Division of Matrix- and Fracture-Type Shale Oils in the Jiyang Depression and Their Differences

This study discussed the division of matrix- and fracture-type shale oils in the Jiyang Depression, and proposed the concept of fracture development coefficient. The fracture development coefficient is defined as the ratio of fault throw to the distance between a shale oil well and the nearest fault. Based on CO_2 content, state of water, oil production and logging response of shale oil formations, the classification of shale oils was established, i.e., a fracture-type shale oil well has a fracture development coefficient greater than 0.2, while a matrix-type one has a fracture development coefficient less than 0.2. Furthermore, the key control factors of matrix- and fracture-type shale oil enrichment were analyzed using typical anatomical and statistical methods. For matrix-type shale oil enrichment, these factors are lithofacies, total organic carbon（TOC）, shale porosity and abnormal pressure; for fracture-type shale oil enrichment, they are lithofacies, extent of fracture development, and abnormal pressure. This study also first described the differences between matrix- and fracture-type shale oils. The results provide reference for the exploration of terrestrial faulted basins in eastern China.

Investigating microstructure of Longmaxi shale in Shizhu area,Sichuan Basin, by optical microscopy, scanning electron microscopy and micro-computed tomography

Microstructure of shale formation is the key to understanding its petrophysical and chemical properties.Optical microscopy, scanning electron microscopy and micro-computed tomography(μ-CT) have been combined for characterization of microstructure of Longmaxi(LMX)shale from Shizhu area, Sichan Basin. The results indicate that laminated LMX shale consists of mineral matrix-rich layers and organic matter(OM)-rich layers at micrometer scale in two and three dimensions. Mineral matrix layers,mainly consisting of interparticle pores and intraplatelet pores, are approximately parallel to the bedding plane.Pyrite-rich layer, mainly containing intercrystalline pores,shows a strong preferred orientation parallel to the bedding plane. OM-rich layer, mainly containing OM pores, seems to be discontinuous. In addition, intercrystalline pores are enriched in some layers, while OM pores are distributed irregularly in matrix layers. This vertical heterogeneity of pore microscopic structures in LMX shale is of great importance to understand its petrophysical and chemical properties.

The influence of moisture on the permeability of crushed shale samples

Shale cuttings and cores recovered from the subsurface and stored for hours to decades tend to dry out and lose moisture and hydrocarbons,leading to an increase in the effective matrix permeability.Moisture loss in shale samples is a fundamental sample preservation problem which can be solved by applying a standard moisture equilibration procedure to restore lost moisture.Our aim was to investigate the relationship between permeability and variable moisture as-received,as-received moisture-equilibrated and saturated moisture-equilibrated samples.Samples were crushed to a series of particle sizes(0.6-2.0)mm and moisture equilibrated at 97% relative humidity.Results show that moisture equilibration in the samples was achieved after 72 h.The permeability of the saturated moisture-equilibrated and as-received moisture-equilibrated samples decreased exponentially with increase in moisture content.The high correlation coefficient between permeability and particle size(r = 0.96 and 0.97)for moisture-equilibrated samples compared to 0.76 for as-received samples indicates that moisture equilibration improves permeability measurements in crushed shale samples.Furthermore,permeability measurements are repeatable for moisture-equilibrated samples compared to samples that were not equilibrated(as-received).We conclude that moisture content affects permeability and moisture equilibration normalizes and improves the repeatability of permeability measurements in crushed shale.

Rock physics and seismic modeling ofshale reservoirs with horizontal fractures

The presence of horizontal fractures enhances seismic anisotropy of shales. Calculation based on the effective medium theory indicates that horizontal fractures have little effects on velocities along the direction parallel to fractures,but can significantly reduce velocities along the direction normal to fractures. Seismic responses of shales with horizontal fractures are calculated based on the reflector model and the anisotropic propagator matrix method,in which the reflections are a combination of the contrast in impedance due to the variations in fracture density,anisotropic propagation of waves within the shales,and the tuning and interferences associated with layer thickness. Calculated results indicate that seismic reflections are sensitive to reservoir layer thickness and fracture density. Anisotropic propagation alters amplitudes and phases of reflections. It corresponds to higher reflection amplitudes for the case of surrounding sandstone with higher velocity because the increase in fracture density increases the contrast in impedance between the shale and sandstone. In contrast,the surrounding sandstone with lower velocity corresponds to lower reflection amplitudes for the increase in fracture density.

Pore-Fracture Distribution Heterogeneity of Shale Reservoirs Determined by using HPMI and LPN_(2 )GA Tests

The compressibility of shale matrix reflects the effects of reservoir lithology, material composition, pore structure and tectonic deformation. It is important to understand the factors that influence shale matrix compressibility(SMC) and their effects on pore size distribution(PSD) heterogeneity in order to evaluate the properties of unconventional reservoirs.In this study, the volumes of pores whose diameters were in the range 6–100 nm were corrected for SMC for 17 shale samples from basins in China using high-pressure mercury intrusion and low-temperature nitrogen gas adsorption analyses,in order to investigate the factors influencing the SMC values. In addition, the variations in fractal dimensions before and after pore volume correction were determined, using single and multifractal models to explain the effects of SMC on PSD heterogeneity. In this process, the applicability of each fractal model for characterizing PSD heterogeneity was determined using statistical analyses. The Menger and Sierpinski single fractal models, the thermodynamic fractal model and a multifractal model were all used in this study. The results showed the following. The matrix compression restricts the segmentation of the fractal dimension curves for the single fractal Menger and Sierpinski models, which leads to a uniformity of PSD heterogeneity for different pore diameters. However, matrix compression has only a weak influence on the results calculated using a thermodynamic model. The SMC clearly affects the multifractal value variations, showing that the fractal dimension values of shale samples under matrix compression are small. Overall PSD heterogeneity becomes small for pores with diameters below 100 nm and the SMC primarily affects the PSD heterogeneity of higher pore volume areas. The comparison of fractal curves before and after correction and the variance analysis indicate that the thermodynamic model is applicable to quantitatively characterize PSD heterogeneity of shale collected from this sampling area. The results show that PSD heterogeneity increases gradually as micro-pore volumes increase.

A Reasonable Approach for the Development of Shale Gas Wells with Consideration of the Stress Sensitivity

High-pressure deep shale gas reservoirs are usually highly stress-sensitive.When the reasonable production mode of shale gas well is built,the impact of strong stress sensitivity should be fully considered.First,this study calculated the relationship between permeability and formation pressure under different elastic modulus based on the shale lithology of Long Ma Xi formation in Sichuan Basin by testing and analysing the mechanical parameters of the rock.According to numerical simulation result,when the elastic modulus exceeds 14.0 GPa,the stress sensitivity of the matrix will slight affect the cumulative gas production of shale gas.Second,the changing relation between fracture conductivity and permeability with fracture pressure and the time of pressure acts were experimentally studied.The numerical simulation result suggested that the 30-year cumulative gas production considering the stress sensitivity was reduced by 13.5%compared with the 30-year cumulative gas production without considering the stress sensitivity.Finally,the production of different production modes under different stress sensitive characteristics was predicted using numerical simulation method.When the matrix and fractures are fixed with a same stress-sensitive curve,the initial production allocation will not significantly impact the cumulative gas production.When the fractured fractures are subjected to a varying stress sensitive curve,the lower production allocation will result in higher post-production and cumulative gas production.

页岩气水平井振动固井套管柱振动特性研究

为了求解页岩气水平井振动固井套管柱振动特性和动力响应,考虑扶正器分布支承的特点,运用传递矩阵法建立了页岩气水平井套管柱的动力学模型,并通过试验验证了套管柱动力学模型的准确性。在此基础上,研究了扶正器支承和套管柱参数对套管柱振动特性的影响,探索了振动固井工况下套管柱的动力响应和振幅衰减规律。研究结果表明:扶正器刚度增大、扶正器支承数量增加和套管外径增大均会导致套管柱固有频率的增加;扶正器刚度增大会加快套管柱振幅衰减;增大激振力的同时利用低频共振能提高套管柱振动有效传播距离。该研究能够为页岩气水平井振动固井装备设计提供有益参考。

裂缝作用下CO_(2)吞吐动用基质页岩油特征

为明确裂缝作用下CO_(2)吞吐过程中基质页岩油的动用特征,通过采用实时在线称质量方法和核磁共振成像技术,研究了裂缝作用下不同混相压力、基质长度以及基质渗透率对CO_(2)吞吐效果的影响,并建立了注CO_(2)提高基质页岩油动用程度的吞吐方法。结果表明:CO_(2)在非混相、多次接触混相和一次接触混相压力下首轮吞吐动用基质深度分别为12.0、22.5、36.5 mm,累计吞吐采收率逐渐升高;但当压力大于多次接触混相压力后,累计吞吐采收率提高幅度减小;采用逐级增大衰竭压差的吞吐方式,能够弥补基质长度增加对吞吐采收率造成的不利影响,提高大尺寸基质原油的动用深度和动用程度;当裂缝密度保持不变时,基质渗透率的降低会导致累计吞吐采收率减小,且裂缝对吞吐采收率的影响程度降低;虽然增加吞吐次数和闷井时间可以提高低渗透率基质的动用程度,但提高裂缝密度、减小基质原油尺寸才是最有效的提高低渗透基质动用程度的开发方式。研究成果可为提高裂缝作用下页岩油CO_(2)吞吐采收率提供借鉴。

四川盆地下志留统龙马溪组页岩裂缝孔隙定量表征

裂缝和孔隙是致密储层重要的储渗空间,对其识别、描述和定量评价也是页岩气储层评价的重点和难点。为此,以四川盆地涪陵气田和长宁气区钻井资料为基础,通过建立双孔隙介质孔隙度解释模型,对该区下志留统龙马溪组（含上奥陶统五峰组）富有机质页岩段的裂缝孔隙进行了定量评价,并得到以下认识：1应用双孔隙介质模型开展页岩裂缝孔隙度解释,是实现页岩储层裂缝孔隙定量评价的有效办法,也是对海相页岩储集空间定量表征技术的丰富和发展;2该区主力产层基质孔隙体积及其构成区域分布稳定,基质孔隙度总体保持在4.6%-5.4%;3裂缝孔隙发育特征在不同构造区、同一构造的不同井区和不同层段差异较大,显示出页岩储渗条件具有很强的非均质性。根据裂缝孔隙定量表征结果判断,四川盆地五峰组—龙马溪组发育基质孔隙＋裂缝型和基质孔隙型这两种类型的页岩气藏：前者主要发育于特殊构造背景区,具有裂缝孔隙发育、含气量大、游离气含量高、产层厚、单井产量高等特点,在该盆地的分布范围可能相对局限;而后者具有基质孔隙度较高、裂缝孔隙不发育、单井产量中高等特征,预计其在该盆地海相页岩气分布区占据主导地位。

页岩基质解吸-扩散-渗流耦合实验及数学模型

采用川南地区龙马溪组页岩样品,设计了页岩基质解吸-扩散-渗流耦合物理模拟实验,揭示了页岩基质气体流动特征以及压力传播规律.推导了页岩气解吸-扩散-渗流耦合数学模型并且利用有限差分法对数学模型进行数值求解,与实验结果相比较表明该数学模型能够很好地描述气体在页岩基质中的流动规律.同时对页岩基质气体流动的影响因素进行了分析,认为页岩基质的渗透率、扩散系数、解吸附常数等因素均能影响页岩基质气体的流量和压力传播规律,在页岩气藏的开发过程中需要考虑这些参数的影响,该数学模型为页岩气井产能计算提供了更准确的计算方法.

油页岩有机碳矿化特征及在栽培基质中应用可行性分析

探讨油页岩有机碳矿化分解过程、有机碳组分变化特征以及环境因素作用规律可为评价油页岩在栽培基质中应用的可行性提供科学依据。试验在室内控制温度和水分条件下，分析了洗盐和未洗盐油页岩有机碳矿化动态变化特征。结果表明：油页岩基质在60d培养期间，温度升高10℃使未洗盐基质总矿化量分别增加2％～28％（100％田间持水量）、2％-22％（80％田间持水量）和1％-15％（60％田间持水量）；洗盐基质则分别增加2％～17％（100％田间持水量）、1％～5％（80％田间持水量）和7％～14％（60％田间持水量）。将第60d基质中活性有机碳含量进行回归分析，发现两种不同供试油页岩活性有机碳含量与温度和水分之间均呈正相关关系；未洗盐油页岩活性有机碳含量与温度和水分间相关性不显著，而洗盐后油页岩活性有机碳含量与温度和水分之间相关性显著（P=0．0214）。用一级动力学方程拟合油页岩基质有机碳矿化动态得到未洗盐基质分解速率常数最大达1．2×10^-3／d，洗盐基质其分解速率常数介于0．5×10^-3-0．7×10^-3／d。油页岩在长达60d的培养过程中表现为有机碳持续分解、活性有机碳递增，证实其在基质栽培中的应用将对养分持续供给和维护作物根系生理活性发挥重要作用。

济阳坳陷页岩油富集主控因素

依据页岩油储集类型、常规油气探明储量单层有效厚度、获页岩油井夹层厚度和夹层比例的分布特征,将济阳坳陷页岩油富集类型划分为基质型、裂缝型和夹层型3种,其中夹层型页岩油夹层厚度上限为2.5 m,夹层比例上限为20%。利用典型井解剖和数理统计相结合的方法,对不同类型页岩油富集主控因素进行了剖析。基质型页岩油富集主控因素包括岩相、储集性能、异常压力和页岩油可动性,其中富有机质纹层状泥质灰岩相和富有机质灰质泥岩相最为有利;出油井段孔隙度大于3%,且储集物性和日产油量呈明显的正相关;异常高压区内的相对低压区页岩油相对富集;S1/TOC>1层段页岩油流动性好。裂缝型页岩油富集主控因素包括岩相、裂缝发育程度和封存条件,其中纹层状岩相易形成网状缝,控制了裂缝型页岩油纵向展布;裂缝发育系数大于0.2范围内裂缝发育,裂缝型高产井主要分布在距断层距离小于1.2 km、断距大于100 m的断裂上盘;异常高压区(压力系数大于1.3)页岩油封存条件好,页岩油富集。夹层型页岩油富集主控因素包括储集物性、烃源岩排烃强度和异常压力。

山东昌乐凹陷油页岩地球化学特征及成因探讨

山东昌乐凹陷油页岩出产于古近系五图群李家崖组,与济阳拗陷和潍北凹陷孔二段相当。利用有机地球化学方法对昌乐凹陷油页岩品质进行分析,结果显示该区油页岩有机质丰度较高、干酪根类型主要为Ⅰ型和Ⅱ1型,处于未熟-低熟阶段,具有较好的勘探开发前景。通过区域构造演化和气候变化分析,昌乐凹陷油页岩形成于郯庐断裂带左旋-右旋转换期,构造活动强度较弱加之温暖湿润的气候环境促成了油页岩的发育。油页岩与煤共生于水进体系域和高水位体系域之中,油页岩成矿模式为断陷湖沼型。

页岩裂缝和孔隙中气体运移方式评价及确定

页岩气储层为双重介质结构,包含裂缝系统和基质孔隙系统.在页岩中,裂缝从微米级到毫米级变化,基质孔隙则为纳米级.不同级别储集空间的发育导致页岩气的运移方式异于常规气藏,其过程是一个包含从宏观尺度到分子尺度的复杂运移过程.为深入了解页岩气运移方式,采用多孔介质中气体运移方式划分原理,利用Knudsen数对不同尺度的页岩气运移方式进行判断.从页岩气的分子平均自由程出发,计算页岩气在不同温度和压力下的分子平均自由程,结合裂缝和基质孔隙的尺度大小,分别计算裂缝和基质孔隙的Knudsen数,确定了裂缝中页岩气存在达西流（非达西流）和滑脱流2种运移方式,基质孔隙中页岩气则可能存在达西流（非达西流）、滑脱流和过渡流3种运移方式.通过绘制临界Knudsen数曲线,建立双对数的页岩气运移方式判定图版,运用该图版可以判断不同压力和孔隙直径下的页岩气运移方式,为准确认识页岩气的运移方式提供了理论依据.

页岩气吸附解吸效应对基质物性影响特征

为了研究页岩气降压开采过程中吸附气解吸作用对基质表观物性(如有效孔隙半径、有效孔隙度、表观渗透率)及气体流动机制的影响,推导了吸附解吸作用下页岩基质孔隙有效半径和表观渗透率动态模型,建立了考虑吸附解吸影响基质表观物性和气体传输机制的页岩气渗流数学模型。采用有限体积法对模型进行求解,利用实验及矿场数据验证了模型的可靠性,最后应用该模型研究了页岩气开采过程中基质物性参数、气体流动机制变化特征以及吸附效应对页岩气开发的影响规律。研究结果表明,页岩气开采过程中基质孔隙有效半径、有效孔隙度和表观渗透率逐渐变大,体积压裂改造区域流动机制由滑脱流转变为过渡流;忽略吸附层影响将导致地质储量和产气量严重高估;随着吸附层厚度增加,累计产气量变化不大,但采收率逐渐降低。

页岩气多场耦合渗透率计算模型

为表征扩散、应力敏感、基质收缩和吸附层对页岩气渗透率的影响,通过加权系数耦合过渡扩散和努森扩散,建立了扩散渗透率数学模型,并通过实验进行验证,同时分析了基质收缩、应力敏感、不同孔径页岩气吸附层厚度对渗透率的影响。研究结果表明,建立的页岩气渗透率模型可以有效表征不同传输阶段的扩散,避免了单独使用努森扩散所带来的渗透率偏大等问题,可以更全面地描述多物理场影响的页岩气传输。该研究成果对页岩气的开发具有一定的借鉴意义。

页岩基质扩散流动对页岩气井产能的影响

本文的目的是对页岩基质中流体的流动进行说细的描述,从而改进压裂页岩气藏的产能模型。本文提出了一个考虑页岩基质中达西流和扩散流的双重流动机理模型,得出了模型的无因次Laplace空间解。结果表明,当基质的渗透率接近纳达西范围时,流动仅在基质的表面附近进行;在现实的生产中,基质颗粒中心是不参与生产的;当基质的渗透率接近纳达西范围时,基质颗粒的表面以达西流动为主,而基质颗粒的中心以扩散流为主;忽略基质中的扩散流动将严重低估气井的产量,并且渗透率越低,估算的误差越大。

页岩储层裂隙渗透率模型和试验研究

页岩储层的裂隙渗透率是评价页岩气开采的重要参数,基于裂隙法向刚度的概念,考虑页岩储层变形过程中裂隙系统和基质系统之间的相互作用以及页岩气解吸引起的体应变,提出了与有效应力相关的页岩储层的渗透率模型。然后分别分析了页岩气藏在单轴应变和常体积条件下的渗透率模型,分析表明,单轴应变和常体积条件下(3个方向的总应变都为0)的裂隙渗透率模型完全一致。采用脉冲衰减渗透率仪测试了煤系页岩的裂隙渗透率,当有效应力从0.7 MPa增加到14.5 MPa时,渗透率从41.81×10-17m2降到5.43×10-17m2。为了阐述渗透率模型的有效性,利用煤系页岩的渗透率数据对有效应力-渗透率模型进行拟合。结果表明,当裂隙的法向刚度、张开度和煤系页岩的初始渗透率分别为57 922.5 MPa/m、0.000 17 m和50.15×10-17m2时,有效应力-渗透率模型和煤系页岩的渗透率拟合程度较好。然后利用现场渗透率数据对该模型进行拟合,结果表明,当裂隙的法向刚度和张开度的关系符合反比例函数时,拟合程度非常好。该渗透率模型适合于单轴应变、常体积和常围压条件,可用于描述页岩气开采过程中页岩储层裂隙渗透率随孔隙压力的变化规律。同时,该渗透率模型和P&M模型以及S&D模型进行了比较,结果表明,该渗透率模型的拟合结果与S&D模型基本一致,但与P&M模型存在一定的差别。

陆相基质型页岩油甜点区成熟度界限探讨--以渤海湾盆地东营凹陷沙三下-沙四上亚段为例

陆相基质型页岩油有望成为我国页岩油增储上产的主力页岩油类型。鉴于成熟度是控制基质型页岩油甜点区分布的重要因素,在分析我国典型陆相不同有机质类型富有机质泥页岩实测镜质体反射率R_(o)值抑制程度基础上,以渤海湾盆地东营凹陷沙三下—沙四上亚段为例,探讨了陆相基质型页岩油甜点区成熟度界限。陆相富有机质泥页岩的有机质类型越好,其实测镜质体反射率R_(o)值抑制程度越显著。东营凹陷的洼陷区沙三下亚段富有机质泥页岩现今真实成熟度(等效镜质体反射率EqVR_(o))主要介于0.69%~1.05%,沙四上亚段富有机质泥页岩EqVR_(o)值则主要介于0.74%~1.20%;综合地质与工程甜点条件的剖析,东营凹陷沙三下、沙四上亚段富有机质泥页岩基质型页岩油甜点区的现今真实成熟度EqVR_(o)值为0.74%~1.20%,4个洼陷的深洼区均具有良好的基质型页岩油商业开发前景。

改进的页岩气藏物质平衡方程及储量计算方法

页岩气主要以吸附状态和游离状态两种形式赋存于发育大量天然微裂缝的页岩中。为此,分别考虑裂缝系统和基质系统的流体性质和储层性质,建立了考虑吸附相体积随地层压力变化的裂缝性页岩气藏物质平衡方程。实例计算结果表明:较之于改进后的物质平衡方程,King提出的物质平衡方程由于未考虑裂缝体系和吸附相体积,储量计算结果偏小;Williams提出的物质平衡方程未考虑裂缝体系,储量计算结果偏大;刘铁成提出的物质平衡方程未考虑吸附相体积,裂缝系统储量偏小;改进的物质平衡方程同时考虑了裂缝体系和吸附相体积两因素,当吸附相密度增大时,页岩气藏吸附气储量就增大,而总地质储量略有减小,而储层温度、压力、孔隙半径与吸附相密度的关系及最终对储量计算的影响还有待进一步研究。结论认为,考虑裂缝体系和吸附相体积对于页岩气藏物质平衡方程的建立和应用十分必要。