Phase Transitions and Seepage Characteristics during the Depletion Development of Deep Condensate Gas Reservoirs

Deep condensate gas reservoirs exhibit highly complex and variable phase behaviors,making it crucial to understand the relationship between fluid phase states and flow patterns.This study conducts a comprehensive analysis of the actual production process of the deep condensate gas well A1 in a certain oilfield in China.Combining phase behavior analysis and CMG software simulations,the study systematically investigates phase transitions,viscosity,and density changes in the gas and liquid phases under different pressure conditions,with a reservoir temperature of 165°C.The research covers three crucial depletion stages of the reservoir:single-phase flow,two-phase transition,and two-phase flow.The findings indicate that retrograde condensation occurs when the pressure falls below the dew point pressure,reachingmaximum condensate liquid production at around 25MPa.As pressure decreases,gas phase density and viscosity gradually decrease,while liquid phase density and viscosity show an increasing trend.In the initial single-phase flow stage,maintaining a consistent gas-oil ratio is observed when both bottom-hole and reservoir pressures are higher than the dew point pressure.However,a sudden drop in bottom-hole pressure below the dew point triggers the production of condensate oil,significantly reducing subsequent gas and oil production.In the transitional two-phase flow stage,as the bottom-hole pressure further decreases,the reservoir exhibits a complex flow regime with coexisting areas of gas and liquid.In the subsequent two-phase flow stage,when both bottom-hole and reservoir pressures are below the dew point pressure,a significant increase in the gas-oil ratio is observed.The reservoir manifests a two-phase flow regime,devoid of single-phase gas flow areas.For lowpressure conditions in deep condensate gas reservoirs,considerations include gas injection,gas lift,and cyclic gas injection and production in surrounding wells.Additionally,techniques such as hot nitrogen or CO_(2) injection can be employed to mitigate retrograde condensation damage.The implications of this study are crucial for developing targeted development strategies and enhancing the overall development of deep condensate gas reservoirs.

Gas-Water Production of a Continental Tight-Sandstone Gas Reservoir under Different Fracturing Conditions

A numerical model of hydraulic fracture propagation is introduced for a representative reservoir(Yuanba continental tight sandstone gas reservoir in Northeast Sichuan).Different parameters are considered,i.e.,the interlayer stress difference,the fracturing discharge rate and the fracturing fluid viscosity.The results show that these factors affect the gas and water production by influencing the fracture size.The interlayer stress difference can effectively control the fracture height.The greater the stress difference,the smaller the dimensionless reconstruction volume of the reservoir,while the flowback rate and gas production are lower.A large displacement fracturing construction increases the fracture-forming efficiency and expands the fracture size.The larger the displacement of fracturing construction,the larger the dimensionless reconstruction volume of the reservoir,and the higher the fracture-forming efficiency of fracturing fluid,the flowback rate,and the gas production.Low viscosity fracturing fluid is suitable for long fractures,while high viscosity fracturing fluid is suitable for wide fractures.With an increase in the fracturing fluid viscosity,the dimensionless reconstruction volume and flowback rate of the reservoir display a non-monotonic behavior,however,their changes are relatively small.

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.

Hydrocarbon accumulation and orderly distribution of whole petroleum system in marine carbonate rocks of Sichuan Basin,SW China

Based on the situation and progress of marine oil/gas exploration in the Sichuan Basin,SW China,the whole petroleum system is divided for marine carbonate rocks of the basin according to the combinations of hydrocarbon accumulation elements,especially the source rock.The hydrocarbon accumulation characteristics of each whole petroleum system are analyzed,the patterns of integrated conventional and unconventional hydrocarbon accumulation are summarized,and the favorable exploration targets are proposed.Under the control of multiple extensional-convergent tectonic cycles,the marine carbonate rocks of the Sichuan Basin contain three sets of regional source rocks and three sets of regional cap rocks,and can be divided into the Cambrian,Silurian and Permian whole petroleum systems.These whole petroleum systems present mainly independent hydrocarbon accumulation,containing natural gas of affinity individually.Locally,large fault zones run through multiple whole petroleum systems,forming a fault-controlled complex whole petroleum system.The hydrocarbon accumulation sequence of continental shelf facies shale gas accumulation,marginal platform facies-controlled gas reservoirs,and intra-platform fault-and facies-controlled gas reservoirs is common in the whole petroleum system,with a stereoscopic accumulation and orderly distribution pattern.High-quality source rock is fundamental to the formation of large gas fields,and natural gas in a whole petroleum system is generally enriched near and within the source rocks.The development and maintenance of large-scale reservoirs are essential for natural gas enrichment,multiple sources,oil and gas transformation,and dynamic adjustment are the characteristics of marine petroleum accumulation,and good preservation conditions are critical to natural gas accumulation.Large-scale marginal-platform reef-bank facies zones,deep shale gas,and large-scale lithological complexes related to source-connected faults are future marine hydrocarbon exploration targets in the Sichuan Basin.

Distribution characteristics, exploration and development, geological theories research progress and exploration directions of shale gas in China

The shale gas resources in China have great potential and the geological resources of shale gas is over 100×10^(12)m^(3),which includes about 20×10^(12)m^(3) of recoverable resources.Organic-rich shales can be divided into three types according to their sedimentary environments,namely marine,marine-continental transitional,and continental shales,which are distributed in 13 stratigraphic systems from the Mesoproterozoic to the Cenozoic.The Sichuan Basin and its surrounding areas have the highest geological resources of shale gas,and the commercial development of shale gas has been achieved in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in these areas,with a shale gas production of up to 20×10^(9)m^(3) in 2020.China has seen rapid shale gas exploration and development over the last five years,successively achieving breakthroughs and important findings in many areas and strata.The details are as follows.(1)Large-scale development of middle-shallow shale gas(burial depth:less than 3500 m)has been realized,with the productivity having rapidly increased;(2)breakthroughs have been constantly made in the development of deep shale gas(burial depth:3500-4500 m),and the ultradeep shale gas(burial depth:greater than 4500 m)is under testing;(3)breakthroughs have been made in the development of normal-pressure shale gas,and the assessment of the shale gas in complex tectonic areas is being accelerated;(4)shale gas has been frequently discovered in new areas and new strata,exhibiting a great prospect.Based on the exploration and development practice,three aspects of consensus have been gradually reached on the research progress in the geological theories of shale gas achieved in China.(1)in terms of deep-water fine-grained sediments,organic-rich shales are the base for the formation of shale gas;(2)in terms of high-quality reservoirs,the development of micro-nano organic matter-hosted pores serves as the core of shale gas accumulation;(3)in terms of preservation conditions,weak structural transformation,a moderate degree of thermal evolution,and a high pressure coefficient are the key to shale gas enrichment.As a type of important low-carbon fossil energy,shale gas will play an increasingly important role in achieving the strategic goals of peak carbon dioxide emissions and carbon neutrality.Based on the in-depth study of shale gas geological conditions and current exploration progress,three important directions for shale gas exploration in China in the next five years are put forward.

Landslide and Rockfall Distribution by Reservior of Stepped Hydropower Station in the Jinsha River

The landslides and rockfalls were studied in this paper from Xiangjiaba to Baihetan in the lower reach of Jinsha river. Their volume, distribution density and landslide index were studied which indicated that there existed close relationships between landslides and rockfalls and geological structure, stratum. The fold and faultage influenced on the stability of slope and offered the geological condition to landslides and rockfalls. The physiognomy controlled their distribution. Slope angles of landslides were 10 °-50°and slope angles of rockfalls were mainly 35°-50° in the valley in the studied area. The results indicated the geology and physiognomy of distribution area of the landslides and rockfalls in the studied area. They offered the theoretical foundation to prevent and cure geological disaster and protect the water power engineering.

Thermal Electromagnetic Radiation of Rarefied Gas

The Boltzmann kinetic equation for rarefied radiating gas is found. It is shown, that process of radiation is defined by excitation of atoms at their collision, and also spontaneous radiation of quantums at transition of electrons to the basic power level and the compelled radiation of quantums at collision of the excited atoms. It is shown, that distributions on velocities of the excited and not excited atoms submit to various laws. Distinctions in laws of distribution of the excited and not excited atoms define power parameters of radiating gas, and also a share of radiating molecules in gas.

Numerical simulation of hydraulic fracture propagation in laminated shale reservoirs

The main area of the Jiaoshiba anticline of the Fuling shale gas field was taken as the research object,laboratory rock mechanical experiments and direct shear experiments were conducted to clarify the mechanical anisotropy characteristics and parameters of rock samples with rich beddings.Based on the experimental results,a 3D fracture propagation model of the target reservoir taking mechanical anisotropy,weak bedding plane and vertical stress difference into account was established by the discrete element method to analyze distribution patterns of hydraulic fractures under different bedding densities,mechanical properties,and fracturing engineering parameters(including perforation clusters,injection rates and fracturing fluid viscosity).The research results show that considering the influence of the weak bedding plane and longitudinal stress difference,the interlayer stress difference 3–4 MPa in the study area can control the fracture height within the zone of stress barrier,and the fracture height is less than 40 m.If the influence of the weak bedding plane is not considered,the simulation result of fracture height is obviously higher.Although the opening of high-density bedding fractures increases the complexity of hydraulic fractures,it significantly limited the propagation of fracture height.By reducing the number of clusters,increasing the injection rate,and increasing the volume and proportion of high-viscosity fracturing fluid in the pad stage,the restriction on fracture height due to the bedding plane and vertical stress difference can be reduced,and the longitudinal propagation of fractures can be promoted.The fracture propagation model was used to simulate one stage of Well A in Fuling shale gas field,and the simulation results were consistent with the micro-seismic monitoring results.

Evolution of lithofacies and paleogeography and hydrocarbon distribution worldwide(Ⅱ)

Based on the compilation and analysis of the lithofacies and paleogeography distribution maps at present and paleoplate locations during six key geological periods of the Mesozoic and Cenozoic,the lithofacies and paleogeography features and their development laws were expounded.Based on our previous research results on lithofacies and paleogeography from Precambrian to Paleozoic,we systematically studied the features and evolution laws of global lithofacies and paleogeography from the Precambrian and their effects on the formation of source rocks,reservoirs,cap rocks and the distribution of oil and gas worldwide.The results show that since Precambrian,the distribution areas of uplift erosion and terrestrial clastic deposition tended to increase gradually,and increased significantly during the period of continental growth.The scale of coastal and shallow marine facies area had three distinct cycles,namely,from Precambrian to Devonian,from Carboniferous to Triassic,and from Jurassic to Neogene.Correspondingly,the development of shallow carbonate platform also showed three cycles;the lacustrine facies onshore was relatively developed in Mesozoic and Cenozoic;the sabkha was mainly developed in the Devonian,Permian and Triassic.The Cretaceous is the most important source rock layers in the world,followed by the Jurassic and Paleogene source rocks;the clastic reservoirs have more oil and gas than the carbonate reservoirs;the basins with shale caprocks have the widest distribution,the most abundant reserves of oil and gas,and the evaporite caprocks have the strongest sealing capacity,which can seal some huge oil and gas fields.

渤海海域明下段岩性油藏油柱高度分布规律及影响因素

渤海海域明下段岩性油藏特征、储量规模差异大,油柱高度作为油藏评价的关键参数,直接影响油藏储量规模,其分布规律及影响因素认识不清。基于渤海海域约460个明下段岩性油藏勘探开发数据,在充分了解地质背景的基础上,利用统计手段并结合地球化学证据,厘清了浅层明下段岩性油藏油柱高度空间展布规律,通过进一步分析油柱高度与油气充注强度、区域盖层展布、圈闭类型和断砂耦合程度等成藏要素关系,明确了油柱高度影响因素。结果表明:①受油气充注强度控制,明下段岩性油藏油柱高度平面上具有“凸起区小、凹陷区大”特征,平均油柱高度相差约2倍;②受区域盖层控制,纵向上具有“盖层之上油柱高度小、盖层之下油柱高度大”特征,下部Ⅲ/Ⅳ油组平均油柱高度为Ⅰ/Ⅱ油组约2倍;③受油气汇聚部位与侧封保存能力控制,高点依靠断裂侧封油藏油柱高度普遍高于岩性尖灭油藏的油柱高度,平均油柱高度相差约2.5倍;④明下段油气成藏受断砂耦合程度影响,但凸起区与凹陷区断裂油气运移能力差异较大,凸起区切穿馆陶组区域油气输导层断裂可起到运移作用,而凹陷区切穿深部汇聚脊的断裂才可作为有效的油源断裂。渤海海域明下段岩性油藏油柱高度分布规律及影响因素,对后续岩性油藏价值勘探、精细勘探具有借鉴意义。

Main models and distribution patterns of gas reservoirs in large-medium gas fields of China

Based on characteristics and trap types of gas reservoirs in large and medium gas fields in China, 4 gas reservoir models have been established; (i)structural trap gas reservoir model I , formed earlier than or simultaneously with generating of gases; (ii) structural trap gas reservoir model II , formed later than generating of gases; ( iii )fossil weathered residuum gas reservoir model; and (iv) mud diapir abnormal temperature and pressure gas reservoir model. Distribution patterns of large-medium gas fields are described with the concept of "sealed compartment". It is concluded that the inner-compartment area, marginal area of the compartment and the areas between two overlapped sealed compartments are the most favourable areas for discovering large-medium gas fields.

普光高含硫碳酸盐岩气田开发调整关键技术

中国石化已在四川盆地成功开发了普光和元坝两大高含硫气田,但进入“十四五”以来气田开发进入稳产中后期,面临水侵及硫沉积日益严重、剩余气分布复杂、部分气井油压接近外输压力等新问题。为实现气田稳产和提高天然气采收率,以普光高含硫碳酸岩盐气田为例(以下简称普光气田),对气田开发调整的关键技术及方法进行了系统研究,梳理了储层精细表征及建模、剩余气精细表征与挖潜、控水、控硫、增压开采等5个方面形成的关键技术。研究结果表明:①揭示了礁滩相碳酸盐岩储层不同储集空间类型的孔-渗特征,形成了“相控+震控”储层精细建模技术,精细表征了储层非均质性空间展布;②建立了普光气田5种类型剩余气分布模式,确定了普光气田储层非均质性控制纯气区剩余气分布,受井网完善程度和高渗条带分布控制,水侵区剩余气分布呈现小零散特征,形成了不同类型剩余气挖潜技术;③提出了普光气田采取“高部位控产、低部位排堵结合”的控水治水对策,实现水侵前缘均匀推进;④明确了储层硫沉积主要发生在近井地带(小于6 m),可导致渗透率最大下降70%~80%(表皮增大6.5~12倍),实验证实了重复酸压治硫效果好于注入溶硫剂;⑤建立了考虑产水及硫沉积的气井多相渗流产能评价方法,确定了气田增压潜力、增压幅度、增压时机及增压方式。结论认为,普光高含硫碳酸盐岩气田开发调整关键技术的实施,确保了气田自“十四五”以来稳产目标的实现,研究成果对我国高含硫气田开发调整具有重要的指导和借鉴意义。

致密油水平井温度剖面影响规律研究

由于目前缺乏可靠的致密油水平井温度剖面预测模型、对致密油水平井温度剖面影响规律认识不清,导致基于分布式光纤的致密油水平井产出剖面定量评价仍是一项技术难题。鉴于此,创建了考虑多种微热效应的致密油水平井温度剖面预测模型,探究了井筒温度剖面受不同单因素变化的影响,通过正交试验,确定不同因素的敏感性由强到弱依次为:产量、裂缝半长、储层渗透率、井筒直径、水平倾角、裂缝导流能力、储层总导热系数(Q>x_(f)>K>D>θ>F_(CD)>K_(t)),明确了影响致密油水平井温度剖面的主控因素为裂缝半长和储层渗透率。研究成果为定量分析致密油水平井井筒流动剖面、人工裂缝等参数提供了可用温度模型和理论支撑。

鄂尔多斯盆地延长期湖盆底面构造定量化演化规律

为定量恢复鄂尔多斯盆地延长期湖盆底面构造及其演化特征,基于盆地500口钻井资料,采用盆地模拟技术方法进行研究。结果表明:延长期盆地中部和南部分别发育有一沉降中心,中部各期沉降中心轴线在定边-甘泉一线迁移,西南部各期沉降中心轴线在环县-旬邑一线迁移;长7期湖盆是中、西南部两个湖盆合二为一的时期,盆地中部湖盆坳陷,长10-长9期湖盆沉降中心轴一致,长8期沉降中心轴逆时针旋转、向北迁移,长7期后沉降中心轴迁移至盆地中部、呈北东-南西向展布,长6期又向东北方向迁移,长4+5至长3期,沉降中心轴线又逆时针旋转迁移至盆地中部;对于盆地西南部湖盆坳陷,各期沉降中心围绕环县-旬邑一线迁移幅度相对较小,沉降中心轴是向东北迁移至盆地中部,中部湖盆坳陷是向西南迁移,长7期整个盆地演变为一个湖盆,湖盆迁移对砂体、油藏的分布具有控制作用。各沉积期湖盆底面凹凸构造面貌特征,对于识别沉积坡折带有一定的指导意义。

Study on fracture characteristics in coal and shale for coal-measure gas reservoir based on 3D CT reconstruction and fractal features

Pores and fractures are important components of flow channels in coal-measure gas reservoirs.While considerable studies have been conducted on pore structure evolution,very few studies have investigated the fracture distribution and self-similarity characteristics.To reveal the characteristics of fracture distribution in coal and shale reservoirs,computed tomography studies were performed on 15 coal and shale samples from the Shanxi and Taiyuan formations.The results show that the fracture distribution of samples of the same lithology differs significantly,and the fracture distribution heterogeneity of shale samples is much higher than that of coal samples.In shale,the heterogeneity of fracture distribution is mainly caused by pores and fractures smaller than 2μm in the z-direction,with relatively little contributions from pores and fractures in the x and y directions.However,the heterogeneity of fracture distribution in coal is mainly controlled by pores and fractures larger than 2μm in all directions,and the difference between the three directions is minor.It was shown that a great number of microscopic pores and fractures contribute to the highest fractions of porosity in different lithological samples.This method is useful for determining the fracture distribution characteristics in shale and coal-measure gas reservoir.

Distribution and transportation of nitrogen in Miyun reservoir waters

The Miyun reservoir is an important water supply for Beijing city. The distribution laws of nitrogen in the Miyun reservoir waters and the transportation factors have been systematically analyzed in space and time by using water monitoring data sampled in the high-water and low-flow periods in 2001 and 2002. The nitrogen in east and west reservoir waters is distributed differently in space. It shows the change characteristics in high-water and low-flow periods and is affected by the source of nitrogen, runoff conditions, hydrodynamic conditions, precipitation and the control of bed mud, of which the source of nitrogen controls the change of concentration of nitrogen, the peripheral runoff controls the distribution law of nitrogen, bed mud controls the vertical distribution of nitrogen, and the contents of nitrogen and its change in the surrounding environment directly cause the change of concentration of total nitrogen in the waters. The improvement and protection of the waters in the Miyun reservoir basically rests with the amelioration of the peripheral environment.

鄂尔多斯盆地陕北斜坡东部三叠系长2油藏分布规律

鄂尔多斯盆地陕北斜坡为一平缓的西倾单斜,构造简单。通常认为包括长2油藏在内的三叠系延长组油藏的形成和分布主要受沉积相控制,油藏类型主要为岩性油藏,构造等其他因素对油藏的形成和分布并不起重要控制作用。但研究发现,陕北斜坡三叠系长2油藏的形成与富集实际上受沉积相带、鼻状隆起背景、断裂、水动力等多重因素控制。鼻状隆起,尤其是大型鼻状隆起的围斜部位油藏最为富集;断裂是长2油藏形成和分布的重要控制因素;水动力条件是油藏上倾方向重要的遮挡因素之一。因此,长2油藏的类型复杂多样,除岩性油藏外,以构造-岩性、构造-水动力油藏为主的复合油藏可能是该区长2油藏的主要类型。

低渗透储层成因机理及优质储层形成与分布

对几个典型的岩性油气藏中低孔隙度低渗透率储层的形成原因,及优质储层的形成与分布规律研究发现,沉积作用是形成低渗透储层的最基本因素,它决定了后期成岩作用的类型和强度,成岩早期强烈的压实作用和胶结作用对形成低孔隙度、低渗透率储层起了决定性作用;优质储层的形成与分布主要受层序界面、有利沉积相带、有机酸性水的溶蚀作用等因素的控制。一般来说,优质储层纵向上主要分布在三级层序的中下部、平面上主要分布在三角洲平原或前缘多期分流河道叠置的部位。它们在有机酸性水形成时期保留了较多的原生孔隙,酸性水容易进入孔隙及溶解其中易溶的碎屑颗粒和胶结物,并产生大量次生溶蚀孔隙,从而形成优质储层。

海拉尔盆地油气分布规律及下步勘探方向

海拉尔盆地是叠置于内蒙—大兴安岭古生代造山带上的中生代、新生代盆地。该盆地由北东向断裂控制的多个相对独立的断陷群组成,盆地内主要为下白垩统地层, 即兴安岭群、铜钵庙组、南屯组、大磨拐河组、伊敏组。铜钵庙组、南屯组和大磨拐河组发育了三套烃源岩,烃源岩厚度较大,有机质含量高。储层类型主要包括基岩风化壳、砂岩、凝灰质砂岩和砾岩。低水位体系域形成的低水位扇和低水位楔,以及高水位体系域形成的扇三角洲砂体为油气的主要储层。在大磨拐河组区域盖层下,发育了多套生储盖组合。纵向上油气主要富集在不整合面上下,形成断块、断层—岩性、岩性和潜山油气藏四大类油气藏,平面上油气主要集中在主生油凹槽及周边的几个断裂带上,扭动断裂带是油气聚集的有利区带。

渤海湾盆地北部奥陶纪岩相古地理

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