Advances in Heavy Oil and Water Property Measurements Using Low Field Nuclear Magnetic Resonance

Abstract

Abstract Low field NMR of fluids can be used to measure physical properties of water and oil such as viscosity and diffusion coefficients. Remarkably accurate measurements can be obtained from simple and fast measurements in a beaker. Algorithms for the determination of heavy oil and bitumen viscosity have been previously developed that can provide first order estimates over a variety of viscosity ranges (10°-107 mPas) covering variable temperatures, water/oil ratios and oil compositions. When the algorithms are tuned for single oils, then the accuracy increases dramatically and the predictions are as accurate as direct viscosity measurements. In this paper, the aforementioned algorithms are extended to predict NMR response and viscosity predictions for live vs. dead heavy oil samples, and virgin vs. solvent-diluted heavy oil samples. The viscosity predictions of oils in beakers are compared to the predictions of the same oils while in reservoir conditions (i.e. in-situ). The proposed algorithms can be used in reservoir characterization and on-line viscosity measurements in heavy oil reservoirs. A NMR based water cut meter was recently introduced for accurate measurement of oil and water cut values. The instrument appears to be superior to conventional measurement devices since it does not seem to be affected by salinity, emulsion characteristics or temperature to date. Extensive field measurements have proved the above claims. The principles of this water cut device are further extended to the measurement of water cut oil cut and gas cut under laboratory conditions. Mixtures of heavy oil and bitumen with water and air were prepared in the laboratory and their NMR characteristics were identified under a broad range of saturations. The results were compared against mass balance measurements. It is demonstrated that the two-phase measurement algorithms can be extended to three phase systems. Thus the first step towards accurate multi-phase measurements can be achieved. Introduction Low field nuclear magnetic resonance (NMR) has great potential as a tool for measuring properties of reservoir fluids and produced liquid streams. From a single NMR measurement of a fluid stream containing oil and water, the relative fractions of both liquids can be determined1,2. Since oil signals can be differentiated from water, the viscosity of the oil phase can also be determined3,4. Low field NMR can therefore be a useful tool for laboratory measurements, or can be implemented as an online tool at the wellhead to monitor the produced liquids. This paper extends the applications of low field NMR to in-situ viscosity estimation and determination of three phase fluid fractions. NMR is also used to investigate oil property changes in the presence of dissolved gas or solvent. The end goal of using low field NMR to predict viscosity is to make these predictions in-situ, on a logging tool. With this technology, reservoir fluids could be characterized much faster and cheaper than they can be through laboratory analysis, and viscosity changes with depth and location in the reservoir can be easily measured. The results of using low field NMR for bulk heavy oil and bitumen viscosity prediction have been very encouraging4. In a produced fluid stream, three phases can be present: oil, water and gas. Field trials have been done1,2, which used low field as an online water cut meter. This paper extends this application to three phase mixtures, made in the lab. In a fluid stream containing oil, water and gas, accurate fluid fraction estimates are necessary for metering and production records, and for estimating the emulsion viscosity4.