Carbon Dioxide Flooding Research Articles

Experimental Comparison of Nitrogen and Carbon Dioxide Oil Displacement in Carbonate Cores

The feasibility of nitrogen and carbon dioxide flooding is being investigated experimentally as possible enhanced oil recovery processes in Iranian carbonate oil fields. Laboratory tests were conducted on a tight permeability sample of an Iranian oil field. Three flooding tests were conducted at back pressures of 1,000, 2,000, and 2,500 psi for both nitrogen and carbon dioxide separately. All tests were conducted at constant temperature of 28°C. Experimental results indicate that immiscible carbon dioxide can mobilize more oil than immiscible nitrogen due to the ability of carbon dioxide to dissolve in oil. The key factor in higher recoveries of carbon dioxide injection compared to nitrogen is the ability of carbon dioxide to extract oil components. Extraction dominates after carbon dioxide breakthrough. Although the only mechanism of oil displacement in nitrogen flooding tests was the displacement energy applied by injection pressure, the oil recoveries in nitrogen flooding are considerable, especially at higher pressures.

Research on the Effect of Supercritical Carbon Dioxide on the Properties of Super Heavy Oil

Carbon dioxide flooding is an important way to exploit heavy oil reservoir. Considering the Zheng411 super heavy oil reservoir in Shengli Oil Field, the solubility of supercritical carbon dioxide in super heavy oil, and the effect of supercritical carbon dioxide on the volume factor, viscosity, component content and oil/water emulsification of super heavy oil are researched. The result shows: the solubility of carbon dioxide in super heavy oil increases with the increasing pressure, but the increasing extent declines gradually, when the pressure is below 28MPa, the solubility of carbon dioxide decreases with the rising temperature under the same saturation pressure; the volume factor increases linearly with the increase of supercritical carbon dioxide solubility; under the condition of unsaturation, the supercritical carbon dioxide is able to reduce the density of super heavy oil substantially, whereas it has little impact on the chemical properties of oil; Demulsification and visbreaking can be realized through dissolving supercritical carbon dioxide in super heavy oil that contains water, and the viscosity reduction capacity of carbon dioxide is hardly affected by water.

Carbon Capture and Sequestration: A Potential "Win-Win" for the Oil Industry and the Public

Public Policy Focus - The status of carbon capture and sequestration. In 1972, the first commercial carbon dioxide (CO2) flood project in the world began with the injection of CO2 into the Scurry Area Canyon Reef Operators Committee (SACROC) unit in the Permian Basin in Scurry County, Texas. The goal was simple: To arrest declining oil production and recover bypassed reserves. Today, nearly 40 years later, CO2 injection is being considered on a much wider scale, and for a different purpose altogether: To help arrest an increase in the average surface temperature of the planet. CO2, among other gases such as methane and nitrous oxide, is a “greenhouse gas,” a gas that traps heat in the Earth’s atmosphere by absorbing and emitting radiation within the thermal infrared range, causing a greenhouselike warming effect. The presence of greenhouse gases in Earth’s atmosphere is vital, for without them, Earth’s surface would be on average about 59°F colder than at present. CO2 is also a key ingredient that nourishes plant life through photosynthesis.

Permeability prediction and its impact on reservoir modeling at Postle Field, Oklahoma

A permeability model was developed for a thin valley-fill reservoir at Postle Field, Oklahoma, with the objective of increasing the accuracy of flow simulation. The presence of high-permeability zones that are below seismic resolution represented the greatest challenge to overcome. This challenge is common as the average reservoir thickness in North America is 17 ft (5 m). Enhanced oil recovery is underway at Postle Field to increase production and to revitalize the field. The process involves carbon dioxide flooding which is fast becoming the dominant mechanism of Tertiary recovery. To optimize the recovery efficiency of this process, it is important to understand the influence of permeability heterogeneity and its role on fluid flow. High-permeability zones have the potential to cause early breakthrough and poor sweep efficiency.

RETRACTED ARTICLE: A simulation approach: Miscible carbon dioxide injection in a carbonate reservoir

The purpose of this study is to optimize the existing carbon dioxide (CO2) flood in deep dolomite formations by improving oil sweep efficiency of miscible CO2 floods and enhancing the conformance control. A full compositional simulation model using a detailed geologic characterization was built to optimize the injection pattern. The model is a quarter of an inverted nine-spot and covers 20 acres of field formation. Geologic description was used to construct the simulation grids. The simulation layers represent actual flow units and resemble the large variation of reservoir properties. History match was performed to validate the model. Several sensitivity runs were made to improve the CO2 sweep efficiency and increase the oil recovery. Finally, the optimum CO2 injection rate for dolomite formations was determined approximately. Simulation results also indicate that a water-alternating-gas (WAG) ratio of 1:1 along with an ultimate CO2 slug of 100% hydrocarbon pore volume (HCPV) will allow an incremental oil recovery of 18%. The additional recovery increases to 34% if a polymer is injected as a conformance control agent during the course of the WAG process at a ratio of 1:1. According to the results, a pattern reconfiguration change from the nine spot to staggered line drive would represent an incremental oil recovery of 26%.

The state of EOR with CO2 and associated seismic monitoring

Carbon dioxide ([Formula: see text]) can be an agent for enhancing recovery from oil reservoirs because it acts like a scrubbing agent to contact residual oil in the reservoir and makes it easier for the oil to flow to producing wells. Old reservoirs that have produced for years are not depleted of oil. They contain residual oil that can't be moved under primary or secondary flood processes. The tertiary process that could move the greatest amount of residual oil is carbon dioxide flooding. To obtain the residual oil, we need to inject [Formula: see text] to enhance oil recovery (EOR). We may be able to produce up to 20% of the original oil in place (OOIP). Seismic monitoring provides a means to proactively manage the flood.

Effect of stress sensitivity on displacement efficiency in CO2 flooding for fractured low permeability reservoirs

Carbon dioxide flooding is an effective means of enhanced oil recovery for low permeability reservoirs. If fractures are present in the reservoir, CO2 may flow along the fractures, resulting in low gas displacement efficiency. Reservoir pore pressure will fluctuate to some extent during a CO2 flood, causing a change in effective confining pressure. The result is rock deformation and a reduction in permeability with the reduction in fracture permeability, causing increased flow resistance in the fracture space. Simultaneously, gas cross flowing along the fractures is partially restrained. In this work, the effect of stress changes on permeability was studied through a series of flow experiments. The change in the flowrate distribution in a matrix block and contained fracture with an increase in effective pressure were analyzed. The results lead to an implicit comparison which shows that permeability of fractured core decreases sharply with an increase in effective confining pressure. The fracture flowrate ratio declines and the matrix flowrate ratio increases. Fracture flow will partially divert to the matrix block with the increase in effective confining pressure, improving gas displacement efficiency.

Characterization of Fracture Network System of the Midale Field

Abstract Enhanced oil recovery from challenging/complex fields requires extensive analysis of reservoir structure and good understanding of the effect of this structure on the dynamics of the process. Naturally fractured reservoirs are good examples of this kind and their fracture network characterization is still a bigchallenge. In this study, we analyzed the fracture network system of a portion of the Midale Field, a naturally fractured carbonate reservoir in the Williston Basin of southeastern Saskatchewan, Canada. Our study aims at an extensive characterization of fracture and fracture network properties and construction of a reliable fracture network model for further use in assessing the oil recovery by CO2 injection and CO2 sequestration potential. We integrated static data such as cores, logs and well tests to build 3D discrete fracture network models. Stochastic numerical approach was applied using a commercial software package. A fracture network constructed from static data was calibrated using well test data. Several parameters were evaluated in sensitivity studies to determine those characteristics of the network which have higher influence on the reservoir performance. Simulated well test response was checked against previously published well test data. This study allowed us to recognize uncertainties in critical parameters and propose some measures to manage those uncertainties. Introduction The Midale is a carbonate field located in southeastern Saskatchewan. Following the discovery in 1953, the field was developed on 32 ha spacing and proved to bear 81.9 ? 106 Sm3 reserves of 28.7 °API oil. The field belongs to the Mississippian oil trend located along the northern margin of Williston Basin. Subsequent to primary production up to 1962, the field was subjected to waterflooding on 83 inverted nine-spot patterns. To maintain the production which declined after 1964, an intensive program of vertical and horizontal infill drilling was undertaken. As of the end of 2006, approximately 1,000 wells exist in the field and more than 25% of OOIP was produced with an average watercut of 92%(1). The Midale Field is currently being subjected to tertiary recovery by miscible CO2 flooding. This field-scale CO2 injection was preceded by a 1.78 ha pilot project in 1984 ? 1989 which paved the way for a larger demonstration project. The CO2 Flood Demonstration Project encompassed 10% of the Midale Unit and paved the way for the field-scale application, which is expected to end up with an incremental recovery of 15% of OOIP(2). The Midale Field does not meet typical screening criteria for CO2 flooding. Nevertheless, extensive research and field applications proved that a proper design based on the analyses of the special combination of petrophysical, lithological and fracturing data can result in a successful carbon dioxide flood. The 24 m thick Midale Reservoir section consists of two main layers: dolomite-dominated "Marly" and vugular limestone, called "Vuggy". Both strata contain systematic fractures, though the degree of fracturing varies. Numerous studies conducted on the field revealed some characteristics of the natural fracture network (NFN) by both inverse methods, such as waterflood and carbon dioxide flood performance analyses, and well test analyses and direct methods such as core and log analyses.

Investigation of supercritical carbon dioxide, aspheltenic crude oil, and formation brine interactions in carbonate formations

Asphaltene precipitation and rock dissolution can significantly hinder the success of carbon dioxide flooding of asphaltenic crude oil in carbonate heterogeneous formations. It is essential during CO 2 flooding when both processes exist to study separately the effect of each phenomenon on the flooding process. Ten core flooding experiments under similar reservoir conditions of 4000 psia pressure and 250 °F temperature were conducted to evaluate each phenomenon separately. Actual rock cores representing different areas of carbonate oil field saturated with actual fluids of filtrated brine and asphaltenic crude oil were used to evaluate the interaction between supercritical (SC)-CO 2, carbonate rock, and its contained fluid. Asphaltene content of the produced crude oil, water and mineralogical rock analyses, and scanning electron microscopic (SEM) photos of rock pores were performed to evaluate the effect of supercritical (SC)-CO 2 flood on the permeability and mineralogical variation characteristics of the limestone cores. Results indicated that calcite dissolution and/or precipitation is the major reason for permeability improvement and/or impairment. It is also proven that the amount of permeability damage depends on the fabric of the rocks, salinity of the brine, and initial core permeability. The results also indicated that CO 2 injection in fresh water saturated carbonate rock led to complete collapse of that rock. It is recommended that fluid assessment should be conducted to the different areas of the field.

Potential for Additional CO2-Flood Projects in the US

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 113975, "The Potential for Additional Carbon Dioxide Flooding Projects in the United States," by Hitesh Mohan, SPE, Marshall Carolus, SPE, and Khosrow Biglarbigi, SPE, Intek, prepared for the 2008 SPE Improved Oil Recovery Symposium, Tulsa, 19-23 April. The paper has not been peer reviewed. There is renewed interest in carbon dioxide enhanced oil recovery (CO2 EOR). Growing concern about climate change and greenhouse gases has increased interest in carbon capture and sequestration. CO2 EOR provides a value-added opportunity to increase crude-oil production while sequestering substantial volumes of industrial CO2. An analysis was conducted to determine the incremental domestic production that could be realized if industrially produced CO2 were available for EOR. Challenges include available volumes of CO2, infrastructure requirements, and prices of the CO2. Introduction US conventional crude-oil production continues to decline while demand for crude and finished products rises. According to the US Department of Energy Energy Information Administration (US DOE EIA) and shown in Fig. 1, the US demand will be greater than 27 million B/D by 2030, while total production will be less than 10 million B/D. Four factors were identified that will have a significant effect on widespread implementation of CO2 EOR.Target resourceTechnologyAvailability of CO2Economics Target Resource There are 1,673 reservoirs onshore in the continental US that are candidates for CO2-miscible flooding. Fig. 2 shows the reservoirs that were identified on the basis of the following criteria.Gravity greater than 22°APIReservoir pressure greater than the minimum miscibility pressureDepth greater than 2,500 ftOil viscosity less than 10 cpCurrent oil saturation greater than 20%Either sandstone or carbonate rock Technology CO2-EOR technologies have been demonstrated to be profitable in commercial-scale applications for nearly 30 years. As of 2006, 80 CO2-EOR projects in the US had a combined production of 234,000 BOPD. Ten of these projects were started between 2004 and 2006. Of the projects active in 2006, 58 are in the Permian Basin. The reason is partly because of the prevalence of candidate reservoirs in that region, and because of the steady availability of natural CO2.

Subsurface characterization and geological monitoring of the CO 2 injection operation at Weyburn, Saskatchewan, Canada

Abstract The IEA Weyburn Carbon Dioxide (CO 2 ) Monitoring and Storage Project analysed the effects of a miscible CO 2 flood into a Lower Carboniferous carbonate reservoir rock at an onshore Canadian oilfield. Anthropogenic CO 2 is being injected as part of a commercial enhanced oil recovery operation. Much of the research performed in Europe as part of an international monitoring project was aimed at analysing the long-term migration pathways of CO 2 and the effects of CO 2 on the hydrochemical and mineralogical properties of the reservoir rock. The pre-CO 2 injection hydrochemical, hydrogeological and petrographical conditions in the reservoir were investigated in order to recognize changes caused by the CO 2 flood and to assess the long-term fate of the injected CO 2 . The Lower Carboniferous (Mississippian) aquifer has a salinity gradient in the Weyburn area, where flows are oriented SW–NE. Hydrogeological modelling indicates that dissolved CO 2 would migrate from Weyburn in an ENE direction at a rate of about 0.2 m/annum under the influence of regional groundwater flow. Baseline gas fluxes and CO 2 concentrations in groundwater were also investigated. The gas dissolved in the reservoir waters allowed potential transport pathways to be identified. Analysis of reservoir fluids proved that dissolved CO 2 and methane (CH 4 ) increased significantly in the injection area between 2002 and 2003. Most of the injected CO 2 exists in a supercritical state, lesser amounts are trapped in solution and there is little apparent mineral trapping. The CO 2 has already reacted with the reservoir rock sufficiently to mask some of the strontium isotope signature caused by 40 years of water flooding. Experimental studies of CO 2 –porewater–rock interactions in the Midale Marly Unit indicated slight dissolution of carbonate and silicate minerals, followed by relatively rapid saturation with respect to carbonate minerals. Carbon dioxide flooding experiments on similar rock samples demonstrated that porosity and gas permeability increased significantly through dissolution of calcite and dolomite. Several microseismic events were recorded over a six-month period and these are provisionally interpreted as being related to small fractures formed by injection-driven fluid migration within the reservoir, as well as other oilfield operations. Experimental studies on the overlying and underlying units show similar reaction processes; however secondary gypsum precipitation was also observed. Reaction experiments were conducted with CO 2 and borehole cements. The size and tensile strength of the cement blocks were unaffected, however their densities increased. Pre- and post-injection soil gas survey data are consistent with a shallow biological origin for the measured CO 2 in soil gases. Isotopic (δ 13 C) data values are higher than in the injected CO 2 , and confirm this interpretation. No evidence for leakage of the injected CO 2 to ground level has been detected. The long-term safety and performance of CO 2 storage was assessed by the construction of a features, events and processes (FEP) database that provides a comprehensive knowledge base for the geological storage of CO 2 .

Deep Hypothermic Circulatory Arrest in Patients With High Cognitive Needs: Full Preservation of Cognitive Abilities

Owing to controversy regarding the efficacy and safety of deep hypothermic circulatory arrest (DHCA) during thoracic aortic surgery, we conducted a psychometric study in which high-cognitive patients and their informants were interviewed to determine whether DHCA had any adverse effect on their daily activities or work performance. A total of 29 patients (18 males, 11 females; age, 26 to 75 years; mean 52.6 years) whose jobs require high cognitive capability and who had undergone aortic surgery using DHCA (range, 17 to 54 minutes; mean arrest time, 27.4 minutes) at Yale-New Haven Hospital were retrospectively studied. These 29 patients represented the responders among 45 such patients to whom questionnaires were mailed. A control group of 21 high-cognitive patients (20 males, 1 female; ages, 36 to 77 years; mean, 54.7 years) who underwent aortic surgery without DHCA were surveyed as well. During surgery, DHCA was used as the sole means of cerebral protection. The head was packed in ice, and carbon dioxide flooding of the field was used in all cases. The ascending aorta was resected with an open distal anastomosis and a hemiarch or total arch replacement. A 21-part questionnaire (adapted from A.F. Jorm's Short Form IQCODE and supplemented by our own questions) was distributed postoperatively to subjects and to their informants (generally a spouse). A value of 3 on the questionnaire indicated "not much change" from preoperative status (1 indicated much worse and 5 indicated much improved). There were no statistically significant differences in any functional outcomes by study group (by patient: DHCA 3.01, control 3.09; by informant: DHCA 3.00, control 3.03; p > 0.05). Mean values of the outcomes for study groups and control subjects were essentially identical and quite close to 3 (the value assigned to "not much change") for overall score, for occupational score, and for memory-related score. These data indicate that high-cognitive patients experienced very little cognitive change as a result of undergoing DHCA. Our assessment strongly supports the adequacy of straight DHCA as a cerebral protectant strategy during short- to moderate-duration circulatory arrest. We found excellent preservation of functional state and no difference from patients undergoing aortic surgery without DHCA.

Economic Analysis for Enhanced CO2 Injection and Sequestration Using Horizontal Wells

Abstract Carbon dioxide flooding has been recognized widely as one of the most effective enhanced oil recovery processes applicable for light to medium oil reservoirs. Moreover, the injection of CO2 into an oil reservoir is a promising technology for reducing greenhouse emissions while increasing the ultimate recovery of oil. Numerical reservoir simulation is an important and inexpensive tool for designing EOR CO2 projects and predicting optimal operational parameters. In this work, reservoir simulations performed with a compositional simulator were applied to investigate the macroscopic mechanisms of a CO2 injection process. Horizontal injectors were used to increase injectivity. Compared to traditional vertical wells, horizontal wells are more attractive to improve CO2 flooding economics by increasing injection rate, improving areal sweep and increasing CO2 storage. The effects of several important parameters on the performance of the CO2 process were studied to optimize the process. Operational parameters such as different production schemes, the injector pressure and injection rate were investigated to determine the optimal - operating conditions for simultaneous objectives of higher recovery and higher CO2 storage. The application of CO2 flooding using horizontal wells can shorten- project life, which is critical to its economics. The simulation results served as the basic input parameters for the economic analysis performed. Furthermore, net present value (NPV) and profitability index results were used to optimize the profitability of the project and to compare the CO2 application using vertical and horizontal wells. The analysis used actual design parameters, including equipment and operating costs. The evaluation emphasized the importance of reservoir characteristics, optimum design of operation parameters and economic factors in the economic feasibility of CO2 injection projects for enhanced oil recovery and sequestration. Introduction The carbon dioxide flooding process can increase oil recovery by means of swelling, evaporating and lowering oil viscosity(1, 2). Many injection schemes using CO2 have been applied(3), including CO2 gas injection (continuously), CO2 gas slug followed by water, and others. There are some important factors to be considered during the design of CO2 flooding, including the availability and amount of CO2 to inject, the reservoir conditions, whether mobility control techniques are required and other general operating conditions(4, 5). Among these factors, the knowledge of reservoir conditions is essential to the injection/production process and, thereafter, the economic success of the project. These include the reservoir temperature and pressure, reservoir permeability and porosity, fractures and faults, etc. Field tests of CO2 floods have shown that reservoir heterogeneities, such as fractures, strata discontinuities and pinch-outs, can reduce the effectiveness of the process. CO2 is a highly mobile fluid because of its low viscosity, so fingering and channeling of CO2 or bypassing of oil can affect the volumetric sweep efficiency in CO2 flooding. In this case, mobility control becomes an important issue for the improvement of CO2 applications(6). With the increase of productivity performance and the decrease of drilling and completion costs, horizontal wells became more cost effective. This paper compares the conventional CO2 flooding process using vertica

Carbon dioxide flooding of the pericardium-An old practice revisited

Background Cerebral air embolism is a known complication of open-heart surgery with devastating consequences. Neurological injury after cardio-pulmonary bypass can be broadly divided into 2 categories: Type I: Focal injury Type II: Intellectual deterioration/neurocognitive impairment. Increasing evidence points to cerebral embolization as the principal culprit. Since the early days of modern cardiac surgery, surgeons have attempted to reduce embolization by various means. One of the early techniques propounded was carbon dioxide insufflation of the pericardial cavity. Carbon dioxide, was uniquely positioned for this, being denser than air, more soluble than air, and easily managed perioperatively if the blood levels became unphysiological.. The technique did not find favor, since there was no instrumentation, in the early days of cardiopulmonary bypass to measure and establish its impact on the actual outcomes.

Effects of Viscous and Capillary Forces on CO2Enhanced Oil Recovery under Reservoir Conditions

Carbon dioxide flooding has been proven to be one of the most effective and viable enhanced oil recovery (EOR) processes for light and medium oil reservoirs. In the past, an extremely large number of laboratory experiments and numerical simulations have been conducted to study the CO2 EOR process. However, the specific effects of viscous and capillary forces on this tertiary oil recovery process are neither thoroughly studied nor well understood yet. In this paper, an experimental study is carried out to examine the detailed effects of viscous and capillary forces on the CO2 EOR under the actual reservoir conditions. First, the equilibrium interfacial tensions between a light crude oil and CO2 are measured at different equilibrium pressures. Second, a series of CO2 coreflood tests are performed to measure the CO2 EOR at different CO2 injection pore volumes, pressures, and rates. Each CO2 coreflood test is terminated after a total of 1.5 pore volume of CO2 is injected. The detailed experimental results show that, in general, the measured equilibrium interfacial tension is reduced with the equilibrium pressure but the measured CO2 EOR at 1.5 pore volume of CO2 is increased with the CO2 injection pressure and rate. Finally, the measured CO2 EOR at 1.5 pore volume versus injection pressure data at different CO2 injection rates are related to the measured equilibrium interfacial tension versus equilibrium pressure data in terms of the complete capillary number, which is defined as the ratio of the viscous force to the capillary force for each CO2 coreflood test. This study shows that if the complete capillary number is in an intermediate range, the CO2 EOR increases quickly with the complete capillary number. Otherwise, the CO2 EOR is lower and remains almost constant for a smaller complete capillary number, or it is higher and remains unchanged for a larger complete capillary number.

Effect of H2S and Pressure Depletion on the CO2 MMP of Zama Oils

Abstract Phase behaviour and minimum miscibility pressure measurements were carried out to evaluate the potential of applying miscible CO2/H2S flooding in the Zama reefs of NE Alberta, Canada. Since there is some variability in the properties of oils from different wells or reefs, the measurements were carried out on recombined reservoir fluids from two different wells. The injection solvent will be supplied from a nearby gas plant that is expected to produce CO2/H2S streams with a range of compositions due to a number of operational factors. Accordingly, three solvent injection gases were considered: pure CO2 and CO2 containing 20 and 40 mol% H2S. Minimum miscibility pressure (MMP) measurements were carried out using the rising bubble apparatus (RBA). The MMP decreased almost linearly with the amount of H2S in the injection gas in the range of compositions studied. Some evidence of precipitation of solids was observed. Measurements were also carried out to determine the CO2 MMP of these reservoir fluids as they were depleted of gas through a differential liberation procedure. The results show that the MMP decreased with decreasing liberation pressure. Key properties of the liberated reservoir fluids were also measured and compared with those of the recombined reservoir fluids. The results show that miscible flooding with sour acid gas is feasible in this case, and could provide an excellent means of storing/sequestering these gases while improving oil recovery. Introduction Vertical gasfloods have an excellent track record for producing additional oil. For example, hydrocarbon miscible floods have been carried out in a number of Canadian reefs(1–5). Vertical gravity-stable carbon dioxide floods were reported in three US fields(4–8), also with excellent additional oil recoveries. The Zama Field(9) is located in northeastern Alberta and contains a large number (600 – 800) of relatively small pinnacle reefs with up to 1.5 ? 106 m3 (10 mmbbl) of original oil in place (OOIP). The wells selected for this study produce from the Keg River Formation. Al-Dilwe and Asghari(10) described the reservoir and its production history from the 1960's. The produced oil and gas are sour and contain an appreciable amount of carbon dioxide. The centrally located Zama Gas Plant (operated by Apache Canada Ltd.) removes the H2S and CO2 from the produced gases by amine absorption. These acid gases constitute an excellent miscible flooding agent for the field, thereby achieving the double advantage of increasing the oil recovery and providing storage capacity for these gases. Trivedi et al.(9) simulated different strategies for solvent injection to maximize oil recovery and gas storage as well as delaying breakthrough, and found that pressure maintenance is a key factor in the operation. A significant degree of acid gas breakthrough is expected to occur due to the reservoir heterogeneity represented by these Zama/Keg River pinnacles. Breakthrough will occur at H2S concentrations that are too high to process through the existing amine systems. To accommodate early breakthrough, recycle compression is to be installed in order to bypass the amine systems and re-inject acid gas back into miscible flooded pinnacles.

CT11 CARBON DIOXIDE FLOODING IN CARDIAC SURGERY: AN OLD TECHNIQUE REVISITED

Cerebral air embolism is a known complication of open‐heart surgery with devastating consequences. Neurologic injury after CPB can be divided into 2 types:Type I: Focal injury.Type II: Intellectual deterioration/neurocognitive impairment (up to 53% at the time of hospital discharge and 42% could be impaired for up to 5 years). Increasing evidence points to cerebral embolization as the principal culprit. Since the early days of modern cardiac surgery, surgeons have attempted to limits its damage by various means. One of the early techniques propounded was carbon dioxide insufflation of the pericardial cavity. Carbon dioxide, was uniquely positioned for this, being denser than air, more soluble than air, and easily managed perioperatively if the blood levels were to go up beyond physiological ranges. The technique gradually went into disuse, since there was no instrumentation, in the early days of CPB to measure and establish its impact on the actual outcomes. Secondly, the devices, through which CO2 was delivered, were not effective.There has been increasing enthusiasm for the technique but no consensus on the technical considerations or on the actual benefits of the practice.Our literature search showed that if practiced properly, carbon dioxide flooding does decrease the embolic counts significantly and that, by inference, could possibly improve the neurocognitive outcome. Since, there are no studies at this point in time, which show a direct beneficial correlation, we intend to do a prospective randomized controlled trial, to put things in proper perspective.

Effect of Oxygen on Minimum Miscibility Pressure in Carbon Dioxide Flooding

Laboratory studies of the effect of oxygen content in CO2 on the minimum miscibility pressure (MMP) are conducted on the n-C5H12/n-C16H34 model oil and Cottonwood Creek crude oil with three injection gases of different oxygen contents. The results indicate that the MMPs for these oils increase unfavorably with increasing O2 concentration in the CO2 stream. The experimental results are also supported by our modeling work using a multiple-mixing-cell model, which is found to capture the effects of compositions and temperature, and is found to be a robust and predictive method for determining the MMP. Our experiments and calculations indicate that the effect of O2 contamination on the MMP is larger for heavier oil and the effect of N2 impurity on the MMP is larger than that of O2 impurity.

Application of an expert system to optimize reservoir performance

The main challenge of oil displacement by an injected fluid, such as in Enhanced Oil Recovery (EOR) processes, is to reduce the cost and improve reservoir performance. An optimization methodology, combined with an economic model, is implemented into an expert system to optimize the net present value of full field development with an EOR process. The approach is automated and combines an economic package and existing numerical reservoir simulators to optimize the design of a selected EOR process using sensitivity analysis. The EOR expert system includes three stages of consultations: (1) select an appropriate EOR process on the basis of the reservoir characteristics, (2) prepare appropriate input data sets to design the selected EOR process using existing numerical simulators, and (3) apply the discounted-cash-flow methods to the optimization of the selected EOR process to find out under what conditions at current oil prices this EOR process might be profitable. The project profitability measures were used as the decision-making variables in an iterative approach to optimize the design of the EOR process. The economic analysis is based on the estimated recovery, residual oil in-place, oil price, and operating costs. Two case studies are presented for two reservoirs that have already been produced to their economic limits and are potential candidates for surfactant/polymer flooding, and carbon-dioxide flooding, respectively, or otherwise subject to abandonment. The effect of several design parameters on the project profitability of these EOR processes was investigated.

Bubbles and bypass: an update.

Bubbles in the bloodstream are not a normal condition--yet they remain a fact of cardiopulmonary bypass (CPB), having been extensively studied and documented since its inception some 50 years ago. While detectable levels of gaseous microemboli (GME) have decreased significantly in recent years and gross air embolism has been nearly eliminated due to increased awareness of etiologies and technological advances, methods of use of current perfusion systems continue to elicit concerns over how best to totally eliminate GME during open-heart procedures. A few studies have correlated adverse neurocognitive manifestations associated with excessive quantities of GME. Newer techniques currently in vogue, such as vacuum-assisted venous drainage, low-prime perfusion circuits, and carbon dioxide flooding of the operative field, have, in some instances, exacerbated the problem of gas embolism or engendered secondary complications in the safe conduct of CPB. Doppler monitoring (circuit or transcranial) primarily remains a research tool to detect GME emanating from the circuit or passing into the patients' cerebral vasculature. Newer developments not yet widely available, such as multiple-frequency harmonics, may finally provide a tool to distinguish particulate microemboli from GME and further delineate the clinical significance of GME.