地震约束下时频电磁法识别富有机质页岩层系研究

湘西北试验区属于典型南方碳酸盐岩山区,富有机质页岩与围岩电性差异及流体极化效应明显,有利于应用大功率时频电磁法勘探.通过采集并测定试验区页岩和其他岩石标本,分析富有机质页岩的物性特征,研究富有机质页岩电磁特性和极化机理,总结了时频电磁法针对富有机质页岩层系的资料处理和异常提取方法.试验区在时频电磁法采集测线上又覆盖了二维地震工作,在地震约束下时频电磁法反演能更好地描述试验区页岩层系展布特征,预测TOC高值异常区.通过反演结果进行分析,结合前期富有机质页岩物性特征研究,时频电磁法具有圈定富有机质页岩层系的能力.     

重磁电综合物探技术在南方页岩气地质调查中的应用研究——以桂中坳陷鹿寨地区为例

广西一直以来面临着"缺煤、少油、无气"的窘境.本次研究工作是在"南方地区页岩气基础地质调查"的工作基础之上,通过对广西桂中坳陷鹿寨地区开展高精度重力、磁法以及大地电磁法综合物探剖面测量,结合地质、物性和钻探等成果资料,对获取的重、磁、电资料进行联合正反演综合研究,定性-定量解释推断了该地区富有机质泥页岩主要有利目标层系——下石炭统鹿寨组泥页岩层的分布、埋深和厚度等特征;并进一步了解了该地区的断裂构造展布特征,最终对该地区页岩气勘探的有利目标区带进行了圈定预测,为该地区下一步的页岩气基础地质调查工作提供了重要的物探依据.同时,也证实了该套物探技术方法组合能够在南方地区页岩气地质勘探工作中取得较为理想的勘探效果,值得推广应用.     

综合地球物理勘探在桂中坳陷页岩气资源潜力调查中的应用研究

在多年的(非)常规油气勘探工作中,地震法一直是无可取代的技术手段之一,但对于类似广西地质条件复杂、地形条件恶劣的地区难以采集到高质量的地震资料,重磁电等非震方法技术则能够发挥重要作用.多年以来,在桂中坳陷针对页岩气开展的地球物理勘探工作程度很低,笔者以来宾地区较系统的重磁电工作为基础,通过联合反演与综合研究,有效减小了物探多解性、提高了推断解释的准确度和可靠性,系统查明了研究区中富有机质泥页岩目标层系的分布、埋深及厚度等特征,利用"厚深比"参数对研究区页岩气有利目标区带进行了圈定预测,为桂中坳陷地区下一步的页岩气资源潜力调查和优选靶区等工作提供了重要的基础和指导.     

桂地区页岩油气地球物理勘探现状及展望

“十三五”规划中桂地区页岩气基础地质调查地球物理勘探正有序开展。桂地区页岩油气地球物理勘探基础较薄弱,如何有效开展地球物理勘探是当前基础地质调查重要课题。着重阐述了桂周边地区页岩油气地球物理勘探研究现状,指出桂周边地区页岩油气地球物理勘探技术成熟并取得了进展性突破。基于桂地区与其周边地区页岩油气地质条件具有较好可比性,重点讨论了周边地区页岩油气地球物理勘探成功经验对桂地区页岩油气地球物理勘探工作开展的几点认识及展望。指出今后开展桂地区页岩油气地球物理勘探及评价项目中需要注意的几个研究方向,即稳健推广二维地震勘探、优先发展2.5维电磁勘探、加强系统物性测试与分析、重磁电震综合为终极目标,为实际勘探开展奠定理论基础。      

页岩气储层地球物理测井评价研究现状

页岩气是以吸附或游离态为主赋存于暗色富有机质、极低渗透率的泥页岩中,自生自储、连续聚集的天然气藏.我国页岩气富集地质条件优越,具有良好资源前景及开发潜力.页岩气勘探开发的"甜点"是富有机质页岩优质储层的发育段和有利区,页岩气储层评价是寻找"甜点"的关键.地球物理测井技术贯穿于页岩气的勘探开发,是识别和评价页岩气储层的重要手段之一.我国的页岩气勘探开发及储层评价正处于起步探索阶段,为了有效利用地球物理测井技术进行页岩气储层评价,在调研国内外大量文献的基础上,结合已有的地质、测井资料,首先介绍了页岩气勘探开发中不同钻井类型所采用的测井系列,对比和分析了页岩气储层测井响应特征.其次从矿物组分、地球化学参数、物性参数、含气性和可压裂性评价等方面全面深入论述了页岩气储层测井评价方法及评价参数的计算,认为矿物组分、地球化学参数、物性参数、含气性和可压裂性是页岩气储层测井评价的重点,并结合实际资料改进了TOC和脆性指数计算公式.最后提出了我国页岩气储层测井评价中存在的主要问题、发展趋势及一些认识和建议.     

湖相泥页岩层系富有机质形成与烃类富集——以长7为例

继海相页岩气之后,陆相页岩油成为中国非常规油气的重要勘探领域.但湖相泥页岩形成环境完全不同于海相页岩,导致有机质形成和储集体构成不同,其含油气性和烃类流动性也不同.本文以鄂尔多斯盆地延长组长7段页岩层系为例,剖析了湖相泥页岩形成过程中火山活动对古生产力、保存条件的影响,发现火山喷发之前发育藻类、细菌,而喷发之后,细菌数...     

广域电磁法在我国南方海相页岩气勘探中的应用（英文）

在中国页岩气勘探开发仍处于起步阶段,为了降低勘探风险和勘探成本,选择广域电磁法具有分辨率高,抗干扰能力强,勘探深度大,工作效率高等优势。我们选择湖南花垣区块叭岩向斜作为试验区,进行广域电磁法勘探。首先我们在试验区系统地采集了相关岩石标本,分析了岩石标本的电阻率和极化率参数,并针对地质条件建立了系列二维模型,以研究广域电磁法探测对不同地质结构的勘探能力,最后研究了页岩含碳量(TOC)与电阻率和极化率之间的相关性,找到了识别目标层电阻率和极化率参数的阈值,并据此划分了页岩气勘探有利区。通过在有利区内部署的钻井揭露结果表明,广域电磁法可很好地识别该地区的地下地质结构、断层,并确定目标层的分布、深度和厚度。通过对岩石的电阻率、极化率和有机碳含量三者之间的相关性分析,有助于进一步评估页岩品质并选择页岩气开发有利区。     

黔东页岩复电阻率各向异性及其与页岩气储层参数关系研究

电法勘探因其成本低、效率高的优势,常被作为寻找页岩气储层的辅助手段.然而,到目前为止,页岩的电性特征,特别是复电阻率各向异性特征,以及其与页岩气储层参数的关系研究甚少,这在一定程度上阻碍了电法勘探在页岩气勘探中的应用.基于此,本文采集了黔东地区几种典型黑色页岩岩样,并测量了 6块黑色页岩在走向、倾向和垂直层理方向的复电阻率,分析了其各向异性特性,讨论了电阻率与总有机碳(TOC)含量、脆性矿物含量、最大镜质组反射率等页岩气储层参数之间的关系.研究表明:(1)页岩复电阻率振幅各向异性存在频率依赖的特征,在中低频阶段,页岩复电阻率振幅各向异性明显,垂直层理方向复电阻率振幅显著大于走向、倾向方向复电阻率振幅,但随频率增加,页岩复电阻率振幅各向异性差异减小,甚至趋于各向同性;(2)复Cole-Cole模型能很好地拟合页岩三方向的复电阻率数据;(3)走向、倾向方向电阻率与TOC含量存在显著的线性正相关关系,通过走向、倾向方向电阻率预测TOC含量有一定可行性;(4)电阻率与脆性矿物含量、黏土矿物含量、最大镜质组反射率关系复杂,未发现简单的线性相关关系.上述研究结果对我们全面了解黔东地区黑色页岩的电性特征,促进电法勘探在页岩气勘探中的应用大有裨益.     

“进源找油”:论四川盆地页岩油气

四川盆地页岩油气资源丰富,具有国内其他页岩层系不可比拟的优越地质条件,是全面开启中国陆上未来页岩油气"进源找油"征程的理想对象.文章整体分析了美国和中国页岩油气的资源特点,提出成熟度对页岩油气构成有重要控制作用,美国页岩油气中轻烃和湿气比重很高,中国海相、海陆过渡相页岩气主要为干气,陆相页岩油油质一般较重.重点对四川盆地页岩油气开展了地质综合研究,取得了3点主要认识:(1)盆地发育三种类型多套富有机质页岩地层,寒武系筇竹寺组、奥陶系五峰组-志留系龙马溪组海相、二叠系龙潭组海陆过渡相、三叠系须家河组湖泊-沼泽相、侏罗系湖相等页岩是盆地富有机质页岩的典型代表,海相页岩气富集主要受深水陆棚相、适中热演化、富钙富硅岩石组合和封闭顶底板"四要素"控制;(2)"甜点段"一般TOC值高、含气量高、孔隙度大、脆性矿物含量多、地层压力高、页/层理及天然微裂缝发育等,"甜点区"一般富有机质页岩厚度大、热演化适中、保存条件好、埋藏深度浅等,重点例举了五峰组-龙马溪组、龙潭组和自流井组大安寨段页岩油气;(3)四川盆地海相、海陆过渡相、陆相页岩油气资源分别约占全国同类页岩油气地质资源量的50%、25%和30%,资源潜力很大,有望成为中国页岩油气工业革命的摇篮,继东部松辽盆地大庆油田"常规石油大庆"和西部鄂尔多斯盆地长庆油田"西部油气大庆"之后,推动建立四川盆地西南油气田"川渝天然气大庆"生产基地.     

中国南方富有机质海相页岩弹性各向异性特征和影响因素

页岩具有独特的组分和微观结构,其弹性性质通常呈现较强的各向异性,这对其地震和声波测井响应具有显著的影响.四川盆地东部及南部的富有机质海相页岩是目前中国页岩气勘探的主要目标之一,为了研究该地区下志留统的五峰组和上奥陶统的龙马溪组页岩的弹性各向异性特征和影响因素,文章开展了包括超声脉冲测量、全岩衍射分析、有机质热解等实验测试和数据分析.实验结果表明:(1)该地区页岩的各向异性普遍较强,但是强度范围变化较大(10～50%);(2)页岩的各向异性与黏土含量的相关性较好,且黏土定向排列程度对这一关系有重要的影响;(3)五峰-龙马溪组页岩的各向异性强度与有机质含量没有明显的相关性,而美国Bakken、西伯利亚Bazhenov等页岩的有机质含量是其各向异性强度的重要决定因素,这一差异主要是由不同页岩的成熟度的差异和有机质形态、分布特征的差异所导致;(4)同时还发现,该页岩的有机质含量与石英含量呈正相关,这在一定程度上也削弱了有机质含量和各向异性强度之间的相关性.文章的研究结论揭示了五峰-龙马溪组页岩弹性各向异性的特征和影响因素,能够为中国南方富有机质海相页岩的地震各向异性勘探、定量解释、资源评价提供重要的理论基础和数据支持.     

页岩气勘探中的地球物理方法综述及展望

地球物理方法是页岩气勘探中最有效、最准确的预测方法之一.在调研国内外利用地球物理方法勘探页岩气研究成果的基础上,分析总结了页岩气勘探中最有效的地震和测井法对页岩气的响应特征,讨论了常规油气勘探中已获得成功的电磁法、重磁勘探以及综合地球物理方法在页岩气勘探中的应用;对我国页岩气勘探技术的发展进行了展望,为我国页岩气勘探与开发提供参考.     

Application of a wide-field electromagnetic method to shale gas exploration in South China

In an effort to reduce the shale gas exploration risks and costs, we applied the wide-field electromagnetic method (WFEM), because of its strong anti-interference capability, high resolution, ability to conduct exploration at large depths, and high efficiency, to the Bayan Syncline in the South Huayuan block, Hunan Province. We collected rock samples and analyzed their resistivity and induced polarization (IP) and built A series of two-dimensional models for geological conditions to investigate the applicability of WFEM to different geological structures. We also analyzed the correlation between TOC of shale and the resistivity and IP ratio to determine the threshold for identifying target formations. We used WFEM to identify the underground structures and determine the distribution, depth, and thickness of the target strata. Resistivity, IP, and total organic carbon were used to evaluate the shale gas prospects and select favorable areas (sweet spots) for exploration and development. Subsequently, drilling in these areas proved the applicability of WFEM in shale gas exploration.     

Circumjacent distribution pattern of the Lungmachian graptolitic black shale (early Silurian) on the Yichang Uplift and its peripheral region

Stratigraphic hiatuses of variable time intervals within the Rhuddanian to early Aeronian (Llandovery, Silurian) are identified in the area bordering East Chongqing, West Hubei and Northwest Hunan in central China. Their distribution suggested the existence of a local uplift, traditionally named the Yichang Uplift. The diachronous nature of the basal black shale of the Lungmachi Formation crossing different belts of this Uplift signifies the various developing stages during the uplifting process. The present paper defines the temporal and spatial distribution pattern of the Yichang Uplift, which might be one of the important controlling factors for the preservation and distribution of the shale gas in this region, as it has been demonstrated that the shale gas exploration is generally less promising in the areas where more of the basal part of the Lungmachi Formation is missing. Therefore, better understanding of the circumjacent distribution pattern developed throughout the uplifting process may provide the important guidance for the shale gas exploration. The present work is a sister study to the published paper, “Stage-progressive distribution pattern of the Lungmachian black graplolitic shales from Guizhou to Chongqing, Central China”. These two studies thus provide a complete Ordovician-Silurian black shale distribution pattern in the Middle and Upper Yangtze, a region with the major shale gas fields in China.     

Continuous TDEM for monitoring shale hydraulic fracturing

Monitoring and delineating the spatial distribution of shale fracturing is fundamentally important to shale gas production. Standard monitoring methods, such as time-lapse seismic, cross-well seismic and micro-seismic methods, are expensive, timeconsuming, and do not show the changes in the formation with time. The resistivities of hydraulic fracturing fluid and reservoir rocks were measured. The results suggest that the injection fluid and consequently the injected reservoir are characterized by very low resistivity and high chargeability. This allows using of the controlled-source electromagnetic method (CSEM) to monitor shale gas hydraulic fracturing. Based on the geoelectrical model which was proposed according to the well-log and seismic data in the test area the change rule of the reacted electrical field was studied to account for the change of shale resistivity, and then the normalized residual resistivity method for time lapse processing was given. The time-domain electromagnetic method (TDEM) was used to continuously monitor the shale gas fracturing at the Fulin shale gas field in southern China. A high-power transmitter and multi-channel transient electromagnetic receiver array were adopted. 9 h time series of Ex component of 224 sites which were laid out on the surface and over three fracturing stages of a horizontal well at 2800 m depth was recorded. After data processing and calculation of the normalized resistivity residuals, the changes in the Ex signal were determined and a dynamic 3D image of the change in resistivity was constructed. This allows modeling the spatial distribution of the fracturing fluid. The model results suggest that TDEM is promising for monitoring hydraulic fracturing of shale.     

Shales in the Qiongzhusi and Wufeng–Longmaxi Formations: a rock-physics model and analysis of the effective pore aspect ratio

The shales of the Qiongzhusi Formation and Wufeng–Longmaxi Formations at Sichuan Basin and surrounding areas are presently the most important stratigraphic horizons for shale gas exploration and development in China. However, the regional characteristics of the seismic elastic properties need to be better determined. The ultrasonic velocities of shale samples were measured under dry conditions and the relations between elastic properties and petrology were systemically analyzed. The results suggest that 1) the effective porosity is positively correlated with clay content but negatively correlated with brittle minerals, 2) the dry shale matrix consists of clays, quartz, feldspars, and carbonates, and 3) organic matter and pyrite are in the pore spaces, weakly coupled with the shale matrix. Thus, by assuming that all connected pores are only present in the clay minerals and using the Gassmann substitution method to calculate the elastic effect of organic matter and pyrite in the pores, a relatively simple rock-physics model was constructed by combining the self-consistent approximation (SCA), the differential effective medium (DEM), and Gassmann’s equation. In addition, the effective pore aspect ratio was adopted from the sample averages or estimated from the carbonate content. The proposed model was used to predict the P-wave velocities and generally matched the ultrasonic measurements very well.     

基于固体替换模型的有机质含量对页岩弹性性质的影响分析

页岩中的TOC(Total Organic Carbon,总有机碳)含量,对页岩的有效弹性模量以及与之相关的弹性波速度(P波和S波)有重要影响,建立弹性模量与TOC含量关系是页岩气甜点预测的重要手段之一.CS和SM两种固体置换理论主要针对孔隙度较大的砂岩,能否适用于孔隙度低、孔隙形态复杂和非均质性强的页岩目前尚未深入研究.鉴于目前已知的富有机质页岩的TOC赋存形态与裂缝以及孔隙形态类似,有关TOC含量对岩石弹性模量的影响可视为孔隙物质充填问题来研究.本文利用数字岩心技术,构造同一数字岩心不同TOC含量的样本群,基于CS和SM两种固体替换理论模型,通过有限元(FEM)数值模拟交叉验证,详细研究了两种固体替换方程对页岩的适用性和TOC含量对页岩弹性性质的影响.研究表明,由于实际岩心孔隙及TOC分布的非均质性,CS替换方程弹性模量预测值与FEM模拟结果存在差异,而SM替换方程预测值与FEM模拟结果基本一致,两种方程的预测差异揭示页岩非均质强度,利用SM替换方程中的参数α_1,α_2,β_1和β_2可详细分析实际岩心孔隙及TOC分布的非均质特征.     

Computation of elastic properties of 3D digital cores from the Longmaxi shale

The dependence of elastic moduli of shales on the mineralogy and microstructure of shales is important for the prediction of sweet spots and shale gas production. Based on 3D digital images of the microstructure of Longmaxi black shale samples using X-ray CT, we built detailed 3D digital images of cores with porosity properties and mineral contents. Next, we used finite-element (FE) methods to derive the elastic properties of the samples. The FE method can accurately model the shale mineralogy. Particular attention is paid to the derived elastic properties and their dependence on porosity and kerogen. The elastic moduli generally decrease with increasing porosity and kerogen, and there is a critical porosity (0.75) and kerogen content (ca. ≤3%) over which the elastic moduli decrease rapidly and slowly, respectively. The derived elastic moduli of gas- and oil-saturated digital cores differ little probably because of the low porosity (4.5%) of the Longmaxi black shale. Clearly, the numerical experiments demonstrated the feasibility of combining microstructure images of shale samples with elastic moduli calculations to predict shale properties.     

Compaction trend versus seismic anisotropy in shaly formations

Shales comprise more than 60% of sedimentary rocks and form natural seals above hydrocarbon reservoirs. Their sealing capacity is also used for storage of nuclear wastes. The world's most important conventional oil and gas reservoirs have their corresponding source rocks in shale. Furthermore, shale oil and shale gas are the most rapidly expanding trends in unconventional oil and gas. Shales are notorious for their strong elastic anisotropy, i.e., so‐called vertical transverse isotropy. This vertical transverse isotropy, characterised by a vertical axis of invariance, is of practical importance as it is required for correct surface seismic data interpretation, seismic to well tie, and amplitude versus offset analysis. A rather classical paradigm makes a clear link between compaction in shales and the alignment of the clay platelets (main constituent of shales). This would imply increasing anisotropy strength with increasing compaction. Our main purpose is to check this prediction on two large databases in shaly formations (more than 800 samples from depths of 0–6 km) by extracting the major trends in the relation between seismic anisotropy and compaction. The statistical analysis of the database shows that the simultaneous increase in density and velocity, a classical compaction signature, is quite weakly correlated with the anisotropy strength. As a consequence, compaction can be excluded as a major cause of seismic anisotropy, at least in shaly formations. Also, the alignment of the clay platelets can explain most of the anisotropy measurements of both databases. Finally, a method for estimating the orientation distribution function of the clay platelets from the measurement of the anisotropy parameters is suggested.     

Definition and sturcture characteristics of pores in mylonitized organic-rich shales

Gas shales with a high gas content were drilled in the Lower Cambrian Lujiaping Formation in the northeastern Sichuan Basin,close to the Chengkou Fault in the Dabashan arc-like thrust fold belt.The equivalent vitrinite reflectance values of organic matters are over 4.0%Ro.The pore structures of the shales were investigated based on microscopy,field emission scanning electron microscopy(FESEM)observations,and low temperature N2 adsorption analysis.The study suggests that cleavages,comprising clay minerals mixed up with organic matter and other insoluble residues,were developed in the rock layers.The clay minerals are directionally arranged,displaying a mylonitized texture.Abundant nanometer-size organic matter and clay mineral particles are well mixed in the cleavage domains,which developed the mylonitized pore system that consists of nanometer-size intergranular pore spaces,aggregate pore spaces in clay mineral flakes and pore network.This mylonitized pore system has high specific surface area,high methane adsorption capacity,and high capillary pressure,which collectively contributes to the preservation of shale gas in such a complex tectonic area.The discovery of the mylonitized pore structure in organic-rich shales may reveal a new mechanism of shale gas enrichment in complex tectonic areas with over-mature organic matter in the northeastern part of Sichuan Basin.