Chronological Study of Coal-seam Water and its Implication on Gas Production in the South Qinshui Basin

The knowledge of the residence time of formation water is fundamental to understanding the subsurface flow and hydrological setting.To better identify the origin and evolution of coal seam water and its impact on gas storage and production,this study collected coalbed methane co-produced water in the southeast Qinshui Basin and detected chemical and isotopic compositions,especially 36Cl and 129I concentrations.The calculated tracer ages of 129I(5.2–50.6 Ma)and 36Cl(0.13–0.76 Ma)are significantly younger than the age of coal-bearing formation(Pennsylvanian-Cisuralian),indicating freshwater recharge after coal deposition.The model that utilises 129I/I and 36Cl/Cl ratios to constrain the timing of recharge and the proportion of recharge water reveals that over 60%of pre-anthropogenic meteoric water entered coal seams since 10 Ma and mixed with residue initial deposition water,corresponding to the basin inversion in Cenozoic.The spatial distribution of major ion concentrations reveals the primary recharge pathway for meteoric water from coal outcrops at the eastern margin to the basin center.This study demonstrates the occurrence of higher gas production rates from wells that accept water recharge in recent times and suggests the possible potential of the non-stagnant zones for high gas production.

Simulation of Paleotectonic Stress Fields and Distribution Prediction of Tectonic Fractures at the Hudi Coal Mine, Qinshui Basin

Study on tectonic fractures based on the inversion of tectonic stress fields is an effective method. In this study, a geological model was set up based on geological data from the Hudi Coal Mine, Qinshui Basin, a mechanical model was established under the condition of rock mechanics and geostress, and the finite element method was used to simulate the paleotectonic stress field. Based on the Griffith and Mohr-Coulomb criterion, the distribution of tectonic fractures in the Shanxi Formation during the Indosinian, Yanshanian, and Himalayan period can be predicted with the index of comprehensive rupture rate. The results show that the acting force of the Pacific Plate and the India Plate to the North China Plate formed the direction of principal stress is N-S, NW - SE, and NE - SW, respectively, in different periods in the study area. Changes in the direction and strength of the acting force led to the regional gradients of tectonic stress magnitude, which resulted in an asymmetrical distribution state of the stress conditions in different periods. It is suggested that the low-stress areas are mainly located in the fault zones and extend along the direction of the fault zones. Furthermore, the high-stress areas are located in the junction of fold belts and the binding site of multiple folds. The development of tectonic fractures was affected by the distribution of stress intensity and the tectonic position of folds and faults, which resulted in some developed areas with level I and II. There are obvious differences in the development of tectonic fractures in the fold and fault zones and the anticline and syncline structure at the same fold zones. The tectonic fractures of the Shanxi Formation during the Himalayan period are more developed than those during the Indosinian and Yanshanian period due to the superposition of the late tectonic movement to the early tectonic movement and the differences in the magnitude and direction of stress intensity.

Geological Controls on the CBM Productivity of No.15 Coal Seam of Carboniferous–Permian Taiyuan Formation in Southern Qinshui Basin and Prediction for CBM High-yield Potential Regions

Coalbed methane(CBM) resources in No.15 coal seam of Taiyuan Formation account for 55% of the total CBM resources in southern Qinshui Basin(SQB), and have a great production potential. This study aims at investigating the CBM production in No.15 coal seam and its influence factors. Based on a series of laboratory experiments and latest exploration and development data from local coal mines and CBM companies, the spatial characteristics of gas production of No.15 coal seam were analyzed and then the influences of seven factors on the gas productivity of this coal seam were discussed, including coal thickness, burial depth, gas content, ratio of critical desorption pressure to original coal reservoir pressure(RCPOP), porosity, permeability, and hydrogeological condition. The influences of hydrological condition on CBM production were analyzed based on the discussions of four aspects: hydrogeochemistry, roof lithology and its distribution, hydrodynamic field of groundwater, and recharge rate of groundwater. Finally, a three-level analytic hierarchy process(AHP) evaluation model was proposed for predicting the CBM potentials of the No.15 coal seam in the SQB. The best prospective target area for CBM production of the No.15 coal seam is predicted to be in the districts of Panzhuang, Chengzhuang and south of Hudi.

Structure and production fluid flow pattern of post-fracturing high-rank coal reservoir in Southern Qinshui Basin

Field geological work, field engineering monitoring, laboratory experiments and numerical simulation were used to study the development characteristics of pore-fracture system and hydraulic fracture of No.3 coal reservoir in Southern Qinshui Basin. Flow patterns of methane and water in pore-fracture system and hydraulic fracture were discussed by using limit method and average method. Based on the structure model and flow pattern of post-fracturing high-rank coal reservoir, flow patterns of methane and water were established. Results show that seepage pattern of methane in pore-fracture system is linked with pore diameter, fracture width, coal bed pressure and flow velocity. While in hydraulic fracture, it is controlled by fracture height, pressure and flow velocity. Seepage pattern of water in pore-fracture system is linked with pore diameter, fracture width and flow velocity. While in hydraulic fracture, it is controlled by fracture height and flow velocity. Pores and fractures in different sizes are linked up by ultramicroscopic fissures, micro-fissures and hydraulic fracture. In post-fracturing high-rank coal reservoir, methane has level-three flow and gets through triple medium to the wellbore; and water passes mainly through double medium to the wellbore which is level-two flow.

A dynamic evaluation technique for assessing gas output from coal seams during commingling production within a coalbed methane well: a case study from the Qinshui Basin

Gas drainage is carried out based on output from each coal bed throughout commingling production of coalbed methane(CBM).A reasonable drainage process should therefore initially guarantee main coal bed production and then enhance gas output from other beds.Permanent damage can result if this is not the case,especially with regard to fracture development in the main gas-producing coal bed and can greatly reduce single well output.Current theoretical models and measuring devices are inapplicable to commingled CBM drainage,however,and so large errors in predictive models cannot always be avoided.The most effective currently available method involves directly measuring gas output from each coal bed as well as determining the dominant gas-producing unit.A dynamic evaluation technique for gas output from each coal bed during commingling CBM production is therefore proposed in this study.This technique comprises a downhole measurement system combined with a theoretical calculation model.Gas output parameters(i.e.,gas-phase flow rate,temperature,pressure)are measured in this approach via a downhole measurement system;substituting these parameters into a deduced theoretical calculation model then means that gas output from each seam can be calculated to determine the main gas-producing unit.Trends in gas output from a single well or each seam can therefore be predicted.The laboratory and field test results presented here demonstrate that calculation errors in CBM outputs can be controlled within a margin of 15%and therefore conform with field use requirements.

High rank coalbed methane desorption characteristic and its application in production in Qinshui basin

Based on spontaneous desorption characteristic, the correlation of desorption time and gas content was analyzed and the application of it in production was researched. The desorption of high rank coalbed methane in Qinshui basin was periodic, and isotope fractionation effect also exists in the process. △δ^13C1 can be used to distinguish the stabilization of coalbed methane wells, associated with desorption rate, the individual well recoverable reserves can be calculated. Economically recoverable time can be predicted according to the logarithmic relationship between desorption gas content per ton and desorption time. The error between predicted result and numerical simulation result is only 1.5%.

Classification of Coalbed Methane Enrichment Units of Qinshui Basin Based on Geological Dynamical Conditions

Coalbed methane enrichment will be controlled by many good macro geological dynamical conditions; there is evident difference of enrichment grade in different area and different geological conditions.This paper has studied tectonic dynamical conditions, thermal dynamical conditions and hydraulic conditions, which affect coalbed methane enrichment in Qinshui basin.Coalbed methane enrichment units have been divided based on tectonic dynamical conditions of Qinshui basin,combined with thermal dynamical conditions and hydraulic conditions.

Evaluation method of coal rank based on X-ray diffraction analysis an example from SE Qinshui Basin

Based on analysis on X-ray diffraction, the metamorphic grade of coal in southeast Qinshui Basin was discussed, and a precise evaluation of coal rank through XRD analysis was made, in addition, the correlation of coal rank and vitrinite reflectance （Ro） was compared. XRD spectra of coal shows （002）-band and γ-band, and based on fitting calculation and multi-peak separation methods, the values of 2θ002 and 2θγ can be obtained, as well as corresponding intensities I002 and Iγ, consequently the coal rank can be quantized as the ratio of I002 and Iγ, that is coal rank=I002/Iγ. The research shows that the values of θ002 and θγ increase with the metamorphic grade, and a very good linear positive correlation exists between calculated Coal Rank and Ro.

Pore Structure Characteristics of Taiyuan Formation Shale in Qinshui Basin

Qinshui Basin is located in the southeast of Shanxi Province, China. Taking the shale of Taiyuan Formation in Qinshui Basin as the research object, the study analyzed the pore size of the shale of Taiyuan formation in detail from micropore to macropore by the methods of mercury injection, liquid nitrogen analysis and combination of liquid nitrogen and mercury injection. The results show that: 1) the visible pores and macropores are poorly developed and distributed unevenly in the shale of Taiyuan formation, and the micropores are well developed in the shale, and there are more open pores in the pore diameter range, and the pore connectivity is good;2) the liquid nitrogen experiment shows that the pores of Taiyuan Shale are relatively developed between 15 nm and 20 nm, and the formation of hysteresis loop may be caused by some narrow slit pores with similar layered structure;3) the comprehensive analysis of liquid nitrogen and mercury injection experiments shows that the shale of the Taiyuan formation mainly develops micropores, the Mesopores is not developed, the pore volume at 10 - 100 nm is more developed than other parts, and the specific surface is mainly contributed by micropores, which can improve the efficiency of shale gas resolution;at the same time, it provides a channel for Shale gas migration, which is beneficial to the development of shale gas.

Influence of depressurization rate on gas production capacity of high-rank coal in the south of Qinshui Basin, China

A desorption simulation experiment with the condition of simulated strata was designed. The experiment, under different depressurizing rates and the same fluid saturation, was conducted on the sample from 3# coal of Daning coal mine in Jincheng, Shanxi Province. The gas production rate and pressure change at both ends of the sample were studied systematically, and the mechanisms of some phenomena in the experiment were discussed. The experimental results show that, whether at fast or slow depressurizing rate, the methane adsorbed to high-rank coal can effectively desorb and the desorption efficiency can reach above 90%. There is an obvious inflection point on the gas yield curve during the desorption process and it appears after the pressure on the lump of coal reduces below the desorption pressure. The desorption of methane from high-rank coal is mainly driven by differential pressure, and high pressure difference is conducive to fast desorption. In the scenario of fast depressurization, the desorption inflection appears earlier and the gas production rate in the stage of rapid desorption is higher. It is experimentally concluded that the originally recognized strategy of long-term slow CBM production is doubtful and the economic benefit of CBM exploitation from high-rank coal can be effectively improved by rapid drainage and pressure reduction. The field experiment results in pilot blocks of Fanzhuang and Zhengzhuang show that by increasing the drainage depressurization rate, the peak production of gas well would increase greatly, the time of gas well to reach the economic production shortened, the average time for a gas well to reach expected production reduced by half, and the peak gas production is higher.

沁水盆地南部中深部煤层气储层特征及开发技术对策

为了实现沁水盆地南部中深部煤层气高效开发,以郑庄北-沁南西区块为研究对象,基于参数井取心分析测试、注入/压降测试、地应力循环测试结果和大量动静态数据,通过与浅部对比,阐述了中深部煤储层特征,分析了从浅部到中深部煤层直井压裂和水平井分段压裂两种开发技术的改进,进而提出了中深部煤层气主体开发技术。结果表明,郑庄北-沁南西区块3号煤平均埋深1200 m左右,为中深部煤层气储层。随着埋深增加,研究区含气量和吸附时间均先增加后降低,含气量和吸附时间峰值分别位于埋深1100~1200 m和800~1000 m;随着埋深增加,研究区地应力场类型发生了2次转换,埋深小于600 m时,为逆断层型地应力场类型,水力压裂易形成水平缝,利于造长缝;埋深大于1000 m时为走滑断层型地应力场类型,水力压裂易形成垂直缝,裂缝延伸较短;埋深为600~1000 m时,地应力场由逆断层型向走滑断层型转换阶段,水力压裂形成的裂缝系统较为复杂。与浅层相比,中深部储层含气量、解吸效率和应力场发生明显转变。随着埋深增加,无论是直井(定向井)还是水平井,均应采用更大的压裂规模才能获得较好的效果。对于直井,埋深大于800 m后,压裂液量达到1500 m^(3)以上、排量12~15 m^(3)/min以上、砂比10%~14%以上,单井日产气量可以达到1000 m^(3)以上;对于水平井,埋深大于800 m后,压裂段间距控制在70~90 m以下,单段液量、砂量分别达到2000、150 m^(3)以上,排量达到15 m^(3)/min以上开发效果较好,单井产量突破18000 m^(3)。随着埋深增加,水平井开发方式明显优于直井,以二开全通径水平井井型结构、优质层段识别技术和大规模、大排量缝网压裂为核心的水平井开发方式是适用于沁水盆地南部中深部煤层气高效开发的主体工艺技术。

矿物对无烟煤力学非均质性影响的分子动力学研究——以沁水盆地南部主要黏土矿物高岭石为例

煤是由有机显微组分和矿物组成的混合物,矿物的存在会导致煤的大分子结构存在差异,使得煤的力学性质具有明显的非均质性,进而影响区块内整体的煤层气产量、压裂改造效果和成熟技术的规模化应用。以沁水盆地典型的无烟煤和高岭石矿物作为研究对象,通过分子动力学的方法定量研究高岭石及其含量对无烟煤力学性质的影响规律,分析不同矿物含量下无烟煤的分子结构和孔隙特征,从能量和有序化的角度揭示其微观机理。结果表明:①煤有机质与高岭石相互结合过程中同时存在范德华力和氢键作用,且氢键作用强度要高于范德华力,煤有机质周围出现高岭石分子的概率、相互作用强度和有序性均随着矿物质量分数的增加而增大。②无烟煤的孔隙率φ随高岭石质量分数a的增大呈线性规律(φ=−0.2293a+9.6295)降低,而无烟煤的体积模量、弹性模量和剪切模量均随高岭石质量分数的增大呈线性规律增强,泊松比随高岭石质量分数的增大呈二次多项式规律降低。③无烟煤的力学非均质程度整体上随着高岭石质量分数增加而增大,其中不同高岭石质量分数下体积模量、弹性模量和剪切模量的变异性可分为很低、低、中等、高和很高5个部分,而泊松比的变异系数均小于0.1,变异性很低。④随着高岭石质量分数的增加,煤有机质与高岭石的相互作用能呈线性规律(Einteraction=4.5585a+443.929)增大,与纯有机质相比,当高岭石质量分数达到20%时,无烟煤的键能和范德华能分别增加了63.86%和48.06%。⑤高岭石增强煤力学性质的内在原因是高岭石进入煤有机质后占据一定的孔隙空间,且与煤有机质的芳香碳骨架和不同官能团进行相互作用,高岭石质量分数越大充填煤大分子结构孔隙的程度越高,煤大分子结构的能量越大,导致煤大分子结构的孔隙率降低,有序性增大,使得力学强度和抵抗变形的能力增强。

柿庄北煤层气区块煤层压裂裂缝扩展规律及影响因素

揭示煤层气储层压裂裂缝扩展规律及影响因素,对于制定压裂工艺及高效开发煤层气资源具有重要的意义。利用沁水盆地柿庄北煤层气区块的钻井取心、测井、井下节理观测、压裂施工及微震监测等数据,系统分析了水力压裂裂缝扩展规律及影响因素。结果表明:研究区主要采用清水压裂液,压裂施工曲线可分划为上升型、下降型、平稳型和波动型4类;微震监测表明压裂裂缝走向主要在37°~55°和42°~70°,压裂裂缝网络长度范围在69.5~157.5 m,宽度在35.0~68.5 m。Ⅰ型地应力(σ_(v)>σ_(H)>σ_(h))状态下,压裂裂缝容易沿着垂向扩展,多数压裂曲线为下降型或稳定型;Ⅱ型地应力(σ_(H)>σ_(v)>σ_(h))状态下,压裂裂缝扩展方向相对单一,多数为单一形状的垂直裂缝,裂缝网络宽度较小;Ⅲ型地应力(σ_(H>σ_(h)>σ_(v))状态下,压裂裂缝沿水平方向扩展,裂缝形态复杂。侧压系数λ与压裂裂缝网络长度呈正相关关系,与压裂裂缝网络宽度呈负相关;若λ大于0.3,压裂裂缝网络长度常大于90 m。压裂裂缝扩展到节理(裂隙)时能够出现穿越、沟通和俘获3种类型;其中沟通型压裂效果较好,多数煤层气井具有高产稳产的特点;穿越型的压裂裂缝延展长度有限,俘获型的压裂裂缝多数与节理(裂隙)重合,这2类压裂井的产气效果相对较差。随着原生+碎裂结构煤占比的增大,压裂裂缝网络长度逐渐增大,宽度逐渐减小;当原生+碎裂结构煤厚度占比小于40%,压裂裂缝网络长度难以超过110 m。上述成果可为煤层压裂改造提供理论基础及地质保障。

沁水盆地南部煤储层赋存环境条件及其对渗透率的影响

煤层气赋存与产出受控于煤储层地应力、压力和地温等赋存环境条件,正确分析煤储层赋存环境条件及其对渗透率的影响是煤层气有效开发所关注的关键问题。采用沁水盆地南部煤层气井63个测试资料,系统分析了研究区煤储层地应力、压力和温度条件,揭示了煤储层应力、压力和温度随埋藏深度的变化规律,建立最小水平主应力与垂直主应力和煤储层压力之间关系模型。采用三轴渗流试验系统,开展了不同应力、压力和温度条件下煤层气渗流试验研究,揭示了不同温度、应力和压力条件下煤样渗透率变化规律及其控制机理。研究结果表明,研究区煤储层最大、最小水平主应力分别为6.62~42.06和3.30~26.40 MPa,其梯度分别为1.20~5.26和0.99~2.95 MPa/hm;煤储层压力及其梯度分别为0.99~12.63 MPa和0.23~1.18 MPa/hm;煤储层温度及其梯度为19.36~38.84℃和1.98℃/hm;且煤储层应力、压力和温度均随深度的增加呈线性增大的规律。随着有效应力的增加,煤储层渗透率不断降低,在初始加压阶段,渗透率下降幅度较大,随着有效应力的增加,下降幅度变缓。在相同的应力条件下,温度的增加使得煤样渗透率不断降低,渗透率的下降速率随温度的升高而减小。随着有效应力和温度的增加,煤储层渗透率按负指数函数规律降低。随着孔隙压力的降低,有效应力增加,煤储层渗透率不断降低。在初始降压阶段,煤储层渗透率急剧下降,随着孔隙压力的降低,渗透率下降速率逐渐变缓;当孔隙压力小于0.6 MPa后,煤储层渗透率随孔隙压力的降低而升高。在高孔隙压力条件下,渗透率随温度的升高呈负指数函数降低,在低孔隙压力条件下,煤储层渗透率随温度的升高呈线性降低。在此基础上,建立了煤储层渗透率与应力、压力和温度之间的关系模型,揭示了煤储层渗透率随应力、压力和温度应力的增加按负指数函数降低的规律和控制机理。

基于机器学习的煤层气产能标定智能算法及影响因素分析

煤层气是我国常规天然气现实可靠的战略补充资源之一,智能化标定煤层气产能对于天然气工业的发展具有重要意义.对山西沁水盆地某煤层气区块的煤层气井进行了实际地质、生产数据的收集及数据预处理,提出了基于生产井史的煤层气单井产能计算公式.利用预处理后的生产数据及储层数据,建立了基于深度神经网络、支持向量回归机、随机森林的煤层气产能标定智能算法,对煤层气单井产能进行了预测,比较了三种机器学习模型的预测结果,分析了不同排采天数的生产数据作为输入参数对模型精度的影响.基于预测效果最好的机器学习模型,进行了动态参数(排采前期的日产气、日产水和井底流压)和静态参数(煤层埋深、孔隙度、渗透率、煤层厚度和含气量)对煤层气产能标定模型的重要性程度分析.结果表明:三种机器学习模型标定煤层气单井产能的平均决定系数为0.828,其中深度神经网络模型决定系数最高,达0.923;增加生产数据前期排采天数,决定系数增长趋势明显,之后增长趋势减缓并最终趋于平稳;动态参数和静态参数对产能的影响都较强,这两类参数对于产能预测模型的贡献度分别为48%和52%.

中国海油陆上天然气勘探进展及增储发展战略

中国海油为快速发展天然气产业,提升天然气产量,逐步加大鄂尔多斯盆地和沁水盆地矿权区块勘探投入,区块内有利于形成致密气、煤层气和常规气等多种天然气类型,天然气资源量可达30000×10^(8)m^(3),在高丰度区和构造简单区已经探明地质储量7500×10^(8)m^(3)。基于资源潜力及品质、成藏条件、勘探技术的全面分析,适时提出了陆上万亿立方米天然气增储的发展战略,并明确了致密气—煤层气并举、多气种立体勘探的指导思想,确定了加快鄂尔多斯盆地东缘深层煤层气和致密气勘探、快速推动沁水盆地中浅层煤层气勘探的部署思路。通过加强勘探领域成藏富集规律和勘探技术攻关方向的综合分析,明确了今后一个时期的重点勘探方向。鄂尔多斯盆地东部区块具有煤系地层全油气系统有序共存特征,需开展煤系地层天然气全成藏系统勘探,夯实增储上产基础,聚焦致密气、深层煤层气,攻关薄层煤层气、奥陶系常规天然气和铝土岩气,通过勘探开发一体化、地质工程一体化推进多气种交互接替勘探,实现天然气全成藏系统勘探开发。在沁水盆地南部、北部,重点推进中浅层煤层气水平井体积压裂达产技术试验和推广应用,并与薄层煤层气形成互补式经济有效开发,推动沁水盆地煤层气的整体增储上产。上述重点领域的勘探部署将保障中国海油陆上万亿立方米大气区的增储实现和健康稳定发展。

煤系氦气富集机理与资源潜力-以鄂尔多斯盆地东缘为例

【背景】氦气因其化学性质稳定、导热性能好等优势,被广泛应用于国防、军工、航空、航天等高科技领域,具有不可替代的作用。目前我国氦气主要源于进口,对外依存度高,氦气资源安全问题突出。前人对氦气的研究主要集中在常规天然气,对煤系氦气的关注较少。【目的和方法】为了明确煤系中氦气资源分布及资源潜力,对鄂尔多斯盆地东缘(鄂东缘)煤系气进行取样分析,系统研究氦气分布规律及其控制因素。并结合沁水盆地煤层气中氦气测试结果,对比这两大盆地煤系中氦气富集机理,深入研究煤系中氦气资源潜力。【结果和结论】结果表明:鄂东缘韩城和大宁–吉县深部煤层气中氦气含量高于中浅部煤层气,其中,韩城深部和中浅部煤层中氦气平均体积分数分别为0.0428%和0.0130%,大宁–吉县深部和中浅部煤层中氦气平均体积分数分别为0.0307%和0.0121%;煤系致密气和深部煤层气中氦气含量相当,其中,韩城和大宁–吉县致密气中氦气平均体积分数分别为0.0467%和0.0355%,但都属于贫氦煤层气;三交北区块煤系气中氦气含量较高,平均0.0930%,近一半的井可以达到富氦煤系气标准。鄂东缘煤系中原位自生氦气极少,主要来源于深部基底岩石、铝土岩和紫金山岩体,氦源岩的分布决定了煤系中氦气的分布。鄂东缘断裂系统是深部氦源和紫金山岩体中氦气的有利运移通道,断裂系统的发育强度和位置是氦气运移、聚集的关键,有效的盖层和封闭的水体环境是氦气保存的必要条件。沁水盆地原位自生氦气较少,成藏后期剧烈构造抬升是煤层氦气散失近90%的主要原因。深部煤层气和煤系致密气中氦气浓度相对较低,但是资源量巨大,应加大煤系氦气资源勘查力度。同时,应加强对贫氦–含氦煤系天然气的提氦技术攻关,有效利用煤系天然气中的低浓度氦气,以保障国家的氦气资源安全。

海陆过渡相煤系页岩孔隙分形特征及影响因素——以沁水盆地北部太原组为例

【目的】为分析沁水盆地北部太原组海陆过渡相煤系页岩孔隙分形特征及影响因素。【方法】通过对阳泉区块太原组样品进行总有机碳(TOC)含量、成熟度测试及X射线衍射、低温氮气吸附实验,基于(Frenkel Halsey Hill,FHH)理论模型计算样品孔隙分形维数,分析矿物含量、有机地化特征及孔隙结构参数对孔隙分形维数的影响。【结果】太原组煤系页岩TOC含量介于0.57%~6.40%,平均为3.18%;有机质镜质体反射率(R_(o))介于1.96%~3.24%,平均为2.49%;煤系页岩微观孔隙具有双重分形特点,其中表面分形维数(D_(1))介于2.507 9~2.663 9,结构分形维数(D_(2))介于2.527 1~2.809 4;有机质含量及成熟度与D_(1)、D_(2)均呈正相关关系,孔隙结构参数与D_(1)、D_(2)具有良好的正相关性,但与D_(2)相关系数高于D_(1),指示微孔对孔隙结构参数的影响更强;分选、磨圆度高的陆源碎屑石英多具规则孔隙形态,造成石英含量与D_(1)、D_(2)呈负相关关系;碳酸盐岩矿物及长石主要提供宏孔,其含量与页岩D_(1)及D_(2)均呈负相关关系;黏土矿物在长期压实作用下孔径减小,微孔数量增加,孔隙形态复杂,其含量与分形维数D_(1)及D_(2)呈正相关关系。【结论】海陆过渡相煤系页岩微观孔隙具有双重分形特点,有机质含量、成熟度、孔隙结构参数和黏土矿物含量增大可导致其微观孔隙分形维数变大,陆源碎屑石英、长石和碳酸盐矿物含量增多可导致其微观孔隙分形维数变小。

沁水盆地煤层气地震资料处理技术

为了准确预测沁水盆地煤层气勘探有利区,开展了煤层气地震资料处理关键技术研究。研究结果表明:1)层析反演技术配合地表一致性剩余静校正技术,可以较好地解决资料中存在的静校正问题,最终99%以上的炮点和检波点校正量约束在一个样点间隔范围内,目的层反射连续性增强,信噪比得到大幅度提高;2)基于AVO正演道集的保幅去噪质控技术,可以定量评价去噪保幅性,去噪后井点位置地震道集的AVO特征与正演道集的AVO特征相似程度达到90%以上;3)对于黄土山地地震资料,近地表Q补偿加串联反褶积可以有效改善地震资料的频谱,最终成果主频可达37 Hz,频宽达到4.5个倍频程,满足叠前、叠后反演对资料的频率需求;4)OVG道集不仅保留了方位角和炮检距信息,同时其近中远炮检距能量均衡,能更好地满足叠前裂缝检测的需求,提高裂缝检测的精度;5)将采区内生产井的产水与产气信息作为验证手段,对成果的构造形态以及断层合理性予以质控,更能保证处理成果的真实性与合理性。以上成果认识对地震勘探技术在煤层气有利区预测中的成功应用具有一定的指导意义,满足煤层气高效开发的需求。

沁水盆地榆社—武乡区块二叠系煤系页岩储层地质建模及“甜点”预测

沁水盆地煤系页岩气资源丰富,但勘探开发处于初期阶段。基于钻井、测井和地震解释资料,结合有机地球化学与储层物性实验测试数据,通过三维地质建模技术,建立了沁水盆地榆社—武乡区块二叠系山西组底部—太原组上部煤系页岩地质模型,并预测了煤系页岩气“甜点”区。研究结果表明:(1)沁水盆地榆社—武乡区块石炭系—二叠系煤系地层模型反映了煤系页岩储层的发育主要受控于构造活动,呈“东浅西深、整体连续”的分布格局。(2)基于序贯指示法建立沉积相模型,指示研究区在太原期—山西期由海陆过渡相转变为近海陆相沉积环境,为稳定优质页岩储层的形成提供了有利的沉积环境。(3)通过相控属性建模实现了储层参数空间分布模拟和精细表征,泥地比、孔隙度、含气量、总有机碳含量和镜质体反射率的平均值分别为0.57,10.02%,1.21 m^(3)/t,2.18%,2.45%,揭示了研究区煤系页岩较好的储集能力、含气性、有机质丰度和资源潜力,脆性指数模型指示出页岩压裂后的有利区带。(4)在精细三维地质建模的基础上,将三维网格单元赋值积分,计算研究区二叠系煤系页岩气地质资源量为1 344.98×10^(8)m^(3),运用层次分析法和模糊评价法预测页岩气“甜点”区,Ⅰ类“甜点”区为地质与工程双重甜点,分布于研究区东北部、中部和西北部局部区域。