viscositiesand phase volumes is that the measured signal comes only from hydrogen, whichis present in both oil and water found in hydrocarbon reservoirs.4,5 Most ofthe low-field NMR applications in the petroleum industry have been inconventional oil, contained in sandstone reservoirs.6 To use low-field NMRtechnology in heavy-oil and bitumen formations like the ones present inAlberta, new methods of interpretation are required. The eventual goal forusing NMR to estimate viscosity is to make these predictions in the fieldthrough logs. Currently, research toward this goal is conducted in thelaboratory.
In previous work,7-9 an oil-viscosity correlation was presented that iscapable of providing viscosity predictions for samples with viscosities lessthan 1 mPa×s to more than 3 000 000 mPa×s. This is a wider range than any otherviscosity correlation presented in the literature.10-15 The correlation is onlyorder-of-magnitude accurate but still could be valuable for applications on alogging tool, where the goal would be to determine viscosity variations withdepth or areal location in a reservoir. The theoretical justification behindthe NMR correlation is given in this work, along with a procedure for tuningthe correlation to improve the viscosity predictions for individual oils as afunction of temperature. Low-field NMR experiments are simple to perform andnondestructive. The same test also can be run by different technicians to yieldthe same results, which is a concern for conventional viscosity tests.3 In thismanner, a properly calibrated NMR model for viscosity can be a very accurateand useful tool for predicting heavy-oil and bitumen viscosity at differenttemperatures.
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