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.

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.

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。

贺兰口岩画载体薄厚互层浅变质砂岩差异损伤特征与机制研究

针对贺兰口岩画赋存区域坡面泥石流和危岩等地质灾害频发的问题,通过对区域内灾害发育特征和岩性条件的详细调查与定性分析得出地质灾害频发的问题是由薄、厚互层浅变质砂岩差异损伤造成。以前期研究为依据,设置不同化学环境两种岩石长龄期的冻融和干湿循环实验,初步揭示了其损伤机制。结果表明:薄层浅变质砂岩试样在所设任意相同劣化条件下的质量损失率、黏聚力与内摩擦角的衰减速率、孔洞数量与面积的增长速率、长石类矿物转化率与损伤变量的变化率均明显高于厚层浅变质砂岩试样,而导致上述差异的原因在于薄层浅变质砂岩中较高的长石类矿物的含量、隐伏层面的存在以及填隙物以泥质为主,三方面的共同作用使薄层浅变质砂岩在相同劣化条件下的矿物水解和溶蚀反应的剧烈程度、胶结的失效程度明显高于厚层浅变质砂岩。

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。

砂泥岩互层储层防砂优化设计试验研究

南海WC疏松砂岩油藏具有出砂严重、储层非均质性强和砂泥岩小层交错分布的特点。传统防砂设计方法适用性差,导致筛管堵塞严重,产能持续下降,严重影响了油田的正常开发。为研究砂泥岩互层对防砂筛管的堵塞机理,优选适合该类储层的防砂方式,基于相似模拟原理研制了可旋转式防砂物理模拟试验装置。利用该试验装置,结合现场实际工况重点考虑砂泥岩互层储层的互层比与井筒井斜角两大因素,评价分析了不同因素对防砂方式的影响。研究结果表明:互层比和井斜角对筛管防砂方式的选择有显著影响,当互层比小于0.4时,优先选用优质筛管防砂,反之则选用砾石充填防砂方式;井斜角小于45°时,互层比对砾石充填和防砂管堵塞程度影响较小;当井斜角超过45°时,井斜角对防砂管堵塞程度的影响不可忽略。研究成果对于指导砂泥岩互层储层的防砂优化设计具有重要的指导意义。

地震资料层间多次波压制方法研究进展

层间多次波压制是目前困扰油气地震勘探的难题之一。为推动层间多次波压制方法的发展,对层间多次波预测及自适应相减方法的研究进展进行了调研,总结了共聚焦点技术、地表数据分离法、逆散射级数法、虚同相轴法、Marchenko自聚焦方法等备受关注的层间多次波预测方法以及自适应相减法的发展进程,分析了上述方法的优缺点。共聚焦点技术中层相关算法相比边界算法具有更强的适应性,但以牺牲计算成本为代价;逆散射级数法虽然具有较高的多次波预测精度,但是巨大的计算量限制了其推广应用;地表数据分离法和虚同相轴法虽然具有较高的计算效率,但是数据分离过于依赖人工操作;Marchenko自聚焦方法目前在实际应用中尚不成熟。自适应相减方法在一次波和多次波非正交情况下的局限性导致了层间多次波压制方法的诞生。在保证层间多次波压制效果的前提下提高计算效率以及实用性,是当前层间多次波压制方法的重要发展方向。结合目前研究热点,层间多次波压制方法与波形反演、深度学习等方法技术的结合可能是未来的发展趋势。

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。

用VIKIZ测井反演砂泥岩薄互层参数的方法研究

俄罗斯的电磁传播电阻率测井阵列仪器VIKIZ具有分辨率极高的探头,利用它的视电阻率曲线可直接识别出砂泥岩薄交互层,但仍难以直观提取到砂岩层的正确物性参数。提出了一种适合于薄交互储层的VIKIZ测井资料的处理与反演方法,采用改进的阻尼型高斯-牛顿优化算法,先对VIKIZ的浅、深探测2条测井曲线分别做纵向一维反演,然后综合其5条曲线再做二维反演,实现了砂泥岩薄交互储层电阻率二维剖面的重建,可为薄互储层评价提供正确的物性参数。

深层砂泥岩薄互层的地震识别方法

深层砂泥岩薄互层油气藏是一类典型的低孔、低渗型油气藏,储层一般具有埋藏深、横向变化快、深层物性差的特点。利用常规的薄层定量描述方法只能识别地层厚度不小于λ/4的孤立薄层,很难实现精细解释。为此,采用正-反演联合预测技术,通过建立符合地下实际情况的的地球物理模型,从正演角度分析目的层的地震波场特征;同时对正演结果进行模型反演,定量分析反演砂体的横向及纵向展布特征。结果表明这种基于模型正演的地震识别方法既能够发挥地震资料在地层横向展布上的优势,又能够提高纵向上的解释精度,为识别前梨园地区深层砂、泥岩互层结构的隐蔽性储层提供参考。

薄窄砂体地震跟踪预测方法

大庆长垣西部地区葡萄花油层主要发育水下分流河道和小片席状砂,砂体厚度1～3m,横向变化快,分布零散,地震储层预测精度受到限制,给油藏评价和开发带来较大风险。为了提高薄窄砂体预测精度,以古龙油田为例,提出了分步逐级井震联合反演方法:以岩石物理响应特征分析为基础,优选反演方法,优化流程参数,不断增加滚动井数,通过5批161口开发井的优选及调整,砂体预测精度不断提高,确保了该油田初步开发方案实施效果,形成了可以推广应用的滚动预测跟踪调整的工作流程。

高分辨率砂泥岩薄互层储层综合预测技术

本文采用地震低频无井约束反演、中频井约束波阻抗模型反演和高频非线性测井参数反演相结合的三步法反演理论 ,结合钻井、测井和油田的生产资料 ,建立精细地质模型 ,对砂泥岩薄互层进行了综合横向预测 ,其预测薄层厚度的精度达 2～ 5m。该方法在松辽盆地北部三个区块的储层预测推广应用中 ,取得了良好的效果。该方法目前已成为一套较为有效和完善的实际生产应用方法 ,它对油田的开发有一定的指导意义。

应用电成像测井识别鄂尔多斯盆地薄互层砂泥岩

鄂尔多斯盆地西北缘上古生界石盒子组盒8段与山西组致密砂岩气藏中发育大量薄互层砂泥岩,此外,还发育少量煤层。薄互层砂泥岩岩性变化快,孔隙结构复杂,储集性能差异大,具有较强的非均质性,薄互层岩性精细识别难度大,资源量评价往往漏掉薄层砂岩的潜力。利用岩心描述、物性测试及常规测井与全井眼微电阻率扫描成像测井等资料,通过岩心刻度测井信息,开展石盒子组盒8段与山西组地层中不同岩性的常规测井与全井眼微电阻率扫描成像测井响应特征分析。优选出对岩性反映较敏感的自然伽马、声波时差和铀测井曲线,建立测井曲线交会图版进行岩性识别。结果表明,交会图版对厚层(≥1 m)砂泥岩及煤层岩性有较好识别效果,对薄层(<1 m)岩性识别效果较差。利用全井眼微电阻率扫描成像测井高分辨率优势对薄层测井响应进行标定,总结薄层砂岩、泥岩的发育规律。结果表明,薄层砂岩通常夹于泥岩之间,自然伽马具有高背景下低回返、三孔隙度曲线略向右偏移、双侧向电阻率具有低背景下的高回返响应模式。将岩性识别图版和薄层岩性测井响应模式应用于目的层段井筒剖面,有效提高薄互层砂泥岩岩性解释精度,为鄂尔多斯盆地西北缘上古生界石盒子组盒8段、山西组储层与烃源岩精细评价提供依据。

一种特低渗透油层有效厚度标准研究

低渗透储层有着不同于常规储层的测井响应,其测井响应中来自油气的成分少,有生产能力的低孔隙度储层与无效层段之间的差异很少,测井解释的难度很大。针对白豹油田长3、长4+5低渗透油层有效厚度及其夹层的测井响应特征,利用自然伽马、自然电位、声波时差、密度、中子、微电极等多种测井曲线,结合岩心分析、地质及试油等资料综合对比研究,充分利用了测井资料识别影响低渗透储层参数变化的地质因素及特点,建立了有效厚度的物性、电性下限和夹层扣除标准。通过该区目的层段80多口井低渗透储层的精细评价处理,有效地剔除了钙质夹层、泥质夹层、致密层、干砂层和不够标准的差油层,确定了各井油层有效厚度,提高了该区目的层段油藏测井解释和有利区预测的精度,为该区特低渗透油田增储上产提供了可靠依据。