Full field reservoir modeling of shale assets using advanced data-driven analytics

Hydrocarbon production from shale has attracted much attention in the recent years. When applied to this prolific and hydrocarbon rich resource plays, our understanding of the complexities of the flow mechanism（sorption process and flow behavior in complex fracture systems- induced or natural） leaves much to be desired. In this paper, we present and discuss a novel approach to modeling, history matching of hydrocarbon production from a Marcellus shale asset in southwestern Pennsylvania using advanced data mining, pattern recognition and machine learning technologies. In this new approach instead of imposing our understanding of the flow mechanism, the impact of multi-stage hydraulic fractures, and the production process on the reservoir model, we allow the production history, well log, completion and hydraulic fracturing data to guide our model and determine its behavior. The uniqueness of this technology is that it incorporates the so-called ＂hard data＂ directly into the reservoir model, so that the model can be used to optimize the hydraulic fracture process. The ＂hard data＂ refers to field measurements during the hydraulic fracturing process such as fluid and proppant type and amount, injection pressure and rate as well as proppant concentration. This novel approach contrasts with the current industry focus on the use of ＂soft data＂（non-measured, interpretive data such as frac length, width,height and conductivity） in the reservoir models. The study focuses on a Marcellus shale asset that includes 135 wells with multiple pads, different landing targets, well length and reservoir properties. The full field history matching process was successfully completed using this data driven approach thus capturing the production behavior with acceptable accuracy for individual wells and for the entire asset.

Unconventional Shale Reservoir’s Property Estimation through Modeling, Case Studies of Australian Shale

A simplified approach is introduced to model production from shale gas resources. In this approach, a multi-fractured horizontal gas well in a shale formation is divided into four zones. Shale formation between each pair of hydraulic fractures consists of four zones: compacted zone around well-bore (1), shale matrix (2), induced fractures (3) and main hydraulic fractures (4). The main contribution of this study is considering varying permeability for each specific zone implemented in the mathematical presentation of gas flow in shale. Further, gas desorption and slippage effect are applied to the model to capture the realistic gas flow in shale. The nonlinear partial differential equation of gas flow obtained from mass conservations law is then solved numerically for each specific zone with respect to their appropriate boundary conditions. This approach then is applied to three case studies, Cooper Basin, Georgina and Galilee shale. A history matching of the mentioned formations is accomplished to find the most uncertain parameters undertaken through this simplified approach. Results of this study are in an agreement with other methods and it is demonstrated that the simplified approach provides more accurate production forecast for the well-established Georgina asset and is in a good agreement for Cooper and Galilee. This study is also valuable since it provides some rough estimation for shale rock characteristics as the basis for rigorous simulation studies.

A Technical Review on Shale Gas Production and Unconventional Reservoirs Modeling

During the past several years, natural gas production from shale gas is increased and has adsorbed much attention worldwide. The reason behind this is because of advances gained in shale gas recovery techniques from this ultra-low permeability/porosity rock. These techniques are considered the horizontal drilling of the length of 3000 to 5000 ft long and conducting multi-stage hydraulic fracturing along the horizontal portion of the wells. The successful application of above has also driven down the gas prices worldwide and also culminated the security of gas supply for the upcoming decades. This paper is a technical literature review of shale gas production and modeling for future performance evaluation that identifies the current challenges in different stages. Several different and complex physics of gas flow in such a low permeability formation is also explained and the state of the art of the challenges encountered in the modeling process is also explained. As such, gas desorption phenomena, non-Darcy Flow, gas Klinkenberg effect are investigated for different shale formations in the US. This technical review also takes a look over the hydraulic fracturing effects on the economics of shale gas wells due to its straight tie to the production from shale and also the overall recovery from such reservoirs.

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.

A Strain Rate Dependent Constitutive Model for the Lower Silurian Longmaxi Formation Shale in the Fuling Gas Field of the Sichuan Basin,China

Shale,as a kind of brittle rock,often exhibits different nonlinear stress-strain behavior,failure and timedependent behavior under different strain rates.To capture these features,this work conducted triaxial compression tests under axial strain rates ranging from 5×10-6 s-1 to 1×10-3 s-1.The results show that both elastic modulus and peak strength have a positive correlation relationship with strain rates.These strain rate-dependent mechanical behaviors of shale are originated from damage growth,which is described by a damage parameter.When axial strain is the same,the damage parameter is positively correlated with strain rate.When strain rate is the same,with an increase of axial strain,the damage parameter decreases firstly from an initial value(about 0.1 to 0.2),soon reaches its minimum(about 0.1),and then increases to an asymptotic value of 0.8.Based on the experimental results,taking yield stress as the cut-off point and considering damage variable evolution,a new measure of micro-mechanical strength is proposed.Based on the Lemaitre’s equivalent strain assumption and the new measure of micro-mechanical strength,a statistical strain-rate dependent damage constitutive model for shale that couples physically meaningful model parameters was established.Numerical back-calculations of these triaxial compression tests results demonstrate the ability of the model to reproduce the primary features of the strain rate dependent mechanical behavior of shale.

Contribution to Gas Production from Minor Coal Seams and Adjacent Shales: Numerical Modelling Results for the Mannville Coal Measures, South Central Alberta

The contribution to production of the gas stored within the coal and shale beds adjacent to the main coal seam in the Mannville Group, in which a lateral is drilled, was investigated through a series of numerical simulations. The results indicate that the added gas from the minor coal seams, with interbedded shales with no gas, results in 1.4 times (×) more produced gas and 3.0× more produced water after 25 years of production than when only the main Mannville coal seam is considered. Including gas in the shales results in 1.7× more produced gas and 2.5× more produced water after 25 years of production than when only the main coal seam is considered. The produced gas recovered from the shales exceeds the produced gas recovered from the coals after ~8.5 years, resulting in 2.1× more produced shale gas than coal gas after 25 years of production. Over half (56%) of the produced coal gas after 25 years of production is recovered from the main coal seam while a quarter (22%) is recovered from the L1 seam, which is the thickest and nearest minor coal seam to the horizontal wellbore located in the main seam. The results from the numerical simulations provide insights that are not intuitive or otherwise predictable in developing complex reservoirs. Although the results are specifically for the Mannville producing fairway, undoubtedly the production from minor coal seams and interbedded gas shales should be considered in other producing and potential coal gas reservoirs to identify higher producible reserves and optimize drilling and completions strategies.

Numerical modeling of time-dependent deformation and induced stresses in concrete pipes constructed in Queenston shale using micro-tunneling technique

Effects of time-dependent deformation（TDD） on a tunnel constructed using the micro-tunneling technique in Queenston shale（QS） are investigated employing the finite element method. The TDD and strength parameters of the QS were measured from tests conducted on QS specimens soaked in water and lubricant fluids（LFs） used in micro-tunneling such as bentonite and polymer solutions. The numerical model was verified using the results of TDD tests performed on QS samples, field measurements of some documented projects, and the closed-form solutions to circular tunnels in swelling rock. The verified model was then employed to conduct a parametric study considering important micro-tunneling design parameters, such as depth and diameter of the tunnel, in situ stress ratio（K;）, and the time lapse prior to replacing LFs with permanent cement grout around the tunnel. It was revealed that the time lapse plays a vital role in controlling deformations and associated stresses developed in the tunnel lining.The critical case of a pipe or tunnel in which the maximum tensile stress develops at its springline occurs when it is constructed at shallow depths in the QS layer. The results of the parametric study were used to suggest recommendations for the construction of tunnels in QS employing micro-tunneling.

陆相坳陷湖盆细粒沉积岩岩相类型及成因——以松辽盆地晚白垩世青山口组为例

页岩油是目前非常规油气研究的热点与难点。细粒沉积岩岩相类型及成因分析是页岩油“源储”特征研究及“甜点”预测的有效途径。松辽盆地青山口组细粒沉积广泛发育,是页岩油富集的有效层段。本文通过岩性、矿物成分、有机质丰度与沉积构造4个参数,将松辽盆地青山口组细粒沉积岩划分为6种岩相:高有机质泥纹层黏土质页岩(A)、中高有机质含细粉砂纹层长英质页岩(B)、中低有机质含粗粉砂纹层长英质页岩(C)、低有机质层状粉砂岩(D)、低有机质层状介形虫灰岩(E)和低有机质层状白云岩(F)。进一步从水动力学与有机质富集方面探讨了不同岩相类型的成因,并建立了相应的沉积模式。具体为:在风暴浪基面之下的静水、咸水环境、高湖泊生产力背景中,浮游藻类与黏土絮状物均匀悬浮沉降,形成贫富有机质黏土质纹层,沉积A岩相;在正常浪基面之下的相对静水(浪基面附近局部动荡)、半咸水环境、高湖泊生产力背景中,三角洲径流与洪流带来的细粉砂颗粒继续向湖盆中央搬运,经均匀悬浮沉降形成长英质纹层,间歇期悬浮沉降形成黏土质纹层,形成B岩相;正常浪基面之下,洪水携带粉砂级颗粒,顺着水下分流河道搬运至外前缘,以稳定性浊流的形式进入前三角洲,随流速逐渐降低,分异形成粗粉砂—细粉砂纹层,间歇期悬浮沉降形成黏土质纹层,形成C岩相;正常浪基面之下,三角洲前缘早期沉积物在阵发性浊流的作用下,滑塌至较深水区,形成D和E岩相;于正常浪基面与风暴浪基面之间,在相对干燥的气候背景下的咸水环境中,形成F岩相。

Model construction of micro-pores in shale: A case study of Silurian Longmaxi Formation shale in Dianqianbei area, SW China

Based on scanning electron microscopy and nitrogen adsorption experiment at low temperature, the pore types and structures of the Longmaxi Formation shale in the Dianqianbei area, SW China were analyzed, and a molecular model was built. According to mathematical statistics, the validation of the model was solved by converting it into a mathematical formula. It is found by SEM that the pores in clay mineral layers and organic pores occupy most of the pores in shale; the nitrogen adsorption experiment at low temperature reveals that groove pores formed by flaky particles and micro-pores are the main types of pores, and the results of the two are in good agreement. A molecular model was established by illite and graphene molecular structures. Moreover, based on the fractal theory and the Frenkel-Halsey-Hill formula, a modified Frenkel-Halsey-Hill formula was proposed. The reliability of the molecular model was verified to some extent by obtaining parameters such as the fractal dimension, replacement rate and fractal coefficients of correction, and mathematical calculation. This study provides the theoretical basis for quantitative study of shale reservoirs.

Analysis of a Pull-Apart Basin and Its Associated Fractures in the Woodford Shale, Central Oklahoma

Pull-apart basins are faulting and folding zones with high intensity of fractures that strongly affect the production in unconventional shale gas. While most observations of pull-apart basins were from surface mapping or laboratory experiments, we investigated a nascent pull-apart basin in the subsurface. We characterized a nascent pull-apart basin along the strike-slip fault within the Woodford Shale by using seismic attributes analyses, including coherence, dip-azimuth, and curvature. The results indicate a 32 km long, N-S striking strike-slip fault that displays a distinct but young pull-apart basin, which is ~1.6 km by 3.2 km in size and is bounded by two quasi-circular faults. The curvature attribute map reveals two quasi-circular folds, which depart from the main strike-slip fault at ~25°, resulting in an elliptical basin. Inside the basin, a series of echelon quasi-circular normal faults step into the bottom of the basin with ~80 m of total subsidence. We propose that the controls of the shape of pull-apart basin are the brittleness of the shale, and we suggest proper seismic attributes as a useful tool for investigating high fracture intensity in the subsurface for hydrofracturing and horizontal drilling within the shale.

基于构造样式的页岩气富集模式分类-以四川盆地五峰-龙马溪组为例

【研究目的】四川盆地及周缘五峰-龙马溪组页岩经历的构造活动复杂且改造作用强,构造改造程度与页岩气的聚集有着直接的影响,根据构造样式对页岩气富集模式进行划分具有重要意义。【研究方法】本文以构造分区及改造强度变化趋势为主线,整体研究四川盆地及周缘奥陶系上统五峰组-志留系下统龙马溪组页岩层系的构造分区、不同区块构造抬升时间差异,总结不同构造区的页岩气富集模式。【研究结果】通过研究不同地区五峰-龙马溪组页岩目的层系构造改造强度、构造形态、埋藏深度、埋藏抬升时间等的差异性,将四川盆地及周缘下古生界主力海相页岩层系划分为9个一级构造区和20个二级构造区。进一步研究了不同构造区典型井的构造埋藏史及生烃史,结合构造形态、保存条件及产气情况,将四川盆地及周缘划分为9种典型的页岩构造样式及页岩气富集模式:盆内大型斜坡型(威远型)、盆内低陡构造与宽缓向斜型(泸州型)、盆缘向斜型(长宁型)、盆缘复杂构造型(昭通型)、盆缘宽缓断背斜型(焦石坝型)、盆缘斜坡逆断层封堵型(丁山型)、盆外复杂背斜型(巫溪型)、盆外残留向斜型(彭水型)、盆外残留向斜逆断层封堵型(正安型),其页岩气富集及保存条件整体上依次变差。【结论】总结出的9种页岩气富集模式,概况了四川盆地内部到盆地外缘的整体构造演化及页岩气保存富集规律,可以为进一步的页岩气有利区优选提供范围和目标,更好地指导四川盆地及周缘的页岩气勘探。

基于生命周期思想的油页岩原位开采碳排放核算

基于油页岩原位开采的生产实际,指出油页岩行业碳排放核算存在的问题,并将开采过程中钻井、压裂、加热、油气收集与处理、油气运输,以及废水、废弃物、生活垃圾的处置作为碳排放核算边界,确定碳排放源,构建碳排放核算模型,进一步确定排放因子。通过碳排放模型对某油页岩原位开采先导示范基地进行核算,结果表明:加热环节的排放量占比最大,为29.44%;各环节中电力消耗产生的排放量最大。最后提出针对性减排措施。

陆相页岩油水平井开发合理生产制度优化——以苏北盆地A区块阜二段为例

为了最大限度提高陆相页岩油全生命周期的采收率,并建立其水平井开发的合理生产制度。选取苏北盆地A区块阜二段为靶区,利用井震资料开展储层发育特征研究,建立“地质—开发—地应力—裂缝扩展”的地质工程一体化模型,进而对页岩油水平井开发合理生产制度进行优化研究。研究结果表明岩石类型、裂缝分布、岩石力学参数和工程施工参数是影响页岩油地质工程一体化模型精度的关键因素,确定了压后合理开井时间为20 d、合理生产压差为10 MPa、CO_(2)合理吞吐时机为井口压力下降至1.5 MPa左右、CO_(2)合理吞吐焖井时间为15 d,形成了页岩油水平井开发合理生产制度优化流程。研究成果对陆相页岩油长期稳产和效益开发具有重要支撑作用。

深层页岩气吸附模型和物质平衡新方法

准确评价深层页岩气井单井最终可采储量(EUR)对页岩气的高效开发具有重要意义。调研深层页岩气吸附模型,基于各模型对吸附数据的拟合程度优选出考虑深层页岩气吸附因素的T-Langmuir模型。基于T-Langmuir模型表征的深层页岩气吸附特征和流动物质平衡方程基本原理,建立考虑深层页岩气吸附特征的流动物质平衡新方法,并计算了四川盆地某页岩气井的单井最终可采储量。研究结果表明:T-Langmuir模型在高压条件下拟合效果较好,可以作为深层页岩气的吸附模型。新方法计算的单井最终可采储量为1.397×10^(8) m^(3),比传统方法的计算结果大0.109×10^(8) m^(3),经过和其他方法对比,新方法计算结果更为准确。

基于区域地质图与数字高程模型的地层埋深预测方法及应用

对于页岩气、水溶气等非常规天然气资源早期选区评价,往往因为缺乏地震资料导致难以依赖地震构造解释获得目的层的埋深,故借助其他非地震资料有效预测目的层区域性埋深具有重要意义。区域地质图与数字高程模型(DEM)都是广泛覆盖且容易获取的基础性资料。利用区域地质图蕴含的地层产状、地下构造起伏趋势、地层埋深和地表出露地层年代的关系等信息,再叠合DEM地表高程,建立了一种有效预测目的层构造高度和埋深的新方法。利用四川盆地及周缘地区36幅1∶20万区域地质图和美国航空航天局(NASA)数字高程模型资料,预测了该区下志留统龙马溪组底界埋深,据此编制的龙马溪组底界埋深等值线图为该区页岩气保存条件评价提供了重要参数。该方法不仅可为页岩气早期选区评价提供有效支撑,还可应用于深部高压含水层中水溶气的资源评价、深部咸含水层CO_(2)地质封存的构造优选。

利用机器学习与改进岩石物理模型预测页岩油层系横波速度

传统的横波速度预测方法包括经验公式法和岩石物理模型法。前者适用于岩石矿物组分相对单一的储层,且受区域限制等因素的影响,不具有普适性,预测精度较低。后者需要根据不同的实际情况选择合适的岩石物理模型,才能达到预期的目的。大多数机器学习横波速度预测方法基于纯数据驱动,数据集的质量和数量将直接决定横波预测模型精度,并缺乏充分的物理内涵。为此,基于深度神经网络(DNN)的方法,假设研究区储层波传播方程的数学形式已知,通过测井数据训练DNN得到未知的弹性参数,以确立目的层的波传播方程。利用平面波分析法得到相应的纵波、横波速度,实现神经网络与理论模型的结合。此外,针对传统Xu-White模型的不足,考虑随深度变化的孔隙纵横比,提出了改进横波速度预测岩石物理模型。利用研究区较丰富的测井数据,分别采用构建的DNN模型和改进横波速度预测岩石物理模型预测横波速度,并与传统的Xu-White模型预测结果进行对比、分析。结果表明,由DNN模型和改进岩石物理模型均可获得较高精度的横波速度预测结果,且前者的预测效果更好。

基于树莓派和视觉图像的钻井振动筛倾角调节系统

目前,我国的钻井振动筛均采用人工监测筛面固液分离状态和手动调节筛面倾角的方式进行操作,无法实现自适应工作,常常出现钻井液“跑浆”现象。针对这一问题,提出了一种基于树莓派和视觉图像的钻井振动筛倾角调节系统。该系统以树莓派及专用摄像头、电机驱动板和2台步进电机为硬件平台,搭载基于OpenCV和改进AlexNet模型开发的图像识别软件,用于实现钻井振动筛的筛面固液分离状态视觉检测与筛面倾角自动调节。首先,根据钻井振动筛固液分离过程中液相终止线的位置特征,将采集的筛面图像分为正常、少浆和跑浆状态三种类别,并构建筛面图像数据集。然后,使用TensorFlow平台搭建基于迁移学习的AlexNet模型,以实现钻井振动筛的筛面固液分离状态的自动识别。最后,基于识别结果,由树莓派的GPIO(general purpose input/output,通用型输入/输出)接口控制2台步进电机同步工作,以实现钻井振动筛的倾角调节。结果表明,所设计的倾角调节系统对筛面固液分离状态的识别准确率达到97.33%,响应时间约为1.5 s,可满足钻井振动筛的倾角调节要求。该倾角调节系统设备体积小,成本低,且便于调试与维护,可有效提高钻井振动筛的自动化水平。

川东北地区侏罗系凉高山组页岩储集空间特征及页岩油可动性探索

侏罗系凉高山组页岩是四川盆地重点勘探层段,但其孔隙结构与页岩油可动性尚不明晰。为揭示川东北地区侏罗系凉高山组页岩储集空间特征及页岩油可动性,本文依据沉积构造和矿物组成划分岩相类型,开展总有机碳测定、岩石热解和镜质体反射率实验获取基础地化特征;利用场发射扫描电镜、核磁共振、低温氮气吸附、高压压汞手段实现孔隙度、孔隙结构的表征及评价,并对比不同岩相间储集空间特征差异;在离心时间为3 h,离心转速为11000 r/min条件下,开展核磁-离心定量评价不同岩相页岩油可动性,并明确影响因素,建立可动油量测井评价模型并选出有利岩相。结果表明:(1)川东北地区凉高山组页岩总有机碳含量主要分布在0.15%~2.95%之间,Ro值介于1.06%~1.68%之间,处于成熟-高熟阶段;轻烃恢复后,S1分布范围为0.03~3.32 mg/g;矿物类型以黏土矿物和石英为主,发育的岩相类型为纹层状黏土质页岩相、纹层状长英质页岩相、层状混合质页岩相和块状粉砂质泥岩相。(2)页岩储集空间主要发育黏土矿物晶间孔、有机孔,另外可见石英溶蚀孔、粒间孔、黄铁矿晶间孔和微裂缝;孔隙度介于1.15%~4.71%;页岩孔径分布范围较宽,孔体积主要由介孔和小于200 nm的宏孔贡献,纹层状黏土质页岩储集物性较好。(3)凉高山组页岩可动油量分布在0.25~3.26 mg/g,可动油率分布在5.13%~44.83%,纹层状黏土质页岩可动性较好,块状粉砂质泥岩可动性较差;TOC、黏土矿物含量和孔隙度是控制凉高山组页岩油可动性的主要因素,利用这3个因素建立并验证了可动油量预测模型,优选出纹层状黏土质页岩为凉高山组重点勘探对象,对四川盆地页岩油的勘探开发具有指示意义。

基于ANSYS FLUENT的自喷页岩油井液量标定研究

华东油气田苏北盆地页岩油井在经过水力压裂后,投产初期的大液量、高液温、高气油比等特征均对油井的液量标定带来一定困难,现有的液量标定方式均无法满足现场液量标定要求。利用三维软件建模,导入ANSYS FLUENT中进行数值模拟,通过模拟地面油嘴前后部分流程,进行液量影响因素分析,明确节流前压力、节流后压力、油嘴直径、含水率为产液量主控因素,并对其进行权重分析,然后将数值模拟结果进行数学回归,得到关于自喷页岩油井液量的数学模型。将数学模型与矿场数据相对比,数学模型能够很好地反映生产参数、生产制度变化后的液量变化,对矿场自喷页岩油井的液量标定有一定的指导意义,能够有效提高液量标定准确度、降低现场劳动强度。

古龙页岩油开发试验钻井设计优化与实践

古龙页岩油与国内外陆相页岩油相比,陆相淡水沉积环境的青山口组黏土矿物体积分数较高,且多孔多缝,呈纹层状结构,易发生层间散裂、性脆,易吸水膨胀垮塌,独特的地质特性给古龙页岩油钻井带来了巨大挑战。针对钻井过程中容易出现井壁失稳、井漏、摩擦阻力大、钻井周期长等钻井技术难题,从平台井部署、井身结构、井眼轨道、提速技术、钻井液、固井等方面开展优化技术研究,创新采用了“双二维”轨道模型、“一趟钻”技术、油基钻井液、多级固井顶替等一系列新技术。结果表明:与GYP1井相比,试验区的平均钻井速度从11.44 m/h提高至27.75 m/h、水平段固井质量优质率从71.51%提升至86.27%,平均钻井周期从108.17 d缩短至26.82 d。研究成果为古龙页岩油实现储量动用最大化、施工效率最优化提供了强有力的技术支撑,也为古龙页岩油立体化、规模化、效益化开发奠定了基础,对推进中国陆相页岩油技术革命具有重要指导意义。