Composition Of Fluid Phase Research Articles

Use of Color Movies for Interpretation and Presentation of Reservoir Simulation Results

Motion pictures made from color-coded spatial distributions for fluid saturations, phase compositions, pressure, and temperature are applied to the interpretation of reservoir simulations. The use of computer animation is described as applied to several enhanced oil-recovery processes. Additional insight into simulation results can increase markedly the potential value of numerical simulation. Introduction Use of mathematical reservoir simulators to correlate reservoir data and to predict the behavior of petroleum reservoir recovery processes has become an important part of modern reservoir engineering. In addition to the major technical difficulties inherent in developing and running these simulators, it has been found that it is frequently difficult and time consuming to interpret and present the results from simulators. One underlying cause of this difficulty of interpretation and presentation of simulator results is the quantity of information provided by simulators. For example, a typical compositional thermal simulation (three components) might employ five wells and 300 grid blocks. At each grid block, temperature, pressure, three saturations, and an additional composition are available at each time step. Well rates and pressures, perhaps at several different completion intervals, also are calculated. If the simulation takes 300 time steps to run to completion, more than 450,000 numbers will represent the "solution" to the particular reservoir engineering problem (approximately 1,350,000 intergrid block fluxes also would have been computed and used by the simulator during the simulation). As several dozen of these simulations might be made during a field study, it is clear that the simulator user can be faced with more information from the computer than can be assimilated or interpreted conveniently.A second source of difficulty is the inherent two- and three-dimensional aspects of many simulations. It is straightforward to represent graphically the dynamic history of one-dimensional quantities such as well rates as a function of time. Two-dimensional quantities, such as water saturation as a function of position in a vertical cross section, are more difficult to display on a graph. One commonly used display method for two-dimensional cross sections is line-printer contour plots (Fig. 1). While contour plots provide for a rapid visual evaluation of spatially distributed quantities, a distinct advantage over tables of numbers, these plots have several disadvantages.1. They have a low information content - i.e., a number of such plots would have to be viewed simultaneously to provide a picture of all the reservoir variables in a given cross section at one point in time.2. The spatial resolution and the contour resolution of the plots are low.3. It is generally difficult to gain an appreciation of reservoir dynamics from these static "snapshot-in-time" representations of reservoir conditions. JPT P. 1331＾

Garnet-cordierite gneisses near the Egersund-Ogna anorthositic intrusion, southwestern Norway

Graphite-bearing garnet-cordierite rocks from the Sjelset-Vikesá region, south Bogaland, Norway have been analysed by microprobe methods. The garnets belong to the pyropealmandine series and contain 28 mole% pyrope, while the cordierites contain about 71% of the Mg end-member. A regional temperature of about 720–750°C and a lithostatic pressure in the order of 6–7 kb have been inferred from the garnet and cordierite compositions. The petrographic observation suggests that such PT conditions might reflect a retrograde metamorphic event. A tentative estimation of the fluid phase composition, based on the study of opaque minerals, is presented.

Crystallization and Fractionation Trends in the System Andesite-H2O-CO2-O2 at Pressures to 10 Kb

Phase relations of a Mount Hood andesite, which has the composition of an average orogenic andesite, have been determined as a function of O 2 fugacity at 1 atm and of H 2 O fugacity to pressures of 10 kb, at O 2 fugacities of the quartz-fayalite-magnetite (QFM) buffer. All runs contained either a H 2 O or H 2 O–CO 2 fluid phase; melts in runs with a H 2 O–CO 2 fluid phase were H 2 O undersaturated. The H 2 O contents of the melts and H 2 O fugacities were calculated from NaAlSi 3 O 8 –H 2 O thermo-dynamic data on the assumption of ideal mixing in the system H 2 O–CO 2 . One-atmosphere runs show that melting relations of silicates are little affected by f o 2 but that both ilmenite- and magnetite-out temperatures are raised by higher f o 2 . Ilmenite precipitates at higher temperature than magnetite. In these runs and in all runs at high pressure with H 2 O and H 2 O–CO 2 fluid phases, oxides were not stable at temperatures of the silicate liquidus. Oxides might be stable on the silicate liquidus if f o 2 rose two or more log units above the Ni–NiO (NNO) buffer. However, calculations indicate that in natural magmas, those processes which might change f o 2 —crystal-liquid equilibria or exchange of H 2 , or H 2 and H 2 O with the wall rocks—cannot raise f o 2 by that magnitude. Because differentiation of basalt melts to andesite must involve iron-rich oxide phase subtraction, such fractionation models appear unreasonable. For the Mount Hood andesite composition, plagioclase is the liquidus phase under H 2 O–saturated conditions to 5 kb and under H 2 O–undersaturated conditions at 10 kb when the H 2 O content of the melt is less than 4.7 wt percent. For higher H 2 O contents, either orthopyroxene or, at H 2 O saturation at pressure greater than 8 kb, amphibole assumes the liquidus. In all cases, clinopyroxene crystallizes at lower temperature than orthopyroxene. Melting curves in the H 2 O–under-saturated region may be contoured either as percent H 2 O in melt or as P e H 2 O ; in either case, the topology of the various silicate melting curves is different from the case of H 2 O–saturated melting. Therefore, melting relations determined at H 2 O–saturated conditions cannot be used successfully to predict melting relations in the H 2 O–undersaturated region. Amphibole melting relations were studied isobarically at 5 kb as a function of temperature and fluid-phase composition. Amphibole has a maximum stability temperature of 940 ± 15°C for fluid compositions of 100 to 44 mole percent H 2 O; for fluids containing more CO 2 than 56 percent (or, equivalently, less than 4.4 wt percent H 2 O in melt), the melting temperature is lower. The same relations would be seen if CO 2 were not present and the melt were H 2 O undersaturated. These rather low melting temperatures, relative to other silicate phases, preclude andesite generation by basalt fractionation involving amphibole at pressures less than 10 kb.

Contact Metamorphism in Some Areas of the Sierra Nevada, California

Metasedimentary rocks of the Tioga Pass roof remnant in the east-central Sierra Nevada, show systematic mineralogical changes with distance from the plutonic contacts. Rocks indicative of the albite epidote hornfels facies occur in the interior of the remnant, whereas those of the hornblende hornfels facies occur near plutonic contacts. Assuming P fluid = P total = 1 to 2 kb, calculated and experimentally determined phase equilibria suggest that calcareous rocks adjacent to the eastern and western contacts were metamorphosed in the presence of a water-rich vapor phase and at temperatures between 550° and 670°C. Basic metavolcanic rocks show no systematic mineralogical changes with distance from the plutonic contacts. Contact metamorphism in the Standard area in the west-central foothills of the Sierra Nevada produced a narrow zone of sillimanite schists adjacent to the plutonic contact. The sporadic occurrence of K-feldspar in the sillimanite schists is interpreted to be the result of variations in the P H 2 O /P total ratio of the rocks during metamorphism. Garnet occurs in some samples of sillimanite schist and is probably stabilized because of the combined effects of relatively high bulk-rock oxidation and high Mn component. Marble inclusions have been metasomatically altered by water-rich fluids supplied by the surrounding schist. Studies of contact metamorphism in these and in other parts of the Sierra Nevada reveal the following: (1) Calcareous assemblages indicative of water-rich vapor phases are common. Large differences existed in the P CO 2 /P H 2 O ratio of nearby calcareous rocks in two areas, supporting the hypothesis that, for the most part, the fluid phase composition of calc-silicate units in Sierran aureoles was controlled by the original rock composition. Assuming P fluid = P total = 1 to 2 kb, calc-silicate assemblages, including grossularite and clinozoisite, suggest temperatures of 550° to 650°C in parts of many aureoles. Several areas show regular mineralogical changes in calc-silicate assemblages with distance from the plutonic contacts. (2) In several localities, pelitic rocks contain the assemblage sillimanite (or andalusite) + K-feldspar + quartz (± muscovite) close to plutonic contacts, whereas the assemblage Al 2 SiO 5 + muscovite + quartz (no K-feldspar) occurs at greater distances from the contact. The coexistence of andalusite and sillimanite (fibrolite or prismatic, or both) has been described from several localities; this observation suggests a limited usefulness of these poly-morphs as PT indicators of Sierran contact aureoles. (3) Basic metavolcanic rocks in many areas have disequilibrium assemblages characterized by relict volcanic plagioclase. The failure of these rocks to recrystallize may indicate that they were closed to externally derived water during metamorphism. In several areas, the outer limit of contact metamorphism is defined by the transition from actinolite to hornblende toward the plutons. Epidote is common in hornblende-bearing basic assemblages, suggesting it may be stable in basic rocks of the hornblende hornfels facies. (4) Magnesian assemblages in contact metamorphosed serpentinites may have developed under the condition P H 2 O total .

Petrology and Structural Geometry of Pre-Granitic Rocks in the Sierra Nevada, Alpine County, California

The petrology and structural geometry of pre-granitic rocks in western Alpine County, California, were investigated by field and laboratory study. Pre-Cretaceous (Triassic?) metamorphosed equivalents of siltstones, sandstones, tuffs, limestones, andesite flows, and conglomerates are preserved in three roof pendants surrounded by a variety of Cretaceous (?) granitic rocks, principally adamellite and granodiorite. The metamorphic rocks exhibit asymmetrical folds in the bedding (S 1 ), the axes (βS 1 ) of which trend northwest with an average plunge of 25°, and the axial surfaces of which dip steeply southwest. A statistically vertical tectonic surface (S 2 ) trends northwest and varies about axes (βS 2 ) approximately parallel to βS 1 in some fields, and inclined to βS 1 in others. Two sets of lineations are recognized, one parallel to βS 1 ( B ) and another plunging steeply at approximately right angles to βS 1 ( B′ ). The geometric symmetry of both field and microscopic structures is triclinic. Deformation was probably by a combination of early flexural slip folding of S 1 about an axis parallel to βS 1 , and later passive folding by slip on an intragranular scale along surfaces parallel to S 2 . The slip on S 2 is thought to have been normal to the axis βS 2 in the plane of S 2 . Strain of the mass involved shortening normal to the trend of the Sierra Nevada, accompanied later by extension in S 2 . A regional study suggests that the orientation and style of the structural geometry of deformed rocks are similar in many parts of the Sierra Nevada, particularly near the present crest of the range. Post-kinematic thermal metamorphism caused recrystallization of most of the tectonites into hornfelses, some of which show relict textures. All the metamorphic rocks are in the hornblende hornfels facies. Three metamorphic assemblages are recognized which are characterized by (1) the pair calcite-amphibole, (2) clinopyroxene, and (3) wollastonite. The three assemblages are thought to be present because of gradients in composition and partial pressure of fluid phases during metamorphism. Metasomatically introduced boron, tungsten, molybdenum, iron, copper, tin, and sulfur are locally important components.