深层砂岩储层破裂压力研究

深部储层的高温高压导致其岩石力学参数与常规储层有较大差异,如使用常规岩石力学理论建立的岩石破裂压力模型计算储层破裂压力,必然会影响影响压裂优化设计,最终影响压裂施工效果。因此正确预测高温下地层岩石破裂压力,对于提高深部地层水力压裂施工效果具有重要意义。本文根据岩石力学和断裂力学理论,结合高温高压对岩石力学参数的实验分析,建立了考虑温度影响的砂岩储层岩石破裂压力计算模型,采用解析解方法对模型进行求解,分别得到了裸眼直井、裸眼水平井、射孔直井及射孔水平井的破裂压力计算模型,计算了不同温度条件下的砂岩储层破裂压力曲线,分析了温度对砂岩储层破裂压力的影响。研究结果表明,随着地层深度的增加,储层温度也随之增加,砂岩储层的破裂压力逐渐上升。该模型对实际压裂施工过程具有一定的指导意义。     

低腐蚀性加重酸室内研究及应用

加重酸化是针对深井、超深井高破裂储层酸压改造的降低地层破裂压力的预处理技术。但因深井、超深井地层温度高,加重酸液体系的腐蚀性强,其应用受到很大限制。针对四川元坝地区储层埋深大、温度高,破裂压力高等特点,开展了加重酸液类型、主体酸浓度和加重剂、缓蚀剂等添加剂的实验优选及配方优化,获得了适合元坝地区深井/超深井高温、高破裂储层酸压改造的低腐蚀性加重酸液体系。优选获得的加重酸液密度达1.8g/cm3以上,在160℃高温条件下,其动态腐蚀速率小于30g/(m2.h),放置稳定性好(室温放置8d不分层、不沉淀)、溶蚀能力好,属典型低腐蚀性加重酸液体系。元坝YB2-X井须二段4600～4640m储层,此前采用密度为1.98g/cm3泥浆两次试挤,井底压力梯度超过3.71MPa/100m,地层仍无破裂迹象,随后采用40m3密度为1.85g/cm3低腐蚀性加重酸进行试破,施工排量由1.0m3/min升至2.4m3/min,酸化吸酸指数最大达19.38L/(min.MPa),地层具明显压裂显示。采用加重酸化技术,对深井超高破裂压力储层进行预处理,可取得较好增产效果。     

碳酸盐岩酸压裂缝内净压力变化规律研究

酸化压裂是开发碳酸盐岩储层最常用的增产技术,而酸压裂缝内净压力是反映裂缝扩展特征、推断裂缝几何形态的重要参数。以水力压裂裂缝延伸机理为基础,基于酸岩反应理论,考虑酸岩反应导致的缝宽变化、CO₂气体膨胀、酸液滤失及岩石力学性质变化,结合PKN模型,建立酸压裂缝内的净压力计算模型并进行验证。研究分析酸压裂缝内净压力的影响因素及其规律,结果表明：距缝口距离越远,水力裂缝与酸压裂缝的缝宽均越小,酸液的溶蚀作用会使裂缝宽度增大。随着液体的滤失,离缝口越远液体越少,水力裂缝与酸压裂缝净压力逐渐减小,越靠近裂缝尖端净压力衰减越快。随着作用时间延长,酸压裂缝缝宽逐渐增大,前期随着大量CO₂生成,净压力迅速增大,随着酸液消耗与滤失增加,之后逐渐减小并趋于稳定。随着排量的增大,滤失增大,酸压裂缝缝宽及净压力均逐渐增大且增量越来越小。在黏度较小的情况下,滤失较大,净压力逐渐减小;在黏度较大的情况下,CO₂膨胀作用大于滤失作用,净压力逐渐增大。随着酸液浓度的增大,酸岩反应速率增大,反应生成CO₂增多,净压力逐渐增大。     

准噶尔盆地石炭系火山岩储层支撑剂段塞技术研究与应用

在水力压裂过程中,准噶尔盆地石炭系火山岩裂缝性油气藏低砂比砂堵、施工压力升高等现象较为常见,导致石炭系储层改造规模受限、施工成功率低、增产效果差。支撑剂段塞技术是对付早期油气井砂堵的有效工艺措施之一。准噶尔盆地陆东石炭系与车排子石炭系由于岩石性质和裂缝发育情况等的不同,造成压裂时天然裂缝的开启宽度大小不同。通过段塞颗粒大小优选以及支撑剂浓度研究,确定了陆东石炭系气藏以及车排子石炭系油藏适合的支撑剂段塞技术。陆东石炭系火山岩储层天然裂缝发育,裂缝开度较大,支撑剂段塞宜采用较大粒径的40/70目陶粒;现场试验16井次,施工成功率93.7%,设计符合率93.7%。车排子石炭系火山岩储层微裂缝发育,裂缝开度较小,支撑剂段塞宜采用较小粒径的70/140目陶粒;现场试验10井次,施工成功率100%,设计符合率100%。     

川西须五气藏完井方式适应性研究

随着勘探开发的不断深入,非常规天然气成为重要的接替资源。四川盆地非常规天然气资源量丰富,须五气藏为典型的砂泥岩互层致密非常规气藏,有效的完井方式是气藏实现提高单井产能、提高气藏可采程度的重要保障。国内外非常规气藏水平井主要采用多段压裂技术、降阻水压裂技术、同步压裂技术,开发效果显著;研究表明,基质裂缝、裂缝网络渗透率、水力裂缝间隙、水力裂缝传导率、岩石压缩性、水力裂缝半长、自然裂缝孔隙度,对页岩气水平井产能影响较大,钻井过程中要对近井地带的基质渗透率、裂缝网络渗透率和自然裂缝孔隙度进行保护。川西须五气藏储层脆性矿物含量与美国其他页岩气相当,同时储层具有天然裂缝发育的特点,完井方式需要考虑储层改造工艺、最大程度上实现缝网压裂的目的;通过深入研究,优选出川西须五气藏完井方式,优选套管射孔完井方式,采用水平井+多段水力压裂和储层改造完井方法进行开发。     

川渝碳酸盐岩储层胶凝酸配方研究

酸压是碳酸盐岩储层改造增产的主要措施,而优选适合的酸液体系是实现酸压成功的重要前提。通过分子结构设计,研发设计了共聚物型耐高温胶凝剂和集络合、防膨、助排功能于一体的多功能剂,同时优选耐高温缓蚀剂,形成了一套适合于川渝碳酸盐岩储层特点的胶凝酸配方体系。综合评价表明,配方的抗剪切、缓蚀、络合、防膨等性能指标均满足标准要求,在不提高酸液黏度的基础上,有效降低了H+传质速率,使酸岩反应速率变小,并降低对储层造成的伤害。利用旋转岩盘酸岩反应测试系统、酸蚀裂缝导流能力测试系统,对胶凝酸体系酸岩反应动力学、裂缝导流能力及刻蚀形态进行系统评价。结果表明,该体系具有优异的缓速性能,在闭合压力60MPa下,酸蚀裂缝导流能力可达到8.48μm2·cm。激光扫描结果表明,酸液非均匀刻蚀程度提高120%,对裂缝形貌改变明显。     

川北阆中-南部地区大安寨段油气藏储层酸压改造技术及实践

川北阆中-南部地区大安寨段油气藏成藏模式以“自生自储”为主,总体上属于常温（74～80℃）、高压（原始地层压力系数〉1．3）、构造-岩性复合圈闭、薄层状、低丰度、无边（底）水碳酸盐岩裂缝性未饱和油藏或凝析气藏。由于大部分油气井地层压力下降快,地层压力梯度低,产量递减率高,限制了常规酸化压裂等增产措施的推广应用。本文针对大安寨油气藏的地质特征,并结合油气藏开采效果评价,提出了采用胶凝压裂酸化（酸压）技术改造储层的增产措施。通过室内试验得到了凝胶酸TC4—1的配方：20％（HCl）＋3．5％（CTl-9）＋1．0％（CTI-31＋1．0％（CT1-7）＋1．0％（CT5-9）＋1．0％（IV-93）。针对不同类型的储层,对酸压工艺进行了优化,并实施了加液氮酸化、压前预处理等配套措施。现场实施效果表明,研制的酸化配方及配套技术具有良好的适应性和显著的增产效果。     

雷家白云岩致密储层改造发展历程与认识

辽河坳陷陈家洼陷北部的雷家地区沙四段发育一套湖相碳酸盐岩致密储层,储集岩性以含泥泥晶云岩、泥晶粒屑云岩为主,具有薄互层发育、天然裂缝发育不均、原油流度低等特点。雷家地区沙四段纵向分为杜家台油层和高升油层上下两段,杜家台组又划分为杜一、杜二、杜三等3个小层。根据油气显示情况,杜三组和高升组是"甜点"相对集中发育的层段。经过大规模加砂、高导流通道、直井复合压裂、水平井体积压裂等4个储层改造发展阶段,得出4点经验认识:地质评价提高"甜点区"辨识是储层改造的基础前提,体积压裂是储层改造理念的发展方向,控破裂泵注方式可有效提高压裂施工成功率,较高的储层钻遇率是水平井分段体积压裂的必要条件。目前雷家致密储层已经形成了相对成熟的水平井分段压裂体积改造工艺,应用于3口水平井,压后平均产量达到13.8m3/d。     

定北区块复杂储层压裂工艺技术研究与应用

定北区块上古生界储层具有低孔、致密、高温、天然裂缝发育、基本无自然产能等复杂特征。勘探前期因地层参数缺乏．采用常规硼交联压裂液体系及常规压裂技术实施作业,压裂工艺的针对性不强,施工过程中极易出现砂堵现象。为此．开展了高温暂堵压裂液体系及测试压裂工艺技术应用研究,研制了有机锆交联高温暂堵压裂液体系,并选择定北7井2储层首先开展了小型压裂测试,获取了储层、压裂裂缝、压裂液等相关参数。根据测试压裂结果,对该储层进行压裂设计与施工：设计排量4．5m3／min．前置液比例37％,平均砂比24％,加砂量38m3,全程使用有机锆交联高温压裂液．前置液添加l％屏蔽暂堵剂。压裂施工结束后,对主压裂数据进行压力拟合,结果显示,研制的高温暂堵压裂液体系能满足区块高温、微裂缝发育储层的压裂造缝、携砂等施工需要,压裂改造达到了预期效果。     

玉北6区块深层稠油油藏压裂技术研究与应用

鲁克沁油田二叠系梧桐沟组深层砂砾岩稠油油藏储层破裂压力高、地层温度高、原油黏度高、岩性复杂,给储层压裂措施带来诸多难题。针对储层特征,压裂以提高施工成功率、提高导流能力、提高储层动用程度、降低储层伤害为思路,以低浓度胍胶高效交联压裂体系、"注水蓄能+压裂"技术、多次加砂、准101.6mm非标油管、组合粒径加砂为技术对策开展研究工作。结果表明:前置液多段塞+段塞式加砂+组合粒径陶粒的加砂方式现场适应性较强,可保证施工成功率与裂缝导流能力;"注水蓄能+压裂"技术使地层能量得到有效补充,弥补了注采井网不完善、高压欠注及地层压力系数下降等缺陷;低浓度胍胶高效交联压裂液体系具有低摩阻、低滤失、低界面张力、返排彻底、对地层伤害小、携砂性能好等特点,现场规模推广应用单井液体成本下降40%;采用准101.6mm非标油管及套管注入压裂可有效降低施工风险。将研究成果应用于玉北6区块17井次,增产、稳产效果明显。     

Multifracture response to supercritical CO2‐EGS and water‐EGS based on thermo‐hydro‐mechanical coupling method

Hydraulic‐fracturing treatments have become an essential technology for the development of deep hot dry rocks (HDRs). The deep rock formation often contains natural fractures (NFs) at micro and macroscales. In the presence of the NF, the hydraulic‐fracturing process may form a complex fracture network caused by the interaction between hydraulic fractures and NF. In this study, analysis of carbon dioxide (CO₂)‐based enhanced geothermal system (EGS) and water‐based EGS in complex fracture network was performed based on the thermo‐hydro‐mechanical (THM) coupling method, with various rock constitutive models. The complexity of the fracture geometry influences the fluid flow path and heat transfer efficiency of the thermal reservoir. Compared with CO₂‐based EGS, water‐based EGS had an earlier thermal breakthrough with a rapid decline in production temperature. CO₂ can easily gain heat rising its temperature thus reducing the effect of a premature thermal breakthrough. Both CO₂‐based EGS and water‐based EGS are affected by in‐situ stress; the increase in stress ratio improved the fracture permeability but resulted in an early cold thermal breakthrough. When the same injection rate is applied to water‐based EGS and CO₂‐based EGS, water‐based EGS displayed higher injection pressure buildup. Water‐based EGS had higher reservoir deformation area than CO₂‐based EGS, and thermoelastic constitutive model for water‐based EGS showed larger deformed area ratio than thermo‐poroelastic rock model. Furthermore, higher values of rock modulus accelerated the reservoir deformation for water‐based EGS. This study established a novel discussion investigating the performance of CO₂‐based EGS and water‐based EGS in a complex fractured reservoir. The findings from this study will help in deepening the understanding of the mechanisms involved when using CO₂ or water as a working fluid in EGS.     

增强型地热系统水力压裂与双井连通实验仿真研究

增强型地热系统（Enhanced Geothermal System, EGS）作为未来新能源和清洁能源利用的一个重要方向,受到了世界各国的广泛关注。一直以来,野外试验场的工程实践和数值模拟分析是进行EGS研究的两种主要方式。本文通过实验室规模的小型试验系统,对EGS的水力压裂、裂隙监测、生产井定位和注水测试进行了仿真,成功实现了注入井−热储层−生产井的水力连通,分别以定井口压力和定注水流量进行水力测试。试验结果表明,热储层的裂隙开度会随着水力特性而发生变化,注水压力较大时热储层的裂隙具有更大的开度和渗流能力。从提升热储层经济性的角度考虑,实践中应当在较大注水压力时对热储裂隙结构进行加固处理。     

塔河油田碳酸盐岩储层酸压酸岩反应影响因素研究

由于地质因素的复杂性,碳酸盐岩储层的酸压效果与酸岩反应的各项影响因素关系密切,通过研究温度、酸液浓度等影响因素,可以采取有效措施控制酸岩反应速率,从而提高酸压效果。     

Model for calculating the temperature and pressure within the fracture during supercritical carbon dioxide fracturing

Supercritical carbon dioxide fracturing not only enhances fossil hydrogen production better than hydraulic fracturing, but also alleviates water consumption and storages some carbon dioxide in reservoirs. In this study, a numerical simulation model for calculating the temperature and pressure within a fracture during supercritical carbon dioxide fracturing was established based on rock mechanics, fluid mechanics, thermodynamics, and heat transfer. Moreover, the effects of impact of in-situ stress of reservoir, reservoir temperature, carbon dioxide temperature at the bottom of the well and injection rate on temperature and pressure in the fracture are analyzed based on this new model. The results show that the temperature and pressure of carbon dioxide in the fracture are constantly changing during the fracturing, due to the propagation of the fracture, which makes the temperature and pressure in the fracture unable to reach a steady state. The effect of supercritical carbon dioxide fracturing in reservoirs with higher temperature and lower in-situ stress is better, and higher injection temperatures and smaller injection rates should be chosen in order for carbon dioxide to quickly reach the supercritical state.     

新疆油田火山岩气藏体积压裂机理研究及应用

进行火山岩气藏压裂改造时,通常采用形成单一裂缝的增产改造技术,气井稳产时间较短.借鉴页岩气开发理念,深入研究火山岩气藏体积压裂机理.根据缝内压力传导的力学模型,研究不同液体体系对压力传导的影响,分析无滤饼压裂液体系对体积压裂的作用,优选出压裂液体系;建立不同角度天然裂缝开启的力学模型,确立体积形成的关键力学条件,并针对火山岩气藏压裂目的层的地应力结构进行实际分析.从储层矿物角度出发,研究对比火山岩储层的脆性系数;根据力学条件,结合压裂工艺过程,建立相关模型,优化研究体积压裂关键工艺参数,包括排量、压裂规模等;分析降阻水、线性胶、浓胶液三种不同黏度液体对裂缝网络的作用.在上述研究基础上,针对新疆油田DX1413井实际地质条件,分析该井进行体积压裂的有利条件,并进行压裂设计与改造施工,对施工曲线、施工过程、施工结果进行分析,得到了一些有益的结论,这些结论对火山岩气藏的开发有重要的启迪作用.     

Study on pressure sensitivity of tight sandstone and its influence on reservoir characteristics

The rocks with low permeability have a strong sensitivity to pressure. By changing the size of confining pressure, we can realize the effective stress change of rocks and calculate the permeability change under different effective stress to evaluate the stress sensitivity of the reservoir. We analyzed the factors affecting the stress sensitivity of tight sandstone reservoir, including material composition, fracture development, and pore structure of rock. The results show that the stress sensitivity of microfractured core is very weak, and the permeability change rate is less than 20%. The sensitivity curve is divided into two stages: the permeability decline rate in the first stage is more than 30%, mainly due to the pseudoplastic deformation of the fracture under compression. In the second stage, the decrease of permeability is less than 30%. At this stage, the elastic deformation mainly depends on the compression of the rock skeleton particles, and the net stress of the actual reservoir is mostly at this stage. Therefore, the application of the second stage to evaluate the stress sensitivity of reservoirs is more practical, and the stress sensitivity of microfracture cores is higher than that of matrix cores. Through the analysis of pressure-sensitive mechanism and experimental data, it is concluded that the main controlling factors affecting rock stress sensitivity are fracture development and pore structure of rock, while rock material composition is a relatively minor factor.     

ROUGH SIZE ESTIMATION OF A THERMALLY FRACTURED ZONE IN AN INFINITE HOT ROCK MASS

Abstract

Concerning the extraction of geothermal energy from a deep thermal reservoir by the downhole coaxial heat exchanger with a thermally insulated inner pipe proposed by Morita et al, we obtained rough estimates of a size of the fractured zone induced by thermal stresses due to injecting cold water into the hot rock mass through the pipe. We assumed complete spherical symmetry of the temperature and stress fields. At the rough estimation, we considered three typical or extreme cases. (1) The fracturing affects neither the loading capacity of a fractured rock mass nor the temperature distribution within the formation. (2) The fractured zone completely loses its loading capacity and is fully invaded by the borehole water. No disturbance of the fracturing makes any difference in the temperature. (3) The rock formation is assumed to have an appropriately increased fictitious conduction substituted for the heat transfer enhanced by the expected convection within the fractured zone in order to discuss the effects of an occurrence of heat convection within the fractured zone on the temperature and stress distributions and the fractured zone size. As a result, the size of the zone has been estimated to be about ten or more times the borehole radius.     

New correlations to predict fracture conductivity based on the formation lithology

Acid fracturing is one of the most important well stimulation methods. Acid fracture conductivity, which represents the available capacity of the fluid pass in fractures, is one the main parameters for designing acid fracturing process. The volume of dissolved rock, rock strength, and closure stress on the fracture are the effective parameters on the acid fracturing conductivity. In this study, regarding above parameters and formation lithology, Genetic Algorithm was used to develop a robust intelligent model to estimate the fracture conductivity by considering experimental data of different formations. Results showed that formation lithology plays a considerable role in fracture conductivity prediction.     

塔河奥陶系6000m~3超大规模酸压实践

针对塔河油田奥陶系碳酸盐岩缝洞型油藏常规酸压存在酸蚀裂缝距离短,导流能力有限,难以沟通远处有效储集体的问题,在TH12312井探索并实践大幅增加酸压液体用量及施工排量的6000m3超大规模酸压工艺技术。优选方案为滑溜水4000m3,施工排量≥7.0m3/min;变黏酸600m3,施工排量≥7.5m3/min;胶凝酸400m3,施工排量≥7.5m3/min;顶替液:滑溜水1000m3,施工排量≥7.0m3/min。动态缝长可达到289.9m,动态缝高可达到77m,酸蚀缝长可达到227m,导流能力可达到426mD·m。整个施工过程交替注入滑溜水和酸液,累计注入总液量6008m3,同时加入粉陶70t,最高泵压达到94.3MPa,最高排量8.5m3/min,酸压施工获得成功。酸压时的裂缝监测及后期生产效果评价表明,该工艺取得了提高造缝长度、改善储层导流能力、沟通远处储集体的效果,刷新了酸压规模的世界纪录。     

地下热流固耦合对EGS热开采的影响

人工热储的孔隙率及渗透率在增强型地热系统（EGS）地下热开采过程中受温度（T）、水力（H）、应力（M）的综合影响。本文建立了EGS热开采过程THM耦合的三维计算模型,并采用局部非热平衡假设处理液岩对流换热。对一理想的五口井EGS系统采热过程进行了THM模拟计算,分析了岩石温度、孔隙压力对岩石应力场的作用机理,进一步研究了应力场对EGS采热性能的影响。结果表明,开采过程中岩石应力场为热储内孔隙压力和温差综合作用的结果,由孔隙压力造成的岩石应力为压应力,仅集中于注入井附近,由岩石温度变化引起的热应力为拉应力,随着热开采区域的扩展而扩展。液−岩温差是触发工质与岩石热交换的动因,同时也是产生热应力的根本。