Integrated modeling of fracturing-flowback-production dynamics and calibration on field data:Optimum well startup scenarios

We aim at the development of a general modelling workflow for design and optimization of the well flowback and startup operation on hydraulically fractured wells.Fracture flowback model developed earlier by the authors is extended to take into account several new fluid mechanics factors accompanying flowback,namely,viscoplastic rheology of unbroken cross-linked gel and coupled“fracture-reservoir”numerical submodel for influx from rock formation.We also developed models and implemented new geomechanical factors,namely,(i)fracture closure in gaps between proppant pillars and in proppant-free cavity in the vicinity of the well taking into account formation creep;(ii)propagation of plastic deformations due to tensile rock failure from the fracture face into the fluid-saturated reservoir.We carried out parametric calculations to study the dynamics of fracture conductivity during flowback and its effect on well production for the set of parameters typical of oil wells in Achimov formation of Western Siberia,Russia.The first set of calculations is carried out using the flowback model in the reservoir linear flow regime.It is obtained that the typical length of hydraulic fracture zone,in which tensile rock failure at the fracture walls occurs,is insignificant.In the range of rock permeability in between 0.01 mD and 1 D,we studied the effect of non-dimensional governing parameters as well as bottomhole pressure drop dynamics on oil production.We obtained a map of pressure drop regimes(fast,moderate or slow)leading to maximum cumulative oil production.The second set of parametric calculations is carried out using integrated well production modelling workflow,in which the flowback model acts as a missing link in between hydraulic fracturing and reservoir commercial simulators.We evaluated quantitatively effects of initial fracture aperture,proppant diameter,yield stress of fracturing fluid,pressure drop rate and proppant material type(ceramic and sand)on long-term well production beyond formation linear regime.The third set of parametric calculations is carried out using the flowback model history-matched to field data related to production of four multistage hydraulically fractured oil wells in Achimov formation of Western Siberia,Russia.On the basis of the matched model we evaluated geomechanics effects on fracture conductivity degradation.We also performed sensitivity analysis in the framework of the history-matched model to study the impact of geomechanics and fluid rheology parameters on flowback efficiency.

Experimental and Numerical Analysis of Particle Migration and Patterning Behavior in a Gravel Pack

Due to its long lifespan and high sand-removal efficiency,gravel packing is one of the most applied sand control methods during the recovery of reservoirs with sanding problems.The blockage and retention of injected sand in a gravel pack is a complex process affected by multiple mechanisms.The majority of existing studies based on the phenomenological deep bed filtration(DBF)theory focused on the gravel pack’s overall permeability damage and failed to obtain the inner-pore particle distribution pattern.In this work,experiments and simulations were carried out to reveal the particle distribution in a gravel pack during flooding.In particular,through real-time monitoring of particle migration,the penetration depth and distribution pattern of invaded particles with different gravel-sand particle ratios,fluid viscosities and injection rates could be determined.By simplifying each unit bed element(UBE)into a pore-throat structure with four tunnels(two horizontals for discharge and two verticals for sedimentation),a new network simulation method,which combines deep bed filtration with a particle trajectory model,was implemented.Cross comparison of experimental and numerical results demonstrates the validity and accuracy of the model.

Effects of fluid flow rate and viscosity on gravel-pack plugging and the optimization of sand-control wells production

Series of experiments were performed to simulate the invasion of formation sand into and the plugging process of gravel-pack at different viscosities and flowing rates of fluid.Two types of formation sands with the medium size of 0.10 mm and 0.16 mm and the quartz sand and ceramsite of 0.6-1.2 mm were used in the experiments.A new viscosity-velocity index(the product of fluid viscosity and velocity)was put forward to characterize the influencing mechanism and law of physical property and flow condition of formation fluid on gravel-pack plugging,and a new method to optimize the production rate of wells controlling sand production with gravel-packing was proposed.The results show that the permeability of formation sand invaded zone and final permeability of plugged gravel-pack have negative correlations with viscosity and flow velocity of fluid,the higher the flow velocity and viscosity,the lower the permeability of formation sand invaded zone and final permeability of plugged gravel-pack will be.The flow velocity and viscosity of fluid are key factors affecting plugging degree of the gravel zone.The viscosity-velocity index(v-v index)can reflect the flow characteristics of fluid very well and make it easier to analyze the plugging mechanism of gravel zone.For different combinations of fluid viscosity and flow velocity,if the v-v index is the same or close,their impact on the final gravel permeability would be the same or close.With the increase of the v-v index,the permeability of plugged gravel zone decreases first,then the reduction rate slows down till the permeability stabilizes.By optimizing production and increasing production step by step,the optimal working scheme for sand-control well can reduce the damage to gravel-pack zone permeability caused by sand-carrying fluid effectively,and increase well productivity and extend the sand control life.

A laboratory study of hot WAG injection into fractured and conventional sand packs

Gas injection is the second largest enhanced oil recovery process, next only to the thermal method used in heavy oil fields. To increase the extent of the reservoir contacted by the injected gas, the gas is generally injected intermittently with water. This mode of injection is called water-alternating-gas (WAG). This study deals with a new immiscible water alternating gas (IWAG) EOR technique, “hot IWAG” which includes combination of thermal, solvent and sweep techniques. In the proposed method CO2 will be superheated above the reservoir temperature and instead of normal temperature water, hot water will be used. Hot CO2 and hot water will be alternatively injected into the sand packs. A laboratory test was conducted on the fractured and conventional sand packs. Slugs of water and CO2 with a low and constant rate were injected into the sand packs alternatively; slug size was 0.05 PV. Recovery from each sand pack was monitored and after that hot water and hot CO2 were injected alternatively under the same conditions and increased oil recovery from each sand pack and breakthrough were measured. Experimental results showed that the injection of hot WAG could significantly recover residual oil after WAG injection in conventional and fractured sand packs.

废弃橡胶粉对水泥稳定碎石抗疲劳性能的影响

为了消除水泥稳定碎石基层因疲劳损伤产生的裂缝,采用三分点加载方法系统研究了不同废弃橡胶粉掺量下水泥稳定碎石的疲劳性能,运用三点弯曲梁法表征了掺加废弃橡胶粉的水泥稳定碎石抗疲劳机理.结果表明:掺加10、20 kg/m^(3)废弃橡胶粉的水泥稳定碎石疲劳寿命优于基准组水泥稳定碎石;当废弃橡胶粉掺量为10、20 kg/m^(3)时水泥稳定碎石的起裂韧度是基准组的1.49、2.58倍,失稳韧度是基准组的1.30、2.21倍,断裂能也较大,抗疲劳性能显著;当废弃橡胶粉掺量为30 kg/m^(3)时,水泥稳定碎石的抗疲劳性能并没有提高,这可能与废弃橡胶粉掺量过大导致弯拉强度降低有关.

注水站高压注水泵盘根盒压帽断裂分析

中原油田高压注水泵盘根盒压帽出现多起断裂事故,给安全生产带来较大风险隐患。通过现场基本情况、压帽化学成分、硬度和金相组织的分析,再加上断口的宏观形貌、微观形貌分析等方法,查找压帽发生断裂原因。结果表明,压帽断裂原因一是由于铸造材质疏松,且存在缺陷;二是由于注水泵高压波动对断裂起到了关键性破坏作用,属于“材质因素和力学因素”共同作用导致的断裂。

改良型加压冰敷袋联合等速髋周肌力训练对踝关节骨折病人术后康复的影响

目的:探讨改良型加压冰敷袋联合等速髋周肌力训练在踝关节骨折术后病人中的应用效果。方法:采用随机数字编号法将82例2020年3月—2023年3月在医院接受手术治疗的踝关节骨折病人分为对照组(n=41,给予改良型加压冰敷袋联合常规干预,观察组n=41,在对照组基础上增加等速髋周肌力训练),对两组病人的等速相对峰力矩、步态功能、踝关节功能、生活质量进行比较。结果:干预8周后,两组病人髋关节外展、伸展等速相对峰力矩均高于干预前,且观察组高于对照组(P<0.05);干预8周后,两组病人步速、患侧步长均高于干预前,且观察组高于对照组(P<0.05),步行周期均低于干预前,且观察组低于对照组(P<0.05);干预8周后,两组病人的Baird-Jackson踝关节与美国足踝外科协会踝-后足评分以及世界卫生组织生存质量调查表4个维度的评分均高于干预前,且观察组高于对照组(P<0.05)。结论:改良型加压冰敷袋和等速髋周肌力训练的联合应用可进一步改善踝关节骨折病人的步态功能及踝关节功能,有利于生活质量水平的提升。

疏松砂岩储层压裂液滤失特性与压裂能效分析

压裂充填是解决渤海油田防砂与增产问题的主导工艺技术,但高渗储层压裂滤失特性及其对压裂能效影响规律不明确,造成压裂选井选层和施工优化缺乏有效指导。通过对储层岩心压裂液滤失评价和疏松砂岩岩心三轴压裂模拟试验,并基于压裂液滤失和裂缝形态,构建了中高渗储层压裂模拟和能效评价指标与方法,实现了对不同储层条件和施工参数下起裂效率和裂缝延伸效率的有效评价。研究结果显示,相对于低渗透储层,非均质性明显的疏松砂岩储层裂缝不规则性更加明显,并且存在主裂缝分支多条细裂缝的情形。基于压裂机理和滤失特性的压裂能效的分析结果,得到了渤海油田典型工况下的推荐作业参数范围:压裂充填实施的储层渗透率低于2.0~4.0μm^(2);滤失系数控制在0.006 m/min^(0.5)以下;压裂排量不低于2.0~2.5 m^(3)/min;压裂液黏度保持在180~200 mPa·s以上。所得结论可为渤海油田中高渗储层压裂充填选井选层和施工参数优化提供理论支撑。

考虑颗粒充填的水平井控水完井产量预测方法

近年来在水平井管柱与井眼环空进行颗粒充填的控水方法在底水油藏得到了广泛的应用,目前尚没有准确的产量预测方法。为此,从宏观流动与微观流动的差异性入手,分析了流体在底水油藏、颗粒充填层、控水工具等不同空间维度内流动之间的相互关系,在油水两相数值模拟模型的基础上,采用“矩阵镶边”的方法将3个维度的流动模型相互耦合,提出了考虑颗粒充填的水平井控水完井产量预测方法,准确度比常规等效方法提高9.17%。研究结果表明,新方法能够实现流体在油藏、颗粒充填层和控水工具间窜流量的定量求解,更直接地体现不同空间维度流动对控水效果的影响,为底水油藏考虑颗粒充填的水平井控水完井产量预测提供了有力工具。

早期冰袋冷敷联合本体感觉训练在踝关节骨折患者术后护理中的应用效果分析

目的:探讨早期冰袋冷敷联合本体感觉训练在踝关节骨折患者术后护理中的应用效果。方法:选取2023年1月—2024年1月于北京积水潭医院贵州医院行骨折固定术治疗的120例踝关节骨折患者作为研究对象,按随机数字表法分为对照组和观察组,各60例。对照组行常规护理,观察组在对照组基础上实施早期冰袋冷敷联合本体感觉训练。比较两组护理效果。结果:护理后,两组疼痛评分低于护理前,且观察组低于对照组(P<0.001)。护理后,两组背伸、跖屈、负重内翻、负重外翻活动度大于护理前,且观察组大于对照组(P<0.05)。护理后,两组疼痛、功能、活动度评分高于护理前,且观察组高于对照组(P<0.05)。护理后,两组社会功能、心理功能、物质生活、躯体功能评分高于护理前,且观察组高于对照组(P<0.05)。结论:早期冰袋冷敷联合本体感觉训练应用于踝关节骨折患者术后护理中,可减轻疼痛,增强踝关节活动度,促进踝关节功能恢复,提高患者生活质量。

海上水平裸眼井分舱防砂与智能分采完井技术

渤海油田水平井高效开发面临防砂难度大和高含水突出等问题,且无人平台的推广增加了生产井远程监控的需求。针对当前的生产需求,研发了一种水平裸眼井分舱防砂与智能分采完井技术。引入旁通隔离封隔器设计了一趟多舱砾石充填管柱,旁通隔离封隔器双重封隔可有效防止层间窜流,为智能分采提供良好的井筒环境;重新设计智能分采管柱产液流动通道,将液控智能滑套优化到顶部封隔器以上位置,以降低现场作业难度,减少作业成本;采用节点分析法分析智能分采管柱的作用机理。该技术在渤海油田S井进行现场试验,试验结果表明:该井分舱砾石充填效率100%,智能滑套顺利实现中心平台远程控制;投产至今未出砂,日产油108 m^(3),超配产10%,实现了增储上产的目的。所得结果可为海上油田水平祼眼井分层开发提供新思路,为祼眼井控水技术提供新途径,为智能油田规模化建设提供新方式。

砾岩水力压裂裂缝扩展研究现状

随着砾岩油气藏在新探明储量中的占比逐年攀升,其开发价值愈发凸显。然而,砾岩油气藏因其独特的地质特性、复杂的孔隙结构、强烈的非均质性以及较弱的导流能力等,使其储量有效动用面临诸多挑战。在诸多增产改造技术中,水力压裂是解决此类问题的较好选择之一。但由于砾石的存在,水力压裂裂缝网络的扩展变得异常复杂,施工难度大幅增加,且增产效果不理想。本文旨在综述砾岩水力压裂裂缝扩展研究现状,明确砾岩水力压裂裂缝扩展的规律及影响因素,通过研究和探讨,期望能够为砾岩油气藏的开发提供一定的借鉴意义。

水平井充填服务工具自切换循环阀改进及测试研究

随着水平裸眼段长度的不断刷新,常规充填工具需要动管柱换位才能实现正循环充填至反循环冲砂通道的切换。在长水平井充填过程中普遍存在应急动管柱的砂卡风险。基于此,文章以152.4mm规格裸眼井工具为例,配套研制了自切换循环阀,通过有限元模拟,对两个通道过流当量尺寸进行优化设计,进行功能试验和下井测试,达到了导通压差最低0.5MPa和反向承压35MPa的设计要求,满足了充填过程中发生应急情况的反循环通道自动切换的作业需要,可为海上水平井充填防砂作业提供安全保障。

海上多层砂岩油藏油井压裂充填时机研究与实践——以渤海L油田为例

渤海多层砂岩油藏L油田目前已进入中高含水期,调整油井压裂充填后的含水率差异较大,部分油井含水率高、日产油达不到设计要求,对油田调整井的部署影响较大。利用多层数模机理,在不同含水时期分别对油井全井各层压裂充填、仅对主力层压裂充填以及仅对非主力层压裂充填3种压裂充填方式进行效果分析,研究表明,当主力层强水淹厚度达到一定比例时,对主力层压裂充填会导致水窜严重,影响产油量,而对非主力层进行压裂充填,有利于控制油井含水率和增加产油量,为油田调整井射孔压裂充填开发提供依据。

双护盾TBM小半径曲线掘进穿越破碎带施工技术

青岛4号线某区间采用双护盾TMB施工,该区间具有连续小曲线半径掘进、频繁穿越破碎带及穿越临近既有结构的特点,采取了超前地表及洞内注浆、豆砾石回填与灌浆、优化TBM设计和加强管片选型及安装等技术措施,监测结果显示地表和拱顶沉降符合安全容许值,隧道周边收敛速度有明显减缓趋势。说明采用的技术措施科学有效,实现了双护盾TBM穿越破碎带的围岩变形控制,为复杂地质条件的小半径曲线双护盾TBM施工提供了借鉴与参考。

Study of hydraulic fracture growth behavior in heterogeneous tight sandstone formations using CT scanning and acoustic emission monitoring

Tortuous hydraulic fractures(HFs) are likely to be created in heterogeneous formations such as conglomerates, which may cause sand plugging, ultimately resulting in poor stimulation efficiency. This study aims to explore HF growth behavior in conglomerate through laboratory fracturing experiments under true tri-axial stresses combined with computed tomography scanning and acoustic emission(AE) monitoring. The effects of gravel size, horizontal differential stress, and AE focal mechanisms were examined. Especially, the injection pressure and the AE response features during HF initiation and propagation in conglomerate were analyzed. Simple HFs with narrow microfractures are created in conglomerate when the gravels are considerably smaller than the specimen, whereas complex fractures are created when the gravels are similar in size to the specimen, even under high horizontal differential stresses. Breakdown pressure and AE rates are high when a HF is initiated from the high-strength gravel. A large pressure decline after the breakdown may indicate the creation of a planar and wide HF. Analyzing the focal mechanism indicates that the shear mechanism generally dominates with an increase in the HF complexity. Tensile events are likely to occur during HF initiation and are located around the wellbore. Shear events occur mainly around the nonplanar and complex matrix/gravel interfaces.

Effects of Shear Fracture on In-depth Profile Modification of Weak Gels

Two sand packs were filled with fine glass beads and quartz sand respectively. The characteristics of crosslinked polymer flowing through the sand packs as well as the influence of shear fracture of porous media on the indepth profile modification of the weak gel generated from the crosslinked polymer were investigated. The results indicated that under the dynamic condition crosslinking reaction happened in both sand packs, and the weak gels in these two cases became small gel particles after water flooding. The differences were： the dynamic gelation time in the quartz sand pack was longer than that in the glass bead pack. Residual resistance factor （FRR） caused by the weak gel in the quartz sand pack was smaller than that in the glass bead pack. The weak gel became gel particles after being scoured by subsequent flood water. A weak gel with uniform apparent viscosity and sealing characteristics was generated in every part of the glass bead pack, which could not only move deeply into the sand pack but also seal the high capacity channels again when it reached the deep part. The weak gel performed in-depth profile modification in the glass bead pack, while in the quartz sand pack, the weak gel was concentrated with 100 cm from the entrance of the sand pack. When propelled by the subsequent flood water, the weak gel could move towards the deep part of the sand pack but then became tiny gel particles and could not effectively seal the high capacity channels there. The in-depth profile modification of the weak gel was very weak in the quartz sand pack. It was the shear fracture of porous media that mainly affected the properties and weakened the in-depth profile modification of the weak gel.

A new laboratory method for evaluating formation damage in fractured carbonate reservoirs

Natural carbonate core samples with artificial fractures are often used to evaluate the damage of fractured carbonate formations in the laboratory. It is shown that the most frequent error for evaluation results directly from the random width characterized by the artificial fractures. To solve this problem, a series of simulated fractured core samples made of stainless steel with a given width of fracture were prepared. The relative error for the width of artificial fracture decreased to 1%. The width of natural and artificial fractures in carbonate reservoirs can be estimated by image log data. A series of tests for formation damage were conducted by using the stainless steel simulated core samples flushed with different drilling fluids, such as the sulfonate/polymer drill-in fluid and the solids-flee drill-in fluid with or without ideal packing bridging materials. Based on the experimental results using this kind of simulated cores, a novel approach to the damage control of fractured carbonate reservoirs was presented. The effective temporary plugging ring on the end face of the simulated core sample can be observed clearly. The experimental results also show that the stainless steel simulated cores made it possible to visualize the solids and filtrate invasion.

Evaluation of numerical schemes for capturing shock waves in modeling proppant transport in fractures

In petroleum engineering, the transport phenomenon of proppants in a fracture caused by hydraulic fracturing is captured by hyperbolic partial differential equations(PDEs). The solution of this kind of PDEs may encounter smooth transitions, or there can be large gradients of the field variables. The numerical challenge posed in a shock situation is that high-order finite difference schemes lead to significant oscillations in the vicinity of shocks despite that such schemes result in higher accuracy in smooth regions. On the other hand, first-order methods provide monotonic solution convergences near the shocks,while giving poorer accuracy in the smooth regions.Accurate numerical simulation of such systems is a challenging task using conventional numerical methods. In this paper, we investigate several shock-capturing schemes.The competency of each scheme was tested against onedimensional benchmark problems as well as published numerical experiments. The numerical results have shown good performance of high-resolution finite volume methods in capturing shocks by resolving discontinuities while maintaining accuracy in the smooth regions. Thesemethods along with Godunov splitting are applied to model proppant transport in fractures. It is concluded that the proposed scheme produces non-oscillatory and accurate results in obtaining a solution for proppant transport problems.

砂砾岩储集层水力压裂裂缝扩展规律与可压性评价

为探究准噶尔盆地二叠系乌尔禾组砂砾岩储集层水力压裂裂缝扩展延伸规律,采用真实破裂过程分析软件,研究砾石特征、地应力等因素对裂缝扩展的影响。根据数值模拟,研究不同条件下裂缝的扩展过程,描述岩石裂缝演化及形态,建立砂砾岩储集层可压裂性的评价模型。结果表明:乌尔禾组砾石强度和基质强度差异较大,砾石强度为216.62~2032.64 MPa,是基质强度的2~4倍,砾岩岩石力学特性差异明显;砾石含量较小时,裂缝扩展主要受主应力的影响;砾石粒径较小时,裂缝扩展方式主要为绕砾;随着粒径增大或砾石含量增加,砾石对裂缝的抑制和屏蔽作用明显,裂缝延伸距离减小;砾石强度与基质强度差异越大,裂缝遇砾石受阻越强,扩展方式越易由穿砾变为绕砾,降低了裂缝延伸距离。运用灰色关联法和层次分析法,综合考虑砾石特征、水平地应力差等因素,建立了砂砾岩储集层可压裂性评价系数计算模型,无因次压裂裂缝面积和米采液指数与可压裂性评价系数呈正相关关系。