天然气水合物储层水力压裂研究进展

天然气水合物是一种广泛分布于海底地层中重要的未来战略能源,但在开采过程中,由于水合物储层介质颗粒粒径较小,孔隙多被固态水合物占据,储层渗透率低,制约着天然气水合物开采的产业化进程。当今水力压裂技术已广泛应用于低渗透油气藏的增产作业中,本文总结了近年来国内外对天然气水合物储层应用水力压裂技术的研究现状,从压裂实验、数值模拟和压裂液等方面进行了讨论。结果表明,水力压裂可以创造人工裂缝,扩大水合物解离面积,提高储层渗透率和天然气产量,有利于商业开发。储层的脆性响应问题、开发新型压裂液以及压裂对水合物储层地质安全的影响,都是水合物储层水力压裂研究亟待解决的问题。     

川西须五气藏完井方式适应性研究

随着勘探开发的不断深入,非常规天然气成为重要的接替资源。四川盆地非常规天然气资源量丰富,须五气藏为典型的砂泥岩互层致密非常规气藏,有效的完井方式是气藏实现提高单井产能、提高气藏可采程度的重要保障。国内外非常规气藏水平井主要采用多段压裂技术、降阻水压裂技术、同步压裂技术,开发效果显著;研究表明,基质裂缝、裂缝网络渗透率、水力裂缝间隙、水力裂缝传导率、岩石压缩性、水力裂缝半长、自然裂缝孔隙度,对页岩气水平井产能影响较大,钻井过程中要对近井地带的基质渗透率、裂缝网络渗透率和自然裂缝孔隙度进行保护。川西须五气藏储层脆性矿物含量与美国其他页岩气相当,同时储层具有天然裂缝发育的特点,完井方式需要考虑储层改造工艺、最大程度上实现缝网压裂的目的;通过深入研究,优选出川西须五气藏完井方式,优选套管射孔完井方式,采用水平井+多段水力压裂和储层改造完井方法进行开发。     

Numerical simulation study on fracture propagation of zipper and synchronous fracturing in hydrogen energy development

Until now, hydraulic fracturing has played prominent role in increasing production of hydrogen energy such as natural gas, geothermal energy, natural gas hydrate. Hydrogen energy stimulation is realized by many methods. Such as multiple-clusters in staged fracturing, and fracture propagation guided by combined radial boreholes in different azimuths. In order to extend lateral stimulation area, the zipper fracturing is investigated continuously. However, the report on the zipper fracturing is limited to the post-frac productivity. In this study, model of simultaneous and zipper fracturing was established in ABAQUS to investigate the effect of six factors on the fracture propagation. The results showed that in simultaneous fracturing, the fracture network is formed spontaneously. With same brittleness of reservoir, fracture in zipper fracturing always propagates slightly longer than that in simultaneous fracturing. The results provide theoretically support for both fracturing modes, which helps design of well completion and fracturing operation parameters.     

新疆油田火山岩气藏体积压裂机理研究及应用

进行火山岩气藏压裂改造时,通常采用形成单一裂缝的增产改造技术,气井稳产时间较短.借鉴页岩气开发理念,深入研究火山岩气藏体积压裂机理.根据缝内压力传导的力学模型,研究不同液体体系对压力传导的影响,分析无滤饼压裂液体系对体积压裂的作用,优选出压裂液体系;建立不同角度天然裂缝开启的力学模型,确立体积形成的关键力学条件,并针对火山岩气藏压裂目的层的地应力结构进行实际分析.从储层矿物角度出发,研究对比火山岩储层的脆性系数;根据力学条件,结合压裂工艺过程,建立相关模型,优化研究体积压裂关键工艺参数,包括排量、压裂规模等;分析降阻水、线性胶、浓胶液三种不同黏度液体对裂缝网络的作用.在上述研究基础上,针对新疆油田DX1413井实际地质条件,分析该井进行体积压裂的有利条件,并进行压裂设计与改造施工,对施工曲线、施工过程、施工结果进行分析,得到了一些有益的结论,这些结论对火山岩气藏的开发有重要的启迪作用.     

Numerical simulation of fracture reorientation during hydraulic fracturing in perforated horizontal well in shale reservoirs

Fracture reorientation affects hydraulic fracturing much in perforated wells. A finite element model used for investigating fracture reorientation is established using the extended finite element method with ABAQUS software. Based on this, both fracture reorientation and fracture propagation during fracturing operation in shale reservoirs are analyzed. Meanwhile, the effect of the difference between the maximum and minimum principal stresses on fracture reorientation during fracturing in shale reservoirs has also been studied. The results demonstrate that the fracture reorients to the direction of the maximum principal stress gradually, and the difference between the maximum and minimum principal stresses impacts the fracture reorientation more than fracture propagation.     

Unsteady seepage solutions for hydraulic fracturing around vertical wellbores in hydrocarbon reservoirs

This paper establishes an analytical model to study the influence mechanism of hydraulic fracturing around vertical wellbores under the unsteady seepage in hydrocarbon reservoirs, deduces the analytical solution of water pressure and hydraulic gradient of the model, and compares the law of water pressure and hydraulic gradient changing with time with the results of numerical simulation. The results confirm the accuracy of these analytical solutions. The variation laws of water pressure and hydraulic gradient in the sample under unsteady seepage are analysed by using the COMSOL Multiphysics software. The results show that: the increasing rate and amplitude of water pressure decrease with the distance of water inlet, however, hydraulic gradient near the water inlet is the largest and decreasing with the distance. In order to better understand the mechanism of hydraulic fracturing of rock mass, we studied the influence of permeability and water injection pressure on water pressure and hydraulic gradient of rock mass. The results show that: large permeability coefficient and high hydraulic gradient will increase the probability of rock mass hydraulic fracturing. The permeability and hydraulic gradient of rock mass is important factor in determining whether the rock has hydraulic fracturing. The distribution law of water pressure and hydraulic gradient in rock mass under unsteady seepage provides important reference and basis in hydrogen developing reservoirs.     

An innovative technology of directional propagation of hydraulic fracture guided by radial holes in fossil hydrogen energy development

Conventional hydraulic fracturing fails to develop low permeability reservoirs of fossil hydrogen energy that are not located in the direction of maximum principal in-situ stress. A new technology of fracture propagation guided by radial holes is proposed, which can realize directional propagation of hydraulic fracture along radial holes in fossil hydrogen energy development. In order to verify this new technology, a model of radial holes combined with hydraulic fracturing is established by the ABAQUS extended finite element method. Simulation results show that radial holes play a guiding role in fractures propagation. The influence extent of seven factors on the directional propagation of hydraulic fracture is listed as follows (from strong to weak): azimuth of radial holes > horizontal in-situ stress difference of fossil hydrogen reservoir > injection rate of fracturing fluid > Young's modulus of rock > permeability of fossil hydrogen reservoir > Poisson ratio of rock > viscosity of fracturing fluid. True tri-axial experiment is carried out to verify the accuracy of numerical simulation, and the result is consistent with numerical model, which indicates that numerical simulation is reliable.     

国内页岩气开采技术进展

因页岩气开发具有资源潜力大、开采寿命长和生产周期长等优点,已成为当前能源研究的热点和突破口.自2009年以来,我国已在页岩气开发实验区钻井62口,其中24口井获得工业气流,这预示着国内页岩气资源开发全面铺开.页岩气储层与常规储层差异很大,必须采用先进技术,尤其是水平井钻井、完井及压裂技术,才能实现经济有效开发.介绍了国外页岩气开采技术以及国内近两年在页岩气钻井技术、钻井液技术、固井技术和压裂技术方面取得的经验,这些经验奠定了国内页岩气开发的技术基础.论述了页岩气开采面临的技术和环境问题,指出下一步页岩气技术发展方向.今后,需要结合国内页岩气藏特点,在借鉴国外新技术及国内经验基础上,通过工具研制、技术配套、方案优化,尽快完善适用于页岩气开发的水平井钻井技术;从流变性、封堵能力方面进一步完善油基钻井液体系,同时开展适用于页岩气水平井钻井的水基钻井液体系研究;针对页岩气水平井多采用油基钻井液的现状,进一步完善冲洗液、水泥浆体系及固井工艺技术.开发适合页岩气水平井多级压裂技术相关的井下工具、工作液和施工工艺,加强压裂裂缝动态监测,优化压裂设计.形成配套的钻井和压裂等作业过程中产生的废液、废水及废渣处理技术,重视贞岩气开采的环境污染评估,保证我国页岩气开发的健康发展.     

Regulating hydraulic fracturing in shale gas plays: The case of Texas

The ability to economically produce natural gas from unconventional shale gas reservoirs has been made possible recently through the application of horizontal drilling and hydraulic fracturing. This new technique has radically changed the energy future of the United States. The U.S. has shifted from a waning producer of natural gas to a growing producer. The Energy Information Administration forecasts that by 2035 nearly half of U.S. natural gas will come from shale gas. Texas is a major player in these developments. Of the eight states and coastal areas that account for the bulk of U.S. gas, Texas has the largest proved reserves. Texas' Barnett Shale already produces six percent of the continental U.S.' gas and exploration of Texas' other shale gas regions is just beginning. Shale gas production is highly controversial, in part because of environmental concerns. Some U.S. states have put hydraulic fracturing moratoriums in place because of fear of drinking water contamination. The federal government has gotten involved and some states, like Texas, have accused it of overreaching. The contention over shale gas drilling in the U.S. may be a bellwether for other parts of the world that are now moving forward with their own shale gas production.     

Latest progress in numerical simulations on multiphase flow and thermodynamics in production of natural gas from gas hydrate reservoir

Natural gas hydrates are promising potential alternative energy resources. Some studies on the multiphase flow and thermodynamics have been conducted to investigate the feasibility of gas production from hydrate dissociation. The methods for natural gas production are analyzed and several models describing the dissociation process are listed and compared. Two prevailing models, one for depressurization and the other for thermal stimulation, are discussed in detail. A comprehensive numerical method considering the multiphase flow and thermodynamics of gas production from various hydratebearing reservoirs is required to better understand the dissociation process of natural gas hydrate, which would be of great benefit to its future exploration and exploitation.     

Semi-analytical modeling of productivity analysis for five-spot well pattern scheme in methane hydrocarbon reservoirs

Five-spot well pattern (FSWP) scheme has shown appealing potentialities to enhance the recovery of coal-bed methane (CBM) from methane hydrocarbon reservoirs (MHR). In this paper, a new framework aimed at systematically investigating productivity performance of FSWP scheme with inter-well pressure interference (IWPI) is presented. First, mathematical models which are used to characterize the fluid flow within MHR and hydraulic fractures (HFs) are separately derived. Second, Laplace transformation and Stehfest numerical algorithm are utilized to couple those two flow systems and obtain the pressure-transient solutions of FSWP scheme. Finally, pressure characteristics are discerned and sensitivity analysis of key parameters is implemented as well. This semi-analytical approach outperforms numerical simulation from the point of computational efficiency. Several common flow regimes, e.g., linear and bi-linear flow regimes, are essentially deformed induced by IWPI. Several significant parameters, including gas rate, fracture half-length, and well spacing on the occurrence of IWPI are systematically analyzed. This work gains some new knowledge about the productivity performance of FSWP scheme with the existence of IWPI when extracting CBM from methane hydrate reservoirs (MHR), which provides energy engineers considerable instructions on optimizing the development of methane hydrate reservoirs.     

页岩气开发现状及成功开发页岩气的关键因素

介绍页岩气的性质、特点、全球分布情况以及国内外勘探开发现状,世界范围内,泥、页岩约占全部沉积岩的60%,页岩气资源前景巨大。全球页岩气资源量为456.24×1012m3,主要分布在北美、中亚和中国、拉美、中东、北非以及前苏联地区等。我国页岩气可采资源量约为26×1012m3,与美国大致相当。在目前的经济技术条件下,页岩气是天然气工业化勘探的重要领域和目标。北美油气生产商把页岩气藏作为重要天然气开发目标,并且取得了巨大成功。通过对北美页岩气藏的深入研究并系统总结其勘探开发历史与成功经验,认为其有效勘探开发的关键在于有政策引导和水平井、水力压裂等先进钻、完井技术的成功应用。我国页岩气资源潜力很大,但我国对页岩气的研究与勘探开发尚处于探索阶段。从勘探技术、钻井技术、开发技术和政策支持四方面论述了页岩气开发的难点和技术对策,提出了国内页岩气成功开发的工作思路,对国内开展相关技术的研究有一定的指导意义。     

Model for calculating the temperature and pressure within the fracture during supercritical carbon dioxide fracturing

Supercritical carbon dioxide fracturing not only enhances fossil hydrogen production better than hydraulic fracturing, but also alleviates water consumption and storages some carbon dioxide in reservoirs. In this study, a numerical simulation model for calculating the temperature and pressure within a fracture during supercritical carbon dioxide fracturing was established based on rock mechanics, fluid mechanics, thermodynamics, and heat transfer. Moreover, the effects of impact of in-situ stress of reservoir, reservoir temperature, carbon dioxide temperature at the bottom of the well and injection rate on temperature and pressure in the fracture are analyzed based on this new model. The results show that the temperature and pressure of carbon dioxide in the fracture are constantly changing during the fracturing, due to the propagation of the fracture, which makes the temperature and pressure in the fracture unable to reach a steady state. The effect of supercritical carbon dioxide fracturing in reservoirs with higher temperature and lower in-situ stress is better, and higher injection temperatures and smaller injection rates should be chosen in order for carbon dioxide to quickly reach the supercritical state.     

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.     

页岩气钻采技术综述

页岩气开采已成为全球资源开发的一个热点。页岩气储集层通常呈低孔、低渗透率,开采寿命长,生产周期长,采收率变化较大,且低于常规天然气采收率。不同于常规天然气的开采特点决定了页岩气开发具有其独特的方式。水平井技术对于扩大页岩气开发具有重大意义,水平井的成本一般是垂直井的1～1．5倍,而产量是垂直井的3倍左右。水平井技术结合geoVISION随钻成像服务和RAB钻头附近地层电阻率仪器等LWD技术可进行更高效、更合理的开采。压裂增产技术是页岩气开采的另一种方式。清水压裂技术用于产生更密集的裂缝网络,形成额外的渗透率,使气体能更容易流向井中,从而生产出大量地层天然气;多层压裂技术常常用于垂直堆叠的致密地层的增产：重复压裂技术用于在不同方向上诱导产生新的裂缝,从而增加裂缝网络,提高生产能力;还有最新的同步压裂技术。即同时对两口或两口以上的井进行压裂。这些压裂技术结合室内实验和测井技术,使得页岩气具有更大的发展潜力。     

Mechanical experiments and constitutive model of natural gas hydrate reservoirs

Natural gas hydrate is a new type of green energy resources and has great development prospects, and it has attracted worldwide attentions. The exploitation of natural gas hydrate may result in a series of geological disasters. Therefore, the constitutive model of natural gas hydrate bearing sediments needs to be established to reveal deformation laws of the reservoir sediments and accurately evaluate mechanical properties of hydrate reservoirs. This is the basic guarantees for the effective exploitation of natural gas hydrate resources. The triaxial compressive tests were conducted on samples of natural gas hydrate sediment. Furthermore, the Duncan-Chang hyperbolic model was modified by considering the influences of hydrate saturation based on the test results to obtain the constitutive model according with the deformation characteristics of natural gas hydrate reservoirs. The results show that the stress-strain curves of natural gas hydrate reservoirs show unobvious compaction stage and peak strength, short elastic stage, long yield stage, and significant strain hardening characteristics. After applying loads on natural gas hydrate bearing sediments, the internal solid particles were dislocated and slid. When the loads were small, the sediments demonstrated elastic deformation. With the increase of loads, plastic flows appeared in the interior, and the hydrate crystals were re-orientated, thus the sediments showing plastic deformation. Initial tangent elastic modulus increased with the effective confining pressures, which had little correlations with hydrate saturation. Furthermore, the damage ratio increases with the increase of effective confining pressures, while slightly decreases with the increase of natural gas hydrate saturation. The predicted results of stress-strain curves of sediments with different hydrate saturations well coincide with the results of triaxial compressive tests, indicting the feasibility and rationality of this model.     

高速通道压裂技术在国外的研究与应用

高速通道压裂技术是近两年出现的新工艺,主要应用在美国、俄罗斯、南美和北非、中东等油气高产地区,已在世界范围内实施超过3800井次,取得良好增产效果。该工艺的主要目标是在人工裂缝内部造出稳定而敞开的油气流动网络通道,显著提高人工裂缝的导流能力,消除由于残渣堵塞、支撑剂嵌入等引起的导流能力损失,从而减小井筒附近的压降漏斗效应,提高压裂改造效果。通过综合多簇射孔、支撑剂段塞注入和拌注纤维等工艺技术,实现了支撑剂在裂缝内非均匀铺砂;经过优化研究,使高速通道保持长期有效。该工艺可提高铺砂效果、减少压裂材料使用量,增加返排率,保持裂缝的清洁,并能有效减少施工中砂堵的风险,其适应性广,可用于砂岩、碳酸盐岩及页岩等各种油气藏。为解决国内低渗透油气藏压后普遍存在的返排困难和裂缝伤害等问题,提供了一种可行的技术方法。     

A comprehensive model for production data analysis in unconventional reservoirs of hydrocarbons

Because of the large amount of energy-rich organic compound, shale gas reservoirs can be good sources of hydrogen energy. To ensure high yield of hydrogen energy, the production data analysis in those shale gas reservoirs is of great significance. However, due to geological and engineering factors, there exist complex mechanisms including stress-sensitivity effect of permeability, gas desorption, complex gas flows, multiple finite-conductivity fractures, and wellbore hydraulics. Unfortunately, little work has been done to focus on these complex mechanisms simultaneously. To comprehensively address this issue, this paper presents a comprehensive model by using a semi-analytical method, and those complex mechanisms are all considered by introducing adsorption index, Knudson diffusion coefficient, reservoir-wellbore constant, and Reynolds number. Both model verification and field application are performed. This study further narrows the gap between theory and practice of production data analysis in shale gas reservoirs, which helps to parameter evaluation, performance forecast, and productivity enhancement in the unconventional reservoirs of hydrocarbons.     

压裂液冻胶在储层微裂缝中的滤失评价

压裂液冻胶作为高黏非反应性液体,一直广泛用于低渗透气藏水力压裂作业的造缝和携砂,对于孔隙型储层具有较好的降滤失性能。通过评价实验,考察了压裂液冻胶在低渗透气藏微裂缝储层中的降滤失性能。实验内容为:考察注液压差、压裂液黏度和微裂缝宽度对压裂液冻胶滤失速率的影响;在恒定微裂缝宽度和注液压差的条件下,通过考察压裂液冻胶滤失速率随时间的变化来评价压裂液冻胶在微裂缝中的造壁性能。实验结果表明:对于微裂缝发育的储层,压裂液冻胶有一定的降滤失性能;滤失速率变化与注液压差、微裂缝宽度成正比关系,与压裂液黏度成反比关系;随着实验时间的延长,压裂液滤失速率变化不大,压裂液冻胶在微裂缝壁面的造壁性能基本失效。建议:对于微裂缝宽度大于0.1mm的储层实施水力压裂作业时,在采用压裂液冻胶辅助降滤的同时,可使用粉砂、纤维等固相降滤剂实施综合降滤;在实施水力压裂作业前,建议通过小型测试压裂来判定地层微裂缝的发育特征。     

Pressure transient responses study on the hydraulic volume fracturing vertical well in stress-sensitive tight hydrocarbon reservoirs

Based on the characteristics of stimulated zone and un-stimulated zone after hydraulic volume fracturing of vertical well, as well as considering the stress-sensitive characteristic of the tight oil reservoir, the two-zone composite pressure transient responses model is built. The inner zone represents the stimulated reservoir volume region and is modeled as a dual-porosity radial reservoir, while the outer zone represents the un-stimulated reservoir volume region and is modeled as a single porosity reservoir. The model is solved by the method of superposition, Laplace integral transformation, Stehfest numerical inverse algorithm, and the perturbation technique. Thus the analytical solutions to the model are obtained. On the basis of the field example verification of the model, the flow regimes of the hydraulic volume fracturing vertical well are analyzed. The results of the study show that the new model can provide the reliable pressure transient responses model for hydraulic volume fracturing vertical well, and the flow regimes can be divided into five stages, including the wellbore storage stage, transition flow from matrix system to fracture system, radial flow of SRV zone, transition flow from UN-SRV zone to SRV zone, and radial flow of whole reservoir system. The new model and study are conducive to the well test interpretation of hydraulic volume fracturing vertical well in stress-sensitive tight oil reservoir.