Minimum Miscibility Pressure Determination: Modified Multiple Mixing Cell Method

Miscible gas injection processes are among the effective methods for enhanced oil recovery (EOR). A key parameter in the design of gas injection project is the minimum miscibility pressure (MMP), whereas local displacement efficiency from gas injection is highly dependent on the MMP. Because experimental determination of MMP is very expensive and timeconsuming, searching for fast and robust mathematical determination of gas-oil MMP is usually wished. A new CO2 MMP correlation based on Multiple-Linear-Regression modeling (MLR) technique has been successfully developed to more accurately estimate the CO2 MMP for a wide range of live and heavy crude oils. The newly developed CO2 MMP correlation is originated from CO2 MMP experimental data in addition to database from the worldwide published literature that covers 103 pure CO2 MMP data for various live and dead oil samples. The proposed model is trained by exploiting 80% (82 data points) of the data bank. This correlation is expressed as a function of reservoir temperature, C7+ molecular weight, mole fractions of; non-hydrocarbon components (CO2, H2S and N2), direct correlating components (C1, C2 and C5) and indirect correlating components (C3, C4, C6 and C7). Further, to investigate the authenticity in depth, the proposed correlation is compared with five most commonly used pure CO2 MMP correlations from the literature. A statistical comparison is performed for both training data set (82 data points) as well as testing data set (21 data points). It is found that the proposed CO2 MMP correlation provides the best reproduction of MMP data with a percentage average absolute error of 6.083% and 6.328% for training and testing categories respectively. Finally, the proposed model shows great performance using new set of samples compared with other correlations.

A miscibility study was conducted to investigate the effects of the C5+ content in injection gases on Minimum Miscibility Pressure (MMP). Currently available common MMP correlations are based on data from injection gases containing no C5+ fraction. However, laboratory analyses suggest that having a small (and yet relatively significant) C5+ fraction could have a large effect on reducing the MMP to considerably below the predicted values from existing correlations. This paper aims at investigating possible benefits for miscibility and CO2 EOR flooding with impurities, particularly with C5+ fraction. Previously, a PVT and miscibility study was conducted on a Cooper Basin (located in central Australia) reservoir fluid, including solubility-swelling and viscosity studies. Slim tube tests were performed using two injection gases – pure CO2 and a CO2-rich synthetic gas (80mol% CO2), which contained a small amount of C5+ fraction (0.3mol%). The MMP was expected to increase substantially due to the presence of a large amount of methane (15mol%). Correlations from literature predicted the MMP to be above 3433psia, but the MMP was measured to be 2880psia1. As most currently available correlations are based on injection gases with no C5+ fraction, a major contributing source to error with these correlations may have been the C5+ content of the gas. In order to investigate the effects of the C5+ fraction in the injection gas, a series of Rising Bubble Apparatus (RBA) experiments were conducted on the reservoir fluid with three injection gases at three different temperatures to investigate the effect of C5+ in the injection gas stream. Results indicate that the C5+ fraction does have a significant effect on the MMP that needs to be factored into current correlations when the injection gas has a C5+ content.

Over the years, the slim tube experiment has been the most commonly used laboratory technique for determination of minimum miscibility pressure (MMP) for designing field miscible floods. However, till now, the design of these experiments is not standardized, neither in terms of set-up nor procedure. Often, the set-up, characteristics of the slim tube coil and even the experimental procedures are left to the discretion of the experimentalist, leading to very uncertain and non-unique MMP values, to say the least. Not just the uniqueness is of great concern, but also the lack of measurement repeatability; two measurements using same fluid samples under the "same experimental conditions" may result in too different MMP values. Matching these experiments with any PVT simulation package may pose a challenge, which even if a match is achieved, may be of questionable reliability. It is on this premise that this work was based. Slim tube experiments were designed and performed to study the effects of some parameters on the uniqueness and repeatability of the MMP measurements. It was found that MMP measurements are different with different injection rates. The lowest tested rate showed slightly lower MMP and better recovery performance than the other tested rates. No clear trend was noted, however. MMP was found to be lower for the larger coil diameter of the two investigated. MMP decreased as the coil length increased. The decrease in MMP with increase in coil length followed a parabolic trend. It was, therefore, concluded that laboratory measurements of MMP using the slim tube apparatus is a function of not just the characteristics of the interacting fluids but also those of the coil used as well as the choice of injection rates. The experimental design and procedure need to be unified to produce more reliable MMP data. It is the recommendation of the authors to design the experimental injection rate based on the expected field gas injection, to use the largest coil diameter possible, and to design the coil length, based on the expected well spacing between the injector and producer.

Objectives/Scope: The purpose of this thesis is to reduce CO2-oil minimum miscible pressure (MMP) in CO2 flooding some heavy oil which is difficult to miscible with CO2 in general cases. 2 Methods, Procedures, Process: In order to reduce CO2-oil minimum miscible pressure (MMP), a brave idea of injection miscible-slug instead of pure CO2 into reservoir was proposed, and then several slim-tube tests with different pressures were deployed to acquire the composition of miscible-slug, and a consecutive series of output samples including oil and gas from slim-tube at different injection pore-volume CO2 were collected, composition of every output samples was tested and analyzed by using equipment of liquid phase chromatograph and gas phase chromatograph. 3 Results, Observations, Conclusions: Composition of consecutive output samples at different injection pore-volume CO2 were obtained through the help of gas & oil phase chromatograph, and the result above shows the quit difference between miscible-slug and immiscible-slug. The components with molecular weight lighter than C18 are mainly extracted by CO2 immiscible-slug, while some additional components with molecular weight between C18 and C25 are also extracted by CO2 miscible-slug. Moreover, low-carbon molecules are initially extracted, with the ongoing flooding, higher-carbon molecules are gradually extracted. Based on the composition of consecutive output samples, man-made miscible-slug for the this oil reservoir was made up and the slug PV was amplified used for injection instead of CO2, another slim-tube test using above man-made miscible-slug was deployed again with pressure lower than MMP obtained from above series of slim-tube tests, the result shows a CO2 –oil miscible flooding and the idea of CO2 –oil MMP reduction comes true. 4 Novel/Additive Information: A method of reduction CO2 –oil MMP by injection man-made miscible-slug made up from slim-tube tests was proved, which would improve a lot of oil reservoir immiscible with CO2 into miscible with CO2 under reservoir temperature.

Summary Determination of the minimum miscible pressure (MMP) of the gas/oil system is essential for a successful carbon dioxide enhanced oil recovery (CO2-EOR) and carbon geological storage applications. Measurement of MMP can be performed with theoretical methods and experimental methods. The slim tube test (STT), the rising bubble apparatus (RBA), and the vanishing interfacial tension (VIT) technique can be considered as the effective experimental methods in the petroleum industry to measure the MMP of oil and gas systems. This paper presents a new experimental method for measuring MMP, named oil droplet volume dynamic analysis (ODVDA) method. The main principle of this method is to dynamically measure the change in the volume of the oil droplets suspended in CO2, and find the pressure point where the oil droplet volume reduction rate is equal to or just exceeds 15% in the interval of 600 seconds. This pressure point is considered to be MMP. The main advantage of ODVDA method over the previous methods is simple, time-saving, and more easily to conduct.

A comparison of CO 2 minimum miscibility pressure determinations for Weyburn crude oil

A Rapid Method for Determining CO2/oil MMP and Visual Observations of CO2/Oil Interactions at Reservoir Conditions

Nitrogen has been found to be a suitable recovery agent for conventional oil with API gravity larger than 35 that provides the reservoir pressure is above the minimum miscibility pressure and the reservoir oil contains a high concentration of intermediate hydrocarbon components. Nitrogen has been found to achieve dynamic miscibility at high pressures. The miscibility obtained by nitrogen injection in light crude oil reservoir is a conditional miscibility, where the fluids are not miscible on first contact, but form two phases, with one of the fluids absorbing components from the other. After sufficient contacts and exchanges of components, at minimum miscible pressure, the system becomes miscible. The main purpose of this study is to investigate, the effect of temperature, composition of the reservoir fluid and injected gas, on the MMP of nitrogen injection in light oil reservoir by a simulator. The injected gas is pure Nitrogen or a combination of nitrogen with other gas like propane. The effect of varying the percentage of nitrogen and CO2 in the injection gas mixture on MMP has been previously investigated by experiment. Results of the Simulation have shown that the most important factor to achieve miscibility between nitrogen and reservoir oil is the amount of light and intermediate components in the oil. Increasing the intermediate components and decreasing the methane content decrease the MMP. Nitrogen develops miscibility of oil by the same mechanism as methane (vaporizing gas drive). With sufficient amount of methane in oil reservoir, MMP of nitrogen and methane injection is almost the same but decreasing the methane content causes difference. Studies have shown that injecting nitrogen-propane combination will decrease MMP but combining nitrogen with methane does not have significant effects on the MMP. Result show that MMP of nitrogen increases slightly when temperature decreases.

Gas–oil relative permeability at near miscible conditions: An experimental and modeling approach

Multiple Equation of State (EOS) models are possible for a reservoir oil if limited laboratory data is used in the EOS model development; each EOS model has its own predicted minimum miscibility pressure (MMP) value with unknown reliability. This article presents a novel approach to estimate a reliable MMP value using the multiple MMP values calculated from multiple EOS models developed with limited laboratory data such as bubble point and density at bubble point. MMP predicted using the proposed approach has better accuracy than the estimated MMP from an EOS model developed using a large set of data at the regression stage. Each possible EOS model for a reservoir oil has a specific set of values of total Gibbs free energy of mixing (g) at bubble point and predicted MMP for a given injection gas. The MMP estimate is developed using the trend of g versus MMP (predicted) from multiple EOS models in the proposed approach. The AARD in MMP prediction for 22 oils is 5.21% using SRK EOS and 6.65% using PR EOS, which is lower than the earlier approach (7.6%) that uses all PVT, swelling test, and multi-contact test data in EOS model development.

Molecular insight into the miscible mechanism of CO2/C10 in bulk phase and nanoslits

Carbon dioxide (CO2) injection is the most promising technique to enhance the recovery of high gravity oil with the existing oil price situation. Even though, challenges still exist for thick and heterogeneous reservoirs at very high temperature. The problems faced in such reservoirs are low displacement efficiency and very high injection pressure requirement for a miscible displacement. The effort being done by researchers to overcome the situations is the use of silica nanoparticle as an agent to form CO2-silica nanoparticle foam. Currently, the related literature shows that CO2 miscible displacement is rarely performed at very high temperature and consequently no relevant effort has been made to investigate the stability of CO2-silica nanoparticle foam, while there are many oil reservoirs with temperature of higher than 250 oF. Therefore, related studies on such situations are needed. The present work consists of two stages. First, slimtube and coreflood experiments of CO2 injection are conducted at about 270 oF, respectively, to both determine the Minimum Miscibility Pressure (MMP) of the selected live oil system and the oil recovery. Secondly, CO2-silica nanoparticle foam stability in various brine salinity at such high temperature will be investigated and effectiveness of the selected stable foam will be tested through an oil displacement using native cores.In this paper, the results of both slimtube and coreflood experiments are first presented. A live paraffinic oil with 34 oAPI is used. The standard slimtube apparatus is employed. Stacked core composing of three native core plugs of different permeability ranging from 75 to 503 milidarcies are used to represent rock heterogeneity. At a temperature of 270 oF, MMP of the oil obtained from the slimtube experiment is 2960 psi, about 100 psi higher than that obtained from the coreflood experiment. The slimtube test gives oil recovery 94.2% and the coreflood as expected yields lower recovery, 84% of the initial oil in place. The importance of the tests is two folds that the MMP of the oil system is firmly known while the existing empirical correlations estimate the values ranging from 2718 to 5578 psi and a relatively low coreflood oil recovery suggests further investigation of stability of CO2-silica nanoparticle foam at that temperature in an attempt for enhancing the oil recovery.

The minimum miscibility pressure (MMP) of crude oil–CO2 systems was determined through analyzing the experimental data of swelling/extraction tests. First, the oil swelling factor (SF) as a result of CO2 dissolution in a crude oil sample was determined at four different temperatures in the range of T=21–40 °C. In addition, three sets of swelling/extraction data of previous studies were collected and included so that more conclusive and satisfactory results can be obtained. The results demonstrated that the oil swelling factor increases with the equilibrium pressure (Peq), reaches the maximum value at light hydrocarbon extraction pressure (Pext), and then reduces with further increase in equilibrium pressure. It was found that the reduction behavior of oil swelling factor occurs in two distinct regions. In the upper extraction phase (UEP), the oil swelling factor decreased sharply at pressures just over extraction pressure and then declined gradually in what is called the lower extraction phase (LEP). Finally, the MMP of the crude oil–CO2 system at a specific temperature was estimated by finding the intersection of the linear regression correlation corresponding to each of the aforementioned regions (i.e., UEP and LEP). The crude oil–CO2 MMP was also determined by employing the vanishing interfacial tension (VIT) technique and a series of CO2 injection tests. Comparing the MMP values of the crude oil–CO2 systems determined by three methods revealed that the MMP values estimated by swelling/extraction data are in approximate agreement with those determined by the two other methods.

In gas injection, which is one of the fascinating enhanced oil recovery techniques, the main mechanism involves decreasing interfacial tension (IFT). Although various mechanisms can affect the IFT of a system, in most experimental and numerical studies, condensation is considered the dominant mechanism among condensation-vaporization and vaporization. Investigating the impact of each mechanism is crucial as they can influence the IFT of the system and, consequently, the effectiveness of the gas injection method. This study introduces a novel model to assess the influence of different mechanisms on system IFT. The model defines system IFT, adjusts fluid relative permeability to represent miscible, immiscible, and near-miscible states, and utilizes the Buckley–Leverett method to analyze gas fractional flow and saturation profiles when injecting carbon dioxide (CO2), methane (CH4), and nitrogen (N2). Furthermore, the research explores the impact of injection pressure and IFT at minimum miscible pressure (IFT0) on gas injection efficiency. Based on our results, for both live and dead oil, the condensation mechanism reduces IFT and near-miscible pressure; switching to a condensing-vaporizing mechanism increases these parameters. This trend was consistent across all gases studied (N2, CO2, CH4), with a more significant effect observed on the CH4-live oil system compared to N2 and CO2. Controlling the condensing mechanism in IFT measurements enhances gas flow rate and relative permeability curve within the medium. Higher injection pressure in the condensing mechanism and IFT0 = 0.5 leads to faster fluid movement and improved relative permeability due to increased driving forces. Higher IFT0 accelerates the relative permeability of fluids and gas movement within the medium by promoting miscibility sooner. The impact of IFT0 was more pronounced on the dead oil–gas system compared to the live oil–gas system in this study.

The analytical theory of one dimensional, dispersion free miscible displacement of oil by injection gas with nc component has shown that: the MMP is the lowest pressure at which any one of the initial oil, injection gas or crossover key tie lines becomes critical, which means that its length approaches to zero. In this paper, we propose a method for a solving multi component system based on analytical calculation of ternary systems, which simplifies and converts the multi component system into a pseudo ternary system and estimates the minimum miscibility pressure without solving complex and time consuming equations of crossover tie lines.