Determination of Oil and Water Compositions of Oil/Water Emulsions Using Low Field NMR Relaxometry

Abstract

During production operations in heavy oil and bitumen formations where thermal recovery methods are applied, the fluids produced are often in the form of emulsions. This is also true in non-thermal recovery methods whenever oil and water are coproduced, but to a lower degree of severity. Conventional flow measuring devices are capable of measuring oil and water streams when they are segregated, but they fail when oil-in-water or water-in-oil emulsions form. Conventional methods are also not reliable when there are solids flowing in the stream. Low field NMR relaxometry was successfully tested as a tool for accurately measuring the oil and water content of such streams with and without emulsions present in the samples. The method was proved to be at least as good as conventional extraction methods (i.e., Dean-Stark). The technology was tested with both artificially and naturally occurring emulsified streams with accuracy better than 96﹪. This extremely encouraging result led to the design of an online NMR relaxometer for oil/water stream measurements under the conditions encountered in the production of heavy oil and bitumen. Introduction In the recovery of bitumen, viscosity reduction becomes important, both below and above the ground. The addition of a liquid diluent is thought to break down or weaken the intermolecular forces which create high viscosity in bitumen(1). The effect is so dramatic that the addition of even 5﹪ diluent can cause a viscosity reduction in excess of 80%; thus, facilitating the in situ recovery and pipe line transportation of bitumen. The knowledge of the bitumen-diluent viscosity is highly important, since without it, calculations in upgrading process, in situ recovery, well simulation, heat transfer, fluid flow, and a variety of other engineering problems would be difficult or impossible to solve. This paper presents the development of a simple correlation to predict the viscosity of binary mixtures of bitumen-diluent in any proportion. Experimental The data used for the development of the correlation was TABLE 1: Bitumen data at 30 °CDATA[C. Available In Full Paper. TABLE 2: Diluent data at 30 °CDATA[C. Available In Full Paper. obtained from Wallace et al.(2) and Wallace and Henry(3).The data consisted of a total of 99 points obtained from three bitumens and five diluents, respectively, listed in Tables 1 and 2. Each of these bitumen samples was diluted at 30 °CDATA[C to 5, 10, 25, 50 and 75 weight ﹪ diluent with each of the diluents. After mixing, the samples were reweighed, and any weight loss was attributed to solvent evaporation. The diluent weight fractions were adjusted accordingly, and the viscosities of the mixtures measured. For a detailed account of experimental procedures, refer to Wallace and Henry(3). Correlation Development Many correlations have been developed to predict the viscosity characteristics of bitumen-diluent mixtures(1-6). While several have been successful in making these predictions, most are cumbersome to use. Low Field Nuclear Magnetic Resonance (NMR) relaxometry techniques were developed in the laboratory to enhance and support comparable NMR logging tools that are currently used downhole.

Insights Into Non-Thermal Recovery of Heavy Oil

“…Low field NMR was therefore used to monitor the produced fluids. This technology uses the fact that oil and water spectra are distinct, and has been well-demonstrated in the literature (32) . In this manner, even if fluids are mixed or oil smeared the walls of the collection vial, the oil and water content could still be determined.…”

NMR relaxometry and diffusometry in characterizing structural, interfacial and colloidal properties of heavy oils and oil sands

“…These were then used to calculate the amplitude index. This equation was used by several workers to determine the water and bitumen amounts in oil/water emulsion samples obtained from thermal production operations [72][73][74]. The same methodology was then applied to determine the oil and water fractions in oil sand cores and froths [23].…”

Evaluation of Bitumen-Solvent Properties Using Low Field NMR

“…NMR measurements are simple and non-destructive, but capable of yielding an incredible wealth of information about the reservoir fluid under investigation in a particular sample (9) (10) . The mixture viscosity decreases dramatically as the ratio of the injected solvent to heavy oil or bitumen increases, and different solvents show different dilution capacity.…”

“…If one could afford the luxury of observation wells, the presented algorithms would be useful in the in-situ oil viscosity and bitumen content determination in a solvent based bitumen recovery process. In addition, NMR can be used for the on-line solvent content and viscosity determination of a produced stream in a solvent based displacement process in a fashion similar to the presented NMR based watercut meter (9) .…”