Recent advances in switchable surfactants for heavy oil production:A review

Surfactants are extensively employed in the cold production of heavy oil.However,producing heavy oil emulsions using conventional surfactants poses a challenge to spontaneous demulsification,necessitating the addition of demulsifiers for oil-water separation.This inevitably increases the exploitation cost and environmental pollution risk.Switchable surfactants have garnered much attention due to their dual capabilities of underground heavy oil emulsification and surface demulsification.This study focuses on the fundamental working principles and classification of novel switchable surfactants for oil displacement developed in recent years.It offers a comprehensive overview of the latest advances in the applications of switchable surfactants in the fields of enhanced oil recovery(EOR),oil sand washing,and oil-water separation.Furthermore,it highlights the existing challenges and future development directions of switchable surfactants for heavy oil recovery.

Innovations and applications of the thermal recovery techniques for heavy oil

Heavy oil represents a vital petroleum resource worldwide.As one of the major producers,China is facing great challenges in effective and economic production of heavy oil due to reservoir complexity.Plenty of efforts have been made to promote innovative advances in thermal recovery modes,methods,and processes for heavy oil in the country.The thermal recovery mode has been shifted from simple steam injection to a more comprehensive“thermal+"strategy,such as a novel N2-steam hybrid process and CO_(2)-enhanced thermal recovery techniques.These advanced techniques break through the challenges of heavy oil extraction from less accessible reservoirs with thinner oil layers and greater burial depths.Regarding thermal recovery methods,China has developed the steam-assisted gravity drainage method integrating flooding and drainage(also referred to as the hybrid flooding-drainage SAGD technology)for highly heterogeneous ultra-heavy oil reservoirs and the fire flooding method for nearly depleted heavy oil reservoirs,substantially improving oil recovery.Furthermore,a range of processes have been developed for heavy oil production,including the open hole completion process using sand control screens for horizontal wells,the process of integrated injection-recovery with horizontal pump for horizontal wells,the steam dryness maintenance,measurement,and control process,efficient and environment-friendly circulating fluidized bed(CFB)boilers with high steam dryness,the recycling process of produced water,and the thermal recovery process for offshore heavy oil.Based on the advances in methodology,technology,and philosophy,a series of supporting technologies for heavy oil production have been developed,leading to the breakthrough of existing technical limit of heavy oil recovery and the expansion into new exploitation targets.For the future heavy oil production in China,it is necessary to embrace a green,low-carbon,and energy-efficient development strategy,and to expand heavy oil extraction in reservoirs with larger burial depth,more viscous oil,thinner oil layers,and lower permeability.Moreover,it is highly recommended to collaboratively maximize oil recovery and oil-to-steam ratio through technological innovations,and boost intelligentization of heavy oil production.

Study of steam heat transfer enhanced by CO_(2) and chemical agents: In heavy oil production

Steam flooding with the assistance of carbon dioxide (CO_(2)) and chemicals is an effective approach for enhancing super heavy oil recovery. However, the promotion and application of CO_(2) and chemical agent-assisted steam flooding technology have been restricted by the current lack of research on the synergistic effect of CO_(2) and chemical agents on enhanced steam flooding heat transfer. The novel experiments on CO_(2)–chemicals cooperate affected steam condensation and seepage were conducted by adding CO_(2) and two chemicals (sodium dodecyl sulfate (SDS) and the betaine temperature-salt resistant foaming agent ZK-05200).According to the experimental findings, a “film” formed on the heat-transfer medium surface following the co-injection of CO_(2) and the chemical to impede the steam heat transfer, reducing the heat transfer efficiency of steam, heat flux and condensation heat transfer coefficient. The steam seepage experiment revealed that the temperature at the back end of the sandpack model was dramatically raised by 3.5–12.8 °C by adding CO_(2) and chemical agents, achieving the goal of driving deep-formation heavy oil. The combined effect of CO_(2) and SDS was the most effective for improving steam heat transfer, the steam heat loss was reduced by 6.2%, the steam condensation cycle was prolonged by 1.3 times, the condensation heat transfer coefficient was decreased by 15.5%, and the heavy oil recovery was enhanced by 9.82%. Theoretical recommendations are offered in this study for improving the CO_(2)–chemical-assisted steam flooding technique.

Investigation of feasibility of alkali-cosolvent flooding in heavy oil reservoirs

Cold production is a challenge in the case of heavy oil because of its high viscosity and poor fluidity in reservoir conditions.Alkali-cosolvent-polymer flooding is a type of microemulsion flooding with low costs and possible potential for heavy oil reservoirs.However,the addition of polymer may cause problems with injection in the case of highly viscous oil.Hence,in this study the feasibility of alkali-cosolvent(AC)flooding in heavy oil reservoirs was investigated via several groups of experiments.The interfacial tension between various AC formulations and heavy crude oil was measured to select appropriate formulations.Phase behavior tests were performed to determine the most appropriate formulation and conditions for the generation of a microemulsion.Sandpack flooding experiments were carried out to investigate the displacement efficiency of the selected Ac formulation.The results showed that the interfacial tension between an AC formulation and heavy oil could be reduced to below 1o-3 mN/m but differed greatly between different types of cosolvent.A butanol random polyether series displayed good performance in reducing the water-oil interfacial tension,which made it possible to form a Type Il microemulsion in reservoir conditions.According to the results of the phase behavior tests,the optimal salinity for different formulations with four cosolvent concentrations(0.5 wt%,1 wt%,2 wt%,and 3 wt%)was 4000,8000,14000,and 20000 ppm,respectively.The results of rheological measurements showed that Type Ill microemulsion had a viscosity that was ten times that of water.The results of sandpack flooding experiments showed that,in comparison with waterflooding,the injection of a certain Ac formulation slug could reduce the injection pressure.The pressure gradient during waterflooding and AC flooding was around 870 and 30-57 kPa/m,respectively.With the addition of an AC slug,the displacement efficiency was 30%-50%higher than in the case of waterflooding.

Distribution and treatment of harmful gas from heavy oil production in the Liaohe Oilfield, Northeast China

The distribution and treatment of harmful gas （H2S） in the Liaohe Oilfield, Northeast China, were investigated in this study. It was found that abundant toxic gas （H2S） is generated in thermal recovery of heavy oil. The H2S gas is mainly formed during thermochemical sulfate reduction （TSR） occurring in oil reservoirs or the thermal decomposition of sulfocompounds （TDS） in crude oil. H2S generation is controlled by thermal recovery time, temperature and the injected chemical compounds. The quantity of SO4^2- in the injected compounds is the most influencing factor for the rate of TSR reaction. Therefore, for prevention of H2S formation, periodic and effective monitoring should be undertaken and adequate H2S absorbent should also be provided during thermal recovery of heavy oil. The result suggests that great efforts should be made to reduce the SO4^2- source in heavy oil recovery, so as to restrain H2S generation in reservoirs. In situ burning or desulfurizer adsorption are suggested to reduce H2S levels. Prediction and prevention of H2S are important in heavy oil production. This will minimize environmental and human health risks, as well as equipment corrosion.

Development Strategies for Achieving High Production with Fewer Wells in Conventional Offshore Heavy Oil Fields in Bohai Bay,China

Development strategy for heavy-oil reservoirs is one of the important research interests in China National Offshore Oil Corp. （CNOOC） that plans a highly effective development for heavy oil fields in multilayered fluvial reservoirs because of their significant influence on marine oil and even on China＇s petroleum production. The characteristics analysis of multilayered fluvial reservoirs in the heavy oil fields in Bohai Bay indicates that large amounts ofoil were trapped in the channel, point bar and channel bar sands. The reserves distribution of 8 oilfields illustrates that the reserves trapped in the main sands, which is 20%-40% of all of the sand bodies, account for 70%-90% of total reserves of the heavy oil fields. The cumulative production from high productivity wells （50% of the total wells） was 75%-90% of the production of the overall oilfield, while only 3%-10% of the total production was from the low productivity wells （30% of the total wells）. And the high productivity wells were drilled in the sands with high reserves abundance. Based on the above information the development strategy was proposed, which includes reserves production planning, selection of well configuration, productivity design, and development modification at different stages.

Quantitative Characterization and Dynamic Law of Interlayer Interference for Multilayer Commingled Production in Heavy Oil Reservoirs by Numerical Simulation

This paper moves one step forward to build?a?numerical model to research quantitative characterization and dynamic law for interlayer interference factor (IIF) in the multilayer reservoir which was heavy oil reservoirs and produced by directional wells. There are mainly four contributions of this paper to the existing body of literature. Firstly, an equivalent simulation method of the pseudo start pressure gradient (PSPG) is developed to quantitatively predict the value of?IIF?under different geological reservoir conditions. Secondly, the interlayer interference is extended in time, and the time period of the study extends from a water cut stage to the whole process from the oil well open to produce?a?high water cut. Thirdly, besides the conventional productivity interlayer interference factor (PIIF), a new parameter, that is, the oil recovery interlayer interference factor (RIIF) is put forward.?RIIF?can be used to evaluate the technical indexes of stratified development and multilayer co-production effectively. Fourthly,?the?effectsof various geological reservoir parameters such as reservoir permeability and crude oil viscosity, etc. on the?PIIF?and?RIIF’s?type curves?are?discussed in detail and the typical plate?is?plotted. The research results provide a foundation for the effective development of multilayer heavy oil reservoirs.

The Calculation of Heating Radius and Determination of Parameters in Heavy Oil Steam Stimulation

在稠油吞吐过程中,加热半径是热采中的重要指标,对注汽参数和生产制度起到了指导性作用。运用能量守恒原理,从热量注入方面考虑了蒸汽相变释放的气化潜热,从热量损失方面考虑井筒热量损失和顶底盖层热量损失,最终得到了新的加热半径计算公式。计算结果表明,加热半径受注汽参数、焖井时间、储层参数等因素影响,并系统阐述了岩层各物性参数的计算及选择方法。最后通过实例验证了该方法的计算值和试井解释出的值较为相符,为现场实际应用提供了可靠的方法。

Lag times in toe-to-heel air injection(THAI)operations explain underlying heavy oil production mechanisms

From a time value of revenue point of view,it is preferred that the time between reservoir stimulation and oil production response is small.Heavy oil combustion processes have a lag time between air injection and liquid production,but the common practice in production data analysis uses simultaneous injection and production data when seeking a relationship between them.In this research,the time scales of production for the Kerrobert toe-to-heel air injection(THAI)heavy oil project in Saskatchewan,Canada,is analyzed by using cross correlation analysis,i.e.time delay analysis between air injection and oil production.The results reveal two time scales with respect to production response with two distinctive recovery mechanisms:(1)a short time scale response(nearly instantaneous)where oil production peaks right after air injection(directly after opening production well)reflecting cold heavy oil production mechanisms,and(2)a longer time scale(of order of 100-300 days)response where peak production occurs associated with the collective phenomena of air injection,heat generating reactions,heat transfer,and finally,heated mobilized heavy oil drainage to the production well.This understanding of the two time scales and associated production mechanisms provides a basis for improving the performance of THAI.

Study on Productivity Model of Herringbone-Like Laterals Wells and Optimization of Morphological Parameters Considering Threshold Pressure Gradient in Heavy Oil Reservoirs

Compared with conventional well, herringbone-like laterals wells can increase the area of oil release, and can reduce the number of wellhead slots of platforms,?and?also can greatly improve the development efficiency. Based on threshold pressure gradient in heavy oil reservoir,?and?the applied principle of mirror reflection and superposition, the pressure distribution equation of herringbone-like laterals wells is obtained in heavy oil reservoir. Productivity model of herringbone-like laterals wells is proposed by reservoir-wellbore steady seepage. The example shows that the productivity model is great accuracy?to?predict the productivity of herringbone-like laterals wells. The model is used to analyze the branching length, branching angle, branching symmetry, branching position and spacing and their effects on productivity of herringbone-like laterals wells. The principle of optimizing the well shape of herringbone-like laterals wells is proposed.

Thermo-Hydrodynamics of Core-Annular Flow of Water, Heavy Oil and Air Using CFX

The transport of heavy and ultra-viscous oil employing the core-flow technique has been increasing recently, because it provides a greater reduction of the pressure drop during the flow. In this context, the effect of temperature and the presence of gas on the thermo-hydrodynamics of a three-phase water-heavy oil-air flow in a horizontal pipe under the influence of gravity and drag forces, using the commercial software ANSYS CFX?, have been evaluated. The standard κ ? ε turbulence model, the mixture model for heavy oil-water system and the particle model for heavy oil-gas and water-gas systems, were adopted. Results of velocity, volume fraction, pressure and temperature fields of the phases present along the pipe are presented and discussed. It has been found that the presence of the air phase and the variation in the temperature affect the behavior of annular flow and pressure drop.

Steam Flooding after Steam Soak in Heavy Oil Reservoirs through Extended-reach Horizontal Wells

This paper presents a new development scheme of simultaneous injection and production in a single horizontal well drilled for developing small block reservoirs or offshore reservoirs. It is possible to set special packers within the long completion horizontal interval to establish an injection zone and a production zone. This method can also be used in steam flooding after steam soak through a horizontal well. Simulation results showed that it was desirable to start steam flooding after six steam soaking cycles and at this time the oil/steam ratio was 0.25 and oil recovery efficiency was 23.48%. Steam flooding performance was affected by separation interval and steam injection rate. Reservoir numerical simulation indicated that maximum oil recovery would be achieved at a separation section of 40-50 m at steam injection rate of 100-180 t/d; and the larger the steam injection rate, the greater the water cut and pressure difference between injection zone and production zone. A steam injection rate of 120 t/d was suitable for steam flooding under practical injection-production conditions. All the results could be useful for the guidance of steam flooding projects.

Considering temperature dependence of thermo-physical properties of sandy soils in two scenarios of oil pollution

We analyzed the heat conductivity and volumetric heat capacity of sandy soil contaminated in two scenarios of oil pollution, and also determined the temperature dependencies of these changed thermophysical properties. In the first pollution scenario, the oil product was introduced into wet river sand, and in the second case, dry sand was contaminated by the oil product and was then moistened with water. By considering these two scenarios as multicomponent dispersion systems with varying degrees of contamination and humidity, and by using a polystructural granular model with pore spaces and closed inclusions, we calculated that the heat conductivity of the sandy soil increased under the first pollution scenario and decreased under the second, but the change in the volumetric heat capacity of the sandy soil was proportional only to the amount of oil pollution, not the manner in which it was introduced. We also determined the temperature dependencies of these two thermophysical properties of sandy soil when polluted by oil, of which information will be useful for future containment and remediation of oil-contaminated soil.

Heat Dissipation Modeling of <i>In-Situ</i>Conversion Process of Oil Shale

In-situ conversion of process of oil shale has been technically proven as a pilot field project. Gradually heating the reservoir by using subsurface electric heaters converts the oil shale reservoir kerogen into oil, gas and other producible components. This process also enhances the internal energy of the porous media as well as the subsurface fluid. Heat is transmitted in the reservoir within each fluid by different processes i.e. , due to the flow of fluid called advective process, and due to molecular diffusion where dispersive and diffusive processes take place. Heat transfer through conduction and convection mechanisms in the porous media are modeled mathematically and numerically incorporating the advective, dispersive and diffusive processes in the reservoir. The results show the production of oil and gas as a result of conversion of kerogen due to modeled heat dissipation.

Calculation of the contribution of single-zone production by ultraviolet spectrum technique:A case study in well QHD32-6-3 field

Based on the established mathematic model and graphic interpretation, a new method, which is used to calculate the contribution of single-zone production in a commingled producing well by the ultraviolet spectrum technique, has been established. The standard plate was drawn using the extinction coefficient E of sample oils formulated artificially as y-axis and the wavelength as x-axis. The curve resulting from the UV analysis of sample oils in the commingled well was inserted into the standard plate and compared. The proportion of each single zone in the commingled producing well was identical with the proportion of the curve which is closest to the curve of sample oils formulated artificially. In the well QHD32-6-3 field, taking well A22 for example and using this method, the production contribution of a single zone was calculated. The result showed that the Nm4 zone is a major "contributor", the proportion of the Nm4 zone is 70%, and that of the Nm1 zone is 30%. The ultraviolet spectrum technique provided a new reservoir geochemical technique of monitoring production contribution, especially for biodegraded heavy oil, but it has some limitation, just depending on the GC fingerprint technique.

Heavy Oil Reservoir Seismic Characteristics during Thermal Production:A Case Study

Most production methods of heavy oil involve thermal production.However,it is challenging to delineate the thermal-affected zone due to complex reservoir conditions.With steam injected,the heavy oil viscosity drops;the reservoir density and velocity decrease accordingly,causing changes to seismic impedance.Moreover,the oil-and-water viscosity ratio and permeability show the difference with changing temperature,indicating that the reservoir’s ability to transmit seismic waves would also be temperature-dependent.Therefore,the seismic responses and attenuation characteristics of the steam chamber can be helpful to monitor the steam-affected zone.We introduce an improved viscoelastic model to approximate the heavy oil reservoir during thermal production,and use the frequency-space domain finite difference algorithm to simulate the seismic wave-fields.Numerical results demonstrate that this model is applicable to a wide temperature range,and can effectively reveal the seismic characteristics of the steam chamber.Through analyzing the propagation differences of seismic waves under different temperatures,it is concluded that the attenuation coefficient,root-meansquare amplitude difference and amplitude ratio of PP-wave and PS-wave under different conditions can reveal the temperature variation in the steam chamber,with which it is possible to detect the steam chamber spatial distribution.

稠油开采中多元热复合流体相态的研究进展

稠油的储量远超常规石油的储量,但因稠油黏度大和密度大的特点而难以开采,高效经济开发稠油已成为石油领域的研究重点。热复合开采技术是目前高效开发稠油油藏的关键技术,其中多元热复合流体的相态特征是稠油油藏开采流程设计与评价的关键。为此,从热复合开采技术中的混合气体系和稠油-气体系2个方面,系统地阐述了多元热复合流体相态的实验和理论研究现状。对于混合气体系相态,多采用静态法进行实验测试,使用状态方程结合混合规则进行理论预测,CO_(2),N_(2),H_(2)O和CH_(4)等常见气体分子组成的二元体系的相态测试趋于成熟,但缺少多元体系的测试数据与预测模型;对于稠油-气体系相态,总结了一般性实验流程与近年实验结果,提出一种加速油气相平衡的新型实验装置构想,指出目前理论预测在气体种类、注气量、气体扩散模型、二元相互作用系数等方面的不足。进而对多元热复合流体相态研究提出展望,以期促进热复合开采技术进一步的机理研究与参数优化。

超稠油老区氮气辅助VHSD开发数值模拟

转直井辅助水平井重力泄油(VHSD)开发方式已成为超稠油老区进一步提高区块采油速度、油藏采收率的重要调整手段。氮气辅助VHSD的增能提压、顶部隔热效应可有效解决超稠油老区吞吐后压力保持程度低、驱泄操作压力低、蒸汽腔温度低的问题,进而实现节约蒸汽用量、提高产油水平、提升油汽比和减耗降碳的目的。以克拉玛依油田九区某VHSD开发单元为例,采用数值模拟方法分析了在氮气辅助VHSD开发过程中注氮时机、注氮方式、注氮量等参数对提压增能、建立隔热层的影响,以及采出速度和累计注采的变化特点。研究表明,转驱泄初期采用段塞方式注入氮气可有效建立隔热层;矿场试验表明,井组油汽比提升0.025,日产油提升0.7 t,取得了较好的应用效果。研究成果为同类型超稠油老区氮气辅助VHSD效益开发提供了技术借鉴。

胜利油田稠油油藏开发技术进展

针对胜利油田不同类型稠油油藏的地质特点及开发矛盾,形成了一套较为完善的稠油油藏开发技术系列,并取得了显著的开发效果。从各项技术的理论基础和矿场应用2个方面,总结了不同类型稠油油藏开发技术进展。对于高轮次吞吐后的稠油油藏,基于非达西渗流理论,形成了井网加密技术;对于敏感性稠油油藏,形成了近热远防理论,降低了水敏对开发的不利影响;对于特超稠油油藏,通过HDCS技术的协同降黏、膨胀增能作用,解决了“注不进、采不出”的开发难题;对于低效水驱稠油油藏,通过转蒸汽驱,达到加密角井流线、水井流线逆向的目的,从而提高该类油藏的采收率;对于深层稠油油藏,以气热协同保热强热、热剂协同接替助驱、气剂协同均衡热前缘的协同增效作用机理认识为基础,形成了多元热复合驱油理论,实现了深层稠油的有效动用;对于薄层稠油油藏,通过热+水平井复合开发模式,提高了油藏的吸汽能力和动用范围;对于浅薄层超稠油油藏,通过HDNS技术增能降黏扩波及,实现了该类油藏的高效开发。胜利油田稠油油藏开发技术系列的应用,为胜利油田稠油效益开发、绿色开发提供了技术支撑。