A Novel Experimental Technique for Studying Solvent Mass Transfer and Oil-Swelling Effect in the Vapour Extraction (VAPEX) Process

Abstract

In this paper, a new experimental technique is presented to study the solvent mass transfer in heavy oil and the resultant oil-swelling effect by applying dynamic pendant drop volume analysis (DPDVA). In the experiment, a pendant drop of heavy oil is formed inside a visual high-pressure cell, which is initially filled with a solvent (e.g. propane). As the solvent gradually dissolves into heavy oil, the volume of the pendant oil drop keeps increasing due to the oil-swelling effect. The sequential digital images of the dynamic pendant oil drop are acquired and analyzed to determine its volumes at different times. Theoretically, a previously formulated mathematical model is applied to describe the solvent mass transfer in heavy oil and the oil-swelling effect. The diffusion coefficient of the solvent in heavy oil and the oil-swelling factor are determined by finding the best fit of the theoretically predicted volumes of the dynamic pendant oil drop to the experimentally measured data. Experimental tests are conducted for the heavy oil-propane system at constant pressures of P = 0.4 − 0.9 MPa and a constant temperature of T = 23.9 °C. It is found that both the diffusion coefficient and the oil-swelling factor of the heavy oil-propane system increase with pressure. The major advantage of this new technique is that simultaneous measurements of the solvent diffusivity in heavy oil and the oil-swelling factor can be completed within two hours at the pre-specified constant pressure and temperature. Introduction In the vapour extraction (VAPEX) process, a solvent (e.g. methane, ethane, propane, butane or carbon dioxide) is injected into a heavy oil reservoir at a pressure close to its vapour pressure(1). Previous studies have already shown that molecular diffusion of the injected solvent in heavy oil plays a vital role in the VAPEX process(2–4). Thus the diffusion coefficient of the solvent in heavy oil under the actual reservoir conditions becomes an important parameter in the reservoir simulation and field design of the VAPEX process. In the literature, there are several experimental methods for measuring solvent diffusivity in heavy oil. These experimental methods can be roughly categorized into conventional and non-conventional methods. Conventional methods involve compositional analysis of liquid samples taken from the heavy oil-solvent mixture at different times and locations during a diffusion test(5). These methods are expensive, intrusive and time-consuming, especially if the diffusion test is conducted at a high pressure. In addition, compositional analysis of the heavy oil-solvent mixture is prone to large experimental error. Non-conventional methods measure the change of a property of the heavy oil-solvent system during the molecular diffusion process. This property can be the gas volume(6), oil-gas interface position inside a capillary(7), laser light intensity of the heavy oil-gas mixture(8), gas pressure(9) and shape of a pendant heavy oil drop surrounded by a gaseous solvent(10). In particular, the decaying gas pressure is measured while the molecular diffusion of the solvent into heavy oil proceeds within a closed high-pressure diffusion cell. This is referred to as the pressure decay method, which has been applied to measure the diffusivities of methane, ethane, propane, nitrogen and carbon dioxide in crude oils(11–14).

Effects of Heavy-Oil/Solvent Interfacial Tension on Gravity Drainage in the Vapor Extraction (VAPEX) Process

“…Once the pendant oil drop is formed, the solvent starts to dissolve into the oil drop. The mass transfer of the solvent into the pendant oil drop continues until the latter is completely saturated with the former 15,16 . In order to examine the effect of mass transfer of the solvent into the heavy oil drop on their interfacial tension, the dynamic interfacial tension is measured in the mass transfer process.…”

“…Figure 2 also shows that, for the heavy oil-propane system at P=0.90 MPa and T=23.9°C, the variations of the measured dynamic interfacial tensions at the early stage (t<180 s) of the mass transfer process are relatively large (about 9%). These variations may be attributed to the fast and large swelling of the pendant oil drop due to propane dissolution 16 .…”

Experimental Comparative Investigation of Hot Solvent/Steam-Assisted Gravity Drainage in Oil Sand Reservoirs

“…The solvent is transferred mainly, via diffusion, to reduce the viscosity of heavy oil in order for gravity forces to overcome capillary forces. Diffusion coefficients can be determined through pressure decay methods, , dynamic pendant drop volume analysis, − NMR and X-ray CAT scanning, , and thermal expansion method . Rezaei et al studied the effect of heat transfer on warm VAPEX and found that the condensation of the solvent on the bitumen surface increased the rate of interface advancement, which increased the production of the upgraded oil.…”

A data analysis of immiscible carbon dioxide injection applications for enhanced oil recovery based on an updated database

“…When the immiscible CO 2 is injected into the reservoir, one of the most significant interactions that occur between the gas and the oil is manifested in CO 2 solubility. During solubility, the CO 2 will diffuse into the oil and thus the oil will begin to swell [5][6][7]. Different crude oils will have different solubility based on their composition and properties, such as API gravity and Molecular Weight (MW) [8,9].…”

“…Most of the experiments conducted to evaluate oil swelling depended on transparent visualization experiments that can permit the ability to see the swelling phenomenon. Of these setups, the flow visualization experiments, and the pendant drop methods are the most widely utilized [6,16,17]. Core flooding experiments have also been conducted to study the ability of immiscible CO 2 to increase oil recovery [18].…”