Geologic characteristics,exploration and production progress of shale oil and gas in the United States:An overview

We present a systematic summary of the geological characteristics,exploration and development history and current state of shale oil and gas in the United States.The hydrocarbon-rich shales in the major shale basins of the United States are mainly developed in six geological periods:Middle Ordovician,Middle-Late Devonian,Early Carboniferous(Middle-Late Mississippi),Early Permian,Late Jurassic,and Late Cretaceous(Cenomanian-Turonian).Depositional environments for these shales include intra-cratonic basins,foreland basins,and passive continental margins.Paleozoic hydrocarbon-rich shales are mainly developed in six basins,including the Appalachian Basin(Utica and Marcellus shales),Anadarko Basin(Woodford Shale),Williston Basin(Bakken Shale),Arkoma Basin(Fayetteville Shale),Fort Worth Basin(Barnett Shale),and the Wolfcamp and Leonardian Spraberry/Bone Springs shale plays of the Permian Basin.The Mesozoic hydrocarbon-rich shales are mainly developed on the margins of the Gulf of Mexico Basin(Haynesville and Eagle Ford)or in various Rocky Mountain basins(Niobrara Formation,mainly in the Denver and Powder River basins).The detailed analysis of shale plays reveals that the shales are different in facies and mineral components,and"shale reservoirs"are often not shale at all.The United States is abundant in shale oil and gas,with the in-place resources exceeding 0.246×10^(12)t and 290×10^(12)m^(3),respectively.Before the emergence of horizontal well hydraulic fracturing technology to kick off the"shale revolution",the United States had experienced two decades of exploration and production practices,as well as theory and technology development.In 2007-2023,shale oil and gas production in the United States increased from approximately 11.2×10^(4)tons of oil equivalent per day(toe/d)to over 300.0×10^(4)toe/d.In 2017,the shale oil and gas production exceeded the conventional oil and gas production in the country.In 2023,the contribution from shale plays to the total U.S.oil and gas production remained above 60%.The development of shale oil and gas has largely been driven by improvements in drilling and completion technologies,with much of the recent effort focused on“cube development”or“co-development”.Other efforts to improve productivity and efficiency include refracturing,enhanced oil recovery,and drilling of“U-shaped”wells.Given the significant resources base and continued technological improvements,shale oil and gas production will continue to contribute significant volumes to total U.S.hydrocarbon production.

Control Factors and Diversities of Phase State of Oil and Gas Pools in the Kuqa Petroleum System

Based on the analysis of the hydrocarbon geochemical characteristics in the Kuqa petroleum system of the Tarim Basin, this study discusses the causes and controlling factors of the phase diversities and their differences in geochemical features. According to the characteristics and differences in oil and gas phase, the petroleum system can be divided into five categories： oil reservoir, wet gas reservoir, condensate gas-rich reservoir, condensate gas-poor reservoir and dry gas reservoir. The causes for the diversities in oil and gas phases include diversities of the sources of parent material, maturity of natural gas and the process of hydrocarbon accumulation of different hydrocarbon phases. On the whole, the Jurassic and Triassic terrestrial source rocks are the main sources for the hydrocarbon in the Kuqa Depression. The small differences in parent material may cause diversities in oil and gas amount, but the impact is small. The differences in oil and gas phase are mainly affected by maturity and the accumulation process, which closely relates with each other. Oil and gas at different thermal evolution stage can be captured in different accumulation process.

An improved data space inversion method to predict reservoir state fields via observed production data

A data-space inversion(DSI)method has been recently proposed and successfully applied to the history matching and production prediction of reservoirs.Based on Bayesian theory,DSI can directly and effectively obtain good posterior flow predictions without inversion of geological parameters of reservoir model.This paper presents an improved DSI method to fast predict reservoir state fields(e.g.saturation and pressure profiles)via observed production data.Firstly,a large number of production curves and state data are generated by reservoir model simulation to expand the data space of original DSI.Then,efficient history matching only on the observed production data is carried out via the original DSI to obtain related parameters which reflects the weight of the real reservoir model relative to prior reservoir models.Finally,those parameters are used to predict the oil saturation and pressure profiles of the real reservoir model by combining large amounts of state data of prior reservoir models.Two examples including conventional heterogeneous and unconventional fractured reservoir are implemented to test the performances of predicting saturation and pressure profiles of this improved DSI method.Besides,this method is also tested in a real field and the obtained results show the high computational efficiency and high accuracy of the practical application of this method.

Hydrate phase transition and seepage mechanism during natural gas hydrates production tests in the South China Sea:A review and prospect

Natural gas hydrates(NGHs)are globally recognized as an important type of strategic alternative energy due to their high combustion efficiency,cleanness,and large amounts of resources.The NGHs reservoirs in the South China Sea(SCS)mainly consist of clayey silts.NGHs reservoirs of this type boast the largest distribution range and the highest percentage of resources among NGHs reservoirs in the world.However,they are more difficult to exploit than sandy reservoirs.The China Geological Survey successfully carried out two NGHs production tests in the Shenhu Area in the northern SCS in 2017 and 2020,setting multiple world records,such as the longest gas production time,the highest total gas production,and the highest average daily gas production,as well as achieving a series of innovative theoretical results.As suggested by the in-depth research on the two production tests,key factors that restrict the gas production efficiency of hydrate dissociation include reservoir structure characterization,hydrate phase transition,multiphase seepage and permeability enhancement,and the simulation and regulation of production capacity,among which the hydrate phase transition and seepage mechanism are crucial.Study results reveal that the hydrate phase transition in the SCS is characterized by low dissociation temperature,is prone to produce secondary hydrates in the reservoirs,and is a complex process under the combined effects of the seepage,stress,temperature,and chemical fields.The multiphase seepage is controlled by multiple factors such as the physical properties of unconsolidated reservoirs,the hydrate phase transition,and exploitation methods and is characterized by strong methane adsorption,abrupt changes in absolute permeability,and the weak flow capacity of gas.To ensure the long-term,stable,and efficient NGHs exploitation in the SCS,it is necessary to further enhance the reservoir seepage capacity and increase gas production through secondary reservoir stimulation based on initial reservoir stimulation.With the constant progress in the NGHs industrialization,great efforts should be made to tackle the difficulties,such as determining the micro-change in temperature and pressure,the response mechanisms of material-energy exchange,the methods for efficient NGHs dissociation,and the boundary conditions for the formation of secondary hydrates in the large-scale,long-term gas production.

海上底水稠油油藏油水相渗特征实验及影响因素研究

海上稠油油田大部分都伴随着边水或底水,底水稠油油藏生产特征为含水率上升快、采出程度低,从而影响油田产量。为了更好地了解底水稠油油藏水驱开发特点,为后期方案调整及提高采收率技术决策提供依据,针对底水稠油油藏地质特点和流体性质,利用物理模拟实验方法,开展了底水稠油油藏条件下油水相对渗透率实验研究,对比了稳态法与非稳态法2种相渗实验方法的差异性,并分析了底水稠油油藏相渗曲线特征。研究表明,油水相渗曲线主要表现为油相水相相对渗透率总体偏低并呈现凸型、油相相对渗透率下降幅度快、油水共渗点低,且稳态法相渗曲线形态更为准确,可为该类型油藏动态预测及精细挖潜提供参考。

油气藏流体-CO_2体系相行为的实验测定与计算

利用高压相平衡实验装置 ,对某油田F6 6A井和F30井的原油在油藏温度下注入不同量的CO2 (注入CO2 与油藏流体的摩尔比为 0～ 2 .0 0 )时的PVT关系进行了测定 ,共取得PVT数据点 16 5个 ,泡点压力点和体积系数点各 11个。实验结果表明 ,由于原始油样的组分结构和组成不同 ,其注气体系相行为有较大的不同。F6 6A井油藏原油的饱和 (泡点 )压力随着CO2 注入量的增加近似呈线性增加 ,而F30井的饱和压力和CO2 注入量之间呈二次曲线关系 ,上升速度比F6 6A井缓慢 ,注气体系的体积系数的增加速度与CO2 注入量近似呈直线关系。对油藏流体中各组分进行适当组合合并为假组分后 ,用PR和SRK状态方程对所测注CO2 原油体系的相行为进行了预测。结果表明 ,PR状态方程的预测精度优于SRK方程 ,但两者均不能用于计算高CO2

基于多轮次注采渗流实验分析的挥发性油藏储气库建库可行性评价

油藏型储气库兼具提高原油采收率及储存天然气两大作用,目前受到了国内外专家的广泛关注。但油藏建库远比气藏建库复杂,国内外针对油藏型储气库渗流特征、相态变化特征、建库可行性等方面的研究较少,严重制约了油藏型储气库的发展。为此,以冀东油田某断块油藏为例,开展多周期注采相渗实验测试、长细管混相压力实验测试,结合油气相态实验与气驱油多周期注采实验,分析明确油藏型储气库建库可行性及建库过程中的渗流规律。研究结果表明:①原油与天然气混相压力为36.2 MPa(高于设计上限压力35 MPa),注采过程中不能发生混相;②注入气溶解能够使原油黏度降低、体积膨胀,经5轮次注采后,天然气抽提能力变弱,原油黏度降低幅度减小,注气改善原油性质的能力略有下降;③经过5轮次油—气和水—气注采后,油和水仍保持较高的渗流能力,但气—油、气—水两相共渗区变窄,渗流能力减弱,气驱油和水效率有一定下降;④相比于水驱,经过5轮次注采后,可提高原油采收率20%,岩心内含气饱和度达到47%。结论认为,多周期注采后能够形成较大库容,且在此基础上能够大幅度提高采收率,该研究成果可为油藏型储气库建设提供技术支持。

不同类型凝析气藏在低渗多孔介质中的相态及采收率研究

用凝析油含量不同的凝析气分别在PVT筒和长岩心中进行了衰竭实验,并应用超声波测试技术测试了其饱和度以及高温、高压平衡凝析油气相渗曲线和常温、低压常规油气相渗曲线。实验表明,凝析油含量高的凝析气在多孔介质中凝析油的采收率比PVT筒中约高1倍。采用不同相渗曲线及CMG数值模拟软件对长岩心衰竭实验中凝析油的采收率进行了预测,结果表明,造成凝析油采收率差别的主要原因是界面张力导致凝析油气相渗曲线的差别。在数值模拟中,应当使用真实相渗曲线。对于含凝析油低的凝析气藏,多孔介质中定容衰竭凝析油饱和度远高于PVT筒中凝析油采收率,多孔介质中蒸发现象不明显。凝析油饱和度达到最大值后,随压力的降低不再变化,这表明低渗凝析气藏中尽管凝析油含量低,其污染仍然存在,不能忽视。

塔里木盆地凝析气藏形成的地质-地球化学条件

塔里木盆地凝析气藏数量多、分布广、储量大，是我国凝析气藏最富集的盆地。在凝析气形成机理及相态成因研究基础上，综合分析了塔里木盆地的成藏特征，并与四川、鄂尔多斯和吐哈等盆地进行对比分析，认为塔里木盆地凝析气藏具有两种形成机理三类相态成因的特征。盆地内富集凝析气藏的内在地化因素是不同类型烃源岩处于有利的热演化阶段，而晚期大幅度沉降和晚期气相运移聚集为凝析气藏的形成提供了重要的温压及保存条件。此外，油气的生成和聚集异步演化有利于过成熟干气富化为凝析气藏。

松辽盆地古龙凹陷典型油气藏相态类型综合判别

油气藏相态类型的判别方法很多,对油气藏相态的认识每种方法所得结果一方面有各自的局限性,另一方面又有其不确定性.利用计算PVT相图法和5种常用的经验统计法(秩数法、Z值法、因子法、汽油比法和相对分子质量法),对4个代表性油气层的相态进行综合判别.结果表明,综合判别既可以相互验证,又可以全面认识油气藏相态信息;英51井和古109井的葡萄花油层为带油环中含凝析油凝析气藏.

凝析气藏油气体系相态测试与拟合

凝析气藏是经济价值很高的特殊类型气藏。凝析气藏的开发与其油气体系的相态特征密切相关,其相态特征直接关系到开发阶段的划分,开发技术政策的制定,油、气井的正常生产开发指标预测等。文章通过实例介绍了凝析气藏油气体系PVT分析的测试、拟合以及流体类型判别方法。

挥发性油藏轻烃回收理论研究

以长春油田为挥发性油藏实例，通过流作物性分析资料和实际生产特征的研究，认为挥发性油藏的特殊性取决于它的烃类体系的组分组成特征。该类油（气）藏开发过程中轻烃回收是必要的。以热力学和相平衡理论为基础，选用PR状态方程建立了轻烃回收的相态模型，并且进行了可行性和精度检验。对长春油田进行了轻烃回收模拟计算，获得了具有理论和实际意义的结论。

石油与天然气运移研究综述

石油与天然气都是流体矿产，在岩石中的运移主要是一种地球物理作用。油气运移研究的主要问题是动力学和运动学机制，也就是运移的动力、相态、通道和数量。初次运移的动力主要是异常高压，二次运移的动力主要是浮力和流体势差。石油运移的相态主要是油相，天然气可以是水溶相、油溶相、气相和扩散相。石油以油相运移、天然气以气相运移最为有效，无需相态转变就能直接成藏。初次运移的通道主要是微裂隙。并不是所有可渗透岩石都是二次运移通道，有效运移通道和主流向是二次运移的特征。断层在活动时具通道性，活动期后的封闭与成岩作用有关，长期活动的断层是油气运移的通道。油气运移动力的积蓄与释放和通道的开启与封闭交替出现，决定了排烃和二次运移都是幕式的，从而决定了充注圈闭和成藏的幕式性，这已得到油藏地球化学研究的证实。油气幕式运移与地流体的幕式流动都与地壳的幕式构造活动相辅相成、互为因果。油气运移是发生在地质历史过程中的事件，因此其研究方法应当是动态分析和综合研究。目前油气运移研究仍存在很多理论和方法上的问题，加强基础理论的研究、总结各类盆地的运聚规律、提高计算机模拟和实验室模拟的水平。

储层非均质性对大涝坝凝析气藏注气开采效果的影响

为有效认识储层非均质性对凝析气藏注气开采效果的影响,以大涝坝凝析气藏基本地质及流体相态特征为基础,利用数值模拟方法研究和对比不同非均质程度对注气效果的影响.研究结果表明:凝析气藏层间非均质性对注气效果有较大的影响,非均质性越强,层间气窜现象越突出,反凝析现象越明显,凝析油采出程度越低.5、10、20倍渗透率级差模型析出的凝析油量分别较均质模型增加了0.88%、1.07%、1.24%,相应凝析油的采收率分别降低了3.76%、4.78%、6.60%;对非均质性较弱的中、高含凝析油凝析气藏,采用注气保压开采可获得较好的开发效果;对于非均质性较强的凝析气藏,是否适宜注气需进一步评价论证.

状态方程及其应用于石油与天然气相平衡计算的有关进展

本文对状态方程的发展历史作了概要的回顾，重点评价在油气藏数值模拟中有重要应用价值的立方型状态方程的有关研究和应用进展，并指出了在地层多相流相平衡计算中的有关难点问题，如天然气采出过程的逆向冷凝、三次采油混相驱、烃－水体系高压液－液平衡等问题的研究方向和提高预测模型精度的方法。

库车油气系统烃类的流体相态特征研究

库车油气系统已经发现了 2 2个油气藏 ,其相态类型的多样性的特点十分鲜明 ,据这些油气藏的 43层PVT实验数据和相图 ,可以把库车油气系统的烃类分为四类 7种。探明的油气储量和油气资源预测结果表明该系统“整体富气” ,黑油、挥发油处于从属地位 ,而且多为分异作用形成的伴生型和残余型的轻质油。综合分析油、气的物理性质、相态参数和系统的油气资源等地质条件 ,可明显地看出天然气的干湿程度及凝析油含量的高低主要受烃源岩成熟度控制 ;系统的成藏条件和勘探成果 (特别是克拉 2大气田的发现 )都说明高温裂解气潜力很大 ,其主要分布在北带中段高—过成熟区 。

凝析油-气不稳态渗流问题及其压降曲线

根据凝析气相态特征,采用凝析气田的原始相态资料,研究了凝析气在相态转换过程中储层内气体中可凝缩液体的体积分数、质量分数与气藏压力的关系及具体计算方法,建立了凝析油-气在多孔介质中的渗流方程。在考虑到井筒内存在凝析油-气相态重分布的情况下,建立了凝析气在复杂气藏内油-气两相不稳态渗流问题的新模型,求出了3种典型气藏外边界条件下的凝析油-气两相拟压力分布解析解,并绘出了井底压降曲线,给出了应用实例。

基于孔隙尺度的低渗透油藏CO_2驱替特征研究

基于多孔介质油气两相渗流理论,采用截断威布尔分布作为孔喉特征分布函数,模拟储层岩心的气驱油过程,建立了能够反映多孔介质孔隙尺度的油气两相三维孔隙网络模型,推导了不同CO2驱替相态下界面张力及接触角计算公式。利用建立的孔隙网络模型,研究了相态变化对驱替效率的影响,从微观角度分析了不同CO2驱替相态下的驱替特征和驱油效果。结果表明:对于孔隙度以及颗粒分布状况相同的储层结构,在注入条件相同的情况下,与非混相驱替相比,实现CO2混相驱可以将原油的驱替效率提高约15%。

改进型Du-Guo状态方程及其在高含CO_2油藏原油中的应用

实验测定了国产抚余、江汉、华北油藏原油及其注CO_2体系的全套PVT数据(共366点)。基于50种纯物质的饱和性质对DG三参数立方型状态方程的参数进行了新的关联,建立了改进型的DG状态方程(MDG方程),并将其扩展应用到高含CO_2油藏原油体系。基于自测及文献数据对该模型应用于高含CO_2油藏原油PVT性质预测的准确性进行了检验,内容包括饱和压力、液相密度、恒组成膨胀和多级脱气过程的模拟。此外,还与石油界知名的商用软件包STATPACK比较了计算结果。

凝析气藏相态计算及储量预测

烃类体系的相态特征研究对油气田的开发与开采具有重要意义。针对实际开采凝析气藏遇到的实际情况 ,研究了凝析气藏的相态计算方法 ,并利用此方法编制出相态计算实用软件。将软件应用于凝析气实例井的相态计算和气藏储量预测 。