Investigation of Inert Gas Injection Through Horizontal Wells

Abstract

Downward displacement of oil by inert gas injection in oil reservoirs results in very high oil recovery efficiencies. Advances made in horizontal drilling technology and increased understanding of the mechanisms and conditions that maximize recovery efficiencies can make the inert gas injection process feasible for a wide variety of oil reservoirs. In this study, laboratory investigation was conducted for the recovery of heavy oil from a 3-D physical model packed with 26°API gravity oil, brine and crushed limestone. A total of 7 runs were conducted using the 3-D physical model with 30 × 30 × 6 cm³ dimensions. Two groups of well configurations were mainly used: (1) horizontal injection and point production wells and (2) horizontal injection and horizontal production wells. In continuous N₂ injection, highest recovery was obtained by horizontal injection-horizontal production well configuration.     

Immiscible CO2 Flooding through Horizontal Wells

Abstract

The CO₂ immiscible process is a potentially viable method of enhanced oil recovery (EOR) for heavy oil reservoirs. In an immiscible CO₂ process, part of the injected CO₂ is absorbed into the reservoir fluids and part forms a free-gas phase in the reservoir. Three groups of well configurations were mainly used: (1) vertical injection and vertical production wells, (2) vertical injection and horizontal production wells, and (3) horizontal injection and horizontal production wells. In immiscible CO₂ injection, highest recovery was obtained by vertical injection-horizontal production (VI-HP), followed by vertical injection-vertical production (VI-VP), and the least by horizontal injection-horizontal production (HI-HP). In VI-HP well configuration, the best recovery was obtained as 15.1% OOIP. In continuous CO₂ injection experiments, oil recovery for the VI-HP well configuration was higher than that of the other well configurations. The lowest ultimate recovery was obtained from HI-HP well configuration. The distance between the horizontal injector and horizontal producer was another important factor for the displacement of oil. In all runs, CO₂ breakthrough occurred very early, showing the dominance of viscous forces and relatively small effect of mass transfer between CO₂ and oil. The total oil recovery varied considerably because of the differences in injection rates and because of the unstable displacement. As a whole, oil recovery increased with an increase in the injection rate of CO₂. The cumulative gas-oil ratio (GOR) appeared to be sensitive to the gas injection rate for all well configurations. An increase in oil recovery with injection rate during initial stages of the runs was affected by the cumulative GOR.     

Case study: Comparison of enhanced heavy-oil recovery by CGI,WAG, and GAGD

Continuous gas injection (CGI) in the conventional horizontal flooding patterns leads to severe gravity segregation and poor reservoir contact (sweep) volumes. To improve the sweep efficiency, the Water-Alternating-Gas (WAG) process has been widely practiced in the industry. However, the WAG process has not measured up to expectations, as evidenced by the low recoveries observed in several field cases.

The Gas-Assisted Gravity Drainage (GAGD) process is designed and practiced based on gravity drainage idea and uses the advantage of density difference between injected gas and reservoir oil to overcome the drawbacks of the WAG process.

In this study, a comparison of enhanced heavy-oil recovery by three methods (CGI, WAG, and GAGD) is conducted by a commercial numerical simulator in a sector model of an Iranian offshore field. For this purpose, different production scenarios are designed. Moreover, the effect of several parameters such as injection fluid (CO₂, hydrocarbon gas), in situ oil viscosity (heavy or extremely heavy oil), rate and volume of injection, and also three different WAG ratios are studied.

The results show that the GAGD method is not suitable for this field as the thickness of pay zone is low for vertical sweep efficiency and causes early breakthrough of injected gas. Also, CGI leads to lower recoveries compared to the WAG process, due to its unfavorable mobility ratio. Injection of CO₂ instead of hydrocarbon gas results in higher sweep efficiency because of its viscosity reduction and swelling effects. In case of extremely heavy-oil recovery, with decreasing well spacing, the oil recovery factor increases as the drainage radius of wells reduces substantially due to high-viscosity oil.     

The effect of capillary-trapped CO2 on oil recovery and CO2 sequestration during the WAG process

This study investigated capillary-trapped CO₂ depending on the consideration of hysteresis effect in relative permeability for various water-alternation-gas (WAG) operating conditions to ascertain the oil production process. From the simulation results of CO₂ WAG flooding method, the trapped CO₂ led to prevent water-flow, in which CO₂ acts as a gas blocker near the well. It caused the injection pressure increase during water injection period. As the trapped CO₂ in pores increased, the reservoir pressure was also increased and maintained above minimum miscibility pressure (MMP). Ultimately, it was concluded that the reservoir was kept under miscible conditions throughout WAG process, reducing residual oil and increasing oil recovery.     

Natural gas vehicles: An option for Europe

In Europe natural gas vehicles play a minor role. A decisive reason for this is the dependence of most European countries from gas imports. Except for Italy, there is no tradition to use natural gas as fuel. In addition, there is a lack of infrastructure (e.g. fuelling stations). In contrast to Europe, in Latin American and Asian countries natural gas vehicles are widespread. Some countries foster natural gas vehicles because they have own gas resources. Many countries must reduce the high air pollution in big cities. Environmental reasons are the main motive for the use of natural gas vehicles in Europe. In last years, high oil prices stimulated the use of natural gas as fuel. European governments have developed incentives (e.g. tax reductions) to foster natural gas vehicles. However, the focus is on hybrid technology and the electric car, which, however, need further technical improvement. In contrast, the use of natural gas in conventional engines is technically mature. Additional gas imports can be avoided by further improvements of energy efficiency and the use of renewable energy. In sum, the market penetration of natural gas as fuel should be promoted in Europe.     

An innovative indicator of carbon dioxide emissions for developing countries: A study of Taiwan

Ever since the Kyoto Protocol entered into force, the issues of climate change and greenhouse gas (GHG) emissions have drawn more and more attention globally. However, the major concern of the Kyoto Protocol to reduce the overall GHG emissions might be inaccessible for most developing countries, which rely heavily on the energy-intensive industries for exports and economic growth. In this study, an innovative indicator of net carbon dioxide (CO₂) emissions, which excludes the emissions corresponding to the exports, is proposed to explicitly reveal domestic situations of developing countries. By introducing the indicator of net CO₂ emissions to top five energy-intensive industries in Taiwan, the analysis indicates that the increase in CO₂ emissions from 1999 to 2004 is mostly contributed by the expanded exports rather than the domestic demand. The distinct growth patterns of the apparent and net CO₂ emissions also imply the transformation of the industrial sector. It is expected that, for developing countries, the concept of net emissions may not only serve as a proper interim target during the process of international negotiations over GHG reductions but also highlights the prominence of addressing the emissions from the industrial sector as the top priority.     

水平井双管注汽配合分段完井技术研究与应用

随着水平井技术开发超稠油油藏实施规模的不断扩大,水平井水平段动用不均的矛盾逐渐加剧。分析认为,水平井完井工艺和注汽管柱工艺不完善,是造成水平段注汽不均、从而导致动用不均的两个主要原因。根据水平井水平段储层沿程物性差异分布特点,在水平井完井时采用分段完井技术,在水平段中间物性差井段下入封隔器,将水平段筛管外与油层裸眼之间分隔成两段独立的井段腔室,并在紧挨封隔器位置下入扶正器,保证筛管在裸眼井段居中下入。注蒸汽时,依据井温监测资料判断水平段动用状况,实施双管注汽工艺技术,采用内、外管双注汽管柱注汽方式,分别对水平井水平段跟端和指端部位同时注汽,井口配套工具采用双四通、双悬挂器,同时应用等干度分配器,实现双管柱内的蒸汽流量灵活控制及等干度分配,实现水平段前后井段同时均匀注汽,调整水平段动用程度。     

水平井实钻轨迹监控的算法研究及应用

在水平井的实际钻进的过程中,需要对实钻井眼轨迹进行实时监控,而实时监控的主要技术指标——实钻轨迹与设计轨迹的距离,即法面距离的计算过程比较复杂,形式也比较繁琐。为解决这一问题,利用空间圆弧模型的矢量描述技术,重新推导出了法面距离计算所需求解的方程,以及横向偏差和纵向偏差的新公式。以某水平井为实际算例进行了验证。采用新公式计算该水平井的法面距离,待钻井眼轨迹能够中靶,并且进入靶体之后一直保持在靶体轴线附近。结果表明,空间圆弧矢量描述技术在有关的数学公式推导中非常简洁,并且具有很直观的几何意义,能够简化理论公式推导过程,不易产生错误。新公式可用于钻井专用计算机软件的开发,不仅可以减少编程工作量,而且有利于代码维护,具有推广价值。     

The environmental impact and risk assessment of CO2 capture, transport and storage - An evaluation of the knowledge base

In this study, we identify and characterize known and new environmental consequences associated with CO₂ capture from power plants, transport by pipeline and storage in geological formations. We have reviewed (analogous) environmental impact assessment procedures and scientific literature on carbon capture and storage (CCS) options. Analogues include the construction of new power plants, transport of natural gas by pipelines, underground natural gas storage (UGS), natural gas production and enhanced oil recovery (EOR) projects. It is investigated whether crucial knowledge on environmental impacts is lacking that may postpone the implementation of CCS projects. This review shows that the capture of CO₂ from power plants results in a change in the environmental profile of the power plant. This change encompasses both increase and reduction of key atmospheric emissions, being: NO_x, SO₂, NH₃, particulate matter, Hg, HF and HCl. The largest trade-offs are found for the emission of NO_x and NH₃ when equipping power plants with post-combustion capture. Synergy is expected for SO₂ emissions, which are low for all power plants with CO₂ capture. An increase in water consumption ranging between 32% and 93% and an increase in waste and by-product creation with tens of kilotonnes annually is expected for a large-scale power plant (1 GW_e), but exact flows and composition are uncertain. The cross-media effects of CO₂ capture are found to be uncertain and to a large extent not quantified. For the assessment of the safety of CO₂ transport by pipeline at high pressure an important knowledge gap is the absence of validated release and dispersion models for CO₂ releases. We also highlight factors that result in some (not major) uncertainties when estimating the failure rates for CO₂ pipelines. Furthermore, uniform CO₂ exposure thresholds, detailed dose-response models and specific CO₂ pipeline regulation are absent. Most gaps in environmental information regarding the CCS chain are identified and characterized for the risk assessment of the underground, non-engineered, part of the storage activity. This uncertainty is considered to be larger for aquifers than for hydrocarbon reservoirs. Failure rates are found to be heavily based on expert opinions and the dose-response models for ecosystems or target species are not yet developed. Integration and validation of various sub-models describing fate and transport of CO₂ in various compartments of the geosphere is at an infant stage. In conclusion, it is not possible to execute a quantitative risk assessment for the non-engineered part of the storage activity with high confidence.     

Experimental and theoretical study of asphaltene deposition and permeability impairment in low-permeability carbonate cores

Asphaltene deposition is one of the problems that oil industries face during oil production, processing, transport, and refining. Deposition of asphaltene flocculation on reservoir rock can plug pore spaces and cause permeability impairment. Carbonate rock, which has low permeability, tend to adsorb asphaltene causing more loss of permeability. In this study, three miscible CO₂ injection core tests were conducted at reservoir conditions and the effects of asphaltene content on the amount of formation damage in carbonate cores with low permeability were investigated. High asphaltene content oil has been used in the experiments. Results show that permeability reduction was more than porosity losses. An empirical model for permeability impairment was derived based on experimental data by considering the activation of the two mechanisms simultaneously. The results may be useful for understanding permeability impairment mechanisms during gas injection in low-permeability carbonate cores.     

Wind-hydrogen utilization for methanol production: An economy assessment in Iran

This study investigates the feasibility to synthesis methanol from its flue gas and wind hydrogen. The concept is to mitigate CO₂ emission through flue gas recovery. Synthesizing methanol, on the other hand requires hydrogen at the rate of 3 kmol/kmol of carbon dioxide. Electrolysis is one method by which hydrogen can be produced cleanly from renewable source. Here it is assumed that the electrolysis unit is fed with the electricity from neighbor wind farms. Oxygen will be produced as a byproduct in electrolysis unit. However, electrolytic oxygen could be utilized for partial oxidation of methane in autothermal reactor (ATR). Onboard water electrolysis facilitates the oxygen and hydrogen storage, delivery and marketing. This study focuses on an integrated system of methanol production which enables green methanol synthesis through a system with zero carbon emission. Green methanol synthesis is comprised of CO₂ capturing and recycling along with renewable hydrogen generation. The produced hydrogen and CO₂ will be directed to methanol synthesis unit. By employing the integrated system for methanol synthesis, we could reduce the cost of using renewable energy technology.     

An application of thickener to increase viscosity of liquid CO2 and the assessment of the reservoir geological damage and CO2 utilization

In comparison to hydraulic fracturing, CO₂ fracturing technology is more efficient and effective in solving environmental problems caused by the fracturing process. However, the low viscosity caused by pure CO₂ under high pressure hinders the development of the entire fracturing technology. Given that, a siloxane that can significantly improve the liquid CO₂ viscosity is prepared and the excellent performance to thicken CO₂ by silicone polymer is shown. Polymerization that occurs under water conditions presents a trend and is more likely to trigger reaction than ring-opening polymerization under anhydrous conditions. The thickening performance test is conducted by capillary viscometer self-designed at 35°C and 10 MPa. Moreover, a rising trend in viscosity is demonstrated with increase in thickener concentration. Smaller damages and chemical residue exists in the stratum after CO₂ fracturing. In addition, there are no changes that occur in the quality of crude oil. A fine conclusion for thickening performance provides a basis for the synthesis of the polymer to thicken CO₂.     

An evaluation of hydrogen production from the perspective of using blast furnace gas and coke oven gas as feedstocks

Blast furnace (BF) is a large-scale reactor for producing hot metal where coke and coal are consumed as reducing agent and fuel, respectively. As a result, a large amount of CO₂ is liberated into the atmosphere. The blast furnace gas (BFG) and coke oven gas (COG) from the ironmaking process can be used for H₂ production in association with carbon capture and storage (CCS), thereby reducing CO₂ emissions. In this study thermodynamic analyses are performed to evaluate the feasibility of H₂ production from BFG and COG. Through the water gas shift reaction (WGSR) of BFG, almost all CO contained in BFG can be converted for H₂ production if the steam/CO (S/C) ratio is no less than unity and the temperature is at 200 °C, regardless of whether CO₂ is captured or not. The maximum H₂ production from WGSR is around 0.21 Nm³ (Nm³ BFG)⁻¹. Regarding H₂ production from COG, a two-stage reaction of partial oxidation (POX) followed by WGSR is carried out. It is found the proper conditions for syngas formation from the POX of COG is at the oxygen/fuel (O/F) ratio of 0.5 and the temperature range of 1000-1750 °C where the maximum syngas yield is 2.83 mol (mol hydrocarbons)⁻¹. When WGSR is subsequently applied, the maximum H₂ production from the two-stage reaction can reach 0.83 Nm³ (Nm³ COG)⁻¹.     

Prediction of asphaltene deposition parameters in porous media using experimental data during miscible gas injection

The study of asphaltene deposition under actual field conditions is impossible. Therefore, many models have been derived based on experimental data. All models have some matching parameters, which are estimated along with numerical solving or simulation to match experimental and simulation data, so it is possible that these were estimated as required (tuning factor).

In this study, two miscible CO₂ injection dynamic tests in porous media were performed. In these tests, CO₂ and live oil were injected into the core simultaneously. The CO₂ concentration was more than the onset concentration for asphaltene precipitation.

The main objective of this work was to determine the deposition coefficients from the experimental data, so these were predicted by using basic equations using the material balance. Also, by mathematical methods, the relation between these parameters was determined.

Results from this work imply that the deposition parameters can be estimated from the experimental data and these parameters are not constant during modeling and simulation.     

水平气井靶点高差对排液的影响

随着川西低渗透致密气藏不断加大水平井开发力度,水平井气井逐渐增多,水平井井筒积液成为气藏水平井开发普遍存在的难题.如果井筒内产生积液,井底回压增大,井口压力下降,产量递减较快,气井携液能力减弱,将导致井筒附近储层的含水饱和度升高,气相渗透率下降,气井难以开采,甚至最终水淹停产.应用水平井筒内流体由分层流向非分层流转变判别式,对影响水平段井筒携液的因素进行分析表明:水平段井筒倾角越大、积液高度越高,水平井筒中气液两相流型更易从层流转向非层流,水平段中的液体也就更易被气流带出.虽然井筒倾角对气体临界流速的影响较小,但井筒倾角越大,井筒内A靶点附近的积液高度越高,液体就更易被气流携带出水平段.通过实例分析也证明,水平井A、B靶点高差对气井排液有影响,B靶点比A靶点越高,越有利于井底积液从水平段排出.     

Can EV (electric vehicles) address Ireland’s CO2 emissions from transport?

In the period 1990–2007, CO₂ emissions from Ireland’s Transport sector increased by 181%. It has been proposed that a transition to EV (electrically-powered vehicles) – either BEV (battery-powered) or PHEV (plug-in hybrids) – offers the potential for significant reductions in these emissions. However, the benefits of PHEV – and of plug-in vehicles generally – accrue because some fraction of the fossil fuel normally consumed by the vehicle is displaced by electricity extracted from the national grid. The net benefit therefore depends on many factors, including the characteristics of the electricity generation and distribution system, and the proportion of vkm (vehicle-kilometres) completed under electric power.     

Stockholm CHP potential—An opportunity for CO2 reductions?

The potential for combined heat and power (CHP) generation in Stockholm is large and a total heat demand of about 10 TWh/year can be met in a renewed large district heating system. This model of the Stockholm district heating system shows that CHP generation can increase from 8% in 2004 to 15.5% of the total electricity generation in Sweden. Increased electricity costs in recent years have awakened an interest to invest in new electricity generation. Since renewable alternatives are favoured by green certificates, bio-fuelled CHP is most profitable at low electricity prices. Since heat demand in the district heating network sets the limit for possible electricity generation, a CHP alternative with a high electricity to heat ratio will be more profitable at when electricity prices are high. The efficient energy use in CHP has the potential to contribute to reductions in carbon dioxide emissions in Europe, when they are required and the European electricity market is working perfectly. The potential in Stockholm exceeds Sweden's undertakings under the Kyoto protocol and national reduction goals.     

Using LMDI method to analyze the change of China's industrial CO2 emissions from final fuel use: An empirical analysis

Based on time series decomposition of the Log-Mean Divisia Index (LMDI), this paper analyzes the change of industrial carbon emissions from 36 industrial sectors in China over the period 1998–2005. The changes of industrial CO₂ emission are decomposed into carbon emissions coefficients of heat and electricity, energy intensity, industrial structural shift, industrial activity and final fuel shift. Our results clearly show that raw chemical materials and chemical products, nonmetal mineral products and smelting and pressing of ferrous metals account for 59.31% of total increased industrial CO₂ emissions. The overwhelming contributors to the change of China's industrial sectors’ carbon emissions in the period 1998–2005 were the industrial activity and energy intensity; the impact of emission coefficients of heat and electricity, fuel shift and structural shift was relatively small. Over the year 1998–2002, the energy intensity change in some energy-intensive sectors decreased industrial emissions, but increased emissions over the period 2002–2005. The impact of structural shift on emissions have varied considerably over the years without showing any clear trend, and the final fuel shift increased industrial emissions because of the increase of electricity share and higher emissions coefficient. Therefore, raw chemical materials and chemical products, nonmetal mineral products and smelting and pressing of ferrous metals should be among the top priorities for enhancing energy efficiency and driving their energy intensity close to the international advanced level. To some degree, we should reduce the products waste of these sectors, mitigate the growth of demand for their products through avoiding the excessive investment highly related to these sectors, increasing imports or decreasing the export in order to avoid expanding their share in total industrial value added. However, all these should integrate economic growth to harmonize industrial development and CO₂ emission reduction.     

Decomposing international polarization of per capita CO2 emissions

The aim of this paper is to analyze the international polarization of per capita CO₂ emissions with exogenous groups based on the Z–K measure (Zhang and Kanbur, 2001), whose main differential advantage lies on its factor-decomposability. In particular, we propose to use the factor decomposition based on Kaya (1989) by applying the methodology suggested by Duro and Padilla (2006). The main empirical results derived can be summarized as follows. First, the international polarization of emissions has significantly decreased over time during the period 1971–2006, when regional sets of nations based on the IEA structure are used; secondly, this decrease can be almost exclusively based on the reduction of the average dissimilarities among sets of countries and not due to a within-group cohesion process. Lastly, this reduction can be mainly attributed to the role of the affluence factor, and to a lesser extent, to the energy intensities. Thus, and given the values achieved for the different components, it seems that further reductions in the international polarization will continue be based on the economic convergence among groups.     

The promoting effect of La, Mg, Co and Zn on the activity and stability of Ni/SiO2 catalyst for CO2 reforming of methane

CO₂ reforming of methane into synthesis gas over Ni/SiO₂ catalysts promoted by La, Mg, Co and Zn was investigated. The catalysts were prepared by impregnation method and characterized by XRD, TPR, SEM and TG-DTA techniques. Ni-La/SiO₂ catalyst was found to exhibit high activity and excellent stability with the addition of suitable amount of La promoter, which increased the dispersion of NiO and the interaction between NiO and SiO₂. Two different types of carbon species, namely, easily oxidized carbonaceous species and inert carbon, were observed on the surface of the used catalysts. The inert carbon deposited on Ni-Mg/SiO₂ catalyst may be the main reason for its deactivation, while the principal reason for the deactivation of Ni-Co/SiO₂ catalyst might be the sintering of metallic Ni. The addition of La and Mg decreased the contribution of reverse water-gas shift reaction, leading to higher H₂ yield.