Pressure transient analysis for fluid flow through horizontal fractures in shallow organic compound reservoir of hydrogen and carbon

Pure hydrogen does not occur in large quantities in nature, and it is usually locked up in energy-rich organic compound. One of the challenges to sustain the usage of hydrogen energy is to produce sufficient energy-rich organic compound from the organic compound reservoir of hydrogen and carbon, which requires understanding the fluid flow behavior through such reservoir. The horizontal fractures can be created during the hydraulic fracturing process in shallow energy-rich organic compound reservoirs due to the geo-mechanical effect. However, it lacks of a comprehensive analytical model to describe the transient flow behavior through the horizontal fractures. In this paper, an analytical model for horizontal fractures in shallow organic compound reservoirs considering the effects of wellbore storage and skin factor with constant pressure, closed and infinite boundary conditions, are presented to investigate pressure transient behavior and flow characteristics. The analytical solution is derived in Laplace domain, which may require numerical inverse transform to obtain the solution real space. To obtain the explicit form in real space, the approximate solutions for early time, middle time and late time are also presented to investigate the characteristics of type curves. Type curves are established for the transient pressure analysis to recognize the flow characteristics through horizontal fractures. Flow for horizontal fractures can be divided into five stages according to characteristics of dimensionless pseudo pressure derivative curve. The effects of parameters on pressure behavior are discussed in detail, which include wellbore storage coefficient, dimensionless formation thickness, dimensionless vertical location, and skin factor. The results indicate that horizontal fractures are more applicable in thin instead of thick reservoirs.     

Pressure transient analysis for asymmetrically fractured wells in dual-permeability organic compound reservoir of hydrogen and carbon

In this paper, a comprehensive semi-analytical model was presented to investigate pressure transient behavior for asymmetrically fractured wells in organic compound reservoir of hydrogen and carbon with dual-permeability behavior. Stehfest inversion algorithm can be used to transform it back into time domain to obtain pressure solution. The presented solution was validated well with numerical solutions. Flow characteristics for asymmetrically fractured wells in dual-permeability organic compound reservoir of hydrogen and carbon were divided into five regime. The effects of some important parameters on dimensionless pressure and its derivative curves were analyzed in details, including inter-porosity flow coefficient from matrix to natural fractures λ, storage coefficient ω, fracture asymmetry factor θ and permeability ratio κ. The presented model can be used to predict production performance and do well test analysis in the development of dual-permeability organic compound reservoir of hydrogen and carbon.     

Optimization experimental design of stable production life and estimated ultimate recovery in gaseous compound of hydrogen and carbon from shale reservoir

In this study, a mixed numerical model is established to simulate the production performance of gaseous compound of hydrogen and carbon in shale reservoir. Estimated ultimate recovery (EUR) and stable production life (SPL) of gaseous compound of hydrogen and carbon are affected by reservoir parameters and production control parameters, such as Langmuir pressure, Langmuir volume, critical desorption pressure, fracture half length, permeability in stimulated reservoir volume (SRV) area, bottom hole flow pressure and production of gaseous compound of hydrogen and carbon. Therefore, in the later research, in order to reduce the number of numerical experiments, the orthogonal experimental method is used to optimize the influence of hydrocarbon ERU and SPL, and analyze the main control factors affecting these two indices at the same time. The purpose of this paper is to optimize the production of hydrocarbons by orthogonal experimental method and find the main controlling factors affecting the production of compound of hydrogen and carbon. Two groups of orthogonal experiments were designed to find the best scheme in the process of compound of hydrogen and carbon development. The calculative results show that the output of hydrogen and carbon compounds has a highly significant impact on SPL, Langmuir volume and capability in SRV have a significant impact, and Langmuir pressure Critical destruction pressure and hydraulic fracture half-length had no significant effects.     

Effect of retrograde condensation on the production performance of organic hydrogen compounds energy

The gas-condensate reservoirs are typical organic fossil reservoirs of hydrogen compounds energy. With the development of gas-condensate reservoirs, a part of condensate liquid of hydrogen compounds will appear under the influence of retrograde condensation mechanism. However, the effects of retrograde condensation on the production performance of organic hydrogen compound energy with different well types are still not clear. In this study, a series of numerical simulation models were established to investigate the law of retrograde condensation with different well types and reservoir permeabilities. Furthermore, the effects of retrograde condensation on gas well productivity were analyzed by the comparison between the compositional modeling and black oil modeling results. Results show that the condensate oil for the fractured wells is mainly distributed around the fracture tips instead of the perforation intervals for the unfractured wells. The maximum oil saturation and condensate area of two fractures at ends are much larger than those of middle fractures. The retrograde condensation exhibits a negligible impact on the production of multiple fractured horizontal wells with a cumulative gas production reduction 0.87%–1.57%. Hydraulic fracturing, multiple fractures and high reservoir permeability are conducive to lower the impact of retrograde condensation on the production of organic hydrogen compounds energy.     

A generalized analytical model for hydrocarbon production using multi-fractured horizontal well with non-uniform permeability distributions

The multi-fractured horizontal well (MFHW) has significantly facilitated the exploitation of unconventional hydrogen-carbon compound reservoirs, which is an abundant source of fossil hydrogen energy. The composite linear flow models were frequently adopted to analytically evaluate the hydrocarbon production using MFHW. Most of the existing composite linear flow models assume uniform permeability in the primary fractures and the Stimulated Reservoir Volume (SRV) region. However, due to the non-uniform proppant distribution in the primary fractures and the heterogeneity in the density of the secondary fractures in SRV region, the permeability field in both regions are non-uniform. For the first time, a generalized analytical model incorporating continuous permeability heterogeneity in both the primary fractures and SRV region is proposed for the hydrocarbon production of MFHW. Any arbitrary permeability distribution functions can be treated as inputs to the proposed model. The mathematical model is solved using the perturbation technique and the Laplace transform method.The good match with the numerical solution verifies the accuracy of the proposed analytical model. Subsequently, the proposed solution is assigned with different modes of permeability heterogeneity to investigate their impacts on well production performances, i.e., cumulative hydrocarbon production and transient bottom-hole pressure (BHP). The results reveal that the incorporation of permeability heterogeneity will enhance the production rate and lower the BHP drawdown compared to the homogeneous case with the same average permeability. Besides, a field case is presented to demonstrate the applicability of the proposed model.     

Productivity analysis of fractured wells in reservoir of hydrogen and carbon based on dual-porosity medium model

Hydrogen is usually locked in energy-rich organic compounds and there is almost no pure hydrogen in nature. Organic compounds produced in reservoirs of hydrogen and carbon are an important source of hydrogen production. Understanding the productivity characteristics reservoirs of hydrogen and carbon is the important step to ensure adequate hydrogen energy. This study analyzes the production of hydraulically fractured organic reservoir of hydrogen and carbon. First, based on the diffusion mechanism in reservoir matrix, a multi-scale dual-porosity medium model of reservoir of hydrogen and carbon is established. Then, the mathematical model is solved and verified through a historical matching of field gas production data. Finally, parameter analysis was performed to determine the key parameters to improve the recovery efficiency in organic reservoir of hydrogen and carbon. Results show that improving fracture permeability can improve gas recovery efficiency of hydrocarbon reservoirs. The matrix desorption can develop natural gas production for a long period. Long sizes of hydraulic fractures have large contact surfaces for gas diffusion and increase gas generation and cumulative gas production. The proposed model can predict and analyze the production performance of reservoirs of hydrogen and carbon.     

贵州合层开发煤层气井产层孔渗特征研究

贵州省煤层发育,煤层气资源富集,对其合层开发煤层气产层孔渗特征进行研究能够为煤层气高产、稳产提供依据。基于贵州合层排采煤层气井产层特征统计,综合现有地质及工程数据,系统研究产层孔渗特征。研究结果表明：贵州境内受煤变质程度高的影响,煤层气产层孔隙度较低,主要在2% ～ 6%之间;煤储层大多发育两组相互近正交的内生裂隙,外生裂隙则与区内深大断裂活动以及煤层厚度有关;产层渗透率均低于0.35 mD,属于中低渗透率产层,且以小于0.1 mD的低渗产层为主。     

GVR成像测井在礁灰岩油田水平井开发中的实例分析

礁灰岩储层的双重介质特征决定了油田开发中水平井钻井风险高,有效储层钻遇难度大。为了确保钻井安全,提高储层钻遇率,在南海东部礁灰岩油田水平井开发中,应用GVR成像测井技术,对水平井进行实时地质导向,快速识别地层倾角以及裂缝,根据地层倾角的变化和裂缝发育程度,优化钻井轨迹。流花油田开发实践表明,利用GVR成像测井技术实施的7口水平井均没有发生严重井漏,成功规避了钻井风险,且单井初始日产油量在283.3~1828.4m3,确保了优质储层钻遇率。同时,GVR成像测井的裂缝解释突破了传统单一依靠地震的识别方法 ,为定量描述井旁裂缝空间分布以及裂缝对产能的影响研究提供了基础。研究表明,礁灰岩储层中单井产能与裂缝发育程度有较好的对应关系,单井裂缝发育程度越高其产能也越高,为油田后期调整井的设计和实施提供了地质依据。     

重力泄水辅助蒸汽驱采油工艺技术研究与试验

洼59块为深层中厚层状特超稠油油藏。区块已进入高轮次吞吐阶段,吞吐效果逐轮变差,采油速度急剧递减。采用重力泄水辅助蒸汽驱技术,探索深层特超稠油油藏蒸汽吞吐开发后期开发方式的转换。该技术采用直井、水平井组合开发模式,上叠置水平井注汽,下叠置水平井辅助排液,周围直井产油。针对工艺技术难点,通过汽水分离器、高效隔热管柱和环空注氮隔热的综合应用,实现了深层稠油油藏井底干度大于45%的目标;采用双管注汽技术使水平段得到高效动用;通过电加热降黏和防偏磨技术的成功应用,解决了试验初期黏度大、水平井杆管偏磨的问题;利用越层深抽和高温大排量举升解决了提液降压、深层高温大排量举升的难题。井组整体效果明显,产液量由179t/d增大到最高值526.9t/d,产油量由31.0t/d增大到最高值96.5t/d,含水由91.1%下降到平均值84.69%。     

A new numerical simulation method of hydrogen and carbon compounds in shale reservoir

Hydrogen energy can be produced by the decomposition of hydrogen and carbon compounds. A numerical analysis method of accuracy and efficiency provides important reference value for optimizing development plans and predicting production performance of hydrogen and carbon compounds. In this work, embedded discrete fracture model (EDFM) is used to study the production performance of hydrogen and carbon compounds under non-liner seepage under the threshold pressure gradient and complex fracture systems consist of the hydraulic fractures, secondary fractures, natural fractures. A dual-permeability model of the same case is also constructed as a comparison study to analyze the development of hydrogen and carbon compounds. On this basis, the influence of threshold pressure gradient on production of hydrogen and carbon compounds is quantitatively evaluated in this paper to modify the numerical model and a novel method for the simulation of fractured hydrogen and carbon compounds reservoirs is provided. Through model comparison, the impact of fractures in the reservoir on production can reach 289.1%. A dual-permeability model of the same case is also constructed as a comparison study to analyze the development of the reservoir and the result shows a 7.9% distinction on the cumulative production. It is analyzed that when the threshold pressure gradient is increased from 0.1 MPa/m to 0.6 MPa/m, the output decline of different models ranges from 6% to 15% and a novel method improving model fidelity for the simulation of fracture reservoirs is provided.     

Well-testing in travale-radicondoli field. Part V. Concluding statement on pressure transient studies made from well tests in the Travele-Radicondoli reservoir

The theory and applications of pressure transient (well test) analysis have been studied intensively for more than 40 yr by petroleum reservoir engineers and groundwater hydrologists. Only in the past decade, however, have geothermal-fluid wells been tested for the purpose of making pressure transient studies. Results of these studies disclose various well conditions, for example, restrictions to fluid flow into the wellbore. They also disclose reservoir heterogeneities, boundaries and permeability-thickness products of reservoir rocks. Probably most important, they can be used in estimations of energy reserves. This powerful analytical tool is discussed with special reference to the Travale reservoir.This reservoir is complicated geologically and hydrologically. It lies on the margin of a graben near a widespread outcrop of the reservoir rocks, which also form an absorption area for the meteoric waters. The area explored can be divided into three zones: in one of these (the nearest to the absorption area) some noncommercial wells produce two-phase water-steam mixtures; in the second zone the wells produce superheated steam, while a well drilled in the graben itself produces a fluid with an uncondensable gas content of about 80%. The reservoir is described in relation to defining areas for further exploration. The nature of the reservoir has affected the design of programs for collecting pressure-production data and other well performance data. The performance history prior to the advent of pressure transient studies pertains mainly to what is known as the ‘old’ Travale reservoir to the southwest of the ‘new’ Travale-Radicondoli reservoir in which the more recent wells are drilled and in which modern well test analysis methods have been applied. Data on the “old” reservoir are discussed first.Because of its initial performance and relationship to nearby wells the most important well in the “new” reservoir is Travale well 22. It has been subjected to extensive well testing. Nearly all the wells in the “new” reservoir have been involved, however, through well-interference tests. In these tests the wells surrounding Travale well 22 are shut in and their pressure responses to different Travale well 22 production rates are measured. Well interference tests indicate the characteristics of fluid flow in the reservoir between test wells and in a qualitative way the heterogeneous nature of the reservoir itself.Pressure transient theory is developed from ideal system behavior: one vertical, fully-penetrating well producing at a constant rate from a horizontal reservoir of uniform thickness and of infinite extent in any direction from the wellbore. A great deal of research has been done to aid well-test analysts in their interpretation of pressure buildup and pressure drawdown curves constructed from data taken on wells in actual reservoirs. This research generally is accomplished with model studies. Some of the models developed in the present research fit reasonably well with the build-up behavior of Travale well 22.The research done on the Travale reservoir is summarized here with the objective of showing what has been learned, how it can be applied, and what should be done next. Confidence in applications of pressure transient analyses in the Travale reservoir has been gained. New concepts of the reservoir system have emerged as a result of the research. Additional testing and more precise measurements in the field should lead to good engineering estimates of energy reserves.     

Numerical study of multi-branch horizontal well coalbed methane extraction

Although multi-branch horizontal well coalbed methane (CMB) extraction has been comprehensively investigated, fewer scholars have taken the effect of temperature into account, which brought a large deviation for the study of multi-branch horizontal well parameter design. In this work, the hydraulic-mechanical-thermal coupled model of multi-branch horizontal well CMB extraction was established. In order to verify the accuracy of the model and study the effect of temperature on CMB extraction, a series of numerical simulations based on engineering geological conditions and drilling arrangement parameters of 24307 face of Shaqu Mine were made, results show that: The CH₄ production rate of both field data and numerical simulation result have the same changing tendency, and the difference between the simulation result and the actual value is not big. In multi-branch horizontal well CMB extraction process, the matrix shrinkage caused by temperature reduction and methane desorption dominates, the permeability continues to increase. Due to the effect of temperature on the amount of gas adsorbed by coal, the CH₄ production decreases with the increase of initial reservoir temperature, and the permeability of coalbed increases with the increase of temperature.     

“U”型井开发煤层气适应性研究

国内外煤层气研究成果和生产实践证明,需要不同类型的钻井开发煤阶、含气量、含水量等关键参数相异的煤层,以实现煤层气产能最大化。作为一个新的钻井类型,研究"U"型井适合钻探的煤层类型对于提高其产能,实现中国煤层气产业化至关重要。为此,选取沁水、鄂尔多斯盆地等中、高煤阶盆地,根据其地质资料及煤层气生产资料,从煤阶、煤层厚度、煤割理与钻进方向关系、含水量、煤层倾角等方面阐述了"U"型井钻井适应性,认为低煤阶煤层因硬度、密度低,采用"U"型井钻探容易引起坍塌;"U"型井采用两井连通、地质导向、远距离穿针等新技术,而厚煤层在有效使用这些技术的同时,更容易实现在煤层中钻进;"U"型井具有水平井和直井两个井口,可以更有效排出高含水煤层中的承压水,同时也可利用煤层坡度,将直井设置在煤层下倾方向,利用重力排水采气;"U"型井中的水平井具有方向性,垂直于面割理方向钻进可以获得较大产能。以上研究成果表明:"U"型井可以有效开发割理发育、具一定倾角、高含水的中高煤阶厚储层。该研究成果为"U"型井高效开采煤层气指明了方向。     

甲烷泄漏的可压缩流动分析与应用

煤层气生产过程中的甲烷(CH4)泄漏属于非定常流动,其计算过程复杂,往往受压力、温度等多种因素的综合影响。为了定量掌握煤层气井口位置的泄漏情况,推导了可压缩定常流动的N-S方程,结合相关假设得到了用于煤层气泄漏计算的小孔模型,考虑现实情况总结出适用于煤层气泄漏计算的经验系数。对多个煤层气区块的实际案例进行计算,并开展对比分析。结果表明,小孔模型的计算平均误差相对较小,将该模型应用于煤层气井口泄漏的计算中是可行的。     

CO2 enhanced coalbed methane production in the Netherlands

The technical and economical feasibility of CO₂ sequestration in deep coal layers combined with enhanced coalbed methane (ECBM) production in the Netherlands has been explored. Annually, 3.4 Mtonne CO₂ from chemical installations can be delivered to sequestration locations at 15 €/tonne and another 55 Mtonne from power generating facilities at 40–80 €/tonne. Four potential ECBM areas have been assessed, of which Zuid Limburg is the best location for a test site, while the Achterhoek is more suitable for future large-scale CO₂ sequestration. Between 54 Mtonne and 9 Gtonne CO₂ can be sequestered in the four areas together, heavily depending on available technology for accessing the coal seams. At the same time, between 0.3 and 60 EJ of coalbed methane can be produced. The optimal configuration may have 1000 m spacing between production wells, and extreme inseam drilling. The price of coalbed methane may become competitive with natural gas when a bonus for CO₂ sequestration is applied of about 25 €/tonne. For the long term, on-site hydrogen or power (SOFC) production with direct injection of produced CO₂ seems most attractive. Further study is required, most notably more accurate geological surveys, assessment of drilling costs in Dutch context, and environmental impacts of ECBM.     

低碳经济下我国煤层气的发展机遇

天然气是最清洁、高效、低碳的化石燃料,提升天然气在能源消费中的比例,将使我国能源消费结构趋于合理,有利于减少碳排放,有助于实现我国发展低碳经济的目标。2010~2020年间预计我国天然气需求量年均增长13.04%,高于同期天然气产量增幅4.12个百分点,天然气需求缺口为煤层气提供了市场,也为我国煤层气(煤矿瓦斯)开发利用储备了充足的用户。"十一五"期间,国家启动了沁水盆地和鄂尔多斯盆地东缘两个煤层气产业化基地建设。截至2010年底,全国形成煤层气产能25×108m3/a,实现煤层气产量15.57×108m3。预计2015年全国煤层气(煤矿瓦斯)产量将达215×108m3,利用率在60%以上,瓦斯发电装机容量超过300×104kW;新增煤层气探明地质储量8500×108m3;建成13条输气管道,总长度2121km,设计年输气能力180×108m3。建议国家应进一步鼓励煤层气(煤矿瓦斯)的开发利用,将煤层气利用量纳入综合利用进行统计;加大政策支持和政府投入力度,适当提高财政补贴标准,设立煤层气发展基金;组建国家煤层气公司,增加煤层气企业的资本金投入,支持煤层气企业重组上市;同时应大力发展二氧化碳捕集技术,将以消灭或减少煤层气(煤矿瓦斯)放空为目标的专项治理纳入国家瓦斯治理计划。     

超稠油水平井蒸汽吞吐开发实践

在跟踪研究现场水平井生产情况的基础上,总结分析了浅层超稠油水平井开发特征,提出了提高开发效果的技术措施。通过优化注汽参数和注汽方式,扩大了蒸汽波及体积,提高了油层的动用程度,从而提高水平井开发的最终采收率。目前,实施了三种均匀布汽方式:步进式注汽、分流式注汽、均点式注汽。工业规模试验结果表明,单一水平井步进式注汽技术能够使得水平段油层逐步得到动用,实施后生产效果良好;分流式注汽方式打孔段油层吸汽效果有所改善,二、三轮产油和油汽比相比第一轮均有所提高;均点式注汽方式使得水平段油层吸汽相对均匀了些,从实施前后的生产效果对比来看,措施后日产液、日产油水平也有明显增加。本文各项措施和手段,对于改善水平井开发效果,指导后续超稠油油藏的开发,以及其他地区此类油藏的开发,具有一定的指导意义。     

Influence mechanism of brine-gas two-phase flow on sealing property of anisotropic caprock for hydrogen and carbon energy underground storage

As the simplest saturated hydrocarbon, methane is an important hydrogen and carbon energy. The stability and sealing of caprock are keys to ensure the safe storage of energy in the process of hydrogen and carbon energy underground storage. A fully coupled two-phase flow model is established to analyze the migration mechanism of methane in caprock. This model considers the characteristics of dual porosity medium composed of caprock fractures and matrix, including the seepage of methane and brine. In the model, the replacement process of methane and brine exists in the fracture network, and the dynamic adsorption desorption process of methane exists in the matrix. Under the action of tectonic stress, obvious differences are observed in the fracture and permeability in different directions. All these characteristics are considered in the fully coupled two-phase flow model. The restraining and strengthening effects of caprock in the process of methane leakage are analyzed. The results show that the gas induces the adsorption expansion of the caprock matrix and reduces the fracture opening and permeability of the caprock. With the gradual invasion of gas into the caprock, the sealing characteristics of caprock show the evolution of self-inhibition first and then self-enhancement. With the increase in dip angle, gas tends to invade vertically rather than horizontally. Realizing gas–brine replacement is easier with the existence of large fractures. This study provides an effective numerical analysis method, which can be used to evaluate the sealing efficiency in the caprock in underground methane storage.     

山西潞安漳村扩区煤层气地质特征研究

结合地质勘查资料成果,研究了漳村扩区井田的煤层气赋存地质特征,并对开发条件进行了评价。总体上漳村扩区地质条件简单,3号煤层厚度大、埋深中等、储量丰富,有利于煤层气开发。3号煤层煤层气含量平均9.14 m3/t,含气饱和度为欠饱和储层。储层特征为低压、低温梯度、低渗储层。储层物性特征条件稍差,在今后的煤层气开发中应引起重视。     

底水油藏水平井中心管、ICD完井工艺技术

西江X-1油田是典型的底水油藏,具有厚底水、薄油层的特点,采用常规水平井开发时,由于流动摩阻和地层非均质性的影响,存在较严重的底水锥进问题,含水率上升过快,开发效果较差。中心管、ICD完井工艺是一种水平井控锥技术,由于其独特的内部结构,能使水平井的供液剖面趋于均衡,从而有效改善底水油藏的水驱效果。为了改善底水油藏的开发效果,对中心管、ICD完井工艺技术进行油藏模拟研究,结果表明,在底水油藏中,中心管、ICD技术的开发效果明显优于常规水平井,单井平均增油2×104~4×104m3。在西江X-1油田范围内进行推广应用,收到了理想的开发效果,实现了底水油藏的成功开发。西江X-1油田的开发实践表明,中心管、ICD完井工艺技术有明显的控锥作用,能有效改善底水油藏的开发效果,也为同类油藏的开发积累了宝贵经验。