Pressure transient characteristics of non-uniform conductivity fractured wells in viscoelasticity polymer flooding based on oil-water two-phase flow

Polymer flooding in fractured wells has been extensively applied in oilfields to enhance oil recovery.In contrast to water,polymer solution exhibits non-Newtonian and nonlinear behavior such as effects of shear thinning and shear thickening,polymer convection,diffusion,adsorption retention,inaccessible pore volume and reduced effective permeability.Meanwhile,the flux density and fracture conductivity along the hydraulic fracture are generally non-uniform due to the effects of pressure distribution,formation damage,and proppant breakage.In this paper,we present an oil-water two-phase flow model that captures these complex non-Newtonian and nonlinear behavior,and non-uniform fracture characteristics in fractured polymer flooding.The hydraulic fracture is firstly divided into two parts:high-conductivity fracture near the wellbore and low-conductivity fracture in the far-wellbore section.A hybrid grid system,including perpendicular bisection(PEBI)and Cartesian grid,is applied to discrete the partial differential flow equations,and the local grid refinement method is applied in the near-wellbore region to accurately calculate the pressure distribution and shear rate of polymer solution.The combination of polymer behavior characterizations and numerical flow simulations are applied,resulting in the calculation for the distribution of water saturation,polymer concentration and reservoir pressure.Compared with the polymer flooding well with uniform fracture conductivity,this non-uniform fracture conductivity model exhibits the larger pressure difference,and the shorter bilinear flow period due to the decrease of fracture flow ability in the far-wellbore section.The field case of the fall-off test demonstrates that the proposed method characterizes fracture characteristics more accurately,and yields fracture half-lengths that better match engineering reality,enabling a quantitative segmented characterization of the near-wellbore section with high fracture conductivity and the far-wellbore section with low fracture conductivity.The novelty of this paper is the analysis of pressure performances caused by the fracture dynamics and polymer rheology,as well as an analysis method that derives formation and fracture parameters based on the pressure and its derivative curves.

Morphological evolution and flow conduction characteristics of fracture channels in fractured sandstone under cyclic loading and unloading

In coal mining,rock strata are fractured under cyclic loading and unloading to form fracture channels.Fracture channels are the main flow narrows for gas.Therefore,expounding the flow conductivity of fracture channels in rocks on fluids is significant for gas flow in rock strata.In this regard,graded incremental cyclic loading and unloading experiments were conducted on sandstones with different initial stress levels.Then,the three-dimensional models for fracture channels in sandstones were established.Finally,the fracture channel percentages were used to reflect the flow conductivity of fracture channels.The study revealed how the particle size distribution of fractured sandstone affects the formation and expansion of fracture channels.It was found that a smaller proportion of large blocks and a higher proportion of small blocks after sandstone fails contribute more to the formation of fracture channels.The proportion of fracture channels in fractured rock can indicate the flow conductivity of those channels.When the proportion of fracture channels varies gently,fluids flow evenly through those channels.However,if the proportion of fracture channels varies significantly,it can greatly affect the flow rate of fluids.The research results contribute to revealing the morphological evolution and flow conductivity of fracture channels in sandstone and then provide a theoretical basis for clarifying the gas flow pattern in the rock strata of coal mines.

Application of Stochastic Fracture Network with Numerical Fluid Flow Simulations to Groundwater Flow Modeling in Fractured Rocks

The continuum approach in fluid flow modeling is generally applied to porous geological media, but has limited applicability to fractured rocks. With the presence of a discrete fracture network relatively sparsely distributed in the matrix, it may be difficult or erroneous to use a porous medium fluid flow model with continuum assumptions to describe the fluid flow in fractured rocks at small or even large field scales. A discrete fracture fluid flow approach incorporating a stochastic fracture network with numerical fluid flow simulations could have the capability of capturing fluid flow behaviors such as inhomogeneity and anisotropy while reflecting the changes of hydraulic features at different scales. Moreover, this approach can be implemented to estimate the size of the representative elementary volume (REV) in order to find out the scales at which a porous medium flow model could be applied, and then to determine the hydraulic conductivity tensor for fractured rocks. The following topics are focused on in this study: (a) conceptual discrete fracture fluid flow modeling incorporating a stochastic fracture network with numerical flow simulations; (b) estimation of REV and hydraulic conductivity tensor for fractured rocks utilizing a stochastic fracture network with numerical fluid flow simulations; (c) investigation of the effect of fracture orientation and density on the hydraulic conductivity and REV by implementing a stochastic fracture network with numerical fluid flow simulations, and (d) fluid flow conceptual models accounting for major and minor fractures in the 2 D or 3 D flow fields incorporating a stochastic fracture network with numerical fluid flow simulations.

DYNAMIC PRODUCTION PREDICTION AND PARAMETER IDENTIFICATION FOR GAS WELL WITH VERTICAL FRACTURE

In order to devoid the hard work and factitious error in selecting charts while analyzing and interpreting hydraulic fracturing fracture parameters, on the basis of the non-Darcy flow factor, this paper put out the non-Darcy flow mathematical model of real gas in the formation and fracture, established the production history automatic matching model to identify fracture parameters, and offered the numerical solutions of those models, which took the variation of fracture conductivity in production process. These results offered a precise and reliable method to understand formation, analyze and evaluate the fracturing treatment quality of gas well.

Rate decline analysis of multiple fractured horizontal well in shale reservoir with triple continuum

Multiple fractured horizontal well(MFHW) is widely applied in the development of shale gas. To investigate the gas flow characteristics in shale, based on a new dual mechanism triple continuum model, an analytical solution for MFHW surrounded by stimulated reservoir volume(SRV) was presented. Pressure and pressure derivative curves were used to identify the characteristics of flow regimes in shale. Blasingame type curves were established to evaluate the effects of sensitive parameters on rate decline curves, which indicates that the whole flow regimes could be divided into transient flow, feeding flow, and pseudo steady state flow. In feeding flow regime, the production of gas well is gradually fed by adsorbed gases in sub matrix, and free gases in matrix. The proportion of different gas sources to well production is determined by such parameters as storability ratios of triple continuum, transmissibility coefficients controlled by dual flow mechanism and fracture conductivity.

基于裂缝闭合理论和3D打印的导流能力预测方法

酸蚀裂缝导流能力对于酸压方案的优化和产能评估具有十分重要的意义,但是在酸蚀导流能力测试过程中存在高闭合压力下岩心柱破裂情况,影响实验数据的准确性。基于以上问题,综合采用3D扫描和3D打印技术以及受压情况下裂缝闭合理论对酸蚀裂缝导流能力进行研究。首先对岩样进行酸蚀实验,通过逆向建模技术获取到酸蚀后岩心三维模型,采用SLA3D打印技术制备含粗糙壁面的三维岩心模型,对酸蚀岩心和3D打印岩心开展不同围压下渗流实验。运用离散化数据处理方法,结合赫兹接触模型和N-K模型编写导流能力预测界面,使用数值模拟方法反映闭合应力下裂缝形变情况。研究结果表明,结合真实岩体三维数字模型及SLA3D打印技术制备真实岩样,为制作复杂裂缝岩心模型提供了有效途径;酸蚀岩心和3D打印岩心导流能力实验结果、3D打印岩心实验结果和数值模拟结果误差均小于7.7%,数值模拟与碳酸盐岩心实验值的误差小于9.6%;以低闭合压力下实验和模拟结果为基础可以预测高闭合压力下裂缝导流能力,提出的研究方法为定量化表征酸蚀裂缝导流能力提供了可靠途径。

致密砂岩储层支撑剂优选研究--以临兴神府区块为例

为了降低水力压裂对致密砂岩储层进行改造的成本,更好地释放临兴神府区块储层产能,首先采用HXDL-2C支撑剂长期导流能力评价系统装置开展了支撑剂导流能力评价实验,主要研究了闭合压力、铺砂浓度、石英砂粒径和不同粒径组合、石英砂和陶粒组合比例对支撑裂缝导流能力的影响,然后结合文中提出的支撑剂优选原则和数值模拟研究来指导临兴神府区块太2段储层在压裂施工时进行的支撑剂优选工作。结果表明,闭合压力的增加会导致支撑剂导流能力减小;闭合压力一定时,导流能力随铺砂浓度增加而增大;不同粒径支撑剂组合,导流能力随小粒径支撑剂比例的增加而减小;石英砂和陶粒支撑剂组合,随陶粒所占比例的增加导流能力增大。在以上研究基础上,优选出石英砂(20/40目)∶陶粒(20/40目)=1∶1的组合比例在铺砂浓度为4 kg/m 2的条件下进行太2段储层压裂施工时,增产效果较好。

Hydro-mechanical-electrical simulations of synthetic faults in two orthogonal directions with shear-induced anisotropy

Fluid flow in fractures controls subsurface heat and mass transport,which is essential for developing enhanced geothermal systems and radioactive waste disposal.Fracture permeability is controlled by fracture microstructure(e.g.aperture,roughness,and tortuosity),but in situ values and their anisotropy have not yet been estimated.Recent advances in geophysical techniques allow the detection of changes in electrical conductivity due to changes in crustal stress and these techniques can be used to predict subsurface fluid flow.However,the paucity of data on fractured rocks hinders the quantitative interpretation of geophysical monitoring data in the field.Therefore,considering different shear displacements and chemical erosions,an investigation was conducted into the hydraulic-electric relationship as an elevated stress change in fractures.The simulation of fracture flows was achieved using the lattice Boltzmann method,while the electrical properties were calculated through the finite element method,based on synthetic faults incorporating elastic-plastic deformation.Numerical results show that the hydraulic and electrical properties depend on the rock's geometric properties(i.e.fracture length,roughness,and shear displacement).The permeability anisotropy in the direction parallel or perpendicular to the shear displacement is also notable in high stress conditions.Conversely,the permeability econductivity(i.e.,formation factor)relationship is unique under all conditions and follows a linear trend in logarithmic coordinates.However,both matrix porosity and fracture spacing alter this relationship.Both increase the slope of the linear trend,thereby changing the sensitivity of electrical observations to permeability changes.

深部开采巷道掘进过导水断层围岩控制技术研究

12201运输巷沿着深部区域的12^(#)煤层底板掘进,巷道掘进区域存在有DF6-1、DF6-3导水裂隙,虽进行超前处理,但在扰动影响下巷道仍会出现淋水情况,加之围岩破碎、岩体为软岩,制约巷道掘进过断层围岩支护工作。结合现场条件,提出通过加固围岩、封堵导水裂隙方式提高围岩自身承载能力,降低淋水对破碎围岩影响,现场应用后,12201运输巷过断层期间,围岩未有淋水情况出现,同时巷道顶底板、两帮变形量均较小,实现了巷道导水断层围岩变形有效控制。

Coupled hydro-thermo-mechanical modeling of hydraulic fracturing in quasi-brittle rocks using BPM-DEM

This paper presents an improved understanding of coupled hydro-thermo-mechanical(HTM) hydraulic fracturing of quasi-brittle rock using the bonded particle model(BPM) within the discrete element method(DEM). BPM has been recently extended by the authors to account for coupled convective econductive heat flow and transport, and to enable full hydro-thermal fluidesolid coupled modeling.The application of the work is on enhanced geothermal systems(EGSs), and hydraulic fracturing of hot dry rock(HDR) is studied in terms of the impact of temperature difference between rock and a flowing fracturing fluid. Micro-mechanical investigation of temperature and fracturing fluid effects on hydraulic fracturing damage in rocks is presented. It was found that fracture is shorter with pronounced secondary microcracking along the main fracture for the case when the convectiveeconductive thermal heat exchange is considered. First, the convection heat exchange during low-viscosity fluid infiltration in permeable rock around the wellbore causes significant rock cooling, where a finger-like fluid infiltration was observed. Second, fluid infiltration inhibits pressure rise during pumping and delays fracture initiation and propagation. Additionally, thermal damage occurs in the whole area around the wellbore due to rock cooling and cold fluid infiltration. The size of a damaged area around the wellbore increases with decreasing fluid dynamic viscosity. Fluid and rock compressibility ratio was found to have significant effect on the fracture propagation velocity.

庆城夹层型页岩油地质工程一体化压裂技术

针对庆城夹层型页岩油储层物性致密、原始油藏压力系数低和湖相沉积非均质性强的特点,采用大型物理模拟试验、水平检查井取心观察和微地震频度与震级分析等方法,明确了裂缝系统以人工主裂缝为主、支/微裂缝为辅;根据细分切割裂缝思路,采用桥塞/球座分段多簇射孔联作工艺为主体技术;从地质工程甜点综合特征出发,优化布缝策略、段簇组合和簇间距;基于限流压裂原理,采用暂堵控制多簇裂缝扩展,以大量现场压裂资料为样本集,优化压裂关键参数;根据压裂对缝网导流能力的需求,优化压裂液和支撑剂的粒径组合。通过上述研究,形成了庆城夹层型页岩油地质工程一体化压裂技术。庆城页岩油区块的180口水平井应用页岩油地质工程一体化压裂技术完成4590段压裂,压裂后单井初期产量达到了14.5 t/d,第1年产量递减率降低10百分点以上。研究和现场应用表明,页岩油地质工程一体化压裂技术可以实现油藏与裂缝的匹配,有效支撑了庆城页岩油百万吨级产能建设,为陆相页岩油资源高效动用和效益开发提供了技术支持。

组合粒径+滑溜水携砂铺置规律及导流能力——以吉木萨尔页岩油储层为例

为了解决页岩油组合粒径+滑溜水的支撑剂加砂工艺中裂缝有效支撑差、导流能力弱的问题,建立支撑剂粒径分布的稠密离散相模型(DDPM),研究压裂主缝中组合粒径支撑剂加砂运移及铺置规律,并基于运移规律模拟结果,开展劈裂页岩岩板组合粒径不同铺置模式下的室内导流能力评价。结果表明:滑溜水携砂液体系下,裂缝内支撑剂叠置铺置时,后注入的支撑剂叠置于先注入支撑剂的顶端,且先注入的支撑剂会被后续注入的支撑剂向远端推移一定距离;组合粒径中粒径配比差异对于支撑剂运移形成的砂堤形态影响较小;大粒径组合逐级注入的方式更利于支撑剂在近缝口和裂缝内垂向铺置;在低闭合压力(p≤40 MPa)、铺砂浓度5 kg/m^(2)条件下,沉降铺置方式最利于提高裂缝导流能力,其次为混合铺置,分段铺置方式最差;高闭合压力下(p>40 MPa),铺置方式对裂缝导流能力影响较弱。综合支撑剂运移模拟和导流能力评价结果,建议吉木萨尔页岩油组合粒径加砂工艺采用逐级注入的方式,并保证组合粒径中大粒径拥有较大配比。

N_(2)泡沫穿层压裂煤岩组合体试验研究

一体化穿层压裂是实现近距离煤系储层多气共采的关键技术,但常规低黏活性水压裂液易沟通层理等弱结构面,限制了水力裂缝纵向穿层扩展。鉴于此,基于泡沫流体高黏、低滤失和易返排等特性,提出N_(2)泡沫低伤害穿层压裂煤系储层方法,通过室内浇筑灰岩、页岩与真实煤样的组合体试样,利用自行研制的大尺寸真三轴压裂渗流模拟装置,分别开展N_(2)泡沫与活性水的真三轴压裂物理模拟实验,对比分析2种压裂介质泵压曲线、压后裂缝形态、缝网导流能力以及主裂缝面粗糙度特征,研究N_(2)泡沫压裂裂缝起裂特征及垂向扩展行为。实验结果表明:(1)高黏与低滤失N_(2)泡沫压裂液穿层扩展能力强于活性水,相同应力条件下纵向穿层数量更多,但泵压曲线压力峰值低于后者,有利于穿层压裂施工;(2)相比活性水,可压缩N_(2)泡沫流体压裂增压时间更长,且其页岩层破裂压力高于前者约8.7 MPa;(3)压裂完成后,原位应力条件下N_(2)泡沫压后缝网的重注压力较活性水低3.6 MPa,表明N_(2)泡沫压裂形成的缝网导流能力更高;(4) N_(2)泡沫与活性水压裂主裂缝面粗糙度分别为20.53和13.56,更粗糙的裂缝面有利于生产过程缝网导流能力的保持。结论认为,可压缩N_(2)泡沫以其高黏与低滤失特性可实现更好的纵向穿层效果,但横向缝网复杂程度相对较低,建议现场采取“泡沫造主缝+气体/活性水压裂造分支缝”复合压裂工艺,实现多岩性煤系储层的一体化穿层压裂与缝网改造。

蒙陕接壤区典型煤层开采地下水系统扰动的定量表征

生态脆弱区煤矿高强度开采扰动地下水系统,造成水资源损失。选取黄河流域中段蒙陕接壤区东南—西北走向剖面典型浅部开采和深部开采矿井为研究对象,利用覆岩破坏理论分析、数值模拟、井下实测3种方法,并通过周边地质和开采条件相似矿井实测数据对比,综合确定了浅埋复合煤层开采和深埋单一煤层开采导水裂隙带发育高度,根据导水裂隙带与顶板主要含/隔水层空间位置关系,划分出浅埋煤层开采直罗组−志丹群含水层充水模式和深埋煤层开采直罗组含水层充水模式;通过概化不同含水层充水模式地下水流系统,构建了典型煤层开采地下水三维非稳定流数学模型,并利用Visual Modflow软件建立了2种工况地下水流数值模型,对接续期2023—2024年工作面开采地下水流场和水资源损失量进行了定量预测,并利用涌水量实测数据验证了模型可靠性。结果显示:受扰动的浅埋区志丹群、直罗组含水层,以及深埋区直罗组含水层地下水呈现向采空区汇集现象的同时,流场也伴随采后煤层顶板二次稳定结构的形成而逐步恢复,但围绕采空区附近,充水含水层地下水流场表现出局部高水力梯度现象;另外,2种采煤工况接续期水资源损失量年均分别达到200万m^(3)和730万m^(3)以上。研究结果为区域水资源损失超前精细控制和矿井水资源化利用提供了参考。

支撑剂嵌入对裂缝长期导流能力的影响研究

运用FCES-100长期裂缝导流仪,在国内首次进行了地层岩心的支撑剂嵌入实验研究,考察了不同类型支撑剂、不同铺砂浓度对不同岩心的嵌入程度以及对导流能力的伤害程度。找到了影响支撑剂嵌入的主要因素和规律,并提出了克服支撑剂嵌入这一不良影响的有效方法。通过实验发现由于支撑剂的嵌入会使导流能力产生很大程度的下降;铺砂浓度越大,嵌入对导流能力的伤害程度越小;只有当闭合压力达到一定值时,嵌入的伤害才表现出来;铺砂浓度对导流能力的影响也很大,铺砂浓度增大一倍,导流能力将成数倍增加;在相同地层条件下,支撑剂在砾岩中的嵌入最为严重,泥岩其次,粉砂岩最小。文中还根据实验结果回归出了导流能力随闭合压力以及随时间变化的关系表达式,可以用来预测支撑裂缝导流能力的衰减趋势,对现场压裂有一定的指导意义。

支撑剂嵌入及对裂缝导流能力损害的实验

对于岩石较软的地层,在压裂过程中的支撑剂嵌入会降低压裂充填后的裂缝宽度,同时嵌入区地层碎屑也会损害支撑剂充填层的导流能力,因而有必要对支撑剂的嵌入进行研究,并为压裂施工中的支撑剂优选提供依据。为此,运用API标准导流室和基于API标准导流室自行研制的测试仪器,对地层岩心的支撑剂嵌入情况进行了实验研究,并在支撑剂嵌入的基础上,考虑了地层碎屑对裂缝导流能力损害的影响。在国内首次对支撑剂嵌入后的岩心进行了微观分析,更加直观地反映了嵌入程度和嵌入状态。实验考察了不同铺砂浓度、不同压力下对不同岩心的支撑剂嵌入情况。实验表明:由于支撑剂的嵌入,会使支撑裂缝宽度有较大程度的减小;铺砂浓度越低,地层岩石越软,嵌入越严重。还模拟了支撑剂嵌入后不同碎屑浓度对同一种岩心的导流能力伤害程度,并发现在嵌入后的碎屑达到一定浓度后会直接堵塞孔道。

支撑剂嵌入程度的实验研究

基于API标准导流室,自行研制了一套支撑剂嵌入程度测试分析系统,对地层岩芯的支撑剂嵌入程度进行了实验研究.对支撑剂嵌入后的岩芯进行微观分析,更加直观地反映了嵌入程度和状态.实验考察了不同铺砂浓度、不同应力下对不同岩芯的支撑剂嵌入情况.通过实验分析出由于支撑剂的嵌入,会使支撑裂缝宽度有较大程度的减小;闭合应力越大,铺砂浓度越低,地层岩石越软,嵌入越严重.

气井压后稳态产能公式和压裂数值模拟研究

低渗气藏在已探明的天然气地质储量中占有相当大的比重。但低渗气藏的低产特征 ,使得这类气藏往往难以直接获得商业性开发利用 ,只有通过储层压裂改造才能达到经济开发要求。文章根据气井压后流体渗流流动规律的变化 ,利用气藏的渗流理论 ,推导出气井压后稳态产能公式 ;并利用油藏数值模拟的方法 ,系统地分析了压裂缝长、导流能力、有效渗透率、有效厚度等对塔巴庙区块压裂初期产量大小和压后产量变化的影响 ,得到塔巴庙区块低渗气藏压裂井筛选原则和压裂设计参数。在做压裂选井时 ,应选择有效渗透率和有效厚度都较大的井进行压裂 ;在压裂设计时 ,应优选出合理的裂缝导流能力和裂缝缝长 ,从而为低渗气藏的高效开发提供科学决策。

压裂液残渣及支撑剂嵌入对裂缝伤害的影响

运用ZCJ-200型导流能力试验装置测试了3种不同压裂液在相同支撑剂类型、铺置浓度、不同闭合压力下对支撑剂充填裂缝导流能力的伤害程度;用蒸馏水作为介质测试了2种支撑剂在不同闭合压力及不同温度下对导流能力影响的差别。通过研究不同压裂液对支撑缝的伤害程度,发现残渣对支撑缝的伤害程度影响显著,应选择低残渣压裂液;对同一种体系,闭合压力升高会导致导流能力、渗透率的降低,通过对两者与闭合压力的关系表达式,总结出其衰减规律;支撑剂颗粒大小、温度变化对导流能力都有很大影响。

VES-SL粘弹性表面活性剂压裂液的研究及现场应用

为了降低压裂改造过程中压裂液对油藏和支撑裂缝的伤害，开发研制了VES—SL粘弹性表面活性剂压裂液，并利用RCV6300毛细管流变仪等试验仪器，对该压裂液的性能进行了研究。室内评价结果表明，VES—SL粘弹性表面活性剂压裂液在100℃和170s^-1的条件下，经过1h的剪切，其粘度在130mPa·s以上；在120℃和170s^-1的条件下，经过1h的剪切，其粘度达50mPa·s以上；随剪切时间的延长，该压裂液粘度变化很小；随温度的降低，该压裂液粘度具有很好的恢复性。试验结果表明，该压裂液粘度高且成本低，对地层的伤害要比HPG压裂液低50％左右。现场试验证实，VES—SL粘弹性表面活性剂压裂液的摩阻相当于清水摩阻的25％-30％，比HPG压裂液的摩阻低1MPa/1000m，2口压裂井共增产原油5600t。使用该压裂液进行压裂施工，可以有效地降低压裂液对油藏和支撑裂缝的伤害，同时提高油井的增产效果。