The kinetics of low-temperature oxidation (LTO) of crude oils in porous media was studied. Isothermal integral reactor data were analyzed to obtain rate equations for the over-all rate of the partial oxidation reactions at temperatures below partial oxidation reactions at temperatures below 500 deg. F. The reaction order with respect to oxygen was found to be between 0.5 and 1.0. The order of the reaction was dependent upon the crude but independent of the properties of the porous medium. The activation energy of the reaction was insensitive to the type of crude or porous medium and is in the neighborhood of 31,000 Btu/lb mol. LTO reactions were found to be in the kinitics-influenced region. The measured reaction rates for a 19.9 deg. API and a 27.1 deg. API crude indicated higher oxidation rates under similar reaction conditions for the higher API gravity crude. Light crudes appear to be m ore susceptible to partial oxidation at low temperatures because of the react ed oxidation reactions rather than by carbon oxidation. Other information includes the fraction of reacted oxygen utilized in carbon atom oxidation by the LTO reaction and the molar ratio of CO2 and CO produced in the low-temperature region. Effect of partial oxidation of the crude on the in-situ combustion process was studied by experimentally simulating the zones preceding the combustion front where temperatures and injection rates of linear reservoir model were programmed with time according to a predesigned schedule. Oxidation of the crude at temperatures below 400 deg.F had significant effects on the behavior of the crude-oil/water system in the porous medium at elevated temperatures and on the fuel available for combustion. A substantial decline in the recoverable oil from the evaporation and cracking zones, an increase in fuel deposition, and drastic changes in fuel characteristics and coked sand properties were obtained when the crude was subjected to LTO during the simulation process. Introduction The application of thermal energy to petroleum reservoirs as a means of increasing crude oil recovery has been given a great deal of attention. In underground combustion, thermal energy is induced by the partial burning of the crude oil in situ. The production of heat by the exothermic oxidation reactions of the hydrocarbons constitutes a unique feature of the in-situ combustion process. The chemical reactions and the accompanying heat released create a new temperature profile and cause drastic redistribution in the reservoir fluid saturations. With oxygen available in the transient zones of variable temperature and hydrocarbon saturations, several oxidation reactions of differing nature can take place during an underground combustion process. Because of the complex composition of process. Because of the complex composition of crudes and the great number of reaction products that can be produced, it is convenient to classify the hydrocarbon oxidation reactions ascombustion reactions that take place in the high-temperature combustion zone (above 600 deg. F) with CO2, CO, and H2O as the principal reaction products andpartial oxidation or low-temperature products andpartial oxidation or low-temperature (LTO) reactions that occur in zones where the temperature is lower than 600 deg. F. Several partial oxidation reactions are known to take place, producing primarily water and oxygenated producing primarily water and oxygenated hydrocarbons such as carboxylic acid aldehydes, ketones, alcohols, and hydroperoxides. High-temperature combustion reactions are desirable because they generate most of the heat required for the in-situ combustion process. Partial oxidation reactions, on the other hand, are in most cases undesirable because of their adverse effect on the viscosity and distillation characteristics of the crude. SPEJ P. 253

Air and water permeabilities of a large number of samples from the Pittsburghand Pocahontas coals were measured at various overburden and mean flowpressures. A wide variation (< 0.0 1 to > 100 md) in the air and waterpermeabilities was obtained for each type of coal, and flow was primarilythrough microfractures. Overburden pressure has the most significant effect onthe single-phase permeability. Considerable hysteresis was observed for bothair and water permeabilities. Gas permeabilities are affected to a lesserdegree by mean flow pressure above atmospheric. However, at subatmospheric meanpressures, appreciable increase in permeability occurs for low-permeabilitysamples. This was attributed to gaseous molecules desorbed at pore necks. At highoverburden pressure (~> 400 psig) water permeabilities are smaller than orequal to air permeabilities measured at the same pressures. Introduction The permeability of coal to gas and water is of interest to engineers in boththe mining and the petroleum industries. Much of the interest of the miningengineer stems from concern for the health and safety of the coal miner becausethe flow of methane into coal mines is one of the major causes of mine disasters in thiscountry. Some deep mines produce 10 to 15 MMscf/D of methane and require thecirculation of as much as 10 to 15 tons of air per ton of coal mined in orderto clear the gas from the mine. If this little-known source of natural gascould be produced from the coal before the coal is mined, it would help relievethe gas shortage as we11 as protect the safety of the coal miner. In recent years a number of petroleum companies have shown an interest in coalas a primary energy material that can be converted into electrical energy orinto gaseous and liquid products. Both above- and below-ground processes arebeing studied intensively. Knowledge of the basic permeability and relativepermeability of coal to gas and water should be very useful to petroleumengineers contemplating these new processes for the conversion of coal intoenergy forms suitable for the consumer. Although some studies of the permeability of coal to gas and to water have beenconducted, no gas/water relative permeability studies have been reported eventhough the presence of significant quantities of water is known to have amarked effect on the flow of methane from the coal seam. In this and a relatedpaper, we present the results of gas/water relative permeability studies onPittsburgh and Pocahontas coal samples.

Air and water relative permeabilities have been measured for numerous samples of Pittsburgh and Pocahontas coals. Tests were performed under steady-state conditions for both drainage and imbibition cycles. Results indicate that the flow of gas is greatly reduced during the latter process, whereas during drainage it is largely undiminished over a wide water-saturation range. It is also shown that imbibition saturation distributions obtained from liquid.water imbibition as opposed to water·vapor adsorption produce gas permeability curves of radically different character. The effective permeabilities to both gas and water were significantly reduced with the application of overburden pressures in the range of a to 1, 000 psig, but the general shapes of the relative permeability curves remained the same.

Drainage air-water capillary-pressure curves were obtained for Pittsburgh and Pocahontas coals at various overburden pressures. Capillary-pressure data were used to investigate pore-size characteristics. Results were indicative of the complex pore structure of coal, consisting primarily of a network of macro- and microfractures. In most cases, however, displacement pressure and residual water saturation increased at higher overburden pressure. Reasonable agreement between measured relative permeabilities and those calculated from capillary-pressure data with Purcell's model was obtained for only a few samples. Fracture permeabilities computed from pore-size distribution were lower than permeabilities pore-size distribution were lower than permeabilities actually measured at the same overburden pressure. Helium porosity was considerably higher than porosity determined by water saturation, indicating porosity determined by water saturation, indicating inaccessible pore volume to water. Pore compressibility was determined under triaxial stress-loading conditions. Changes in porosity with overburden pressure were more significant at pressures below 1,500 psig. Above this pressure, pore compressibility appeared to approach a pressure, pore compressibility appeared to approach a constant value averaging about 0.5 × 10(−4) psi(−1) for the coal samples studied. Introduction Increased interest in underground coal gasification and coal-seam degasification for the purpose of producing clean energy stimulated fundamental producing clean energy stimulated fundamental research into the phenomena of multiphase fluid flow through coal. Two previous papers presented results of investigation of the air- and water-permeability and relative-permeability characteristics at various overburden pressures for two different types of coal. However, to understand the mechanisms of two-phase flow (usually gas and water) through a complex porous system such as coal, one needs a clear insight into the internal pore structure of coal and the interaction between pore structure of coal and the interaction between this structure and the associated fluids. Such knowledge of the make-up of the pore structure helps in modeling fluid flow through the system and in interpreting permeability and relative-permeability data. Interaction between the pore structure and fluids results in the capillary-pressure phenomena. Capillary-pressure data have been used extensively to determine the pore characteristics of many petroleum reservoir rocks and to relate these petroleum reservoir rocks and to relate these characteristics to the single- and two-phase flow behavior in the rock. It is also known that natural fracture systems are the principal source of flow capacity of many petroleum reservoir rocks and contribute materially petroleum reservoir rocks and contribute materially to the storage capacity of some. Changes in fracture capacity resulting from changes in net overburden pressure have an important influence on the flow pressure have an important influence on the flow properties of the rock, as reported by Jones. In our properties of the rock, as reported by Jones. In our previous work with coal, which is a naturally previous work with coal, which is a naturally fractured system, absolute and effective permeabilities were found to be highly sensitive to overburden pressure (pov). Thus, it would be expected that the pressure (pov). Thus, it would be expected that the effect of Pov on the fracture flow capacity, capillary pressure, and pore compressibility is more dramatic pressure, and pore compressibility is more dramatic for coal. The internal structure of coal has been studied by microscopic methods, gas sorption measurements, and by mercury porosimetry. Data on helium porosity of different types of coal also can be porosity of different types of coal also can be found in Ref. 5. However, we are not aware of any determinations of capillary pressure in coal at different overburden pressures. In this paper gas-liquid capillary-pressure relationships for coal at different overburden pressures are presented. pressures are presented. SPEJ P. 261

SPE Members Abstract This paper describes the development, monitoring programs and evaluation methodology of a gas injection programs and evaluation methodology of a gas injection pilot project carried out in a fractured carbonate reservoir pilot project carried out in a fractured carbonate reservoir with a strong water drive. Immiscible gas injection was recognized as a potentially viable economic recovery process, and a gas injection pilot was initiated in the field. process, and a gas injection pilot was initiated in the field. The reservoir contained an undersaturated, intermediate gravity oil with a recovery of less than 6 percent after 40 years of primary depletion. The major areas of performance that were monitored thoroughly during the performance that were monitored thoroughly during the gas injection pilot project were:Production (oil, gas and water)Reservoir pressureH2S concentration of the produced gasReservoir gas saturation and gas-cap advance A numerical reservoir simulator was used to history match reservoir performance under gas injection, and to investigate operative reservoir mechanisms which had resulted in improved oil recovery. The results were also used to confirm the validity of assumptions made in the design and performance prediction of the pilot project. The importance of collecting accurate data during the monitoring phase of the pilot was recognized so that meaningful field expansion guidelines and economic evaluation parameters could be established with a reasonable level of confidence. Immiscible gas injection in this watered-out carbonate reservoir resulted insubstantial increases in oil production rates and is expected to double the recoverable reserves from the field. Introduction First production from the Reefal Miocene Limestone reservoir in this field was in 1943. The field has been developed both onshore and offshore. The productive area of the reservoir is approximately 10 square kilometers, the majority of which lies offshore. The reservoir is an unfaulted east-west trending anticline, which pinches out to the west by onlap and facies changes. The pinches out to the west by onlap and facies changes. The aquifer circles the reservoir in the northwest around to the southeast The crest of the reservoir is at 350 m ss and the original water oil contact was at about 750 m ss, bearing an original oil column of about 400 meters. The reservoir originally contained an undersaturated, intermediate gravity oil of 6 centipoise viscosity. Initial reservoir pressure, at a datum depth of 1,875 ft ss, was 822 psia, with an oil saturation pressure of 449 psia at 108 degrees F, the datum reservoir temperature. Pressure declined rapidly from the start of production until about 1950, and then declined slowly due to natural water influx. During the 1960's and early 1970's, pressure stabilized and increased slightly, then began to decline slowly from 1973 as the water cut began to increase. The production-pressure history of the reservoir is depicted on production-pressure history of the reservoir is depicted on Figure 1. Water production performance throughout the history appeared anomalous. The behavior of many wells was similar to coning, although in most of the onshore portion of the field there was no indication of bottom water. It was contemplated that diagonal fractures extending updip from the aquifer was contributing to the pseudo-coning behavior and anomalous water-production. P. 199