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 co-produced, 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 percent. This extremely encouraging result lead to the design of an on-line NMR relaxometer for oil/water stream measurements under the conditions encountered in the production of heavy oil and bitumen.

Introduction

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. Low field NMR relaxometry has shown that discrimination of water and oil saturation in core and ore can be easily determined. In such cases the NMR can detect the total water weight fraction and the total oil weight fraction, the viscosity of the oil, the amount of bound or mobile water and the amount of mobile or bound oil1–6.

Since these measurements are done in-situ and the accuracy of the tools is at least as good as that of conventional extraction methods (i.e., Dean-Stark) NMR has emerged as a leading tool for heavy oil and bitumen characterization tool. Our research group proved that many techniques that are routinely used in conventional oil could now be extended in heavy oil and bitumen characterization1–6. This technology is now extended in the determination of oil and water content of specific hydrocarbon streams. Of particular interest are the streams that contain emulsified fluids (water-in-oil or oilin- water emulsions) which are currently very common in thermal production operations and are very difficult to handle. Test separators are currently used as the standard way of measuring the flow of thermally produced wells (CSS, SAGD, steam flooding). The test separators are inherently incapable of measuring emulsified flow. Other probe-type devices suffer from inaccuracies related to the presence of solids or gas, salinity, temperature, velocity, emulsion type, and range of cut.

Low field NMR emerges as the only currently proven alternative to discriminate accurately and precisely the amount of oil and water in such streams.

METHODOLOGY

The NMR spectra of a mixture of heavy oil or bitumen with water consist of two sets of T2 relaxation peaks. The water peaks are at a range of 10-3000 ms, while the oil/bitumen peaks are in the range of 0.2–10 ms at the specific temperature of 30 °C.

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