FCC Study of Canadian Heavy Gas Oils—Comparisons of Product Yields and Qualities between Reactors

Several series of cracking tests in a comprehensive study were conducted on separate occasions involving all or parts of ten Canadian vacuum gas oils (VGOs) and two catalysts with bottoms-cracking or octane-barrel capability. VGOs were cracked in fixed- and/or fluid-bed microactivity test (MAT) units, in an Advanced Cracking Evaluation (ACE) unit, and in a modified ARCO riser reactor. Individual yields of gas, liquid, and coke from the MATs at 55, 65, 70, and 81 wt% conversion levels were compared with their respective pilot plant data. Good linear correlations could be established between MAT and riser yields except for liquefied petroleum gas (LPG) and light cycle oil (LCO). At a given conversion, correlations existed among the fixed- and fluid-bed MAT units and the ACE for each product yield. Liquid products from the fixed or fluid-bed MAT were analyzed for hydrocarbon types, sulfur, nitrogen and density, most of which showed good agreement with those obtained from the riser study. When cracking Canadian oil-sands-derived VGOs, the bottoms-cracking catalyst containing a large-pore active matrix was found to be more suitable than the octane-barrel catalyst with smaller pores to produce higher yields of valuable distillates, but with less superior qualities (in terms of sulfur and nitrogen contents). The advantages of hydrotreating some poor feeds to improve product yields and qualities were demonstrated and discussed.

Design of artificial neural networks using a genetic algorithm to predict saturates of vacuum gas oil

Accurate prediction of chemical composition of vacuum gas oil （VGO） is essential for the routine operation of refineries. In this work, a new approach for auto-design of artificial neural networks （ANN） based on a genetic algorithm （GA） is developed for predicting VGO saturates. The number of neurons in the hidden layer, the momentum and the learning rates are determined by using the genetic algorithm. The inputs for the artificial neural networks model are five physical properties, namely, average boiling point, density, molecular weight, viscosity and refractive index. It is verified that the genetic algorithm could find the optimal structural parameters and training parameters of ANN. In addition, an artificial neural networks model based on a genetic algorithm was tested and the results indicated that the VGO saturates can be efficiently predicted. Compared with conventional artificial neural networks models, this approach can improve the prediction accuracy.

Egyptian heavy vacuum gas oil hydrotreating over Co-Mo/CNT and Co-Mo/γ-Al2O3 catalysts

The catalytic activity of CoMoS /CNT towards the Egyptian heavy vacuum gas oil hydrotreating was studied. The delivered CNT was functionalized with 6 mol /L HNO_3. The CNT were loaded with 12% MoO_3( by weight) and 0.7 Co /Mo atomic ratio with impregnation methods. The γ-Al_2O_3 catalyst was also prepared by impregnation method to compare both catalysts activities.The analysis tools such XRD,Raman spectroscopy,TEM,and BET were used to characterize the catalysts. The autoclave reactor was used to operate the hydrotreating experiments. The hydrotreating reactions were tested at various operating conditions of temperature 325-375 ℃,pressure 2-6 MPa,time 2-6 h,and catalyst /oil ratio( by weight) of 1 ∶75,1 ∶33 and 1 ∶10. The results revealed that the CoMoS /CNT was highly efficient for the hydrotreating more than the CoMoS /γ-Al_2O_3. Also, the hydrodesulfurization( HDS) increased with increasing catalyst /oil ratio. Additionally,results showed that the optimum condition was temperature 350℃,pressure 4 MPa,catalyst /oil ratio of 1 ∶75 for 2 h. Furthermore,even at low CoMoS /CNT catalyst /oil ratio of 1 ∶75,an acceptable HDS of 77.1% was achieved.

Adsorption of Naphthenic Acids from Dewaxed Vacuum Gas Oil by Activated Clay: Kinetics, Equilibrium and Thermodynamic Studies

This work was mainly concentrated on the removal of naphthenic acids(NAs) from dewaxed vacuum gas oil(VGO) by adsorption using a commercial grade activated clay(AC) adsorption during lube base oil refining. The NAs in dewaxed VGO cut-4 were identified by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry(ESI FT-ICR MS). The AC sample from a refinery was characterized by XRD, BET, TG/DTA, and SEM. A series of experiments were carried out to investigate the performance of NAs adsorption by AC using a batch adsorption technique, in which some key experimental parameters such as temperature, contact time, initial concentration of NA in oil sample as well as the dosage of adsorbent were investigated. Equilibrium isotherms were analyzed using the Langmuir, Freundlich, Tempkin and Dubinin-Radushkevich(D-R) adsorption models. The pseudo-first order, the pseudo-second order, and intraparticle diffusion models were employed to describe the kinetics data. The results revealed that the D-R isotherm provided a better fit to the experimental data than other isotherms, and the adsorption kinetics followed the pseudo-first order kinetic equation. The thermodynamic data indicated that the adsorption process was feasible and spontaneous as an endothermic process. The results could provide a clear understanding of the NAs adsorption by AC during lube base oil processing at refineries.

Molecular reconstruction of vacuum gas oils using a general molecule library through entropy maximization

Vacuum gas oil(VGO)is the most important feedstock for hydrocracking processes in refineries,but its molecular composition cannot be fully acquired by current analysis techniques owing to its complexity.In order to build an accurate and reliable molecular-level kinetic model for reactor design and process optimization,the molecular composition of VGO has to be reconstructed based on limited measurements.In this study,a modified stochastic reconstruction-entropy maximization(SR-REM)algorithm was applied to reconstruct VGOs,with generation of a general molecule library once and for all via the SR method at the first step and adjustment of the molecular abundance of various VGOs via the REM method at the second step.The universality of the molecule library and the effectiveness of the modified SR-REM method were validated by fifteen VGOs(three from the literature)from different geographic regions of the world and with different properties.The simulated properties(density,elemental composition,paraffin-naphthene-aromatics distribution,boiling point distribution,detailed composition of naphthenes and aromatics in terms of ring number as well as composition of S-heterocycles)are in good agreement with the measured counterparts,showing average absolute relative errors of below 10%for each property.

FCC coprocessing oil sands heavy gas oil and canola oil. 2. Gasoline hydrocarbon type analysis

This study set out to gain a deeper understanding of a fluid catalytic cracking(FCC)coprocessing approach using canola oil mixed with bitumen-derived heavy gas oil(HGO),for the production of partially-renewable gasoline,with respect to its composition and quality.The FCC coprocessing approach may provide an alternative solution to reducing the carbon footprint and to meet government regulatory demands for renewable transportation fuels.In this study,a mixture of 15 v%canola oil in HGO was catalytically cracked with a commercial equilibrium catalyst under typical FCC conditions.Cracking experiments were performed using a bench-scale Advanced Cracking Evaluation(ACE)unit at a fixed weight hourly space velocity of 8 h^(à1),490–530C,and catalyst/oil ratios of 4–12 g/g.The total liquid product samples were injected via an automatic sampler and a prefractionator(to removet254C)into a gas chromatographic system containing a series of columns,traps,and valves designed to separate each of the hydrocarbon types.The analyzer gives detailed hydrocarbon types of à200C gasoline,classified into paraffins,iso-paraffins,olefins,naphthenes,and aromatics by carbon number up to C_(11)(C_(10)for aromatics).For a feed cracked at a given temperature,the gasoline aromatics show the highest selectivity in terms of weight percent conversion,followed by saturated iso-paraffins,saturated naphthenes,unsaturated iso-paraffins,unsaturated naphthenes,unsaturated normal paraffins,and saturated normal paraffins.As conversion increases,both aromatics and saturated iso-paraffins increase monotonically at the expense of other components.Hydrocarbon type analysis and octane numbers with variation in feed type,process severity(temperature and catalyst/oil ratio),and conversion are also presented and discussed.

Cocracking and Separate Cracking of Straight-Run Gasoline and Light Gas Oil

This paper presents experimental results of cocracking of straight-run gasoline (SRG) and light gaS oil (LGO) in an improved pulsed-micro-pyrolyzer. It is shown that there are negative opergistic effect on the yields and selectivities of ethylene and propylene in cocracking. The difference in coking tendencies betWeen the cocracking and the separate cracking is compared as well.

Geochemical prerequisites for the formation of oil and gas accumulation zones in the South Turgay basin,Kazakhstan

This study predicts favorable oil and gas source-rock formation conditions in the Aryskum Depression of the South Turgay Basin,Kazakhstan.This study assesses the thermal maturity and characteristics of organic matter by determining its environmental conditions using data from geochemical analysis of core(pyrolysis)and oil(biomarkers and carbon isotopic compositions)samples.According to the geochemical parameters obtained by pyrolysis,the oil generation potential of the original rocks of most studied samples varies from poor to rich.The facies–genetic organic matter is predominantly humic and less frequently humus–sapropel,indicating organic matter accumulation in the studied samples were under moderately reducing conditions(kerogenⅢand Ⅱ types)and coastal–marine environments(kerogen typeⅠ).The carbon isotopic compositions of oils derived from the Jurassic deposits of the Aryskum Depression also indicate the sapropelic and mixed humic–sapropelic type of organic matter(kerogenⅡandⅠ).Biomarker analysis of oils indicates original organic matter formation in an anoxic environment.

Discovery and inspiration of large-and medium-sized glutenite-rich oil and gas fields in the eastern South China Sea:An example from Paleogene Enping Formation in Huizhou 26 subsag,Pearl River Mouth Basin

Based on the practice of oil and gas exploration in the Huizhou Sag of the Pearl River Mouth Basin,the geochemical indexes of source rocks were measured,the reservoir development morphology was restored,the rocks and minerals were characterized microscopically,the measured trap sealing indexes were compared,the biomarker compounds of crude oil were extracted,the genesis of condensate gas was identified,and the reservoir-forming conditions were examined.On this basis,the Paleogene Enping Formation in the Huizhou 26 subsag was systematically analyzed for the potential of oil and gas resources,the development characteristics of large-scale high-quality conglomerate reservoirs,the trapping effectiveness of faults,the hydrocarbon migration and accumulation model,and the formation conditions and exploration targets of large-and medium-sized glutenite-rich oil and gas fields.The research results were obtained in four aspects.First,the Paleogene Wenchang Formation in the Huizhou 26 subsag develops extensive and thick high-quality source rocks of semi-deep to deep lacustrine subfacies,which have typical hydrocarbon expulsion characteristics of"great oil generation in the early stage and huge gas expulsion in the late stage",providing a sufficient material basis for hydrocarbon accumulation in the Enping Formation.Second,under the joint control of the steep slope zone and transition zone of the fault within the sag,the large-scale near-source glutenite reservoirs are highly heterogeneous,with the development scale dominated hierarchically by three factors(favorable facies zone,particle component,and microfracture).The(subaqueous)distributary channels near the fault system,with equal grains,a low mud content(<5%),and a high content of feldspar composition,are conducive to the development of sweet spot reservoirs.Third,the strike-slip pressurization trap covered by stable lake flooding mudstone is a necessary condition for oil and gas preservation,and the NE and nearly EW faults obliquely to the principal stress have the best control on traps.Fourth,the spatiotemporal configuration of high-quality source rocks,fault transport/sealing,and glutenite reservoirs controls the degree of hydrocarbon enrichment.From top to bottom,three hydrocarbon accumulation units,i.e.low-fill zone,transition zone,and high-fill zone,are recognized.The main area of the channel in the nearly pressurized source-connecting fault zone is favorable for large-scale hydrocarbon enrichment.The research results suggest a new direction for the exploration of large-scale glutenite-rich reservoirs in the Enping Formation of the Pearl River Mouth Basin,and present a major breakthrough in oil and gas exploration.

Whole petroleum system and ordered distribution pattern of conventional and unconventional oil and gas reservoirs

The classical source-to-trap petroleum system concept only considers the migration and accumulation of conventional oil and gas in traps driven dominantly by buoyance in a basin,although revised and improved,even some new concepts as composite petroleum system,total petroleum system,total composite petroleum system,were proposed,but they do not account for the vast unconventional oil and gas reservoirs within the system,which is not formed and distributed in traps dominantly by buoyancedriven.Therefore,the petroleum system concept is no longer adequate in dealing with all the oil and gas accumulations in a basin where significant amount of the unconventional oil and gas resources are present in addition to the conventional oil and gas accumulations.This paper looked into and analyzed the distribution characteristics of conventional and unconventional oil/gas reservoirs and their differences and correlations in petroliferous basins in China and North America,and then proposed whole petroleum system(WPS)concept,the WPS is defined as a natural system that encompasses all the conventional and unconventional oil and gas,reservoirs and resources originated from organic matter in source rocks,the geological elements and processes involving the formation,evolution,and distribution of these oil and gas,reservoirs and resources.It is found in the WPS that there are three kinds of hydrocarbons dynamic fields,three kinds of original hydrocarbons,three kinds of reservoir rocks,and the coupling of these three essential elements lead to the basic ordered distribution model of shale oil/gas reservoirs contacting or interbeded with tight oil/gas reservoirs and separated conventional oil/gas reservoirs from source rocks upward,which is expressed as“S\T-C”.Abnormal conditions lead to other three special ordered distribution models:The first is that with shale oil/gas reservoirs separated from tight oil/gas reservoirs.The second is that with two direction ordered distributions from source upward and downward.The third is with lateral distribution from source outside.

Evaluation of the oil and gas preservation conditions, source rocks, and hydrocarbongenerating potential of the Qiangtang Basin: New evidence from the scientific drilling project

The Qiangtang Basin of the Tibetan Plateau,located in the eastern Tethys tectonic domain,is the largest new marine petroliferous region for exploration in China.The scientific drilling project consisting primarily of well QK-1 and its supporting shallow boreholes for geological surveys(also referred to as the Project)completed in recent years contributes to a series of new discoveries and insights into the oil and gas preservation conditions and source rock evaluation of the Qiangtang Basin.These findings differ from previous views that the Qiangtang Basin has poor oil and gas preservation conditions and lacks high-quality source rocks.As revealed by well QK-1 and its supporting shallow boreholes in the Project,the Qiangtang Basin hosts two sets of high-quality regional seals,namely an anhydrite layer in the Quemo Co Formation and the gypsum-bearing mudstones in the Xiali Formation.Moreover,the Qiangtang Basin has favorable oil and gas preservation conditions,as verified by the comprehensive study of the sealing capacity of seals,basin structure,tectonic uplift,magmatic activity,and groundwater motion.Furthermore,the shallow boreholes have also revealed that the Qiangtang Basin has high-quality hydrocarbon source rocks in the Upper Triassic Bagong Formation,which are thick and widely distributed according to the geological and geophysical data.In addition,the petroleum geological conditions,such as the type,abundance,and thermal evolution of organic matter,indicate that the Qiangtang Basin has great hydrocarbon-generating potential.

Influence of the Moho surface distribution on the oil and gas basins in China seas and adjacent areas

Owing to the strategic significance of national oil and gas resources,their exploration and production must be prioritized in China.Oil and gas resources are closely related to deep crustal structures,and Moho characteristics influence oil and gas distribution.Therefore,it is important to study the relationship between the variation of the Moho surface depth undulation and hydrocarbon basins for the future prediction of their locations.The Moho depth in the study area can be inverted using the Moho depth control information,the Moho gravity anomaly,and the variable density distribution calculated by the infinite plate.Based on these results,the influences of Moho characteristics on petroleum basins were studied.We found that the Moho surface depth undulation deviation and crustal thickness undulation deviation in the hydrocarbon-rich basins are large,and the horizontal gradient deviation of the Moho surface shows a positive linear relationship with oil and gas resources in the basin.The oil-bearing mechanism of the Moho basin is further discussed herein.The Moho uplift area and the slope zone correspond to the distribution of oil and gas fields.The tensile stress produced by the Moho uplift can form tensile fractures or cause tensile fractures on the surface,further developing into a fault or depression basin that receives deposits.The organic matter can become oil and natural gas under suitable chemical and structural conditions.Under the action of groundwater or other dynamic forces,oil and natural gas are gradually transported to the uplift or the buried hill in the depression zone,and oil and gas fields are formed under the condition of good caprock.The research results can provide new insights into the relationship between deep structures and oil and gas basins as well as assist in the strategic planning of oil and gas exploration activities.

The gradual subduction-collision evolution model of Proto-South China Sea and its control on oil and gas

This study involved outcrop,drilling,seismic,gravity,and magnetic data to systematically document the geological records of the subduction process of Proto-South China Sea(PSCS)and establish its evolution model.The results indicate that a series of arc-shaped ophiolite belts and calcalkaline magmatic rocks are developed in northern Borneo,both of which have the characteristics of gradually changing younger from west to east,and are direct signs of subduction and collision of PSCS.At the same time,the subduction of PSCS led to the formation of three accretion zones from the south to the north in Borneo,the Kuching belt,Sibu belt,and Miri belt.The sedimentary formation of northern Borneo is characterized by a three-layer structure,with the oceanic basement at the bottom,overlying the deep-sea flysch deposits of the Rajang–Crocker group,and the molasse sedimentary sequence that is dominated by river-delta and shallow marine facies at the top,recording the whole subduction–collision–orogeny process of PSCS.Further,seismic reflection and tomography also confirmed the subduction and collision of PSCS.Based on the geological records of the subduction and collision of PSCS,combined with the comprehensive analysis of segmented expansion and key tectonic events in the South China Sea,we establish the“gradual”subduction-collision evolution model of PSCS.During the late Eocene to middle Miocene,the Zengmu,Nansha,and Liyue–Palawan blocks were separated by West Baram Line and Balabac Fault,which collided with the Borneo block and Kagayan Ridge successively from the west to the east,forming several foreland basin systems,and PSCS subducted and closed from the west to the east.The subduction and extinction of PSCS controlled the oil and gas distribution pattern of southern South China Sea(SSCS)mainly in three aspects.First,the“gradual”closure process of PSCS led to the continuous development of many large deltas in SSCS.Second,the deltas formed during the subduction–collision of PSCS controlled the development of source rocks in the basins of SSCS.Macroscopically,the distribution and scale of deltas controlled the distribution and scale of source rocks,forming two types of source rocks,namely,coal measures and terrestrial marine facies.Microscopically,the difference of terrestrial higher plants carried by the delta controlled the proportion of macerals of source rocks.Third,the difference of source rocks mainly controlled the distribution pattern of oil and gas in SSCS.Meanwhile,the difference in the scale of source rocks mainly controlled the difference in the amount of oil and gas discoveries,resulting in a huge amount of oil and gas discoveries in the basin of SSCS.Meanwhile,the difference of macerals of source rocks mainly controlled the difference of oil and gas generation,forming the oil and gas distribution pattern of“nearshore oil and far-shore gas”.

Shale oil and gas exploitation in China:Technical comparison with US and development suggestions

The shale oil and gas exploitation in China is technically benchmarked with the United States in terms of development philosophy,reservoir stimulation treatment,fracturing parameters,fracturing equipment and materials,oil/gas production technology,and data/achievements sharing.It is recognized that the shale oil and gas exploitation in China is weak in seven aspects:understanding of flow regimes,producing of oil/gas reserves,monitoring of complex fractures,repeated stimulation technology,oil/gas production technology,casing deformation prevention technology,and wellbore maintenance technology.Combined with the geological and engineering factors of shale oil and gas in China,the development suggestions of four projects are proposed from the macro-and micro-perspective,namely,basic innovation project,exploitation technology project,oil/gas production stabilization project,and supporting efficiency-improvement project,so as to promote the rapid,efficient,stable,green and extensive development of shale oil and gas industry chain and innovation chain and ultimately achieve the goal of“oil volume stabilizing and gas volume increasing”.

Global oil and gas development in 2022:Situation,trends and enlightenment

Through analysis of four aspects,including the distribution and production of global oil and gas fields,the distribution and changes of remaining recoverable reserves,the differences in oil and gas production between regions/countries,and the development potential of oil and gas fields with production capacity not built and to be built,this paper presents the situation and trends of global oil and gas development in 2022.It is found that,in 2022,oil and gas fields are widely distributed worldwide,and upstream production activities continue to recover;the oil and gas reserves decrease slightly year on year,and the oil and gas reserves in sea areas increase significantly;the oil and gas production increases continuously,and the key resource countries make a significant contribution in oil and gas production growth;the oil and gas fields with production capacity not built and to be built hold abundant reserves,and their development potential will be gradually released with the economic benefits increase.Further analysis is conducted from the perspectives of global oil and gas resources continuity,geopolitical risks,potential of international cooperation,and upgrade of unconventional oil and gas technology.Finally,in view of core business domains and strategies under the new situation,the Chinese oil companies are recommended to:(1)keep a foothold in onshore conventional oil and gas development by virtue of their comparative advantages and learning from other’s experience in cooperation;(2)carry out pilot tests on development adjustment,and deepen the international cooperation in enhanced oil/gas recovery;(3)improve the oil and gas operation capabilities in sea areas to transform from follower as minority shareholder to joint venture and then to independent operations;and(4)seek appropriate ways for shale oil/gas development to reduce the dependence on foreign oil and gas.

Review on the challenges and strategies in oil and gas industry's transition towards carbon neutrality in China

In light of carbon-neutral pledge, the oil and gas industry has been facing several critical new challenges in China. The current status and new challenges in terms of market mechanism reform, supply-consumption balance and key technology innovation in China's oil and gas industry are reviewed in the present study, and new strategies and roadmaps are proposed to cope with the challenges. The study found that (i) the oil and gas market faces challenges such as incomplete pricing mechanisms, unclear subject rights, and the lack of recognition and trading of carbon assets. (ii) the trade-off between short-term supply security and long-term low-carbon supply is the most critical issue. (iii) in addition to typical challenges such as immature technology and lack of funding support, the unclear multiple technology coupling development mode also poses problems for the low-carbon transformation of the oil and gas industry. To address these new challenges, comprehensive strategies and roadmaps for China's oil and gas industry towards carbon neutrality are proposed and discussed in the aspects of participating in market transactions, restructuring production and consumption, deploying key technology innovations, and planning enterprise strategies. The present study is expected to provide a blueprint for the future development of China's oil and gas industry towards carbon neutrality.

Origin of gas condensate reservoir in Fuman Oilfield, Tarim Basin, NW China

To understand the reservoir property and hydrocarbon accumulation conditions of the Middle and Upper Ordovician intraplatform shoal between ultra-deep main strike-slip faults in Fuman Oilfield of the Tarim Basin, China, the main strike-slip faults in and around well FD1 in the basin were analyzed in terms of sedimentary facies, sequence stratigraphy, intraplatform shoal reservoir property, and oil and gas origins, based on drilling data. The Yingshan Formation intraplatform shoal between the main strike-slip faults is superimposed with low-order faults to form a new type of hydrocarbon play. Firstly, hydrocarbons generated from the Lower Cambrian Yuertusi Formation source rocks vertically migrated into the second member of Yingshan Formation through the main strike-slip faults, and then migrated laterally until they were accumulated. A small amount of oil from Well FD1 came from the Yuertusi Formation source rocks in the mature stage, and a large amount of gas originated from oil cracking in the ultra-deep reservoirs. Therefore, the secondary gas condensate reservoir in Well FD1 is characterized by high gas to oil ratio, dry gas (dryness coefficient being 0.970) and hybrid origin. This new type of hydrocarbon play characterized by intraplatform shoal and low-order fault suggests a prospect of continuous hydrocarbon-bearing area in Fuman Oilfield, which will expand the ultrap-deep oil and gas exploration in the oilfield.

Research progress and key issues of ultra-deep oil and gas exploration in China

Based on the recent oil and gas discoveries and geological understandings on the ultra-deep strata of sedimentary basins, the formation and occurrence of hydrocarbons in the ultra-deep strata were investigated with respect to the processes of basin formation, hydrocarbon generation, reservoir formation and hydrocarbon accumulation, and key issues in ultra-deep oil and gas exploration were discussed. The ultra-deep strata in China underwent two extensional-convergent cycles in the Meso-Neoproterozoic Era and the Early Paleozoic Era respectively, with the tectonic-sedimentary differentiation producing the spatially adjacent source-reservoir assemblages. There are diverse large-scale carbonate reservoirs such as mound-beach, dolomite, karst fracture-vug, fractured karst and faulted zone, as well as over-pressured clastic rock and fractured bedrock reservoirs. Hydrocarbons were accumulated in multiple stages, accompanied by adjusting and finalizing in the late stage. The distribution of hydrocarbons is controlled by high-energy beach zone, regional unconformity, paleo-high and large-scale fault zone. The ultra-deep strata endow oil and gas resources as 33% of the remaining total resources, suggesting an important successive domain for hydrocarbon development in China. The large-scale pool-forming geologic units and giant hydrocarbon enrichment zones in ultra-deep strata are key and promising prospects for delivering successive discoveries. The geological conditions and enrichment zone prediction of ultra-deep oil and gas are key issues of petroleum geology.

Proppant transport in rough fractures of unconventional oil and gas reservoirs

A method to generate fractures with rough surfaces was proposed according to the fractal interpolation theory.Considering the particle-particle,particle-wall and particle-fluid interactions,a proppant-fracturing fluid two-phase flow model based on computational fluid dynamics(CFD)-discrete element method(DEM)coupling was established.The simulation results were verified with relevant experimental data.It was proved that the model can match transport and accumulation of proppants in rough fractures well.Several cases of numerical simulations were carried out.Compared with proppant transport in smooth flat fractures,bulge on the rough fracture wall affects transport and settlement of proppants significantly in proppant transportation in rough fractures.The higher the roughness of fracture,the faster the settlement of proppant particles near the fracture inlet,the shorter the horizontal transport distance,and the more likely to accumulate near the fracture inlet to form a sand plugging in a short time.Fracture wall roughness could control the migration path of fracturing fluid to a certain degree and change the path of proppant filling in the fracture.On the one hand,the rough wall bulge raises the proppant transport path and the proppants flow out of the fracture,reducing the proppant sweep area.On the other hand,the sand-carrying fluid is prone to change flow direction near the contact point of bulge,thus expanding the proppant sweep area.

Analysis of the world deepwater oil and gas exploration situation

The global trends in deepwater oil and gas exploration,characteristics of deepwater oil and gas discovery,and layout of deepwater oil and gas exploration business by seven major international oil companies are systematically analyzed using commercial databases(e.g.S&P Global and Rystad)and public information of oil companies.The deepwater area is currently the most important domain for global oil and gas exploration and discovery,with the most discoveries and reserves in passive continental margin basins.The deepwater discoveries have the greatest contribution to the total newly discovered oil and gas reserves in the sea areas,with an increasing number of lithological reservoirs discovered,and oil and gas discoveries mainly distributed in the Mesozoic–Cenozoic.The seven major international oil companies are widely active in various aspects of deepwater oil and gas exploration and development,and play a leading role.Based on years of theoretical understanding of global oil and gas geology and resource evaluation,it is proposed that favorable deepwater exploration areas in the future will mainly focus on three major areas:the Atlantic coast,the Indian Ocean periphery,and the Arctic Ocean periphery.Six suggestions are put forward for expanding overseas deepwater oil and gas exploration business:first,expand the sources for obtaining multi-user seismic data and improve the scientific selection of deepwater exploration areas;second,increase efforts to obtain deepwater exploration projects in key areas;third,adopt various methods to access into/exit from resource licenses flexibly;fourth,acquire licenses with large equity and operate in“dual-exploration”model;fifth,strengthen cooperation with leading international oil companies in deepwater technology;and sixth,improve business operation capabilities and gradually transform from“non-operators”to“operators”.