页岩储层网络压裂技术研究与试验

页岩储层压裂技术是页岩油气高效勘探开发的关键技术和核心技术。与常规低渗油气储层压裂单一长缝改善压裂效果不同,低孔极低渗的页岩压裂主要目标是形成具有有效导流能力的网络裂缝,确保压裂改造体积足够大,且经济有效。提出了页岩网络压裂有效改造体积（ESRV）的概念。在借鉴北美页岩气压裂的经验和前期国内页岩气压裂实践的基础上,针对我国页岩储层的具体特点,在压前进行评价方法、射孔参数优化、诱导复合测试压裂、网络压裂对策和排采技术等方面进行了探索性的研究,初步形成了页岩网络压裂技术,现场试验效果明显,解决了裂缝性脆性页岩压裂易砂堵、成功率低的难题。     

Geomechanical optimization of hydraulic fracturing in unconventional reservoirs: a semi-analytical approach

Unconventional drilling and completion architecture includes drilling multilateral horizontal wells in the direction of minimum horizontal stress and simultaneous multistage fracturing treatments perpendicular to the wellbore. This drilling and stimulation strategy is utilized in order to raise the connectivity of the reservoir to the wellbore, thereby remedying the low permeability problem, increasing reserve per well, enhancing well productivity, and improving project economics in this type of reservoir. However, in order to have the highest production with the least cost, an optimization technique should be used for the fracturing treatment. According to the fact that aperture, propagation direction, and propagation potential of hydraulic fractures are of paramount importance in optimization of the fracking treatment, in this research paper, these three major factors are studied in detail, the control variables on these three factors are examined, and the effect of each factor is quantified by proposing a complete set of equations. Using the proposed set of equations, one can make a good estimate about the fracture aperture (directly controlling the fracture conductivity), the stress shadow size (directly controlling the fracture path), and the change of stress intensity factor (directly controlling the fracture propagation potential). A geomechanical optimization procedure is then presented for toughness-dominated and viscosity-dominated regimes based on the proposed equations that can be used for estimation of different optimal fracturing patterns. The most efficient fracturing pattern can be determined afterward via considering the cumulative production using a reservoir simulator e.g. ECLIPSE, Schlumberger. This procedure is likely to offer an optimal simultaneous multistage hydraulic fracture treatment without deviation or collapse, with no fracture trapping, with the highest possible propagation potential in the hydrocarbon producing shale layer, and a predicted aperture for proppant type/size decision and conductivity of the fractures.     

Numerical simulation study of shale gas reservoir with stress-dependent fracture conductivity using multiscale discrete fracture network model

The exploitation of shale gas has increasingly become the focus of worldwide energy industry. Due to the existence of natural/hydraulic fractures, most of the shale gas reservoirs exhibit high degree of heterogeneity and complexity which leads to the stress-dependent fracture conductivity of shale gas reservoir. Discrete fracture network (DFN) model is adopted in this research since the conventional continuum model cannot meet the numerical simulation requirements of fractured shale gas reservoir. A series of experiments about the fracture properties stress-dependent have been conducted on some shale core samples, the stress-dependent fracture conductivity correlation is selected and incorporated into the mathematical model to characterize the reduction of fracture conductivity potential with the reservoir pressure drop. The DFN model is applied to a shale gas reservoir with fracture network to study the effect of the stress-dependent fracture conductivity on the shale gas well performance. The results show that the effect of fracture conductivity reduction with pressure drop on the shale gas well performance depends on both the initial fracture conductivity and matrix permeability. The complex interactions between the fracture and matrix permeability should be considered when select the appropriate size of proppants for fracturing.     

A Review on Shale Gas Development in Fuling

The Fuling Marine Shale Deposit contains vast gas resources. Due to tectonic activities, complex surface and geological conditions, significant differences make it unlike that of North America. Thus, it is not suitable to completely copy the technology and the development model from North America. Therefore we need engineering technology and a business development model fit for Fuling Shale Gas Development (FSGD). Through difficulties and characteristics analysis of the shale gas development area, we determined geological engineering design methods and integrated workflow, established a series of the core technologies, including horizontal well drilling with long laterals, staged fracturing and completion technology, developed main fluids, tools and equipment, put forward “well factory” mode in mountain region and “full cycle learning and system optimization” management methods. Break through was made in China’s first large-scale shale gas fields commercial development. By the end of 2014, production capacity reached 25 × 10⁸ m³/a, and cumulative gas production reached 12.24 × 10⁸ m³, which made a solid foundation to build production capacity of 50 × 10⁸ m³/a in 2015 and 100 × 10⁸ m³/a in 2017. Not only has FSGD established a demonstration for the other shale gas fields’ development, but also will be taken as reference to other large and extra-large construction projects of the industry.     

中国页岩气资源潜力及其在天然气 未来发展中的地位

中国页岩气勘探已在四川、鄂尔多斯等盆地及重庆、云南、贵州、湖南等地区获得发现,证实具有良好资源前景。依据最新资料,落实了稳定区面积、集中段厚度、可采资源丰度、含气量等资源评价关键参数,采用3种方法预测了我国页岩气可采资源量及分布。借鉴美国典型页岩气区发展经验,采用多种方法预测了我国页岩气未来达到的产量规模和发展路线图,明确提出了页岩气在我国未来天然气发展中的地位和作用。     

Poro-elasto-plastic modeling of complex hydraulic fracture propagation: simultaneous multi-fracturing and producing well interference

With the increasing wide use of hydraulic fractures in the petroleum industry, it is essential to accurately predict the behavior of fractures based on the understanding of fundamental mechanisms governing the process. For effective reservoir exploration and development, hydraulic fracture pattern, geometry and associated dimensions are critical in determining well stimulation efficiency. In shale formations, non-planar, complex hydraulic fractures are often observed, due to the activation of preexisting natural fractures and the interaction between multiple, simultaneously propagating hydraulic fractures. The propagation of turning non-planar fractures due to the interference of nearby producing wells has also been reported. Current numerical simulation of hydraulic fracturing generally assumes planar crack geometry and weak coupling behavior, which severely limits the applicability of these methods in predicting fracture propagation under complex subsurface conditions. In addition, the prevailing approach for hydraulic fracture modeling also relies on linear elastic fracture mechanics (LEFM) by assuming the rock behaves purely elastically until complete failure. LEFM can predict hard rock hydraulic fracturing processes reasonably, but often fails to give accurate predictions of fracture geometry and propagation pressure in ductile and quasi-brittle rocks, such as poorly consolidated/unconsolidated sands and ductile shales, even in the form of simple planar geometry. In this study, we present a fully coupled poro-elasto-plastic model for hydraulic fracture propagation based on the theories of extend finite element, cohesive zone method and Mohr–Coulomb plasticity, which is able to capture complex hydraulic fracture geometry and plastic deformations in reservoir rocks explicitly. To illustrate the capabilities of the model, example simulations are presented including ones involving simultaneously propagating multiple hydraulic fractures and producing well interference. The results indicate that both stress shadow effects and producing well interference can alter hydraulic fracture propagation behavior substantially, and shear failure in ductile reservoir rocks can indeed make a significant difference in fracturing pressure and final fracture geometry.     

全球页岩气发展启示与中国未来发展前景展望

中国页岩气勘探开发已开展了大量露头地质调研、前期研究与勘探开发先导试验等工作,尤其是在中国南方海相页岩气区,完钻了页岩气井40余口,获气10余口,多口井经压裂初期日产量超过了1万m3。实践表明,中国页岩气资源发展前景较好,但也具有明显的特殊性,许多地质与开发难题亟待解决,随着页岩气勘探开发理论与关键技术的突破、经济条件的改善和国家政策的支持,未来中国页岩气资源发展前景广阔。     

Interactions between the Design and Operation of Shale Gas Networks,Including CO2 Sequestration

As the demand for energy continues to increase, shale gas, as an unconventional source of methane (CH₄), shows great potential for commercialization. However, due to the ultra-low permeability of shale gas reservoirs, special procedures such as horizontal drilling, hydraulic fracturing, periodic well shut-in, and carbon dioxide (CO₂) injection may be required in order to boost gas production, maximize economic benefits, and ensure safe and environmentally sound operation. Although intensive research is devoted to this emerging technology, many researchers have studied shale gas design and operational decisions only in isolation. In fact, these decisions are highly interactive and should be considered simultaneously. Therefore, the research question addressed in this study includes interactions between design and operational decisions. In this paper, we first establish a full-physics model for a shale gas reservoir. Next, we conduct a sensitivity analysis of important design and operational decisions such as well length, well arrangement, number of fractures, fracture distance, CO₂ injection rate, and shut-in scheduling in order to gain in-depth insights into the complex behavior of shale gas networks. The results suggest that the case with the highest shale gas production may not necessarily be the most profitable design; and that drilling, fracturing, and CO₂ injection have great impacts on the economic viability of this technology. In particular, due to the high costs, enhanced gas recovery (EGR) using CO₂ does not appear to be commercially competitive, unless tax abatements or subsidies are available for CO₂ sequestration. It was also found that the interactions between design and operational decisions are significant and that these decisions should be optimized simultaneously.     

Engineering Philosophy-based Reflections on Efficient Development of Shale Gas in China

The Shale Gas Revolution began to have a significant impact on global supply and demand of natural gas; also the price trend of natural gas has been greatly affected. This phenomenon raised concerns among natural gas producers and consumers. China has abundant shale gas resources, but the development scale is small while facing problems including weak exploration and evaluation basis, overlapping royalties, complex terrestrial environment, lack of technical practices and accumulation, inadequate management and regulatory mechanisms, etc. To overcome these challenges for large-scale shale gas development, we believe that shale gas development is not only a single technical problem, but a systematic engineering demanding multidisciplinary research that will be bound to spread to humans, nature, and society. Therefore, to ensure the healthy development of China’s shale gas, it is required to coordinate global and local relationships, engineering and community relations, as well as to break up the conflicts between engineering and nature, engineering and economy, along with engineering and society.     

Stimstream等孔径深穿透射孔弹在页岩气井中的应用

针对套管孔眼大小不一致造成页岩气井水力加砂压裂施工难度大的问题,从国外引进了一种Stimstream等孔径深穿透射孔弹,分析了其结构特点,并和国产射孔弹进行了地面环靶试验和现场应用效果比较。结果表明:该射孔弹套管孔眼受射孔枪和套管间隙大小影响不大,对降低水力加砂压裂破裂压力和施工压力具有明显的效果。     

An Evolutionary Lagrange Method For Mixed-Integer Constrained Optimization Problems

This study proposes a method for solving mixed-integer constrained optimization problems using an evolutionary Lagrange method. In this approach, an augmented Lagrange function is used to transform the mixed-integer constrained optimization problem into an unconstrained min—max problem with decision-variable minimization and Lagrange-multiplier maximization. The mixed-integer hybrid differential evolution (MIHDE) is introduced into the evolutionary min—max algorithm to accomplish the implementation of the evolutionary Lagrange method. MIHDE provides a mixed coding to denote genetic representations of teal and integer variables, and a rounding operation is used to guide the genetic evolution of integer variables. To fulfill global convergence, self-adaptation for penalty parameters is involved in the evolutionary min—max algorithm so that small penalty parameters can be used, not affecting the final search results. Some numerical experiments are tested to evacuate the performance of the proposed method. Numerical experiments demonstrate that the proposed method converges to better solutions than the conventional penalty function method     

中国石化非常规油气资源潜力及勘探进展

中国石油化工集团有限公司(简称中国石化)矿权区内拥有较为丰富的非常规油气资源,煤层气可勘探面积为10.19万km2,煤层埋深小于2 000 m的煤层气地质资源量为11.02万亿m3。页岩气可供勘探面积为17.5万km2,初步估算页岩气地质资源量为15.9万亿m3。页岩油勘探面积为11.76万km2,具有较大的资源基础及潜力。中国石化自2004年开始关注非常规油气资源,先后启动了页岩油气、煤层气等非常规油气资源的研究和勘探工作。目前在泌阳凹陷页岩油勘探泌页HF-1水平井分段压裂后获日产油23.6 m3;元坝地区多口陆相钻井测试获得高产气流,建南地区建页HF-1井日产气12 300 m3;延川南区块煤层气已探明地质储量为106.47亿m3,多口井排采获工业气流,初步形成了中国石化非常规油气资源多类型、多阶段的勘探开发格局。     

油井高聚能压裂技术及其在煤层气开采中的应用

为解决煤层气的增产改造难题,将油井工程中较成熟的高聚能压裂技术应用到煤层气开采中,并通过加入强行支撑剂、新型高聚能材料,改变点火孔数量及位置等方式对其进行改进,以提高煤层气井的采收率。为验证高聚能压裂技术在煤层气井中的应用效果,选择了部分井层开展了现场试验及应用效果评价。结果显示:煤层气井中实施高聚能压裂技术的工艺简单、成本较低、不污染地层,对煤层气井降压解析、提高产气量具有较好效果。     

Using integrated process and microeconomic analyses to enable effective environmental policy for shale gas in the USA

As one of the largest consumers of energy and emitters of greenhouse gases in the world, the USA must balance energy demand and security with environmental responsibility. Recently, shale gas has emerged as a promising element toward a solution to this dilemma. Currently, shale gas production is regulated under the same rules that govern traditional oil and gas operations, without consideration for the unique environmental challenges associated with the unconventional gas extraction process. It involves small independent operators that typically utilize the most cost-effective extraction processes without necessarily prioritizing the environmental impact of their operations. As a result, opposition to shale gas extraction threatens the continuity and sustainability of the shale gas industry. The negative externalities and information asymmetry associated with this market continue to be captured in a price of natural gas which is not inclusive of the environmental costs of the extraction processes. The objective of this work is to determine the environmental policies that will lead to sustainable shale gas production. A hierarchical approach is developed to benchmark current technologies and to generate, assess and select technologies and policies that overcome market hurdles while addressing EHSS objectives. The approach analyzes the technical and microeconomic impacts of environmental remediation techniques and then takes a multipronged policy approach which supports the microeconomic, environmental, health and safety goals. To illustrate the usefulness of the proposed approach, a case study is solved for the Barnett Shale play to assess at the microeconomic and environmental implications of environmental remediation technologies for shale gas operations. Based on the results of the analysis, technology changes create both economic and environmental benefits for operators indicating a market failure resulting in the priceless favorable technologies do not reflect their impact on the environment. The market failures in the process are analyzed and four policy alternatives to the status quo are evaluated against four policy goals. The primary recommendation resulting from the analysis, the Comprehensive policy alternative, uses a phased approach to drive ongoing innovation in the shale gas industry, stimulate demand for natural gas and reduce the information asymmetry. The implementation of this policy is then applied to an economic and environmental model of a cluster of wells in the Barnett Shale to determine how the policy would be implemented.     

Implementation of Discrete Capability into the Enhanced Multipoint Approximation Method for Solving Mixed Integer-Continuous Optimization Problems

Multipoint approximation method (MAM) focuses on the development of metamodels for the objective and constraint functions in solving a mid-range optimization problem within a trust region. To develop an optimization technique applicable to mixed integer-continuous design optimization problems in which the objective and constraint functions are computationally expensive and could be impossible to evaluate at some combinations of design variables, a simple and efficient algorithm, coordinate search, is implemented in the MAM. This discrete optimization capability is examined by the well established benchmark problem and its effectiveness is also evaluated as the discreteness interval for discrete design variables is increased from 0.2 to 1. Furthermore, an application to the optimization of a lattice composite fuselage structure where one of design variables (number of helical ribs) is integer is also presented to demonstrate the efficiency of this capability.     

A new harmony search algorithm for solving mixed–discrete engineering optimization problems

In general design optimization problems, it is usually assumed that the design variables are continuous. However, many practical problems in engineering design require considering the design variables as integer or discrete values. The presence of discrete and integer variables along with continuous variables adds to the complexity of the optimization problem. Very few of the existing methods can yield a globally optimal solution when the objective functions are non-convex and non-differentiable. This article presents a mixed–discrete harmony search approach for solving these nonlinear optimization problems which contain integer, discrete and continuous variables. Some engineering design examples are also presented to demonstrate the effectiveness of the proposed method.     

Optimizing gas-lift production of oil wells: piecewise linear formulation and computational analysis

Because the internal pressure of a reservoir can recover only a fraction of its oil reserve, system operators apply artificial lifting techniques to force the flow of oil to the surface. A favored technique is gas-lifting which consists of injecting compressed gas into the production tubing to reduce the weight of the oil column and, thereby, sustain a continuous flow of oil. The optimal allocation of a limited amount of compressed gas to wells gives rise to the gas-lift optimization problem, a mixed-integer nonlinear programming problem, whose decision variables determine which wells should produce and the rate of gas injected into the active ones. This paper investigates a piecewise linear formulation of the problem, presenting some properties of the polyhedron associated with the space of feasible solutions, and delivering families of valid inequalities that are shown to improve the performance of optimization software.     

美国Eagle Ford页岩气开发对我国页岩气勘探开发的启示

据估计,我国的页岩气可采储量高达20万亿～36万亿m3,虽然我国页岩气储量评估处于初级阶段,但仍然可以肯定我国是页岩气资源丰富的国家之一,如果都能开发,按当前的天然气年产量计算,可以开发200多年。目前国内外多家企业聚焦中国,逐鹿页岩气,页岩气有望成为我国常规能源替代品,页岩气的勘探开发必将对我国乃至世界能源格局产生重大影响。但是由于页岩气储层致密,渗透率低至纳达西级,若不采取特殊的增产措施难以实现商业开发。美国是目前唯一实现页岩气商业开采的国家,技术和商业模式都相当成熟,中海石油斥资10多亿美元收购了美国页岩气主产区Eagle Ford 33.3%的股份,该地区页岩气地质储量高达6 000亿m3,开发前景广阔。为提升我国页岩气总体水平,笔者率领技术专家深入考察了美国Eagle Ford页岩气项目,增进了对水平钻井与分段压裂等关键技术的了解,同时分析了相应扶持政策,对中国页岩气的勘探开发具有重要的参考价值。     

低渗油藏人工裂缝监测技术在现河地区的应用

针对高压低渗透油藏渗透率低、孔隙度小的特点,在压裂改造时进行裂缝监测,根据监测出的裂缝方位（方向）、裂缝长度、裂缝的高度（范围）和产状以及地下主应力的方向,为下步布井和井网调整提供了依据。2008年以来,现河地区已成功实施裂缝监测79井次,为低渗透油藏的高效开发提供了有力支持。     

低渗油藏裸眼水平井压裂技术及应用

针对大庆外围朝长地区未动用储量属于低渗透扶余油层,采用常规直井开发,单井产能低、开发效益差,为进一步提高低渗透扶余油层开发效果,通过水平井近平衡钻井、裸眼完井,减少了钻井及固井对储层污染,采用打孔管结合油膨胀封隔器工艺进行压裂改造,探索低产低渗透储层有效的开发途径。试油及投产效果表明,低渗透油藏采用近平衡钻井、裸眼完井能有效地保护储层,实施裸眼水平井储层压裂改造能够提高单井日产油,对进一步改善低渗透油藏开发效果有重要意义。