Viscosity Determination of Heavy Oil and Bitumen Using NMR Relaxometry

Abstract

Knowledge of oil viscosity is important when estimating hydrocarbon reserves and evaluating the potential for waterflooding or EOR processes. This information is especially important in heavy oil and bitumen, as viscosity is usually the major impediment to recovery of these reserves. As oil viscosity increases, obtaining a laboratory measurement is difficult and prone to error, and viscosities measured in the lab may not be representative of field conditions. Nuclear magnetic resonance (NMR) is therefore presented as an attractive alternative method for determining oil viscosity. Several correlations already exist for determining oil viscosity using NMR. Some of these correlations compare the geometric mean T2 relaxation time to oil viscosity, while others relate viscosity to the apparent hydrogen index. This paper examines these different models on a suite of conventional and heavy oil samples. It is concluded that none of the existing models can accurately predict oil viscosity for both conventional and heavy oils, especially for oils with viscosity higher than 20,000 cP. All the measured oil samples show a correlation between oil viscosity and the geometric mean T2 relaxation time, and also between viscosity and relative hydrogen index. This is consistent with what other experimenters have noticed. An empirical model is developed, correlating oil viscosity to both of these parameters. Unlike previous models, this model can accurately predict oil viscosity for both conventional and heavy oil. The wider range of this model makes it useful for laboratory analysis of oil viscosity using NMR. If the results of this model can be applied to in situ oils, NMR can be used as a logging tool to characterize heavy oil and bitumen formations. The model presented in this paper is the first step towards successfully predicting viscosity in situ. Introduction Determination of oil viscosity is extremely important to the development of any potential oil reservoir. If waterflooding is being considered as a recovery scheme, the mobility ratio between oil and water will have a strong effect on the macroscopic sweep efficiency of the waterflood. Likewise, when considering possible EOR schemes, oil viscosity is one of the most serious impediments to the success of these schemes. Oil viscosity is also a required input parameter for reservoir simulation and well testing. In heavy oil and bitumen reservoirs, the high oil viscosity is often the limiting factor to efficient oil recovery. Waterflooding cannot be used in these reservoirs, due to the adverse mobility ratio between oil and water. The oil is so much more viscous than water that injected water will move through the oil in the form of "viscous fingers," which lead to early water breakthrough and poor sweep efficiency. If attempting a miscible solvent or gas flood, knowledge of oil viscosity is necessary for estimating the efficiency of the flood. Due to the negative effects of the adverse mobility ratio, viscosity reduction is the main focus of EOR schemes in heavy oil reservoirs.

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

“…However, as was also demonstrated by Bryan et al [22], the oil phase dependence of the fitting parameters shown in Table 2 requires that oil-specific calibrations would be required to convert T 2gm values to viscosity. Further work has involved the development of NMR viscosity models that relate in-situ oil viscosity to T 2gm and RHI at lower temperatures [48].…”

“…These include investigations into wettability [21], viscosity [22], fluid saturations [23] and emulsions [24]. In the present article, a brief overview of the relevant NMR theory (full details of which can be found in established texts, e g., [25][26][27]) will be followed by an evaluation of the literature, in conjunction with some new experimental results.…”

“…8) an inverse (8) relationship between NMR T 2 measurements and viscosity was developed based on previous work that can provide order of magnitude viscosity estimations up to around 10 5 mPa.s [36] and more recently up to 10 6 mPa.s from measurements on 100 samples [22,37]. In the latter case, the following semi-empirical equation was developed by Kantzas and co-workers to relate the NMR and viscosity measurements via [22,37] .…”

Characterization of Crosslinked Gel Kinetics and Gel Strength Using NMR

“…In the laboratory, the fluid sample is placed in a homogeneous magnetic field, so there is also negligible accelerated relaxation due to diffusion in a magnetic field gradient. This means that the measured transverse relaxation is due only to bulk relaxation 38 . Bulk relaxation is a fluid property, and is a measure of how easily the protons give off energy to one another.…”

Experimental evaluation of different strategies for improving oil recovery at high-water-cut by quantitative etched-glass micro-models

“…The scale of distinguishability can reach up to 0.1 mm; and the clarity of images is far more satisfying when compared with CT. NMR has been intensively applied in petroleum research for the past 20 years. These applications include investigation on viscosity, emulsions, wettability, and fluid saturations (Bryan et al, 2003;Hum and Kantzas, 2006;Jiang et al, 2007;Kantzas et al, 2005). Etched-glass micro-model can be used to mimic the pore structures with high distinguishability (Sun and Qu, 2004;Sun and Tang, 2006).…”