Search

Fault stability refers to the risk level of reactivation of the pre-existing fault in the stress field. Fault reactivation within the oilfield is mainly caused by the increase of fluid pressure in the fault zone. The quantitative evaluation index of the fault stability is the critical fluid pressure (that is, additional fluid pressure) required for fault reactivation under the current pore fluid pressure. When the formation pore pressure reaches the critical value, the corresponding fault part will be in the critical stress state. The sliding of the fault in the critical stress state will easily cause oil and gas leakage and casing damage at the edge of the fault. Therefore, it is of great significance to study fault stability for oilfield production. Ground stress is a key parameter for fault stability evaluation. There are many methods to calculate the geomechanics including hydraulic method, acoustic emission method, and the use of the logging data, among which the hydraulic fracturing method can be used to obtain the most accurate horizontal minimum principal stress. This paper calculates the continuous geomechanics by using the logging data. There are many methods available for evaluating fault stability, among which fault sealing analysis technology (FAST) method is most widely used. FAST can be used to not only quantitatively evaluate fault stability, but also evaluate the impact of fault cohesion on fault stability. There are many factors affecting fault stability. The relationship between the differential stress and tensile strength of the fault rock will affect the trend of the fault reactivation.The direction of the stress field also affects the fault stability greatly. The argillaceous material weakens the strength of fault rock. When a large amount of argillaceous material enters the fault zone, the fault tends to reactivate. The change of reservoir fluid pressure will also lead to the change of horizontal stress to affect the stability of the fault. In addition, the accuracy of seismic interpretation will also affect the evaluation results of fault stability. Based on the geological model framework and one-dimensional geomechanical model calibration, this paper establishes a three-dimensional geomechanical model by using the finite element simulation method to carry out four-dimensional geomechanical research to evaluate the fault stability in the development of the Donghe 1 Reservoir in Tarim basin. The research results show that the fracture sealing gradually strengthens during the development of Donghe 1 Reservoir, and the quantized critical fracture opening pressure is 67.38MPa.

While there has been considerable success in the three-dimensional bioprinting of relatively large standalone filamentous tissues, the fabrication of solid fibers with ultrafine diameters or those cannular featuring ultrathin walls remains a particular challenge. Here, an enabling strategy for (bio)printing of solid and hollow fibers whose size ranges could be facilely adjusted across a broad spectrum, is reported, using an aqueous two-phase embedded (bio)printing approach combined with specially designed cross-linking and extrusion methods. The generation of standalone, alginate-free aqueous architectures using this aqueous two-phase strategy allowed freeform patterning of aqueous bioinks, such as those composed of gelatin methacryloyl, within the immiscible aqueous support bath of poly(ethylene oxide). Our (bio)printing strategy revealed the fabrication of standalone solid or cannular structures with diameters as small as approximately 3 or 40 μ m, respectively, and wall thicknesses of hollow conduits down to as thin as μ m. With cellular functions also demonstrated, we anticipate the methodology to serve as a platform that may satisfy the needs for the different types of potential biomedical and other applications in the future, especially those pertaining to cannular tissues of ultrasmall diameters and ultrathin walls used toward regenerative medicine and tissue model engineering.

The mutant form of the guanosine triphosphatase (GTPase) KRAS is a key driver in human tumors but remains a challenging therapeutic target, making KRAS MUT cancers a highly unmet clinical need. Here, we report a class of bottlebrush polyethylene glycol (PEG)–conjugated antisense oligonucleotides (ASOs) for potent in vivo KRAS depletion. Owing to their highly branched architecture, these molecular nanoconstructs suppress nearly all side effects associated with DNA–protein interactions and substantially enhance the pharmacological properties of the ASO, such as plasma pharmacokinetics and tumor uptake. Systemic delivery to mice bearing human non–small-cell lung carcinoma xenografts results in a significant reduction in both KRAS levels and tumor growth, and the antitumor performance well exceeds that of current popular ASO paradigms, such as chemically modified oligonucleotides and PEGylation using linear or slightly branched PEG. Importantly, these conjugates relax the requirement on the ASO chemistry, allowing unmodified, natural phosphodiester ASOs to achieve efficacy comparable to that of chemically modified ones. Both the bottlebrush polymer and its ASO conjugates appear to be safe and well tolerated in mice. Together, these data indicate that the molecular brush–ASO conjugate is a promising therapeutic platform for the treatment of KRAS -driven human cancers and warrant further preclinical and clinical development.

Low-permeability oil reservoirs generally have the low production, production rapid productivity decline, and low-ultimate recovery. Staged fracturing is usually conducted for horizontal wells. Hydraulic fracturing technology is generally used to improve fracture conductivity and well productivity, which is one of the key technologies for Enhance Oil Recovery (EOR). How to accurately characterize and simulate the distribution characteristics of hydraulic fracture network in 3D space is particularly important. The stress interference between hydraulic fractures as the objective mechanical behavior in the process of staged fracturing affects the geometry fracture network and the productivity of the reservoir post-fracturing. The hydraulic fractures simulation in natural fractured reservoirs is complex shapes, mainly because natural fractures affect the propagation path of hydraulic fractures. The theoretical model used to describe the hydraulic fracturing in homogeneous reservoirs cannot accurately show the complexity of the spatial morphology of hydraulic fractures in naturally fractured formations. CNCP (the operator) urgently need a mechanical model that can show the stress interference behavior between multiple fractures and the direction of hydraulic fracture propagation, and be used to simulate the spatial form of multiple hydraulic fractures in staged fracturing of horizontal wells and their propagation behavior in naturally fractured formations. Aiming at the impact of natural fractures in the reservoir on the propagation path of hydraulic fractures, this paper established a mechanical model for distinguishing interference behavior of natural fractures and hydraulic fractures. And analyzed the stress field at the tip of the hydraulic fracture and the stress field acting on the natural fracture surface based on the theories related to rock mechanics and fracture mechanics. On the basis of coupling the 3D geomechanical model and the 3D Discrete Fracture Network (DFN) model, this paper established the discriminant model for hydraulic fractures penetrating natural fractures in 3D space to conduct hydraulic fracture propagation simulation for the horizontal well. The research results can be used to optimize the hydraulic fracturing treatment design, and provide technical support for the effective production and profitable development of low-permeability reservoir resources.

Fault stability is the risk of reactivation under dynamic stress conditions. The reactivation of faults in the oilfield is mainly caused by the increase of fluid pressure in the reservoir zone, with the quantitative evaluation index of the critical reservoir pressure required for fault reactivation under the current pore pressure condition. When the formation pore pressure reaches the critical stress, the corresponding fault part will be in a critical stress state. The slippage of the critical stress fault tends to cause fluids leakage. Therefore, the study of fault stability is of great significance to oilfield production; In order to guarantee national natural gas peak regulation and supply, the YH underground gas storage (UGS) has been proposed and is carried out with the project of expanding storage capacity and increasing production. The operator hopes to effectively guide the optimization of the limit operation pressure and ensure its long-term safe operation. It is urgently required to carry out fault stability evaluation for the YH underground gas storage. The operator plans to find out the conditions for the activation of the faults, with studies about the stability of the fault under the impact of mining and the impact of the system parameters on the stability of the fault. The results suggest that: whether the fault is in a stable or active state depends on the magnitude relationship between the apparent friction factor (k1) and the fault friction factor (k). When k1 < k, the fault will be in a self-locking state. However, when k1 ≥ k, the fault is in a reactive state. The apparent friction factor reflects the stress risk level of the fault under the collective impact of the in situ stress (including σ1 and σ3), the cohesion of the fault plane (c) and fluid pressure of fault (pi). Higher k1 indicates higher tendency of fault re-activation. k is a quantity factor determined by the friction angle (φ) within the fault. The larger friction angle of fault indicates higher friction factor and the more stable state. The system parameters (includingφ, c, pi, σ1 and σ3) will affect the stability of the fault after the change of initial stress conditions: the smaller cohesion of the fault plane and greater fracture fluid pressure indicate the fault will be easier to reactivate. This paper established the 4D dynamic geomechanical model of the YH underground gas storage and took the fault stability as the judgement basis to analyze the in-situ stress characteristics of different faults. The research results could be used to evaluate the UGS operation safety quantitatively under the impact of the dynamic stress conditions, which will provide technical guidance for optimizing the operation plan of the UGS.

Three-dimensional (3D) bioprinting of vascular tissues that are mechanically and functionally comparable to their native counterparts is an unmet challenge. Here, we developed a tough double-network hydrogel (bio)ink for microfluidic (bio)printing of mono- and dual-layered hollow conduits to recreate vein- and artery-like tissues, respectively. The tough hydrogel consisted of energy-dissipative ionically cross-linked alginate and elastic enzyme–cross-linked gelatin. The 3D bioprinted venous and arterial conduits exhibited key functionalities of respective vessels including relevant mechanical properties, perfusability, barrier performance, expressions of specific markers, and susceptibility to severe acute respiratory syndrome coronavirus 2 pseudo-viral infection. Notably, the arterial conduits revealed physiological vasoconstriction and vasodilatation responses. We further explored the feasibility of these conduits for vascular anastomosis. Together, our study presents biofabrication of mechanically and functionally relevant vascular conduits, showcasing their potentials as vascular models for disease studies in vitro and as grafts for vascular surgeries in vivo, possibly serving broad biomedical applications in the future.

Gas flooding is a promising way to enhance oil recovery in unconventional oil reservoirs, but accurate identification of the distributions of movable and residual oil during gas flooding is difficu...

Constructing surface topographies in the micro- or nanometer range is an effective way to improve the biocompatibility of biomaterials. For the present work, anatase coatings with controllable micro/nanoscale characteristics were successfully prepared on an MgZn alloy surface via solvothermal route, and their formation mechanisms are discussed. The features of the as-prepared coatings were characterized using a scanning electron microscope (SEM), a transmission electron microscope (TEM), an atomic force microscope (AFM), X-ray diffraction (XRD), and a contact angle goniometer. The corrosion behavior of the coatings was also evaluated by testing the open circuit potential (OCP) in SBF (Simulated Body Fluid). The results show that a gradual variation of the anatase coating morphologies was obtained through adjusting the solvothermal reaction conditions. With the increase of NH4F concentration in the solution, the cross-combined anatase nanosheets became more dispersed. The micro/nanostructured anatase coatings provide the MgZn alloy with good corrosion resistance, which increased with the density of anatase nanosheets in the coatings. In addition, the coatings exhibit the inhibition of platelet aggregation, and the micro/nano structures can also adsorb endothelial cells.

Hydraulic fracturing is one of the major production enhancement measures for low permeability fractured reservoirs, where a large amount of oil and gas is stored worldwide. In recent years, during the development and research of these reservoirs, it has been found that the hydraulic fractures formed are no longer the single planar fractures produced by fracturing in homogeneous reservoirs, but complex, non-planar, multiple hydraulic fractures are formed, and the post-fracturing production often shows a positive correlation with the fracture complexity. A large amount of hydraulic fracturing diagnostic data indicates that the interaction between pre-existing natural fractures and induced hydraulic fractures is the key condition leading to the formation of complex hydraulic fractures. Simulation of hydraulic fracture extension in fractured reservoirs requires simulation of fluid pressure changes after the intersection of hydraulic fractures and natural fractures, as well as hydraulic fracture steering and other complex conditions. The traditional hydraulic fracture extension simulation models and theories are no longer suitable for such inhomogeneous reservoir conditions, but the relevant theoretical research is still immature and the interaction between hydraulic fractures and natural fractures during hydraulic fracture extension in fractured reservoirs is still not well understood. It is necessary to further develop theoretical research on hydraulic fracture expansion in fractured reservoirs to understand the mechanism and influencing factors of complex fracture formation, in order to promote the development of field development and theoretical research system of similar reservoirs. In this paper, we simulate and analyze the factors influencing hydraulic fracture expansion in fractured reservoirs. Through a series of numerical simulations, we found that horizontal bedding may open up during hydraulic fracturing to form horizontal fractures, and horizontal and vertical fractures intersect each other to form a complex volumetric fracture network; The distribution length of volumetric fractures increases and the distribution width decreases when the horizontal principal stress difference increases, and the aspect ratio of volumetric fractures increases; the distribution length of volumetric fractures decreases and the width increases when the fracturing construction displacement increases, and the aspect ratio of fractures increases. The residual tensile strength of natural fractures increases, the distribution width of volumetric fractures decreases, the distribution length increases, and the aspect ratio of volumetric fractures increases. The research results can provide some reference and reference for the fracture design and construction of fractured reservoirs.

Mud loss is one of the most severe incidents encountered while drilling. As the focus of exploration has moved to the deeper and more complicated formations, mud loss happens more frequently, causing safety incidents and lowering the drilling efficiency. The lost mud invades into formations, makes harm to the reservoir and affects the accuracy of formation evaluation. Large numbers of studies have proved that the key strategy to deal with mud loss is to prevent it and follow with remedial action. The prerequisite of such measurements is locating the formation of mud loss. Loss pressure is the highest pressure that formation can hold before mud loss happens. It is important for deciding mud weight and critical for fractured formations. Therefore, an innovative ring-cracking loss model is created by integrating minimum horizontal principal stress loss model, statistical loss model, and critical crack width loss model after analyzing the loss mechanism of fractured formation. These four models are applied to the fractured formation of block X, and the results are compared to the actual downhole pressure.The result from ring-cracking-based loss model is less than the actual downhole pressure. This model is suitable for field application and can guide the design of mud density.

This paper provide several improved miscible assistants, trying to mitigate the problem that CO2 miscible flooding is difficult to achieve in reservoirs because of the high miscible pressures, which leads to a lower recovery up to expectations. These miscible assistants could be easily mixed with crude oil by adding into CO2 and reduce the interfacial tension to drive down the minimum miscible pressure (MMP) in order to enhance sweep efficiency. Some efforts have been made to improve this situation. The effective method is to draw the experiences from structure characteristics of surfactants applied in micro emulsion of CO2-water systems. Amphiphilic organic assistants were designed to synthetize with fluoro-alkane chains and non-fluoro-OAc chains as the CO2-philic ends, as well as alkane structure as the lipophilic ends. The minimization of MMP of CO2 miscible processing assistants has been analyzed and optimized by surface tension testing in CO2-kerosene system and CO2-crude oil system. The crude oil was obtained from field test pilot in L Reservoir. The results of interfacial tension tests show that per-acetylated glucose dodecyl ester molecules have the ability to lower the interfacial tension most in these five kinds of new miscible processing assistants in two categories. Citric acid triisopropyl ester molecules take the second place, and others almost make no difference. The probable reason is that kerosene is mainly composed of C12 and lack of heavy components, which cause a weak interaction between independent hydroxyl of citric acid and tartaric acid assistant and hydrogen bond of kerosene. The results of interfacial tension tests show that all these miscible assistants possess good effects on minimizing the interfacial tension of the CO2-crudes system, and could also definitely reduce the MMP. Among these, per-acetylated glucose dodecyl ester molecules and citric acid isopropyl ester molecules perform most excellent, and could decrease the MMP of CO2 flooding by 27.5%. The assistants have been implemented in the CO2 flooding plan of L Reservoir with 4 gas injectors and 15 producers. After 15 years’ development simulation, cumulated oil production will reach 3.4 MMbbl with recovery increasing from 41.6% (only CO2 flooding) to 46.6%. Injection test shows that 1400 tons CO2 has been injected with 3800 bbl oil produced. The improved miscible assistants provided perform as well as other existing assistants in reducing interfacial tension and enhancing sweep efficiency in CO2 flooding. Compared with assistants of light hydrocarbon, these assistants require a little quantity to improve the miscible flooding, which could break the economic limits. Compared with the traditional fluoride assistants, these assistants are quite different in molecular structure and could cause little pollution and have been applied in field test.

China has abundant low-permeability oil and gas resources. A lot of practice has proved that low-permeability reservoirs must undergo hydraulic fracturing to obtain commercial production capacity. Geomechanical characteristics are the key factor for fracturing. It plays a very important role in the oil field exploration and production. It is not only the driving force for oil and gas migration, but also provides a basis for wellbore stability analysis and drilling optimization design. The state of the formation stress field and the mechanical properties of the rock jointly determine the direction, shape and orientation of the fracture extension of the fracturing. Together it affects the stimulation effect of fracturing. Realizing the high-efficiency development of low-permeability reservoirs is a key and difficult problem facing for oil filed operator. Horizontal wells drilling and hydraulic fracturing are the core technology for increasing single well production in low-permeability reservoirs. The effectiveness of reservoir reconstruction directly determines the production capacity of the reservoir. In order to clarify the influence of static and dynamic geomechanics on the scale of reservoir stimulation in the process of horizontal well fracturing, and ultimately provide effective technical support for the formulation and optimization of reservoir stimulation design. This study is based on the study of single well one-dimensional geomechanics, using the structural characteristics and seismic attributes of low-permeability reservoirs to study the characteristics of the three-dimensional spatial distribution of mechanics. On this basis, combined with real-time fracturing treatment data and micro-seismic monitoring data, dynamic (four-dimensional) stress field simulations are continuously carried out. The research results can be mainly used to guide the optimization of reservoir stimulation and the evaluation of filed development plan.

Different from other gas drive processes, phase behavior performs more significant roles in natural gas drive process. The main reason is that more severe mass transfer effect and similar phase solubility effect have been caused by multicomponent interaction. This paper provides a series of methods to study the phase behavior in natural gas drive process, aiming to reveal further mechanism and give technical supports to the on-site practice in T_D Reservoir with HTHP. Four key parameters of natural gas drive have been determined. Firstly, laboratory compounding method has been improved to obtain real components of formation fluids and actual injected gas at formation condition (140°C, 45MPa). Secondly, 19 sets of slim tube test has been carried to determine MMP (minimum miscible pressure) and the injected gas components ensuring miscibility. Thirdly, swelling test and laser method have been used to separately obtain the viscosity reduction degree and solid deposition effects. Finally, multiple contact test has been carried to describe the miscibility behavior. All the above have been applied in T_D Reservoir. Conclusions could be drawn from the results obtained by the methods above. Firstly, swelling capacity of crude oil could be enhanced by natural gas for the formation volume factor of crude oil in T_D Reservoir increased by 57% and the viscosity decreased by 83% after natural gas injection. Secondly, MMP of dry gas and crude oil in T_D Reservoir is 43.5MPa with a miscible displacement efficiency above 90% (>30% compared with immiscible displacement efficiency), and the content of N2+C1 should be controlled over 88%. Thirdly, results of 5 levels contact experiments shows that miscibility behavior of natural gas and oil from T_D Reservoir performs an evaporative-condensate composite miscible process in which the condensate miscible process takes the lead. Finally, obvious solid point has not been observed in natural gas drive process of crude oil from T_D Reservoir at the formation temperature, and the effect of solid deposition on the fluid flow in formation could be ignored because of trace amount of solid solution ( A systematic methods have been reorganized to research the phase behavior in natural gas drive process and half of these methods mentioned above get partially improvement. These physical simulation experiments have covered most mainly processes and the key parameters in reservoirs with HTHP and natural gas drive, including mass transfer, viscosity, expansion, volume coefficient, MMP, miscibility behavior and solid deposition. Every experiment gives a quantitative analysis which possesses satisfied practicability in field application.

Leak-off pressure is a main factor to induce formation leak-off so that it can be utilized as a crucial parameter to analyze the causation of well leak-off accidents, and that in-depth investigation on leak-off pressure is of vital importance for secure drilling. By analyzing the characteristics of leak-off formation, this paper divides the leak-off into natural leak-off and fractured leak-off, and then defines the conception of minimal leak-off pressure. The leak-off mechanism of fractured formation is investigated. Investigation results show that the currently existent prediction method of fracture pressure is established on the foundations of non-filtration borehole wall assumption as well as the Terzaghi effective stress model. These foundations are not consistent with the practical features of thief formation, which would inevitably cause deviation of calculated results with actualization. Natural leak-off formation constitutes the majority of formation leak-off phenomena. Therefore, it is urgent to build up the leak-off pressure curve instead of fractured pressure curve and take precautions against natural leak-off. The technique of leak-off pressure prediction with fully-coupled 3D natural fracture modeling was applied in the fractured reservoir which located in the northwest of Junggar Basin, China. Case analyses have proved that this lost circulation pressure model is of sufficiency in scientific bases and pertinence. The prediction result derived from the model is relatively consistent with the actual situation and consequently provides a substantial basis for a rational design of the drilling fluid density as well as the leak resistance and sealing. Therefore it is suggested that the design of drilling engineering should take the lost circulation pressure into consideration.

Due to the poor mechanical properties of many hydrogel bioinks, conventional 3D extrusion bioprinting is usually conducted based on the X-Y plane, where the deposited layers are stacked in the Z-direction with or without the support of prior layers. Herein, a technique is reported, taking advantage of a cryoprotective bioink to enable direct extrusion bioprinting in the vertical direction in the presence of cells, using a freezing plate with precise temperature control. Of interest, vertical 3D cryo-bioprinting concurrently allows the user to create freestanding filamentous constructs containing interconnected, anisotropic microchannels featuring gradient sizes aligned in the vertical direction, also associated with enhanced mechanical performances. Skeletal myoblasts within the 3D-cryo-bioprinted hydrogel constructs show enhanced cell viability, spreading, and alignment, compared to the same cells in the standard hydrogel constructs. This method is further extended to a multimaterial format, finding potential applications in interface tissue engineering, such as creation of the muscle-tendon unit and the muscle-microvascular unit. The unique vertical 3D cryo-bioprinting technique presented here suggests improvements in robustness and versatility to engineer certain tissue types especially those anisotropic in nature, and may extend broad utilities in tissue engineering, regenerative medicine, drug discovery, and personalized therapeutics.

The three-dimensional bioprinting technologies have attracted increasing attention due to their flexibility in producing architecturally relevant tissue constructs. Here, we present an enabling vertical embedded extrusion bioprinting strategy using uniaxial or coaxial nozzles, which allows formation of vertical structures of homogeneous or heterogeneous properties in nature. By adjusting the bioprinting parameters, the characteristics of the bioprinted vertical patterns could be precisely controlled. Using this strategy, we demonstrated two proof-of-concept applications in tissue biofabrication. Specifically, intestinal villi and hair follicles, two liner-shaped tissue types in the human body, were successfully generated with the vertical embedded bioprinting method, reconstructing some of their key structures as well as restoring partial functions in vitro. Caco-2 cells in the bioprinted intestinal villus constructs proliferated and aggregated properly, also showing functional biomarker expressions such as ZO-1 and villin. Moreover, preliminary hair follicle structures featuring keratinized human keratinocytes and spheroid-shaped human dermal papilla cells were formed after vertical bioprinting and culturing. In summary, this vertical embedded extrusion bioprinting technique harnessing a uniaxial or coaxial format will likely bring further improvements in the reconstruction of certain human tissues and organs, especially those with a linear structure in nature, potentially leading to wide utilities in tissue engineering, tissue model engineering, and drug discovery. This article is protected by copyright. All rights reserved.

Three-dimensional (3D) bioprinting has emerged as an enabling tool for various biomedical applications, such as tissue regeneration and tissue model engineering. To this end, the development of bioinks with multiple functions plays a crucial role in the applications of 3D bioprinting technologies. In this study, we propose a new bioink based on two immiscible aqueous phases of gelatin methacryloyl (GelMA) and dextran, further endowed with anti-bacterial and anti-inflammatory properties. This micropore-forming GelMA-dextran (PGelDex) bioink exhibited excellent printability with vat-polymerization, extrusion, and handheld bioprinting methods. The porous structure was confirmed after bioprinting, which promoted the spreading of the encapsulated cells, exhibiting the exceptional cytocompatibility of this bioink formulation. To extend the applications of such a micropore-forming bioink, interleukin-4 (IL-4)-loaded silver-coated gold nanorods (AgGNRs) and human mesenchymal stem cells (MSCs) were simultaneously incorporated, to display synergistic anti-infection behavior and immunomodulatory function. The results revealed the anti-bacterial properties of the AgGNR-loaded PGelDex bioink for both Gram-negative and Gram-positive bacteria. The data also indicated that the presence of IL-4 and MSCs facilitated macrophage M2-phenotype differentiation, suggesting the potential anti-inflammatory feature of the bioink. Overall, this unique anti-bacterial and immunomodulatory micropore-forming bioink offers an effective strategy for the inhibition of bacterial-induced infections as well as the ability of immune-regulation, which is a promising candidate for broadened tissue bioprinting applications.

This paper provide improved phase behavior models, trying to mitigate the problem that phase behavior of gas-crude system is difficult to describe in L block with low permeability and high water cut in China. This situation leads to a series of problems in CO2 flooding process and lower recovery up to expectations. The models is evaluated to possess both high calculation speed and accuracy compared with existing others.Characteristics of CO2-crude systems had been considered into repulsion-attraction type EOS (equation of state) based on the analysis of repulsion parameter and attraction parameter in EOS, and the improved EOS had been applied in developing calculation method of MMP (minimum miscible pressure). No ideality of CO2-crude systems had been considered into mixing rules of CO2-crude systems based on analysis of mixing rules of repulsion-attraction type EOS. Promotion had also been put into the obtain methods of parameters in phase behavior, including density, viscosity, MMP, critical parameters of plus components etc. All these methods are applied in L Block.The phase behavior models of CO2-crudes system promoted in this paper mainly include EOS, mixing rule and viscosity model and have been applied in CO2 flooding process in T Reservoir. The relative error of density calculation is reduced from 7% ∼ 20% to less than 1%and the modified EOS is applied to predict the MMP of the CO2-crude systems from 8 different blocks in T reservoir. The modified EOS also works well for the relative error of MMP prediction is reduced from 20% ∼ 70% to less than 5%. Compared with the existing mixing rules, the modified mixing rule is with higher calculation speed and accuracy. The relative error of components mole fraction calculation is reduced from 30% ∼ 80% to less than 10%. Compared with the existing viscosity models, there are large improvements of the modified viscosity model in accuracy. The relative error of viscosity simulation is reduced from more than 50% to about 5%. According to the simulation results, C2∼C15 are the key hydrocarbons with positive effect on the miscibility of CO2-crude systems, while C16+ are the key hydrocarbons with negative effect. The recovery of the pilot has increased by 23% by these methods.The improved phase behavior models provided in this paper possess as good performance as existing models in calculation speed, and accustom a big step forward in simulation accuracy. The modified components of the models also partially complete physical meaning in describing phase behavior of CO2-crude system. All the models mentioned above are finally applied in L block with HP/HT and high water cut and obtained an increase in recovery by 19.2%.

Owing to the low productivity of single well, rapid productivity decline and low ultimate recovery of low-permeability reservoirs, multistage fracturing is usually employed for reservoir stimulation of horizontal wells, which helps to increase fracture conductivity and single well productivity by creating artificial fractures. It is very vital to accurately characterize and simulate 3D spatial distribution of fracture networks for hydraulic fracturing technology. Sufficient production data has proved that the hydraulic fracture geometry simulation integrating 1D geomechanics, without considering natural fractures, resulted in low accuracy of fracture modeling, which could not effectively support the deployment and implementation of oilfield development plan. Thus, artificial fracture networks simulation technology fully coupling 3D geomechanics with natural fracture model will be urgently required to guide oilfield development economically. The technical research process is divided into 4 steps. Step 1, set up 1D geo-mechanical modeling in single well using conventional and image logging data, formation integrity testing, drilling logs, as well as rock mechanical laboratory tests. Then, 3D static geomechanical modeling of the reservoir can be performed by incorporating seismic data and structural modeling. Step 2, identify natural fractures in single well based on image logging data and core data to create fracture intensity curve modeling. Establish 3D natural fracture model constrained by fracture sensitive seismic attributes analysis and 3D fracture intensity trend body. Step3, based on rock and fracture mechanics, simulate hydraulic fracture extension of stimulated well coupling 3D geo-mechanical model with 3D natural fracture model. Then, verify modeling accuracy through micro-seismic data. Step 4, compare and analyze differences in fracture geometry, proppant placement, and fracture conductivity between 3D coupled fracture modeling (3DCFM) and 3D uncoupled fracture modeling (3DUFM). After gridding 3DCFM and 3DUFM to geological modeling, predict production post fracturing using numerical simulation technology. Finally, crosscheck the accuracy of 3DCFM and 3DUFM with predicted and actual production data. By comparing and analyzing the fracture geometry and numerical simulation results of 3DCFM and 3DUFM, it was concluded that 3DUFM could not characterize natural fracture shielding effect and diversion during fracture extension due to 3D geo-mechanical spatial anisotropy. Thus, greater uncertainties of the fracture modeling occurred, resulting in low consistency between single well productivity prediction and numerical simulation. Compared with 3DUFM, the uncertainty of the fracture modeling geometry can be greatly reduced in 3DCFM verified by micro-seismic patterns, so the consistency between productivity prediction and numerical simulation will be significantly increased. Hydraulic fracture simulation technology fully-coupling geomechanics with natural fracture model was applied in the low permeability fractured reservoirs of the northwestern margin of Junggar Basin, China. The cross-over analysis among research results, the actual micro-seismic patterns and production data indicated that compared with 3DUFM, the uncertainty of 3DCFM reduced by 25.2%;, and the consistency of numerical simulation and productivity prediction increased by 18.5%. The research results would be a guideline on location optimization of horizontal wells, stimulation optimization of multistage fracturing and strategy optimization of oilfield development.