State Key Laboratory of Enhanced Oil Recovery

Multi-scale (nano-to-micro) three-dimensional CT imaging was used to characterize the distribution and texture of micro-scale pore throats in tight sandstone reservoirs of the Triassic Yanchang Formation, Ordos Basin. First, the low-resolution Micro-CT was used to reflect the micro-pore texture of the core column with a diameter of 2.54 cm. Then, some samples with a diameter of 65 μm was derived from different areas according the different characteristics of micro-pore texture of the core scanned by low-resolution Micro-CT and scanned by high-resolution Nano-CT. Thus, a three-dimensional texture model of nano-scale micro-pores was reestablished and the permebility and porosity data of the sample could be obtained. On a micrometer scale, the size of the micro-pores varies, and their diameters range from 5.4 to 26.0 μm. The micro-pores are isolated, locally in the shape of a band. On a nanometer scale, the quantity of nanoscale micropores increases, the diameter of which ranges from 0.4 to 1.5 μm. The pore throats are arranged in the shape of tube and ball inside or on the surface of mineral particles(crystals). The ball-shaped micropores in nanoscale, often isolated in the three-dimensional space, show the poor connectivity and consequently act as the reservoir space. By contrast, the tube-shaped micropores in nanoscale show certain connectivity with micro-scale tube-shaped micropores and adjacent isolated ball-shaped micropores in nanoscale. Therefore, these tube-shaped micropores in nanoscale serve as throats and pores. Based on the calcution, the permeability of the samples is 0.843×10−3 μm2 and porosity is 10%.

Carbon dioxide capture, EOR-utilization and storage (CCUS-EOR) are the most practical and feasible large-scale carbon reduction technologies, and also the key technologies to greatly improve the recovery of low-permeability oil fields. This paper sorts out the main course of CCUS-EOR technological development abroad and its industrialization progress. The progress of CCUS-EOR technological research and field tests in China are summarized, the development status, problems and challenges of the entire industry chain of CO2 capture, transportation, oil displacement, and storage are analyzed. The results show a huge potential of the large-scale application of CCUS-EOR in China in terms of carbon emission reduction and oil production increase. At present, CCUS-EOR in China is in a critical stage of development, from field pilot tests to industrialization. Aiming at the feature of continental sedimentary oil and gas reservoirs in China, and giving full play to the advantages of the abundant reserves for CO2 flooding, huge underground storage space, surface infrastructure, and wide distribution of wellbore injection channels, by cooperating with carbon emission enterprises, critical technological research and demonstration project construction should be accelerated, including the capture of low-concentration CO2 at low-cost and on large-scale, supercritical CO2 long-distance transportation, greatly enhancing oil recovery and storage rate, and CO2 large-scale and safe storage. CCUS-EOR theoretical and technical standard system should be constructed for the whole industrial chain to support and promote the industrial scale application, leading the rapid and profitable development of CCUS-EOR emerging industrial chain with innovation.

As technologies advance in oilfield development, mature oilfields are able to keep sustainable production and complex oilfields difficult to produce in the past are put into production efficiently. In this work, new progresses of main development technologies for medium-high permeability and high water cut, low permeability, heavy oil, complex faulted block and special lithology reservoirs in the past decade, especially those international achievements made in enhanced oil recovery, were summarized, the key problems and major challenges that different oilfields are facing were analyzed, and the development route and direction of three-generation technologies were proposed as “mature technology in industrialized application, key technology in pilot test and innovative technology for backup”. The key research contents should focus on: (1) Fine water flooding and chemical flooding for mature oilfields, improving oil recovery after chemical flooding, and gas flooding for low permeability reservoirs must be researched and tested in field further. (2) Study on subversive technologies like nanometer smart flooding, in-situ upgrading and injection and production through the same well should be strengthened. (3) EOR technologies for low oil price, new fields (deep sea, deep layer, unconventional reservoirs etc.) and highly difficult conditions (the quaternary recovery after chemical flooding, tertiary recovery in ultra-low permeability reservoirs) should be stocked up in advance. The development cost must be lowered significantly through constant innovation in technology and reservoir management to realize sustainable development of oilfields.

The application and characteristics of CO2 flooding in the USA were analyzed and summarized. Supporting techniques of CO2 flooding were generalized, and then the enlightenment was expounded for CO2 flooding in China. The development process and forming reasons of CO2 flooding technology were analyzed and summarized based on systematic tracking of EOR survey data all over the world and sufficient investigation of CO2-EOR technology application. With the number of CO2 flooding projects, scale and annual production as indicators, the current situation of American CO2-EOR technology was evaluated. The characteristics of the projects and development-driving force of CO2 flooding in America were also summed up. The characteristics of formation properties, crude oil properties and project timings of American CO2 miscible flooding projects were outlined emphatically. Meanwhile, the application scale and reservoir adaptability differences between American CO2 miscible and immiscible flooding were comparatively analyzed. A series of supporting techniques were illuminated with the SACROC CO2 flooding project as an example. The challenges, technical bottlenecks and suggestions were analyzed and proposed for the promotion of CO2 miscible flooding technology in China.

Great progress and success have been achieved in the fundamental study and field test of chemical combination flooding in recent years. In China, a low concentration ASP formula is employed to achieve ultra-low interfacial tension by the synergistic effect of alkali and surfactant. The viscosity of polymer solution prepared from produced water can meet the technological requirement when salt tolerance polymer is applied. ASP or SP flooding can increase both oil displacement efficiency and sweep volume. ASP pilot tests and industrial field tests in Daqing Oilfield have resulted in an oil recovery increase of 18.5%-26.5%. The chemical combination flooding has entered into the industrial promotion and application stage, with a series of supporting techniques formed in the field tests. The main challenges in this technique include short pump-checking period and difficulty in produced liquid handling and high cost. Micelle-polymer flooding as the major chemical combination flooding technique was applied abroad in the early stage of chemical flooding tests. However, the micelle-polymer flooding has not been applied widely due to its high cost. With the rise of oil price in recent years, low concentration chemical combination flooding has drawn more attention. Because of high temperature and high salinity in most reservoirs abroad where chemical combination flooding is used, high performance temperature and salt tolerance oil displacement agents are the bottleneck for future chemical flooding.

Based on the main geological features and technical breakthroughs made in tight oil exploration, the major challenges facing tight oil development are analyzed, and the key technical trend for tight oil development is discussed in this paper. Mainly found in continental deposits, tight oil reservoirs in China feature small area, poor physical properties, big differences in geological characteristics between different basins, but low porosity, low permeability and pressure in general. In contrast to marine tight oil, tight oil in continental deposits faces such challenges as low production and recovery, and poor economics. Through nearly three years of research and pilot test, an integrated development mode with repeated fracturing of horizontal wells as the principal technique has been proposed, which includes integrated design, platform long horizontal well drilling, massive volume fracturing, re-fracturing stimulation, controlled production, factory-like operation, concentrated surface construction etc. It is recommended that study be strengthened on basic tight oil development theory, practical development technologies, and economic evaluation of tight oil development over the whole life cycle.

An improved CO 2 –oil minimum miscibility pressure (MMP) correlation has been successfully developed to more accurately determine the CO 2 –oil MMP for a wide range of live and dead crude oils. Experimentally, slim-tube tests have been conducted to determine the CO 2 –oil MMPs for four crude oil samples with high molecular weights of C 7+ fraction. Theoretically, the newly developed CO 2 –oil MMP correlation is originated from a CO 2 –oil MMP database from the literature that covers 51 CO 2 –oil MMP data for various live and dead oil samples, especially those with high C 7+ molecular weights. The new CO 2 –oil MMP correlation is expressed as a function of reservoir temperature, C 7+ molecular weight, and mole fraction ratio of volatile components (N 2 and CH 4 ) to intermediate components (CO 2, H 2 S, and C 2 –C 6 ). Compared to nine commonly used CO 2 –oil MMP correlations in the literature, it is found that the new CO 2 –oil MMP correlation provides the best reproduction of the literature CO 2 –oil MMP data with a percentage average absolute deviation (% AAD) of 8.08% and a percentage maximum absolute deviation (% MAD) of 22.99%, respectively. To further examine its predictive capability, the new CO 2 –oil MMP correlation is then validated with the four experimentally measured CO 2 –oil MMPs in this study. The newly developed CO 2 –oil MMP correlation leads to the best prediction accuracy of the four measured CO 2 –oil MMPs with a % AAD of 4.18% and a % MAD of 7.01%, respectively.

Based on distribution of oil and gas in the world, the connotation and characteristics of “continuous” petroleum reservoirs are elaborated in this paper. “Continuous” petroleum reservoirs refer to unconventional trap reservoirs existing in a large-scale unconventional reservoir system, and the distribution of oil and gas is continuous. The main geological characteristics of “continuous” petroleum reservoirs are as follows: located in the center and slope of a basin, large-scale distribution and rich locally; mainly of large-scale unconventional reservoirs; traps have no clear boundaries; mainly of self-generating and self-preserving; mainly of primary migration; accumulated by diffusion and buoyancy is limited; non-Darcy flow; poor oil-water differentiation and different saturation; oil, water and gas coexist and have no common interface and pressure system; resources abundance is low and reserves are calculated by well-control region; the mining technologies are special and tailored techniques are required. In this paper are discussed the cause of deep-water “sandy debris flow” and a few examples on “continuous” reservoirs, the shallow-water delta low or ultra-low porosity and permeability reservoirs, coal-bed methane and shale-cracked reservoirs and so on.

This paper reviews the basic research means for oilfield development and also the researches and tests of enhanced oil recovery (EOR) methods for mature oilfields and continental shale oil development, analyzes the problems of EOR methods, and proposes the relevant research prospects. The basic research means for oilfield development include in-situ acquisition of formation rock/fluid samples and non-destructive testing. The EOR methods for conventional and shale oil development are classified as improved water flooding (e.g. nano-water flooding), chemical flooding (e.g. low-concentration middle-phase micro-emulsion flooding), gas flooding (e.g. micro/nano bubble flooding), thermal recovery (e.g. air injection thermal-aided miscible flooding), and multi-cluster uniform fracturing/water-free fracturing, which are discussed in this paper for their mechanisms, approaches, and key technique researches and field tests. These methods have been studied with remarkable progress, and some achieved ideal results in field tests. Nonetheless, some problems still exist, such as inadequate research on mechanisms, imperfect matching technologies, and incomplete industrial chains. It is proposed to further strengthen the basic researches and expand the field tests, thereby driving the formation, promotion and application of new technologies.

The dynamic interfacial tensions (IFTs) of two zwitterionic surfactants with different hydrophobic groups, alkyl sulfobetaine (ASB) and benzyl substituted alkyl sulfobetaine (BSB), against hydrocarbons, acidic model oils containing fatty acids, and three crude oils have been investigated by a spinning drop interfacial tensiometer. The influences of concentration and alkyl chain length of fatty acids on the IFTs of two betaine solutions were expounded. The effect of the alkyl chain carbon number (ACN) of the oil phase on the IFTs has also been researched. The experimental results show that the whole hydrophilic part of the betaine molecule (anionic-cationic part and the hydroxyl) is almost flat at the interface, which results in the larger occupied space of the hydrophilic part at the interface. Therefore, the branched and benzyl-substituted betaine, BSB, has a larger sized hydrophobic part and can form a more compact adsorption film than linear ASB molecules. The IFT values decrease obviously when fatty acids are added into the oil phase due to the formation of mixed adsorption films. This synergism in reducing IFT is controlled by the “chain length compatibility” and the optimum acid concentration. The ultralow IFT values can be reached when the carbon number of the alkyl chain of the fatty acid is more than 12. The IFTs of both BSB and ASB solutions against different crude oils are lower than those against pure hydrocarbons due to the formation of mixed adsorption films of betaine and petroleum acid molecules. These experimental results also confirm that the acidic model oils can represent crude oil for IFT studies to some extent.

This paper presents an integrated workflow for investigating hydrocarbon charge history using fluid inclusions using the Ordovician reservoirs from the Tazhong Oilfield, Tarim Basin as an example. The work flow involves the delineation of fluid inclusion assemblage (FIA) using fluid inclusion petrography and spectroscopy for microthermometric analysis. The interpretation of microthermometric data is based on data derived from synthetic inclusion experiments and takes consideration of the P-T re-equilibration of fluid inclusions in carbonate and over pressure effect on fluid inclusion trapping. The workflow also emphasizes on the requirements of adequate sample preparation, FIA identification, quantitative spectroscopic data (CIE), coeval petroleum and aqueous fluid inclusions, adequate number of microthermometric measurements and integrated interpretation using borehole temperature. In the study reservoirs in the Tazhong area, fluid inclusion spectroscopy reveals the presence of three groups of oil inclusions of near yellow, near blue and near white fluorescence colours. The fluid inclusion microthermometry data indicate the presence of at least two predominant hydrocarbon fluid inclusion assemblages including: homogenous liquid phase yellow fluorescence inclusions and liquid phase oil and condensate fluid inclusion assemblages with homogenous near blue, near white and near yellow fluorescence colours. The aqueous inclusions from the Ordovician reservoirs in the Tazhong area reveal the presence of low, moderate, high and very high salinities in the reservoirs. The extremely high salinity is believed to be caused by regional brine intrusions relating to regional structural movement and deformation.

The mechanism and problems associated with development engineering of fire-flooding in post-steam-injected heavy oil reservoirs was studied using 1D & 3D physical simulation experiments and reservoir numerical simulation. The temperature of combustion zone decreased and high-temperature zone enlarged because there existed secondary water formed during steam injection, which could absorb and carry heat towards producers out of the combustion front during fire flooding, but high saturation of water in layers caused by secondary water had less influence on the quantity of fuel deposit and air consumption. In the process of 3D fire flooding experiment, air override was observed during the combustion front moving forward and resulted in a coke zone in the bottom of the layer, and the ultimate recovery factor reached 65% on fact that the remaining oil saturation within the coke zone was no more than 20%. The flooding model, well pattern, well spacing, and air injection rate were optimized according to the specific property and the existed well pattern in the post-steam-injected heavy oil reservoir, and the key techniques of ignition, lifting, and anticorrosion was also selected at the same time. The pilot of fire flooding in the H1 block in the Xinjiang Oilfield was carried out from 2009 based on these research works, and now begins to show better performance. ：通过室内一维、三维物理模拟实验和油藏数值模拟，系统研究了稠油油藏注蒸汽后期转火驱开发的机理和相关油藏工程问题。研究表明：注蒸汽后期地层次生水体的存在会降低火驱燃烧带峰值温度、扩大热前缘波及范围，其干式注气过程同样具有湿式燃烧的机理。，由次生水体造成的高含水饱和度对单位体积地层燃料沉积量、氧气消耗量等燃烧指标影响不大。三维物理模拟物模实验火驱最终采收率可以达到65%，火驱过程中有明显的气体超覆现象，油层最底部存在未发生燃烧的结焦带，但结焦带中大部分原油已被驱扫，剩余油残余油饱和度低于20%。结合稠油油藏注蒸汽后期的储集层特征和现有井网条件，对火驱驱替模式、井网、井距和注气速度等进行了优化，并筛选了点火、举升、防腐等关键工艺技术。研究结果应用于新疆H1井区火驱矿场试验中，目前矿场试验初见成效。图1110表4参1720

A process for identifying marine hydrocarbon source rocks is established based on outcrop measurement, ground-penetrating radar survey, core analysis, logging evaluation, seismic interpretation, etc. It is used to identify the Cambrian and Ordovician marine hydrocarbon source rocks and to predict their spatial distribution in the Tarim Basin. Four suites of marine hydrocarbon source rocks are identified in the Tarim Basin, and they are distributed, respectively, in the Lower-Middle Cambrian of the Awati and Manjiaer sags, the Heituao Formation of the Lower-Middle Ordovician in the Tadong region, the Saergan-Tumuxiuke-Queerqueke formations of the Middle-Upper Ordovician from the Awati Sag to the Manjiaer Sag, and the Yin'gan and Lianglitage formations of the Upper Ordovician from the Awati Sag to the Tazhong area. The development of these source rocks was controlled by the sea level rise and they are characterized by different facies in the same stage, namely, different source rocks are deposited in sedimentary facies zones at the same stage. The formation of the source rocks shifted with the carbonate basin and was interrupted when there are large quantities of siliciclastic influx.

To improve the oil recovery and economic efficiency in heavy oil reservoirs in late steam flooding, taking J6 Block of Xinjiang Oilfield as the research object, 3D physical modeling experiments of steam flooding, CO2-foam assisted steam flooding, and CO2 assisted steam flooding under different perforation conditions are conducted, and CO2-assisted steam flooding is proposed for reservoirs in the late stage of steam flooding. The experimental results show that after adjusting the perforation in late steam flooding, the CO2 assisted steam flooding formed a lateral expansion of the steam chamber in the middle and lower parts of the injection well and a development mode for the production of overriding gravity oil drainage in the top chamber of the production well; high temperature water, oil, and CO2 formed stable low-viscosity quasi-single-phase emulsified fluid; and CO2 acted as a thermal insulation in the steam chamber at the top, reduced the steam partial pressure inside the steam chamber, and effectively improved the heat efficiency of injected steam. Based on the three-dimensional physical experiments and the developed situation of the J6 block in Xinjiang Oilfield, the CO2 assisted steam flooding for the J6 block was designed. The application showed that the CO2 assisted steam flooding made the oil vapor ratio increase from 0.12 to 0.16 by 34.0%, the oil recovery increase from 16.1% to 21.5%, and the final oil recovery goes up to 66.5% compared to steam flooding after perforation adjustment.

With the development of drilling techniques and oil-gas exploration,deep hydrocarbon exploration has gained more and more attention and may become an important fungible field for rising reserves.Analysis on the data of drilling and oil-gas geology of deep wells over 7 000 m in depth shows that the low limit of depth range for generation of deep hydrocarbon is possibly large,and there still exists the hydrocarbon-generation potential for the high mature source rocks.The low limit of preservation depth for the effective reservoir can shift downward,and the fractured reservoir is predominant.The oil-gas pools mainly include the earlier accumulation-later deep burying pattern,the later accumulation pattern after deeply burying and the multi-stage charging pattern.The earlier accumulation pattern can restrain the shrink of rock porosity during the deep burying process.The fractured reservoir is predominant and more developed near the fault belts,when the burial depth is more than 6 000 m.Faults connected with the deep source rocks are usually the important migration pathways for the later oil accumulation.The hydrocarbon enrichment degree near the fault belts is very high.The multi-stage hydrocarbon charging and strong charging processes can often improve the reserve abundance.The hydrocarbon resource in the strata beyond 7 000 m in depth is of considerable potential in the basins in central and western China.

To figure out the oil and gas distribution pattern in the Tarim Basin, the adjustment and reformation of oil and gas reservoirs under the background of late Himalayan Orogeny are analyzed. Strongly affected by the tectonic movement, the oil and gas reservoirs in the Tarim Basin experienced secondary actions in physical adjustment and chemical alteration: on the one hand, during the course of physical adjustment, reversed strata caused the early-formed oil to seep vertically and to migrate laterally along the sandstone in large scale with long distance; on the other hand, in the process of chemical alteration, the deposition of massive strata accelerated the thermal evolution of organic matter, generating large amounts of cracking gas, which went into the pre-existing reservoirs and led to big change in oil and gas properties and the coexistence of heavy oil, light oil, waxy oil and condensate gas in the same area. The physical adjustment and chemical reformation of oil and gas reservoirs in late Himalayan period resulted in the lateral differential distribution of oil and gas in large area and multiple vertical oil-bearing layers with complex and diverse oil and gas properties.

Microbial enhanced oil recovery (MEOR), characterized with the virtues of low cost and environmental protection, reflects the prevalent belief in environmental protection, and is attracting the attention of more researchers. Nonetheless, with the prolonged slump in global oil prices, how to further reduce the cost of MEOR has become a key factor in its development. This paper described the recent development of MEOR technology in terms of mechanisms, mathematical models, and field application, meanwhile the novel technologies of MEOR such as genetically engineered microbial enhanced oil recovery (GEMEOR) and enzyme enhanced oil recovery (EEOR) were introduced. The paper proposed three possible methods to decrease the cost of MEOR: using inexpensive nutrients as substrates, applying a mixture of chemical and biological agents, and utilizing crude microbial products. Additionally, in order to reduce the uncertainty in the practical application of MEOR technology, it is essential to refine the reservoir screening criteria and establish a sound mathematical model of MEOR. Eventually, the paper proposes to combine genetic engineering technology and microbial hybrid culture technology to build a microbial consortium with excellent oil displacement efficiency and better environmental adaptability. This may be a vital part of the future research on MEOR technology, which will play a major role in improving its economic efficiency and practicality.

Characterized by complex lithology and strong heterogeneity, volcanic reservoirs in China developed three reservoir space types: primary pores, secondary pores and fractures. The formation of reservoir space went through the cooling and solidification stage (including blast fragmentation, crystallization differentiation and solidification) and the epidiagenesis stage (including metasomatism, filling, weathering and leaching, formation fluid dissolution and tectonism). Primary pores were formed at the solidification stage, which laid the foundation for the development and transformation of effective reservoirs. Secondary pores were formed at the epidiagenesis stage, with key factors as weathering and leaching, formation fluid dissolution and tectonism. In China, Mesozoic–Cenozoic volcanic rocks developed in the Songliao Basin and Bohai Bay Basin in the east and Late Paleozoic volcanic rocks developed in the Junggar Basin, Santanghu Basin and Tarim Basin in the west. There are primary volcanic reservoirs and secondary volcanic reservoirs in these volcanic rocks, which have good accumulation conditions and great exploration potential.

Five kinds of n-alkanes, which have high proportions in crude oil from China, were mixed with CO2 of different molar fractions forming oil-gas systems. The dissolution of CO2 in the five n-alkanes and the system volume swelling were studied through the constant component expansion (CCE) experiments in different temperatures. The pressure-volume curves of the n-alkanes–CO2 systems are not strictly two-part straight lines. The bending degree is affected by the parameters of temperature, pressure, CO2 molar fraction and n-alkanes. Bubble point pressure of the oil-CO2 system is a linear relationship with the temperature. Besides, as the CO2 fraction increases, the bubble point pressure goes up largely. There is a fact that the CO2 solubility in different kinds of alkanes is nearly the same in low pressure condition, while the solubility is inversely proportional to the carbon number in high pressure. The dissolution of CO2 may swell the system, and temperature and pressure are not the main reasons. However, the swelling factor increases quickly as the CO2 molar fraction goes up, and lowers with the carbon number increase. The oil swelling has a great significance for oilfield development and well production.

By analyzing the relationship between throat threshold and fluid forces of oil charge in tight reservoirs and according to the oil-charging mechanical conditions, the lower limits of throat at the interface between source and reservoir rocks and in the middle of reservoirs were determined theoretically. On the basis of Young-Laplace formula and the equilibrium between driving forces and capillary resistance, the threshold models were set up by using the maximum driving forces near the source-and-reservoir interface and inside reservoirs respectively. They were applied to the Yanchang Formation in the Ordos Basin, the middle-lower Jurassic in the Sichuan Basin and the Bakken Formation in the Williston Basin in America. The corresponding results near the interface are 15.74 nm, 29.06 nm, and 14.22 nm, and the ones in the middle of reservoirs are 39.45 nm, 37.20 nm, and 52.32 nm respectively. Accordingly, the threshold permeabilities of the three typical tight oil reservoirs calculated are 0.002 1×10−3 μm2, 0.006 1×10−3 μm2, 0.001 8×10−3 μm2 near the interface and 0.010 0×10−3 μm2, 0.009 4×10−3 μm2, 0.016 9×10−3 μm2 at the inner reservoirs. The rocks near the interface are complex, so there is a poor correlation between porosity and permeability, while inside reservoirs, homogeneous lithology results in good correlation between porosity and permeability. The porosity thresholds were determined as 2.16%, 2.00% and 3.50% respectively.