Summary Low-field nuclear magnetic resonance (NMR) relaxometry has been used successfully to perform estimates of oil and water content in unconsolidated oil-sand samples. This work has intriguing applications in the oil-sands mining and processing industry, in the areas of ore and froth characterization. Studies have been performed on a database of ore and froth samples from the Athabasca region in northern Alberta, Canada. In this paper, new automated algorithms are presented that predict the oil- and water-weight content of oil-sand ores and froths. Suites of real and synthetic samples of bitumen, water, clay, and sand have also been used to investigate the physical interactions of the different parameters on the NMR spectra. Preliminary observations regarding spectral properties indicate that it may be possible in the future to estimate the amount of clay in the samples, based upon shifts in the NMR spectra. NMR estimates of oil and water content are fairly accurate, thus enhancing the possibility of using NMR for oil-sands development and in the oil-sands mining industry. Introduction The oil sands of northern Alberta contain some of the world's largest deposits of heavy oil and bitumen. As our conventional oil reserves continue to decline, these oil sands will be the future of the Canadian oil industry for years to come and will allow Canada to continue to be a world leader in both oil production and technology development. Approximately 19% of these bitumen reserves are found in unconsolidated deposits that lie close enough to the surface that they can be recovered with surface-mining technology (Alberta Energy and Utilities Board 2004). In 2003, this translated to 35% of all heavy-oil and bitumen production (Alberta Energy and Utilities Board 2004), and numerous companies have invested billions of dollars in oil-sands mine-development projects. Furthermore, many in-situ bitumen-recovery options are currently being designed and field tested for recovering oil in deeper formations (Natl. Energy Board 2004). Being able to predict oil properties and fluid saturation in situ and process optimization of bitumen extraction (frothing) is therefore of considerable value to the industry. There are several areas in oil-sands development operations where it is important to have an estimate of the oil, water, and solids content of a given sample. During initial characterization of the reservoir, it is necessary to determine oil and water content with depth and location in the reservoir. Fluid-content determination with logging tools would be beneficial for all reservoir-characterization studies, whether for oil-sands mining or in-situ bitumen recovery. In mining operations, during the processing of the mined oil-sand ore, having information about the oil, water, and solids content during the extraction process will allow for improved process optimization and control. The industry standard for measuring oil, water, and solids content accurately is the Dean-Stark (DS) extraction method (Core Laboratories 1992). This is essentially a distillation procedure, whereby boiling solvent is used to vaporize water and separate the oil from the sand. Oil, water, and solids are separated and their contents measured separately. The problem with DS is that it requires large amounts of solvents and is time consuming. Centrifuge technology is often used for faster process control, but this can be inaccurate because of similar fluid densities and the presence of emulsions. New methods for fast measurements of oil, water, and solids content are needed.
L ow fi eld nuclear magnetic resonance (NMR) has opened a wide spectrum of opportunities for reservoir characterization. NMR logging tools and laboratory systems can explore the physical interactions of proton bearing fl uids when they are exposed to magnetic fi elds at frequencies of 1 to 2 MHz. Several service companies currently market NMR-based logs focusing primarily on determining properties of the reservoir such as rock porosity and permeability, as well as the distribution of mobile and immobile fl uids. Parallel to the development of logging tools, laboratory based bench-top instruments have also been developed for research and calibration purposes.Low fi eld NMR technology was initially developed for formations in Texas and the North Sea. The primary targets for the development of this technique were sandstones in the Gulf of Mexico and Texas Chalks, followed by the large sandstone reservoirs in the North Atlantic. NMR has been used in the reservoir characterization of Canadian formations since the A number of techniques have previously been developed that use low fi eld nuclear magnetic resonance (NMR) relaxometry for conventional and heavy oil reservoir characterization. In the current work, the adaptation of these algorithms for use in the oil sands industry is presented. NMR based methods have been developed for identifi cation of water and bitumen content in ore and froth samples. Consistent algorithms have been used to analyze over 500 ore samples and 50 froth samples from the Athabasca oil sands in northern Alberta. Preliminary analyses are shown, with applications for in-situ fl uid determination using NMR logging tools and improved process control in oil sands processing plants.Plusieurs techniques reposant sur la relaxométrie à résonance magnétique nucléaire (RMN) pour la caractérisation des réservoirs conventionnels et d'huiles lourdes ont été mises au point antérieurement. Dans le présent travail, on présente l'adaptation de ces algorithmes à des fi ns d'utilisation dans l'industrie des sables bitumineux. Des méthodes reposant sur la RMN ont été mises au point pour la détermination de la teneur en eau et en bitume dans des échantillons de minerai et d'écume. On a utilisé des algorithmes consistants pour analyser plus de 500 échantil-lons de minerai et 50 échantillons d'écume venant des sables bitumineux d'Athabasca dans le nord de l'Alberta. Des analyses préliminaires sont présentées dans le cadre de la détermination des fl uides in situ au moyen de sondes de RMN et d'une régulation de procédé amélioré dans les usines de traitement des sables bitumineux.
Methods commonly used to measure the wettability of unconsolidated porous media are quick and easy to perform, but these tests do not provide reproducible results. This paper outlines the use of low-field nuclear magnetic resonance (NMR) as an alternative method of wettability assessment due to this tool's ability to discriminate bound fluid from bulk fluid. Water bound to the grain surfaces of water-wet samples relaxes quickly and produces signal amplitude peaks at low transverse relaxation (T2) values. Bulk water, on the other hand, relaxes much more slowly and signal amplitude peaks consequently appear at higher T2 values. It is expected that the contribution of surface-bound water in water-repellent samples is lower than in water-wet samples. NMR measurements performed on water-wet sand and on the same sand coated with organic matter clearly show significant differences in solid-fluid interactions between water and sands of different wettabilities. Numerous NMR measurements were obtained over time to monitor relaxation shifts because it was expected that the resulting spectra would provide insight into the rate of fluid uptake in sands of varying wettability. Water uptake appears to be spontaneous in water-wet samples and much slower in water-repellent samples, however all samples will eventually reach the same equilibrium endpoint regardless of wettability. NMR spectra also show that the results from water in uncoated and coated sands closely resemble that from water in wettable and water-repellent soils. Consequently, uncoated and coated sands can be used to analyze wettability mechanisms in unconsolidated porous media. The results also show that causative agents of soil water repellency include asphaltenes that are insoluble to n-pentane. Introduction Wettability is defined as "the tendency of one fluid to spread on or adhere to a solid surface in the presence of other immiscible fluids(1)." This parameter is not a fixed and constant property(2) due to factors such as saturation and climate history, as well as sample handling(3). Wetting and non-wetting fluids interact with a porous medium differently and these differences can be detected by low-field nuclear magnetic resonance (NMR)(4–6). One can infer the state of fluids within a porous medium from looking at NMR spectra based on type-specific transverse relaxation time (T2) cutoffs(7–9). Relaxation time is the time that a hydrogen-bearing molecule needs to revert to its original state, after it is excited by an oscillating magnetic field pulse sequence. Contributions to spectra at values of T2 that are lower than the cutoff are considered due to bound water while contributions at higher T2 values are considered due to water in the bulk phase(7, 10). Amplitude peaks at progressively lower T2 values indicate the presence of fluid in progressively smaller pores. The location of the amplitude peaks in NMR spectra can be used to infer sample wettability(9). While this has been done in porous media such as sandstones, carbonates, and chalk(11–14), no work has been done on soils. NMR can be a viable tool for assessing soils wettability because other wettability measurements such as the contact angle are impossible to make in unconsolidated porous media.
Summary Highly crosslinked gels are used in high-permeability reservoirs to achieve appropriate fluid-loss control during well completion and workover operations. Crosslinked gels are also used to shut off unwanted gas and/or water influx into production wells and to improve the conformance of the near-wellbore injection profile in naturally fractured or high-permeability reservoirs. In all these applications, the appropriate design of the gel treatment is critical to ensure an efficient gel placement. Important variables of gel systems are gel rheology and gel strength during and after the gelation reaction is completed. The rheology of gels and gelation rates is commonly determined by rheometry or, in a qualitative mode, through bottle testing with well-known gel-strength codes (i.e., Sydansk's code). Rheological measurements can be time-consuming, while bottle testing can lead to an inconsistent gel description as a result of the subjective nature of the gel-strength code. This paper evaluates the use of low-field nuclear magnetic resonance (NMR) as a nonin-trusive technique to monitor gelation rates and to characterize gel strength. Because of the nonintrusive nature of this technique, it could be considered to be a better alternative to conventional rhe-ological measurements and common qualitative methods, such as gel-strength codes. In addition, NMR could offer faster and more accurate gel-strength characterization and gelation monitoring compared to rheological methods. Furthermore, it can be used in porous media. NMR parameters are predicted and calibrated conducting concentration sweeps of polymer, crosslinker, and brine, as well as gelation-time sweeps. This then allows for a standardized method for gel characterization. The findings of this work include a preliminary assessment of the use of different techniques, such as low-field NMR, rheometry, and bottle testing, for monitoring the gelation reaction and gel strength of partially hydrolyzed polyacrylamide chromium [(HPAm)/Cr(III)] acetate gel. The experimental results also include the initial identification of the gel point for different formulations of the gel system using low-field NMR.
Fresh water scarcity and increasing demand are worldwide concerns and arebeing addressed by a number of water man-agement initiatives in Alberta and Canada. In 2003, 0.3 bil-lion m3 of produced water was injected intodisposal wells associated with oil and gas production in Alberta. Thisvol-ume of water is a potential resource for recycling and benefi-cial reuse inAlberta, which would have a significant impact on sustainable development inAlberta. This water must first be treated to meet water qualityrequirements and regulatory guidelines for specific applications. Thispaper provides a comprehensive technical and economic review of watertreat-ment technologies and shows that water treatment processes arecommercially available. Although the cost of implement-ing suitabletreating processes to meet drinking water quality guideline is estimated atthree times the current cost of mu-nicipal water supply in Alberta, it is morefeasible to recycle produced water for other purposes, such as agricultural orpe-troleum application (i.e., waterflooding, etc.). This is because waterquality guidelines for most other applications are not as stringent as that fordrinking water and there is increasing pub-lic resistance for industry to usefresh water for commercial applications. A multi-disciplinary researchand development team studying water recycle and beneficial reuse is necessaryto look into these issues. The University of Calgary is set tocollaborate on such projects due to the current research em-phasis onsustainable energy and environmental impact. Col-laboration between thegovernment, industry and academia to develop initiatives aimed at reducingfresh water is possible in Calgary for several reasons. One is theproximity of many major oil and gas companies in this city, which would allowfor easy communication. Another is the fact that the current price of oilwould not inhibit producing companies from in-vesting in this kind ofresearch. The result can be well-developed initiatives to treat andrecycle produced water for beneficial reuse, thus reducing fresh water demandfor many applications in the petroleum and agricultural industries. Introduction Fresh water is a limited resource as only one percent of all the water inthe world is available for worldwide demand. Even Canada, which has thelargest per capita water supply in the world, experiences watershortages. This water is needed for agricultural, industrial/commercial/institutional (ICI) and do-mesticapplications. Domestic water use actually constitutes the least of allmajor water users[1]. On the other hand, the need for fresh water inwaterflood operations and steam generations in enhanced oil recovery projectsare major concerns in Al-berta. These issues, along with the need forsustainable pro-ject development and increasing public resistance towards usingfresh water for industrial applications, increase the awareness for industrialwastewater treatment and reuse. Treating produced water for reuse is aviable alternative to withdrawing fresh water from surface and ground watersources. This paper reviews both commonly used and novel water desalinationtechnologies, identifies major challenges in produced water recycle andbeneficial reuse based on applicable water quality guidelines and points outpotential research and development activities in this area. The purpose isto show that water treatment isn't as prohibitively expensive as commonlybelieved and point out areas where further research and development can makewater reuse a sustainable activity. Figure 1 shows the breakdown of fresh water allocation in Alberta during2003[2]. This figure shows that out of the 9.7 billion m3 of fresh waterallocation, 4.5 billion m3 was allocated for irrigation and approximately 0.5billion m3 was allocated to the petroleum industry. By comparison to thevolume allocted to the petroleum industry, there was almost 0.6 billion m3 ofproduced water in Alberta during 2003[3]. Approximately half of thisvolume was injected for reservoir pressure maintenance and waterflood. Almost0.3 billion m3 of produced water were injected into deep disposalwells[4]. A relatively small volume of produced water, 5.6 millionm3was recycled as steam in steam recovery projects.
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