Phase behavior of CO2/Crude-oil mixtures which exhibit liquid/liquid (L/L) and liquid/ liquid/vapor (L/L/V) equilibria is examined. Results of single-contact phase behavior experiments for CO2/separator-oil mixtures are reported. Experimental results are interpreted using pseudoternary phase diagrams based on a review of phase behavior data for binary and ternary mixtures of CO2 with alkanes. Implications for the displacement process of L/L/V phase behavior are examined using a one-dimensional finite difference simulator. Results of the analysis suggest that L/L and L/L/V equilibria will occur for CO2/crude-oil mixtures at temperatures below about 120 degrees F (49 degrees C) and that development of miscibility occurs by extraction of hydrocarbons from the oil into a CO2-rich liquid phase in such systems. Introduction The efficiency of a displacement of oil by CO2 depends on a variety of factors, including phase behavior of CO2/crude-oil mixtures generated during the displacement, densities and viscosities of the phases present, relative permeabilities to individual phases, and a host of additional complications such as dispersion, viscous fingering, reservoir heterogeneities, and layering. It generally is acknowledged that phase behavior and attendant compositional effects on fluid properties strongly influence local displacement efficiency, though it also is clear that on a reservoir scale, poor vertical and areal sweep efficiency (caused by the low viscosity of the displacing CO2) may negate the favorable effects of phase behavior.Interpretation of the effects of phase behavior on displacement efficiency is made difficult by the complexity of the behavior of CO2/crude-oil mixtures. The standard interpretation of CO2 flooding phase behaviour, given first by Rathmell et al. is that CO2 flooding behaves much like a vaporizing gas drive, as described originally by Hutchinson and Braun. During a flood, vaporphase CO2 mixes with oil in place and extracts light and intermediate hydrocarbons. After multiple contacts, the CO2-rich phase vaporizes enough hydrocarbons to develop a composition that can displace oil efficiently, if not miscibly. The picture presented by Rathmell et al. appears to be consistent with phase behavior observed for CO2/ crudeoil mixtures as long as the reservoir temperature is high enough. Table 1 summarizes data reported for CO2/crude-oil mixtures. Of the 10 systems studied, all those at temperatures above 120 degrees F (50 degrees C) show only L/V equilibria while those below 120 degrees F exhibit L/L/V separations (Stalkup also reports two phase diagrams that are qualitatively similar to the other low-temperature diagrams but does not give temperatures). Thus, at temperatures not too far above the critical temperature of CO2 [88 degrees F (31 degrees C)], mixtures of CO2 and crude oil exhibit multiple liquid phases, and at some pressures L/L/V equilibria are observed. It has not been established whether Rathmell et al.'s interpretation of the process mechanism can be extended to cover the more complex phase behavior of low-temperature CO2/crude-oil mixtures. In a recent paper, Metcalfe and Yarborough argued critical temperature CO2 floods behave more like condensing gas drives, whereas Kamath et al. concluded that an increase in the solubility of liquid-phase CO2 in crude oil at temperatures near the critical temperature of CO2 should cause more efficient displacements of oil by CO2. SPEJ P. 480^

Orr Jr., Franklin M.; SPE; New Mexico Petroleum Recovery Research Center Petroleum Recovery Research Center Silva, Matthew K.; SPE; New Mexico Petroleum Recovery Research Center Petroleum Recovery Research Center Lien, Cheng-Li; SPE; New Mexico Petroleum Recovery Research Center Abstract Results of phase composition and density measurements for CO2/ crude-oil mixtures at 32C and four pressures are reported for a system in which liquid/liquid and liquid/liquid/vapor phase separations occur. The experiments demonstrate that a CO2-rich liquid phase can contain as much as 30 wt% hydrocarbons and show that a CO2-rich vapor phase at the same conditions extracts hydrocarbons less efficiently. Pseudoternary phase diagrams are presented that summarize the results of the detailed phase composition measurements. Results of slim-tube displacements at the same four pressures are also given. They indicate that displacement is efficient when the pressure is high enough that a liquid CO2-rich phase appears. Predictions of the performance of the slim-tube displacements based entirely on the performance of the slim-tube displacements based entirely on the experimental measurements of phase compositions and densities are obtained using a simple one-dimensional (1D) simulator. The simulation results clarify the roles of phase behavior and volume change on mixing in the slim-tube tests. Finally, the advantages and limitations of the slimtube and continuous multiple-contact (CMC) tests are compared. We conclude that the CMC experiment yields more information useful for prediction of the performance of a CO2 flood. Introduction The laboratory experiment most commonly performed in the evaluation Of CO2 flood candidates is the slim-tube displacement. The experiment is an attempt to isolate the effects of phase behavior on displacement efficiency in a flow setting that minimizes the effects of the viscous instability inherent in the displacement of oil by low-viscosity CO2. It provides useful information about the pressure required to produce high displacement efficiency in an ideal porous medium. It is not, however, a direct measurement of the phase behavior Of CO2/crude-oil mixtures. The physical behavior of such mixtures is usually studied by combining known quantities of oil and CO2 in a visual cell and measuring phase volumes at various pressures. The volumetric data obtained, along with saturation pressure pressures. The volumetric data obtained, along with saturation pressure data, do not give any direct evidence concerning displacement efficiency, but they can be used to adjust and tune representations of the phase behavior with an equation of state (EOS). For instance, Sigmund et al., used that procedure to match EOS calculations to PVT data and then simulated slimtube displacement experiments, obtaining good agreement between calculation and experiment. Gardner et al., used a combination of phase composition and volumetric measurements to construct ternary diagrams phase composition and volumetric measurements to construct ternary diagrams for a CO2/crude-oil system and then used the ternary diagrams in 1D simulations of slim-tube displacements. They also obtained good agreement between calculation and experiment. Thus there is at least some experimental confirmation of the relationship between equilibrium phase behavior and flow in an ideal porous medium. The connection between phase behavior and displacement efficiency has, of course, long been recognized. SPEJ p. 281

Summary Exploration play-analysis methods are designed for individual or conceptual exploration plays to assess conventional petroleum resources. Play-analysis techniques usually are applied to a small area of appraisal, such as a geologic trend comprising a series of stratigraphic traps or structural traps. Play-analysis procedures, incorporating Monte Carlo techniques, also have been applied to entire geologic horizons, formations, or stratigraphic units of a geologic basin or province. The application of exploration play-analysis techniques to broad frontier provinces for the assessment of conventional petroleum resources by the USGS are reviewed and the results for the Natl. Petroleum Reserve of Alaska (NPRA) and the William O. Douglas Arctic Wildlife Range (WODAWR) are discussed. Introduction Exploration play-analysis methods have been designed for identified or conceptual exploration plays within a basin or province in order to assess conventional petroleum resources. The basic definition of an exploration play is: A practical meaningful planning unit around which an integrated exploration program can be constructed. A play has geographic and stratigraphic limits and is confined to a formation or a group of closely related formations on the basis of lithology, depositional environment, or structural history. However, many variations of this definition and of the basic assumptions applied to play concepts have been accepted by various resource estimators when using play-analysis techniques. Play-analysis methods usually have been applied to the appraisal of relatively small areas, such as a geologic trend consisting of a reef play or a channel or a bar sand. However, the play-analysis procedure has been applied to some entire geologic horizons or stratigraphic units for the appraisal of a total basin or province--e.g. the total Cretaceous potential within a basin or the potential of an entire basin. Although the estimator may have called the procedure a "play analysis," the basic concepts are obviously no longer those of the original definition. Thus, there are some extreme variations in this method and in the respective assumptions from one estimator to another. Recently, exploration play-analysis techniques have been applied to frontier areas where geological and geophysical data are limited and the geologic variables have been described by subjectively derived probability functions based on the judgment of the estimators or by the use of selected analogs. A simulation model was designed in the U.S. Dept. of the Interior, Office of Minerals Policy and Research Analysis (DOI/OMPRA), in response to a directive resulting from the Naval Petroleum Reserves Production Act of 1976. This act required that the president of the U.S. have a study conducted to determine the best overall procedures to be used in the development, production, transportation, and distribution of any petroleum resources in the reserve and to determine the economic and environmental consequences of alternative procedures. The activities simulated by the integrated model are the exploration, development, production, transportation, and distribution activities for oil and gas on the basis of the results of the play-analysis approach in the geologic sub model. Only the geologic and exploration sub models are discussed here.

SynopsisKinetics of 1-hexene polymerization was studied by following the amount of unreacted monomer using gas chromatography. The Ziegler-Natta catalyst system used was comprised of TiC1,-AlEt, with A1 : Ti ratio of 0.85. The sampling and monomer analysis techniques developed can be applied to study the kinetics of higher a-olefins polymerizations, in general. Also, with minor modifications in this technique, a precise profile of molecular weight can be obtained during polymerization.