Insights into the Tectonic Fractures in the Yanchang Formation Interbedded Sandstone-Mudstone of the Ordos Basin Based on Core Data and Geomechanical Models

The distribution and intensity of tectonic fractures within geologic units are important to hydrocarbon exploration and development. Taken the Upper Triassic Yanchang Formation interbedded sandstone-mudstone in the Ordos Basin as an example, this study used the finite element method（FEM） based on geomechanical models to study the development of tectonic fractures. The results show that the sandstones tend to generate tectonic fractures more easily than mudstones with the same layer thickness, and the highest degree of tectonic fractures will be developed when the sandstone-mudstone thickness ratio is about 5.0. A possible explanation is proposed for the tectonic fracture development based on two important factors of rock brittleness and mechanical layer thickness. Generally, larger rock brittleness and thinner layer thickness will generate more tectonic fractures. In interbedded sandstone-mudstone formations, the rock brittleness increases with the increasing mechanical layer thickness, hence, these two factors will achieve a balance for the development of tectonic fractures when the sandstone-mudstone thickness ratio reaches a specific value, and the development degree of tectonic fractures is the highest at this value.

Study on the Law of Hydraulic Fracture Propagation in Low Permeability Thin Interbed Reservoir

The third member of Weixinnanliu in the west of the South China Sea develops thin interbeds, and the vertical extension of fracturing fractures is excessive. Once the fractures extend vertically to the upper and lower aquifers, it is easy to cause water flooding of oil wells, and the effect after fracturing is not obvious. The present work aims to explore the longitudinal extension law of fractures in Low Permeability Thin Interbed Reservoir based on the finite element calculation platform. A three-dimensional expansion model of hydraulic fractures in the target reservoir was established, and the displacement, fracturing fluid viscosity, minimum horizontal principal stress difference, vertical stress, interlayer thickness, perforation point separation were studied. The interlayer distance and other factors affect the crack propagation law. The research results show that the thin interbed fractures have three forms: T-shaped fractures, through-layer fractures, and I-shaped fractures;for the target layer, the overlying stress is relatively large, and the minimum principal stress is along the horizontal direction. Vertical cracks;the farther the perforation point is or the greater the stress difference, the smaller the thickness of the interlayer required to control the fracture height;the stress difference is 3 MPa, and the distance between the perforation points exceeds 10 m, the thickness of the interlayer is required to be ≥4 m;In order to ensure that the width of the fracture in the middle spacer does not affect the placement of the proppant, it is recommended that the displacement be controlled within 3 m3/min and the viscosity of the fracturing fluid is 150 mPa·s;in addition, the thickness of the spacer required to control the fracture height is different due to different geological parameters. Different, different wells need targeted analysis.

Understanding hydraulic fracture propagation behavior in tight sandstone–coal interbedded formations: an experimentalinvestigation

Whether hydraulic fractures could connect multiple gas zones in the vertical plane is the key to fracturing treatment to jointly exploit coalbed methane and tight sandstone gas through integrative hydraulic fracturing in tight sandstone–coal interbedded formations. Laboratory true triaxial hydraulic fracturing experiments were conducted on layered specimens with di erent combination types of natural sandstone and coal to simulate the propagation behavior of hydraulic fractures. The effects of the fracture initiation position, fracturing fluid viscosity and injection rate were discussed. The results showed that di erent fracture morphologies could be found. When initiating from coal seams, three patterns of fracture initiation and propagation were obtained:(1) The main hydraulic fracture initiated and propagated along the natural fractures and then diverged due to the effects of in situ stress and formed secondary fractures.(2) The hydraulic fracture initiated and propagated in the direction of the maximum horizontal stress.(3) Multiple fractures initiated and propagated at the same time. With the same fracturing fluid viscosity and injection rate, the hydraulic fractures initiating in sandstones had greater chances than those in coal seams to penetrate interfaces and enter neighboring layers. Excessively small or large fracturing fluid viscosity and injection rate would do harm to the vertical extension height of the induced fracture and improvement of the stimulated reservoir volume. Compared with operation parameters(fracturing fluid viscosity and injection rate), the natural weak planes in coals were considered to be the key factor that a ected the fracture propagation path. The experimental results would make some contributions to the development of tight sandstone–coal interbedded reservoirs.

Prediction of Interbeds Intercalated into Complex Heterogeneous Reservoirs at a High Water Cut Stage

The occurrence of interbeds in thick oil formations is one of the main reasons that cause the difference of remaining oil distribution. A quantitative method for predicting interbeds was proposed and the sedimentary origin and division criterion were demonstrated. The distribution of interbeds in different types of sedimentary sand bodies were predicted and analyzed by combining the theory of sedimentology and reservoir bed architectural-element analysis. The interbeds in a single well were recognized from high resolution well logs, and inter-well interbeds were predicted by using the methods of cyclothem correlation, physical properties trtmcation, and conditional simulation. Finally a 3-D model of interbed was built. Application to the Gudao Oilfield was successful.

The effect of interbeds on distribution of i ncremental oil displaced by a polymer flood

This paper discusses the effect of influencing factors on the distribution of incremental oil displaced by a polymer flood （extra-displaced oil） using numerical reservoir simulation. These factors include the location, area and permeability of a thin low-permeability interbed, and the perforation location relative to the interbed. Simulation results show the locations from where the incremental oil was displaced by the polymer solution. The interbed position from the oil formation top affects the location of extra-displaced oil. The interbed area has a slight influence on the whole shape of extra-displaced oil. Larger interbed area leads to higher partition extent of extra-displaced oil. Higher vertical permeability of interbeds contributes to worse partition extent of extra-displaced oil and the partition effect disappears if the ratio of vertical to horizontal permeability is more than 0.05. The perforation location relative to the interbed affects polymer displacement efficiency, and also has a significant effect on the distribution of extra-displaced oil in polymer flooding.

Mechanism and Distribution of Calcareous Interbeds in Songtao Uplift and Its Periphery of Qiongdongnan Basin

Based on core and casting slice observation, well drilling and logging data, the source of carbonate materials, lithology together with electric properties, types, genesis mechanism and distribution of calcareous interbeds in Songtao uplift and its periphery of Qiongdongnan Basin have been thoroughly analyzed. Results show that typical features have been appeared from well logging curves, containing low gamma-ray, low acoustic travel time, low neutron value, high density, as well as bright white calcium nodules or bands in electrical imaging well-logging curves. Drilling results reveal that calcareous interbeds developed mostly in high position of paleostructures and their distribution was controlled by the combined effects of macroscopic and microscopic factors. Macroscopically, calcareous interbeds relate to paleogeomorphology together with the combination of sandstone and mudstone. They are also controlled microscopically by the source of carbonate cements and pore space. Under normal circumstances, with regard to the same sand, the closer to the mudstone and the thicker of mudstone, the more conducive to the formation of calcareous interlayer. Low compaction strength, high content of rigid particles, coarse grain size, well-sorted sandstone and large pore space during carbonate cementation are favorable for the development of calcareous interbeds.

渤南洼陷页岩油储层夹层组测井曲线重处理检测与油气特征

胜利油田济阳坳陷渤南地区沙三下泥岩是良好的页岩油储层,其中广泛发育碳酸盐岩夹层和砂岩夹层,纵向上密集分布构成夹层组。夹层组的分布对页岩油的富集具有较大的控制作用,对夹层组的检测成为页岩油勘探的关键。但夹层单层厚度薄(1 m~2 m),纵向叠置复杂,横向变化快,加上测井曲线不具有良好对应的电性特征,因而夹层组检测难度极大。笔者首先以钻井岩屑、取心所描述的岩性特征为控制,对测井曲线进行重处理,极大地突出了夹层组电性特征。通过对水平井夹层组密度与产能分析,夹层组发育段产能占总产能的54%以上。同时在测井曲线重处理基础上进行高分辨率GR反演,获得夹层组的平面分布特征,与目前页岩油的开发结果非常吻合,从而有效地揭示了目标层位页岩油可能的富集区,为后期页岩油的勘探开发提供了坚实依据。

基于地震波波形相似的薄互层识别方法

随着油田勘探开发程度的深入,目标储层大都具有薄、小、深、碎的特点,高精度薄互层识别成为储层预测的热点和重点。目前常用的时频分析方法和谱分解技术受限于地震数据,无法满足薄互层精确刻画的要求;高分辨率反演方法也因地球物理反演的非线性特征导致结果存在多解性。为此,提出基于地震波波形相似的薄互层识别方法:首先采用波形库思想,构建井旁道—测井敏感曲线波形库;之后利用改进Manhattan距离联合线性相关系数法计算波形相似度,进行波形匹配;最后将波形相似度作为唯一驱动,建立地震数据与高分辨率测井数据间的数学联系,最终得到高分辨率处理剖面。该方法充分利用了地震、测井数据分别具有的横向和纵向高分辨率优势,能够有效识别薄互层目标,极大地降低了反演结果的多解性。模型试算验证了方法的可行性;实际资料处理结果表明该方法显著提高了纵向分辨率,对调谐尺度内的薄互层识别提供了技术支撑。

A区块砂泥岩薄互层气藏改建储气库的可行性研究

随着大庆油田原油、伴生气产量逐年递减,冬夏季供气不平衡的矛盾日益突出,在无法满足季节调峰需求时,需压减工业用气。因此,从满足冬季下游用户的用气需求、合理利用有限的油气资源和保护环境等角度出发,建设储气库势在必行。根据大庆油田库址筛选标准,优选出A区块进行库址规划,与大庆油田已建储气库相配合,联合保障大庆及周边地区用气季节调峰。A区块属于砂泥岩薄互层气藏,从地质特征、气藏开采特征等方面分析改建储气库的可行性,详细评价建库的地质条件和气藏条件,并设计库容参数和两套井位部署方案,建立数值模型进行优选对比。结果表明,A区块砂泥岩薄互层气藏具备建库的可行性。

薄互层煤层气井出砂综合治理研究

煤层气井出砂(煤粉)问题制约煤层气井生产寿命,造成高额维修费用、产能降低,而薄互层煤层因为与围岩接触面积大,出砂(煤粉)问题突出。澳大利亚苏拉特盆地储层胶结疏松,煤/泥/砂岩夹层复杂,在统计井中,100%的生产井都有不同程度的出砂问题,其中33.5%出砂严重,修井作业频繁,开采成本居高。在系统分析苏拉特盆地储层特征、出砂特点和生产规律的基础上,根据颗粒沉降规律研究,结合出砂层位预测和防砂工艺优选,采用“膨胀式封隔器+盲管”与“螺杆泵+浆式转子+自动分流阀+钻穿套管鞋”结合的综合防排砂技术,阶段性地解决了苏拉特盆地煤系地层出砂问题。现场应用结果表明:该技术使得单井平均连续生产时间由275 d增至近400 d,降低修井频率近50%。

湖北省三峡库区砂泥岩互层岩体劣化特征与劣化机理分析

受水位周期性变动影响,三峡库区地质环境产生复杂变化,尤其是对碎屑岩岸坡砂泥岩互层岩体劣化的影响显著。本文通过对湖北省三峡库区碎屑岩岸坡砂泥岩互层岩体进行现场调查,结合现场测试与室内试验成果,对比分析碎屑岩砂泥岩互层岩体两种结构单元的劣化差异,结合岸坡互层岩体的劣化现状,分析砂泥岩互层结构的岸坡岩体劣化变形过程,揭示砂泥岩互层岩体的劣化机理及其对岸坡致灾发展的影响,为后期合理进行岸坡岩体劣化评价及防治提供理论支撑。

煤层长波长地震各向异性的多尺度效应初探

在勘探地震频带范围内,我国陆相沉积的含煤地层均是典型的薄互层。含煤地层中各向同性薄层叠置,在不同地震波长尺度下呈现长波长地震各向异性特征,地震勘探中一般做横向各向同性(Transverse Isotropy with a Vertical Axis of Symmetry,VTI)等效或均匀各向同性(Isotropy,ISO)等效简化处理。但是针对不同弹性性质的地层,长波长等效理论的适用条件不同。以淮南煤田的含煤地层为例,利用钻孔声波和密度测井曲线建立二维水平层状薄互层模型,分析含煤地层的长波长地震各向异性的多尺度效应。通过不同平均长度均化测井曲线,重点分析了2种等效建模方法在不同平均长度下所建立的等效模型弹性参数的差异及其各向异性特征;最后通过不同等效模型弹性波场的数值模拟分析不同等效模型的适用性。结果表明:随着平均长度增加,等效模型的速度、密度和各向异性参数的单点数据异常减弱;ISO等效P波速度大于VTI等效;存在某个临界窗长(本次淮南含煤地层为λ_(min)/L≈3)使等效模型的层状各向异性开始减弱;当平均长度与地层厚度比(L/d)和最小主波长与平均长度比(λ_(min)/L)都满足长波长假设条件时,含煤薄互层等效模型弹性波传播特征才能逼近原始模型。研究结果有助于厘定含煤地层长波长地震各向异性特征,为含煤地层的正演模拟和反演模型建立提供理论指导,以进一步提高煤田地震勘探精度。

鄂尔多斯盆地甘泉地区长7页岩油储层非均质性及其控油规律

为揭示鄂尔多斯盆地伊陕斜坡东南部甘泉地区长7油层组页岩油储层的宏观非均质性及其对石油分布的控制作用,通过隔夹层识别统计、渗透率统计及劳伦兹曲线构建等方法,定量表征并比较了长7_(1)、长7_(2)油层亚组的宏观非均质性,利用相关分析和多因素叠合的方法,分析了宏观非均质性对石油分布的影响。研究结果表明:研究区长7_(1)、长7_(2)页岩油储层平均发育夹层数分别为3.8、5.1层,砂体渗透率以复合韵律为主,且非均质性强;平均发育隔层数分别为3.4、2.8层,单隔层的平均厚度分别为6.0、4.9 m;长7_(1)较长7_(2)表现为稍弱的层内非均质性和较强的层间非均质性。页岩油砂岩储层的韵律性对含油饱和度有明显的影响,厚度大于10.0 m的隔层对油气有明显的封盖作用,“物性”隔夹层则构成油气聚集的侧向遮挡。长7_(1)油层亚组较长7_(2)油层亚组隔层更为发育,而长7_(2)油层亚组油气更富集。平面上,油气富集区分布呈条带状,多位于砂体厚度大且连续性较好、渗透率大于0.2 mD的区域,顺河道砂体延伸的方向上油层厚度变化小,垂直河道延伸方向上变化较大。研究结论可为鄂尔多斯盆地伊陕斜坡东南部长7夹层式页岩油有利区评价及开发参数优选提供理论参考。

大斜度井精细分段压裂技术研究及应用

冀东油田属于典型的复杂断块油藏,储层埋藏3300~4400 m、温度120~150℃、敏感性强、油层厚度为1.2~4.0 m、纵向跨度200~300 m。主要采用人工岛、陆岸平台开发,井斜平均35°以上,单井自然产能低,须压裂改造后才能获得产能。针对隔层薄、跨度大、井斜大、套变井等难题,研制了一种缝口暂堵转向体系,暂堵体系配方为变形粒子(5~6 mm)∶纤维∶粉末(0.106~0.212 mm)=5∶1∶1,最高突破压力56.3 MPa,变形粒子遇水膨胀,膨胀速度0.15~0.30倍/min,具有强变形性,杨氏模量80 MPa,泊松比达0.48。在水力压裂过程中,大斜度井易产生多裂缝、裂缝扭曲、施工压力异常、易砂堵等问题,配套了大斜度井K344可控封隔器,具有逐级坐封、逐级压裂、逐级解封的功能,优化了一种超低浓度瓜胶压裂液体系、可降低稠化剂用量在30%以上,并通过支撑剂段塞打磨等措施,形成了高温大斜度井精细分段压裂技术。

软硬互层反倾岩质边坡稳定性影响因素分析及破坏模式研究

反倾边坡破坏会诱发严重的地质灾害,因此对软硬互层反倾岩质边坡的稳定性及破坏模式进行研究具有重要的意义。本文基于数值模拟的方法,利用离散元UDEC软件,首先基于正交试验设计法,考虑了边坡坡角、岩层倾角、坡高、相邻软硬岩层总厚度、硬软岩层厚度比、硬软岩层力学参数序号比、结构面力学参数7个因素的影响,设计了32组正交试验,利用强度折减法对边坡的稳定性及可能的破坏模式进行模拟,并从边坡稳定系数和位移两个方面对计算结果进行敏感性分析。结果表明,边坡坡角和岩层倾角对稳定系数影响较大,结构面力学参数和坡高对边坡位移影响较大;然后对边坡的破坏模式进行归纳总结,将软硬互层反倾边坡的破坏模式分为弯曲倾倒破坏、坍塌滑动破坏和块体倾倒破坏3种类型,并对每种破坏类型的边坡特征进行详细分析。

煤岩两用液动锤钻头的结构设计研究

为了提高煤矿井下穿层孔硬岩施工的效率,解决液动锤一趟钻实现煤岩互层钻孔的问题,设计了煤岩两用液动锤钻头,并分析了其工作原理。通过对钻头水力结构参数的计算和模拟分析,得出了可以通过调整切换阀的水力结构以及阀芯和阀座弹簧弹力匹配设计,实现对钻头功能切换所需的压力和钻头切削推力的精确控制,从而达到液动锤随钻切换冲击-切削模式的目的,实现不退钻完成煤岩互层的高效钻进。

低渗砂泥交互油藏压裂多裂缝扩展规律

针对低渗砂泥交互储层水平井多段多簇压裂裂缝扩展特征复杂的问题,建立多裂缝扩展数值模型,研究不同储隔层应力差、隔层厚度、施工参数条件下压裂裂缝的扩展规律。研究表明:中低储隔层应力差、薄泥质隔层条件下,裂缝穿透隔层扩展,中间裂缝在应力干扰下纵向大幅扩展;高应力差条件下,缝高扩展受到抑制,中间缝长低于两侧缝长;高施工排量条件下,裂缝在中低储隔层应力差储层上下突进幅度增大;高黏压裂液可导致中低应力差储层压裂裂缝上下突进幅度增大,缝高与缝宽明显增加。以X低渗砂泥交互油藏区块水平井为例,开展模拟研究,分析储隔层应力差、隔层厚度、施工排量、压裂液黏度对缝高扩展影响。对于低应力差、低隔层厚度储层,采用低排量、低黏压裂液降低穿层风险。

薄互层致密砂岩水力压裂裂缝扩展特征研究

薄互层致密砂岩储层由于其砂泥叠置沉积,纵向非均质性强的特点,在水力压裂施工中,裂缝难以垂向扩展,有效沟通储层,明确薄互层水力裂缝垂向扩展规律对薄互层致密砂岩的开发具有重要意义。针对鄂尔多斯盆地临兴区块下石盒子组薄互层致密砂岩储层,通过建立薄互层致密砂岩地层裂缝扩展模型,研究了储隔层间应力差、储隔层厚度、岩石力学性质等地质因素和压裂液黏度、施工排量等工程因素对水力压裂裂缝扩展的影响,并通过现场井压裂效果和微震检测数据验证了模型的可靠性与准确性。研究结果表明:储隔层间应力差和储隔层厚度是影响水力裂缝穿层扩展最主要的地质因素,当应力差大于4 MPa时,裂缝垂向扩展受到抑制;弹性模量大的隔层有利于裂缝垂向扩展;泊松比对裂缝垂向扩展几乎没有影响;压裂液黏度对裂缝垂向扩展影响较小;泵注排量对裂缝垂向扩展有促进作用,但当排量增加到一定程度后,裂缝扩展放缓,对于不同的应力差,存在不同的最优排量。因此,对于薄互层致密砂岩水力压裂,低储隔层厚度、低储隔层应力差、高弹性模量和高注入排量能有效促进裂缝垂向扩展。研究成果可为该类储层水力压裂施工设计提供一定理论依据。

砂泥岩互层岩质边坡爆破振动衰减规律现场试验研究

为保证砂泥岩互层岩质边坡在爆破振动作用下安全稳定,需明确爆破振动在砂泥岩互层岩质边坡中的衰减规律。为此,以平陆运河青年枢纽一期工程为依托,通过开展现场爆破试验,对比分析高程效应修正前后爆破振动衰减模型的拟合结果,深入研究砂泥岩互层岩质边坡的爆破振动衰减规律。结果表明:边坡岩体在爆破振动作用下的最大位移会产生高程放大效应,最终位移可能不为零;考虑高程效应的爆破振动衰减模型较未修正的萨道夫斯基公式的拟合精度更高,岩质边坡的爆破振动衰减规律应考虑高程效应;受层理倾向和倾角的影响,砂泥岩互层岩质边坡的爆破振动衰减规律存在差异,建立不同层理下的爆破振动衰减预测模型是后续重要的研究方向。