Vanishing Interfacial Tension Technique Research Articles

A novel experimental-theoretical method to improve MMP estimation using VIT technique

In the gas injection process for enhanced oil recovery (EOR), the interfacial tension (IFT) and the minimum miscibility pressure (MMP) are two key parameters for evaluating the miscibility condition. The vanishing interfacial tension (VIT) method is an efficient method for measuring the interfacial tension of oil and gas versus pressure and can estimate the minimum miscibility pressure. A problem in the VIT test of a hydrocarbon system is that during this test, oil and gas densities vary due to the composition variation of both phases. But in the conventional interfacial measurement, this issue is ignored, and the initial and non-equilibrium densities are utilized for estimating the interfacial tension. In this study, it is tried to nominate a novel method for estimating the most accurate value of IFT. Hence, for this purpose, first a VIT test has been performed for a hydrocarbon gas and a live oil system and using the axisymmetric drop shape analysis (ADSA), the oil droplet has been analyzed, and the geometry factor, which has been defined in this paper, was calculated. After that, the volume of oil droplet and the gas have been measured and were used for vapor-liquid-equilibrium (VLE) or flash calculation using Peng-Robinson equation of state (PR-EOS). By VLE calculation fulfillment, the final composition of two phases is determined. Eventually, the densities of two phases have been calculated for VIT modification. Finally, the IFT results were plotted versus the pressure steps, and the MMP were estimated. Furthermore, to evaluate the results of VIT test and its modification, slim tube displacement (STD) test, which is known as the most reliable laboratory method for measuring the MMP in the oil industry, has been performed. The results show that the values obtained for MMP values for the VIT test with the corrected densities which are lower than the values obtained for the VIT test for not-corrected densities and the suggested experimental-theoretical method has been estimated the MMP more accurately. The MMP obtained by VIT test and modified VIT method was equal to 3858.72 and 3722.0 psi, respectively. Meanwhile, the slim tube test has measured the MMP equal to 3667.13 psi.

A comparative study of the carbon dioxide and nitrogen minimum miscibility pressure determinations for an Iranian light oil sample

ABSTRACTMiscible gas injection is an approved profitable process that could significantly enhance oil recovery from different types of reservoirs while the major factor affecting its efficiency would be the minimum miscibility pressure (MMP) value. A recent experimental technique, known as vanishing interfacial tension (VIT), can estimate the MMP for gas–oil mixtures by measuring interfacial tension values and extrapolating them to zero at a sequence of pressures. Compositional simulation models are also useful in MMP determination by tuning an equation of state to compute the realistic phase behavior of reservoir fluid. In this paper, the capability and quality of MMP prediction via different methods such as laboratory slim tube tests, VIT technique, compositional simulation, and various empirical correlations were examined using a light oil sample taken from an Iranian carbonate reservoir, employing two pure gases of CO2 and N2 as the injectants. The accuracy and validation of the mentioned methods were then confirmed successfully by obtaining negligible overall absolute deviation percentages (AD%) compared with the conducted slim tube tests results.

Two new quantitative technical criteria for determining the minimum miscibility pressures (MMPs) from the vanishing interfacial tension (VIT) technique

In this paper, two new quantitative technical criteria are developed to determine the minimum miscibility pressures (MMPs) from the vanishing interfacial tension (VIT) technique: the linear correlation coefficient (LCC) criterion and the critical interfacial thickness (CIT) criterion. Six series of dynamic interfacial tension (IFT) tests for the dead and live light crude oil–CO2 systems are conducted under different test conditions. The MMP is determined when the LCC is smaller than 0.990 or the interfacial thickness is smaller than 1.0nm for the first time. The determined respective MMPs of 12.9MPa and 13.2MPa for the dead and live light crude oil–CO2 systems from the VIT technique agree well with the MMPs of 12.4–12.9MPa for the former system from the coreflood tests and fairly well with 15.2–15.4MPa for the latter system from the slim-tube tests. In addition, the specific effects of three experimental factors on the determined MMPs are studied by applying the two new quantitative technical criteria: (a) the initial vs. equilibrium IFTs; (b) the oil composition; and (c) the initial gas–oil ratio (GOR). The measured initial other than equilibrium IFTs are found to be sufficiently accurate to determine the MMP from the VIT technique. This is because the pendant oil drops used in the dynamic IFT tests are so small that they can be saturated with CO2 almost instantaneously. The live light crude oil pre-saturated with CH4-dominated hydrocarbons has a slightly higher MMP in comparison with the dead light crude oil. Moreover, the initial GOR effect on the MMP is found to be negligible in a lower GOR range (1:1–10:1 in volume) or in a large CO2 concentration range (31.76–94.69mol%). It becomes pronounced in a higher GOR range (200:1–4000:1 in volume) or in an extremely small range of high CO2 concentrations (98.79–99.99mol%).

Uniqueness, repeatability analysis and comparative evaluation of experimentally determined MMPs

Miscible gas injection processes like CO2 flooding are recommended to be carried out at minimum miscibility pressure (MMP) for effective enhanced recovery of trapped oil. There are several methods for MMP determination, but slim tube and vanishing interfacial tension (VIT) are deployed experimental techniques in this study. Uniqueness and repeatability of slim tube determined MMP was tested by conducting 55 slim tube runs for three different Omani crude oil samples (L-721, MZE and N) using three different coil lengths of constant diameter and three different injection rates. VIT technique accuracy and reliability was evaluated by comparing VIT determined MMPs, for same three considered crude oil samples, with aforementioned different slim tube systems determined MMPs. A trend of decrease in MMP with increase in coil length was found. No unique trend was found between MMP and injection rate. Lowest MMP and highest recovery were observed with highest coil length and lowest injection rate. It may be attributed to more stable displacement process which results in earlier developed miscibility and almost complete displacement of remaining more coil length retained oil. Therefore, both slim tube design and procedure need to be standardized. PVT software predicted MMP close to lower coil length slim tube system determined MMP for sample L-721 and higher coil length measured MMP for sample MZE. VIT approach determined MMPs were found to lie in between the MMPs measured by slim tube system with medium and longer coil lengths for same three oil samples. Since VIT estimated MMPs are in close match with more liable slim tube design determined MMPs, this technique can be utilized as a reliable and cheap alternative compared to more expensive and time consuming slim tube technique for accurate MMP determination without any potential of significant error.

An Investigation of the Robustness of Physical and Numerical Vanishing Interfacial Tension Experimentation in Determining CO2 + Crude Oil Minimum Miscibility Pressure

Different experimental and theoretical methods are used for predicting the minimum miscibility pressure (MMP) of complex CO2 + reservoir crude oil systems that are of particular interest to petroleum industry. In this paper, published physical and numerical vanishing interfacial tension (VIT) experimentations are critically examined for identifying best practices to reliably predict the CO2 + crude oil MMP. Some of the reported physical VIT experimentation studies appear to follow a portion of full scale VIT experimentation (i.e., a combination of the pendent drop method and the capillary rise technique). The physical VIT experimentation method in which the IFT measurements are made at varying pressures but with the same initial load of live oil and gas phases in the optical cell seems to be the most robust mechanistic procedure for experimentally studying the pressure dependence of IFT behaviors of complex CO2 + crude oil systems and thus determining the MMP using the VIT technique. The results presented here suggest that a basic parachor expression based on numerical VIT experimentation can reasonably follow the physical VIT experimentation in low IFT region, provided measured input data such as equilibrium phase densities and compositions are used in calculations.

New qualitative and quantitative technical criteria for determining the minimum miscibility pressures (MMPs) with the rising-bubble apparatus (RBA)

In this paper, one novel qualitative criterion, the bubble break-up (BBU), and two new quantitative criteria, the bubble-rising height (BRH) and bubble-rising velocity (BRV), are proposed and studied to determine the minimum miscibility pressures (MMPs) with the rising-bubble apparatus (RBA). Two respective series of pure and impure CO2-bubble tests in a light crude oil are conducted at six different test pressures and the actual reservoir temperature of Tres=53.0°C. First, the MMPs of the light crude oil–pure and impure CO2 systems are estimated and compared by using four existing (i.e., the bubble shape, size, colour, and rising height) and BBU qualitative criteria. Second, the BRH and BRV quantitative criteria are used to determine the MMPs of the light crude oil–pure CO2 system, in comparison with those from the coreflood tests and vanishing interfacial tension (VIT) technique. Third, these two new quantitative criteria are also applied to determine the MMPs of the light crude oil–impure CO2 (74.87mol.% CO2+25.13mol.% CH4) system and compare them with that from the VIT technique. It is found that the BBU criterion is consistent with the four existing qualitative criteria for estimating the MMPs. By means of the BRH and BRV criteria, two respective MMP ranges of the light crude oil–pure and impure CO2 systems are found to be 11.7–12.4MPa and 23.4–23.5MPa at Tres=53.0°C. Such determined MMPs with the RBA are slightly lower than those from the coreflood tests for the light crude oil–pure CO2 system but relatively higher than those from the VIT technique for the two respective light crude oil–CO2 systems. The newly developed BRH and BRV quantitative technical criteria, plus the novel BBU qualitative technical criterion, can be used to objectively and accurately determine the MMPs with the RBA.

Modified vanishing interfacial tension (VIT) test for CO2–oil minimum miscibility pressure (MMP) measurement

Miscible gas injection is one of the most popular and applicable enhanced oil recovery method in oil fields. Minimum miscibility pressure (MMP) is an important parameter for an enhanced oil recovery process involving carbon dioxide or hydrocarbon miscible gas injection. There are many methods for measuring MMP but the most standard method for measuring MMP value in oil field gas injection process is slim tube method, which is very time consuming (4–6 weeks). Measurements of the interfacial tension of mixtures of a reservoir fluid and injection gas at various pressures have been proposed recently as an experimental method for predicting the minimum miscibility pressure (MMP) in an experiment called the vanishing interfacial tension (VIT) technique. This method is quantitative in nature and fast (2–3 days) with respect to slim tube method. VIT technique is based on the concept that the interfacial tension between the gas and crude oil phases at reservoir temperature must reduce to zero as these two phases approach the point of miscibility. The concept of zero interfacial tension at miscibility is, in turn, based on the well-accepted fact that the interface between the phases must vanish, as they become miscible with one another.Our results show the MMP value obtained from VIT method exceeds the slim tube MMP and miscibility pressure does not necessarily occur at zero IFT. Using zero IFT criteria cause MMP overestimation. In this study, by using the VIT and slim tube test, we measured the IFT in which slim tube MMP occur in VIT test for CO2–oil system for various types of reservoir oil. These IFT values are correlated by oil properties and test condition to help us measure the accurate value of MMP by using VIT method.

Evaluation of Interfacial Tension by Image Processing of the Shape Drops

An interface of fluid phases is created by unbalanced molecular attracting and repulsive force. Evaluating the gas-liquid interfacial tension is very important and major interest in injection processes. The interfacial tension between gas and liquid phases can be measured by different methods in the reservoir and surface condition. VIT (vanishing interfacial tension technique) is a laboratory method that calculates interfacial tension for mixture of oil-gas in the series of pressure. Estimating the amount of the minimum miscibility pressure (MMP) is taken to be the pressure at which the interfacial tension tends to zero when plotted against pressure. The surface tension calculation is done by image processing of sessile and pendant drops of crude oil enclosed in a surrounding medium of the injection gas. In this paper use a computer program for processing and digestion the shape of a pendant drop has been brought.

Effects of Four Important Factors on the Measured Minimum Miscibility Pressure and First-Contact Miscibility Pressure

The vanishing interfacial tension (VIT) technique is applied to determine the minimum miscibility pressures (MMPs) and first-contact miscibility pressures (Pmax) of five light crude oil–CO2 systems from the measured equilibrium interfacial tensions (IFTs) at different equilibrium pressures. The equilibrium IFTs are measured under various experimental conditions by applying the axisymmetric drop shape analysis technique for the pendant drop case. It is found that in each IFT test, the measured equilibrium IFT is reduced almost linearly with the equilibrium pressure in two pressure ranges. The MMP of each light crude oil–CO2 system is thus determined from the measured equilibrium IFTs in range I by applying the VIT technique. The first-contact miscibility pressure (Pmax) of each light crude oil–CO2 system is extrapolated from the measured equilibrium IFTs in range II. Moreover, the test temperature, crude oil composition (dead/live oil), gas composition (pure/impure CO2), and initial gas–oil ratio (GOR) are studied to examine their specific effects. The experimental data show that the measured MMPs and Pmax values of five light crude oil–CO2 systems increase linearly with the temperature. The presence of CH4 in the CO2 phase results in substantially higher MMP and Pmax. An increased initial GOR leads to marginally higher MMP and Pmax.

Temperature and Composition Effect on CO2 Miscibility by Interfacial Tension Measurement

Crude oil reservoirs have different temperatures, compositions, and pressures, therefore oil recovery performance by CO2 injection varies from one case to another. Furthermore, it is predicted that lower interfacial tension between injected CO2 and reservoir fluid results in more oil recovery. In this study, we investigate the effect of temperature on the equilibrium interfacial tension between CO2 and three different oil fluids at different pressures. Also minimum miscible pressure (MMP) is measured by the vanishing interfacial tension (VIT) technique to determine the temperature effect on the CO2 miscible gas injection. The results on different pure and mixtures of hydrocarbon fluids show that for pressures up to 5.2 MPa, the higher the temperature was, the lower was the interfacial tension (IFT) measured. However, for the cases with pressure higher than 5.2 MPa, as the temperature was increased, the IFT increased too. In addition the VIT technique is used to measure the MMP of CO2 and pure paraffin; the heavier paraffin was, the higher was the MMP noticed. Also, we have learned that paraffin groups have an important effect on multicomponent interfacial tension behavior.

Comparative Evaluation of a New Gas/Oil Miscibility-Determination Technique

Summary A new experimental technique of vanishing interfacial tension (VIT) has been reported in recent literature for quick and cost-effective determination of gas/oil miscibility. However, this technique has been criticized because of the perceived absence of compositional-path specification and lack of confirmation against standard gas/oil systems. In this paper, we address these concerns by conducting interfacial-tension (IFT) measurements at elevated pressures and temperatures in two standard gas/oil systems and at varying molar compositions of gas and oil in feed mixtures. Though gas/oil ratio was found to have an impact on mass-transfer rates, the IFT between gas and oil was unaffected in the two standard gas/oil systems as the fluid phases approached equilibrium. This indicates compositional-path independence of gas/oil IFTs measured at near-equilibrium conditions; hence, miscibilities determined using the VIT technique. The minimum miscibility pressures (MMPs) determined using the VIT technique acceptably matched (within 5 to 8%) with the reported slim tube miscibilities for both the standard gas/oil systems. These experimental results clearly support wide use of the VIT technique for rapid and cost-effective determination of MMPs and minimum miscibility enrichments (MMEs) in improved-oil-recovery applications.

Miscibility Determination from Gas‐Oil Interfacial Tension and P‐R Equation of State

AbstractRecently a new experimental technique of vanishing interfacial tension (VIT) has been developed to enable rapid and cost‐effective determination of miscibility in gas‐oil systems. In this study, VIT experiments have been extended to two standard gas‐oil systems of n‐decane‐CO2 and live decane‐CO2 at elevated pressures and temperatures. The VIT miscibilities of the two standard gas‐oil systems and the two reservoir crude oil‐gas systems, namely Rainbow Keg River (RKR) and Terra Nova, were compared with Peng‐Robinson (P‐R) equation of state (EOS) calculations. The close match of VIT miscibilities with other conventional experimental techniques in the standard gas‐oil systems, as well as the reasonable match obtained with untuned PR‐EOS calculations for several systems studied, clearly demonstrates the sound conceptual basis of VIT technique to determine fluid‐fluid miscibility in multi‐component hydrocarbon systems.

Solubility, miscibility and their relation to interfacial tension in ternary liquid systems

The terms, miscibility and solubility, are widely used in phase behavior studies of multicomponent hydrocarbon systems. The distinction between these two terms appears to be still hazy, leading to their synonymous use in some quarters. Also, the relation of these two thermodynamic properties with interfacial tension has largely remained unexplored. However, recently a new experimental technique of vanishing interfacial tension (VIT) has been reported relating miscibility with interfacial tension in gas–oil systems. Therefore, the objectives of this study are to correlate miscibility and solubility with interfacial tension and to investigate the applicability of the new VIT technique to determine miscibility conditions in ternary fluid systems. For this purpose, a standard ternary liquid system of benzene, ethanol and water was chosen since their phase behavior and solubility data were readily available. The interfacial tensions of benzene in aqueous ethanol at various ethanol enrichments were measured using the drop shape analysis (DSA) and capillary rise techniques. The experimental results indicate the applicability of VIT technique to determine miscibility conditions for ternary liquid systems as well. Comparison of IFT measurements with solubility data showed a strong mutual relationship between these two properties, in addition to demonstrating a clear distinction between solubility and miscibility. The interfacial tension appears to be independent of solvent–oil ratio in feed, provided that complete equilibration of fluid phases is allowed to incorporate all the mass transfer effects during experimentation. All these experimental observations have immense application in fluid–fluid phase equilibria studies and to determine the miscibility conditions of gas injection improved oil recovery projects.

Application of the new vanishing interfacial tension technique to evaluate miscibility conditions for the Terra Nova Offshore Project

Terra Nova oil pool is the second largest oil pool discovered in the Grand Banks of the Canadian East Coast and is under development. As a part of the oil recovery process selection criteria, miscibility conditions were determined for Terra Nova oil with various enrichment levels of gas available from the offshore production facilities using the recently developed vanishing interfacial tension (VIT) technique. The VIT technique is based on the concept that the interfacial tension between the gas and crude oil phases at reservoir temperature must reduce to zero as these two phases approach the point of miscibility. The concept of zero-interfacial tension at miscibility is, in turn, based on the well-accepted fact that the interface between the phases must vanish, as they become miscible with one another. Thus, the minimum miscibility pressure (MMP) and minimum miscibility composition (MMC) can be determined precisely by measuring gas–oil interfacial tension as a function of pressure and gas composition, down to as low an interfacial tension as the measurement technique allows, and then extrapolating the data to zero-interfacial tension. This paper presents the details of this new VIT technique and its evaluation against slim-tube tests, and discusses its application to the Terra Nova gas injection scheme. The interfacial tension data obtained at reservoir conditions using the computerized axisymmetric drop shape analysis (ADSA) technique are presented as a function of pressure, gas composition, and the mode of gas–oil contact (first-contact or equilibrium). In addition to providing visual evidence of miscibility as the point of zero-interfacial tension is approached, the VIT technique is rapid in that it enables the experimental determination of MMP and MMC within about 2–3 days as against 4–6 weeks required by the slim-tube technique.

Application of a New Technique to Optimize Injection Gas Composition For the Rainbow Keg River F Pool Miscible Flood

Abstract A new experimental technique, called the Vanishing Interfacial Tension (VIT) technique, has been successfully utilized in this study to optimize solvent composition for the miscible gas injection project being considered for the Rainbow Keg River F Pool. The VIT technique consists of measuring the interfacial tension between the injected gas phase and the reservoir crude oil at the temperature of the particular oil containing formation and at varying pressures and/or enrichment levels of the gas phase. These interfacial tension measurements are carried out by computer digitization of the image of the profiles of sessile and pendant drops of crude oil enclosed in a surrounding medium of the injection gas. By fitting these experimental drop profiles with the iterative solution of the Laplace capillary equation, the value of the interfacial tension is obtained at each pressure or enrichment level. By making a plot of the interfacial tension against the independent variable (either pressure or enrichment), accurate values of the minimum miscibility pressure (MMP) and/or the minimum miscibility composition (MMC) are obtained by extrapolation to zero interfacial tension. This paper describes the new VIT technique and provides experimental evidence for its validity by comparing the VIT-MMP with slim-tube-MMP. Each MMP determination using the VIT technique was accomplished within 4 – 6 hours, while 4 – 6 weeks were required for the slim-tube technique. The paper also describes the application of the VIT technique to the problem of optimizing the injection gas composition at the Rainbow Keg River F Pool miscible flood. For this field application of the technique, live reservoir crude oil as well as lean and rich gas mixtures, matching field gases in composition, were used in the experiments. Gas/oil interfacial tension measurements were made in "first contact" as well as "equilibrium" modes. The optimized solvent composition was then verified by a single slim-tube test and compared with equation of state predictions. It has been demonstrated through this study that the new VIT technique is a reliable, accurate and fast technique for cost effective determination of MMPs and optimum injection gas compositions. Introduction Hydrocarbon miscible flooding is by far the most important conventional oil EOR process in Canada. It accounts for 83% of the 164,600 b/d of Canadian conventional oil EOR production(1). Furthermore, it is worth noting that most of the 104,300 b/d EOR production increase in 1992 (over that in 1990) in the US was also due to miscible projects based on both CO2 and hydrocarbon gases(1). Further improvements in the economics of miscible flooding could be accomplished by minimizing the cost of solvent blends and the cost of their injection. These can be achieved by (1) optimizing the solvent composition so that minimum enrichment of the dry gas by the C2+ fraction would yield cheaper solvents for injection and enable increased sales of the natural gas liquids, (2) increasing the accuracy of determination of minimum miscibility pressures for a given solvent composition and reservoir temperature which, in turn, would enable operation at near miscible conditions resulting in considerable compression cost savings.

A new technique of vanishing interfacial tension for miscibility determination

A new technique is presented in this paper to enable rapid and cost-effective determination of minimum miscibility pressure and composition. This new technique, called the Vanishing Interfacial Tension (VIT) technique, consists of measuring the interfacial tension between the injected gas phase and the crude oil at the temperature of the reservoir and at varying pressures and/or enrichment levels of the gas phase. These interfacial tension measurements are carried out by computer digitization of the image of the profiles of the sessile and pendant drops of crude oil enclosed in the surrounding medium of injection gas. By fitting these actual drop profiles with the iterative solution of the Laplace capillary equation, the value of interfacial tension is obtained at each pressure or enrichment level. By making a plot of the interfacial tension against the independent variable (either pressure or enrichment), accurate values for the minimum miscibility pressure (MMce:simple-para) or composition (MMC) are then obtained by extrapolation to zero interfacial tension. The paper provides experimental evidence for the validity of the new VIT technique by comparing the results with slim-tube displacement tests. While the slim-tube technique requires 4–6 weeks for obtaining MMP or MMC, the VIT technique yields the MMP in about 4–6 h, and MMC in about 16–24 h. The paper also presents an application of the VIT technique to optimize injection gas composition for an Alberta field project. The Alberta Energy and Utilities Board (a Government of Alberta agency) has accepted the optimized composition based on the VIT technique.