Should You Trust Your Heavy Oil Viscosity Measurement?

Abstract

Heavy oil viscosity is one of the few criteria available to help predict if cold production will give economic rates, or if thermal processes will be required to reduce the oil viscosity to achieve the required rates. If cold production is selected, viscosity is again used to help determine whether vertical or horizontal wells should be used. Viscosity data are also used to adjust cold production exploitation strategies if the production rates are significantly lower than expected. Petrovera conducted an extensive viscosity data collection project in a newly developed Elk Point area reservoir with lower than expected, and more erratic than expected, cold production rates. Oil samples collected over short periods of time resulted in viscosity values for the same well varying by a factor of four or more, with similar variations between close-spaced wells. Collection of repeated samples and submission of those samples to several commercial labs resulted in similar viscosity measurement scatter. To further evaluate viscosity data scatter, multiple samples were collected from one well at the same time using the same procedures. These samples were then submitted to several labs in triplicate using three different well names to achieve an unbiased test. Reported viscosity scatter was again large. The objectives of this article are to:display the results of the study to bring this issue to the forefront for discussion; and,encourage commercial labs to develop an industry-wide standard method of heavy oil sample cleaning and viscosity measurement. Introduction Why Is It Important to Know Heavy Oil Viscosity Accurately? Heavy oil exploitation is an important segment of the oil and gas industry in Canada(1) and a number of other countries(2). Motivating factors for exploitation of Canadian heavy oil and bitumen are the large volumes of resources in place and the high historic demand for asphalt-based products that are more readily obtained from heavy oil and bitumen. Western Canadian heavy oil and bitumen reservoirs (Figure 1) have been exploited with varying degrees of success for more than 60 years(3). Early workers in the field of heavy oil and bitumen exploitation quickly determined that primary production responses (also called cold production responses) varied greatly from field to field. They also discovered that the addition of heat in the form of steam often greatly increased the production response. Viscosity became one of the most valued criteria in their efforts to predict production response from a new field using easily measured parameters. The popularity of the viscosity screening criterion has been demonstrated by the fact that virtually all technical papers on heavy oil production response or production process development include a discussion of oil viscosity. What is missing from the literature is an industry-wide standard of viscosity ranges and the corresponding recommended exploitation processes. This is because each company has its own 'best exploitation process vs.

Empirical Modeling of Viscosities and Softening Points of Straight-Run Vacuum Residues from Different Origins and of Hydrocracked Unconverted Vacuum Residues Obtained in Different Conversions

“…The accuracy and repeatability of VR viscosity measurements are affected by the selection of viscometers and the experimental procedures followed by different operators [4,36]. A study published by Miller et al [4] indicated that heavy oil viscosities measured by different viscometers, or by the same type of viscometer but measured in different laboratories following different operating procedures, were found to be quite different. The inconsistency of the measured viscosities makes data interpretation very difficult.…”

“…The lower fluidity and volatility make vacuum residues difficult to analyze. For that reason, sometimes strange values for a VR's physicochemical properties are reported [4,5]. The proper preparation of a VR sample before analyzing is important to reduce the probability of misinterpretation of the obtained results [5,6].…”

“…The best viscosity model employed the molecular weight and specific gravity, whereas the best SRVR softening-point model used the molecular weight and asphaltene content. 4.…”

Low field NMR as an alternative technique to estimate of density and viscosity in toluene-heavy oil mixtures

“…Moreover, these properties are directly involved in the optimization of oil refining operations, the determination and quality control of derivatives, the estimation of transport and storage conditions [4], the development of reservoir simulation processes [1], and the selection of a suitable oil recovery. However, measurements with conventional techniques take time, usually requiring tedious and expensive experimental processes, where accuracy decreases as oil viscosity increases, as equipment designs and protocols are focused on light and medium oils [5] [4] . Furthermore, human error in these measurements occurs more frequently and reflects a low reliability level in the characterization of oil, leading to failures in equipment designs for facilities, numerical simulations, and evaluation of reservoirs [6].…”

Heavy Oil Viscosity Measurements: Best Practices and Guidelines

“…Accuracy and repeatability of heavy oil viscosity measurements are not only affected by sample handling, storage, and cleaning procedures, but they are also affected by the selection of viscometers and the experimental procedures followed by different operators. A study published by Miller et al indicated that heavy oil viscosities measured by different viscometers or the same type of viscometer but measured in different laboratories following different operating procedures were found to be quite different. The inconsistency of the measured viscosities makes data interpretation and application to process designs difficult.…”