特低渗储层应力敏感性实验研究

采用砂岩储层敏感性评价实验方法（SY／T5358--2002）对长庆油田安塞县沿河湾地区长6储层14块岩心（岩心空气渗透率为0．0536×10^-3～2．4×10^-3μm2）进行了应力敏感性实验。实验结果表明,沿河湾长6特低渗储层存在中偏强应力敏感性。应力敏感系数为0．1601～0．8247。对14块岩样的渗透率随围压上升的变化曲线进行了拟合,并推导了应力敏感系数与初始渗透率之间的幂函数关系式。通过该式可以计算该储层渗透率应力敏感性伤害程度。同时,通过分析指出了该储层的应力敏感性和应力滞回效应、岩石组分和孔隙结构有关,岩石的有效孔隙越细小,黏土矿物和胶结物含量越高．岩石的渗透率对应力越敏感;当地层压力下降5MPa时,该储层应力敏感性造成的油井产量的降低范围在5．5％～25．2％,地层压力越低,则产量下降幅度越大。     

含密实填充物的平行双裂隙岩体模型渗透特性试验研究

针对含填充物的双裂隙岩体,利用惰性气体渗透测试系统,在一次围压加卸载下对试样进行渗透率和孔隙度的精确测量,研究了裂隙中填充物及交界面渗透特性随裂隙间距变化的规律。结果表明,单裂隙与双裂隙试样渗透率随围压变化规律大致相同;在加载阶段,随着裂隙间距的减小,裂隙之间的相互作用增大,孔隙度随围压减小的更为显著,而单裂隙孔隙度随围压变化最不明显;随着裂隙间距的增大,各试样渗透率相应减小,而由于单裂隙试样比双裂隙试样缺少两个渗透交界面,因此其渗透率在低围压下远小于双裂隙试样。     

基于卸围压试验的砂岩卸荷本构模型及其应用

鉴于岩体本构模型受岩样应力路径、加卸载状态等因素的影响,为研究卸荷条件下砂岩的本构模型,采用RMT-150C岩石力学试验系统对宜昌砂岩岩样进行了升轴压峰前卸围压、轴压和围压等量减小两种应力路径下的卸围压试验。结果表明,卸荷应力路径不同时,卸荷变形阶段的应力—应变曲线形态有很大差异,但岩样变形模量随围压降低而劣化的规律一致;岩样卸荷破坏强度特征可用Hoek-Brown准则拟合。由此推导出增量形式的卸荷弹脆塑型本构模型,并以算例分析验证了该模型的正确性。     

含钙质砂无粘性土的渗透特性试验及经验模型

为进一步分析含钙质砂无粘性土的渗透特性,采用南海钙质砂与细颗粒石英粉作为试验材料配置试验土样,利用GDS高压三轴仪试验系统和常水头渗透仪,开展钙质砂含量、初始孔隙比和有效应力对无粘性土的渗透特性影响研究,并建立考虑有效应力的渗透系数经验模型。试验结果表明,钙质砂含量低于40%时,土颗粒结构为无粘性土基质,孔隙结构由细颗粒土决定;钙质砂土样结构为砂颗粒骨架结构,渗透系数量级显著增大;随有效应力的增加,试样渗透系数呈幂函数降低;建立含钙质砂无粘性土的渗透系数经验模型,模型参数与土样性质关系密切,计算值与试验值吻合度较好。研究结果可为工程实践提供参考。     

基于颗粒离散元岩石模型的熵变规律研究

以岩石单轴压缩试验为基础,借助离散元软件PFC 2D建立岩石破坏的数值模型,将熵变曲线与试样的应力应变曲线、裂缝数量及能量曲线等进行对比分析,以便研究岩石破坏时的熵变规律。结果表明,岩石在破坏过程中,微裂隙的产生会造成熵值的下降;岩石在峰值应力点破坏时,熵值曲线会有明显的下降趋势;在不同围压条件下,高围压试样的初始熵值较高。因此,以熵变规律分析岩石的破坏过程,对岩石的破裂演化具有诊断评价和辅助判断的作用。     

Hoek-Brown准则高应力条件下断续节理岩体复合损伤本构模型及演化特征

针对岩石损伤本构模型中岩石微元强度采用M-C、D-P等强度准则作为判定依据存在的局限性,基于概率统计理论与连续损伤力学理论,采用应力不变式表示的H-B准则来描述岩石微元强度并假设岩石微元强度服从Weibull分布,认为岩石材料承载能力可以分为弹性和损伤两部分,基于Lemaitre应变等效性假设,推导出基于H-B准则的宏细观复合损伤本构模型,并通过预置裂隙粗晶大理岩试样的三轴试验数据验证了其合理性。结果表明,该模型获得的应力应变理论曲线与试验数据吻合较好,宏细观复合损伤演化过程能反映岩石应力随应变的变化过程,优于同类型本构模型的拟合效果;随着围压的增加,试样强度逐渐增加,峰值应力对应的复合损伤值逐渐增大;在围压一定的条件下,节理岩样的宏细观复合损伤在节理倾角为45°左右时最小,这与节理岩体强度随节理倾角的变化规律相一致。     

砂岩和碳酸盐岩的酸性改向缔合聚合物技术开发

本文介绍缔合聚合物技术在酸化处理过程中使流体改向的作用．缔合聚合物技术包括使用一种粘度非常低的含水聚合物溶液．这种溶液与储层表面一经接触便立即发生反应，从而大大降低了后注含水流体向岩石高渗透层渗流的能力．第一阶段注入的舍缔合聚合物流体大部分进入高渗透区域，使接下来注入的酸改向进入渗透率相对较低的区域．缔合聚合物技术对剩余油的流动产出没有或只有极小的影响．而且，在岩石中，包括大部分砂岩类岩石，经处理后的层段水相渗透率永久性地降低，从而降低了酸化处理后的岩层产水率．文章详细描述了缔合聚合物技术及其性质，以及当前系统试验的发展情况．实验数据说明，缔合聚合物技对术降低含水流体通过多孔介质能力的效果．利用水饱、油饱和岩心所作的平行流动试验证明缔合聚合物技术在砂岩和碳酸盐岩中使酸液改向的作用．这些试验同时也证明：在水饱和岩心中，缔合聚合物技术降低了水相渗透率；改向的酸增加了油相渗透率．     

EGS地热能开发过程中水岩作用对热储层特征的影响

增强型地热系统(EGS)是一种从地下深部低孔低渗高温岩层提取大量热能的能量利用工程,通过注水孔注入的冷水在高温岩层中循环实现热量的提取。在EGS地热能开发过程中,冷水的循环扰乱了地下深部水岩系统的热平衡和化学平衡,导致部分矿物溶解或沉淀,进而改变储层的孔隙度和渗透率。文章利用不锈钢密闭反应釜进行室内高温水岩反应试验,结合数值模拟分析水岩相互作用对EGS热储层特征的影响。研究结果表明,注入冷水到花岗岩热储层中导致石英矿物沉淀,其相对质量分数增大13%,碱性长石、斜长石、黑云母矿物溶解,其相对质量分数分别减小7%,5%,1%,总体上使得溶液中Si元素浓度降低,Ca2+,Na+,K+浓度升高,储层孔隙度、渗透率均随时间逐渐增大,提高了EGS储层地热能开发的热提取效率。     

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。     

上覆压力对深厚覆盖层地基渗透及渗透稳定性的影响

为了研究不同上覆压力对深厚覆盖层中管涌型土层的渗透及渗透稳定性影响,利用土体渗流—应力耦合装置,在施加不同上覆压力(0、0.3、0.5、0.7 MPa)的条件下,对缺级配砂砾石进行渗透破坏试验。结果表明,随着上覆压力的增大,土体在渗透破坏过程中,局部的渗透特性变化和渗流场分布均存在差异性,反映了细土颗粒被运移和填充孔隙的情况不同,从而影响了水力坡降在局部的分配情况;上覆压力的增大使得土体稳定渗流阶段和渗透破坏阶段的渗透性出现不同程度的减小,临界坡降和破坏坡降的变化与上覆压力之间存在相同形式的非均匀变化关系。     

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.     

Unsteady seepage solutions for hydraulic fracturing around vertical wellbores in hydrocarbon reservoirs

This paper establishes an analytical model to study the influence mechanism of hydraulic fracturing around vertical wellbores under the unsteady seepage in hydrocarbon reservoirs, deduces the analytical solution of water pressure and hydraulic gradient of the model, and compares the law of water pressure and hydraulic gradient changing with time with the results of numerical simulation. The results confirm the accuracy of these analytical solutions. The variation laws of water pressure and hydraulic gradient in the sample under unsteady seepage are analysed by using the COMSOL Multiphysics software. The results show that: the increasing rate and amplitude of water pressure decrease with the distance of water inlet, however, hydraulic gradient near the water inlet is the largest and decreasing with the distance. In order to better understand the mechanism of hydraulic fracturing of rock mass, we studied the influence of permeability and water injection pressure on water pressure and hydraulic gradient of rock mass. The results show that: large permeability coefficient and high hydraulic gradient will increase the probability of rock mass hydraulic fracturing. The permeability and hydraulic gradient of rock mass is important factor in determining whether the rock has hydraulic fracturing. The distribution law of water pressure and hydraulic gradient in rock mass under unsteady seepage provides important reference and basis in hydrogen developing reservoirs.     

低渗砂岩气藏储层物性与孔喉结构分析

采用铸体薄片、扫描电镜和岩石矿物含量与结构分析技术,结合岩样压汞资料等多种技术手段,对荷包场—界市场(简称包界)试验区须家河组气藏储层的物性特征和微观孔喉结构进行了深入分析和研究。研究发现储层孔隙类型以原生残余粒间孔、次生粒间孔隙和混合孔隙为特征。当孔隙度大于7%时,储层孔隙以粒间孔为主,其喉道类型以缩颈喉道为主,次为片状喉道;当孔隙度小于7%时,孔隙以粒内溶孔为主,其喉道类型以片状喉道为主,次为管状喉道;储层内粘土矿物含量较高,伊利石呈片状、丝缕状桥接孔隙,造成对孔隙、喉道的堵塞或封隔,使孔隙的连通性进一步降低。孔喉分布总体具有单峰状,以小孔细喉型为主体,平均中值喉道半径小,渗透率贡献值与喉道分布不一致,岩样渗透性主要由少数粗喉道提供,占据大部分比例的小喉道对岩样渗透性的贡献极小。鉴于储层含水饱和度较高、气井产凝析油以及粘土含量高的现象,建议尽量保持地层压力以防止凝析油过早析出,降低经济极限产量以提高低渗、特低渗区储层的动用能力。     

Effect of the water–steam phase transition on the electrical conductivity of porous rocks

The effect of the water–steam phase transition on electrical conductivity was experimentally investigated in volcanic and sandstone samples to support the interpretation of resistivity data to determine changes in steam saturation in geothermal reservoirs. The measurements were performed at simulated in situ conditions with controlled pore fluid chemistry, temperature, and confining and pore pressures. At constant temperature (150 °C) and confining pressure, pore fluid was withdrawn from the sample by steadily increasing the volume of the pore fluid system. At the vapor saturation pressure, the pore water progressively boiled to steam, resulting in a continuous conductivity decrease by a factor of approximately 20. The study showed that: (1) for rocks in which conduction is controlled by the pore fluid, the concurrent changes in both electrical conductivity and pore (vapor) pressure are defined by the pore size distribution; the changes in liquid–steam saturation are approximately proportional to those in conductivity and can thus be quantified; and (2) for rocks in which surface conduction is predominant there is no direct relation between conductivity, pore pressure and drained fluid volume; this implies that the conduction mechanism controls the pattern of electrical conductivity variations as steam saturation changes.     

Geochemical interpretation of long-term variations in rare earth element concentrations in acidic hot spring waters from the Tamagawa geothermal area,Japan

The rare earth elements (REE) concentrations in the waters of Obuki hot spring, Tamagawa geothermal system, Akita Prefecture, Japan, have been determined in order to investigate their long-term variations over a 30-year period. The temporal patterns of REE and SO₄²⁻ concentrations are synchronous. Leaching experiments using source rock demonstrated that the relatively high REE concentrations in the waters were likely the result of dissolution of near-surface rocks by the acidic waters. The non-magnetic mineral group, enriched in light rare earth elements (LREE) and Eu(II), is easily attacked by the acid solution. The LREE will be selectively dissolved from the non-magnetic mineral group when the SO₄²⁻ concentration is increased by SO₂ derived from magmatic gases.     

基于水气两相流的降水渗水桩渗水性分析

渗水桩是一种可以提高地表降雨入渗效率的设施,主要应用于海绵城市建设。渗水桩通过改变地表透气边界,降低土体内孔隙气压力,促使雨水快速入渗,达到"排气减压、促进入渗"的目的。基于水气两相流理论,采用数值模拟方法分析渗水桩的渗水性。结果表明,土体埋设渗水桩可以显著减小孔隙气压力,提高地表入渗率;渗水桩渗水性在中锋型降雨时发挥最优;桩材料的饱和渗透系数越大土壤累积入渗量越大,增长率呈减速增长;保证体积不变渗水桩由窄变宽更利于雨水入渗,超过宽深比阈值后,渗水桩的促渗效果无显著变化。渗水桩有利于提高雨水入渗量,降低地表径流量,研究成果为渗水桩的适宜条件、材料选择及几何形态的设计提供了依据。     

土石坝原型观测资料分析方法的研究

基于土石坝变形和孔隙水压力产生机理,提出了新的土石坝变形和渗流统计模型及土石坝反馈分析的基本原理和方法,并通过工程实例得到了验证。     

Effect of supercritical CO2 as the organic solvent on cap rock sealing performance for underground storage

Supercritical CO₂ fluid is capable of extracting organic matter from rocks. Although the sealing performance of cap rock is essential for CO₂ underground storage, typical cap rock such as shale or mudstone usually contains organic matter. To determine how well cap rocks can seal supercritical CO₂, cap rock samples from the Nagaoka injection test site were treated with supercritical CO₂, and then the porosity and pore radius distribution of the samples were measured by mercury porosimetry. The results showed that the pore radius distributions slightly shifted to a larger size after treatment, while the porosity and permeability changed less than 1%.