Research progress on temperature field evolution of hot reservoirs under low-temperature tailwater reinjection

This paper focuses on the study of the evolutionary mechanism governing the temperature field of geothermal reservoir under low-temperature tailwater reinjection conditions,which is crucial for the sustainable geothermal energy management.With advancing exploitation of geothermal resources deepens,precise understanding of this mechanism becomes paramount for devising effective reinjection strategies,optimizing reservoir utilization,and bolstering the economic viability of geothermal energy development.The article presents a comprehensive review of temperature field evolution across diverse heterogeneous thermal reservoirs under low-temperature tailwater reinjection conditions,and analyzes key factors influ-encing this evolution.It evaluates existing research methods,highlighting their strengths and limitations.The study identifies gaps in the application of rock seepage and heat transfer theories on a large scale,alongside the need for enhanced accuracy in field test results,particularly regarding computational effi-ciency of fractured thermal reservoir models under multi-well reinjection conditions.To address these shortcomings,the study proposes conducting large-scale rock seepage and heat transfer experiments,coupled with multi-tracer techniques for field testing,aimed at optimizing fractured thermal reservoir models'computational efficiency under multi-well reinjection conditions.Additionally,it suggests integrat-ing deep learning methods into research endeavors.These initiatives are of significance in deepening the understanding of the evolution process of the temperature field in deep thermal reservoirs and enhancing the sustainability of deep geothermal resource development.

Progress and prospect of mid-deep geothermal reinjection technology

Mid-deep geothermal reinjection technology is crucial for the sustainable development of geothermal resources,which has garnered significant attention and rapid growth in recent years.Currently,various geothermal reinjection technologies lag behind,lacking effective integration to address issues like low reinjection rates and thermal breakthrough.This paper reviews the basic principles and development history of mid-deep geothermal reinjection technology,focusing on various technical methods used in the process and analyzing their applicability,advantages,and disadvantages under different geological conditions.It highlights the unique challenges posed by deep geothermal resources,including high temperature,high pressure,high stress,chemical corrosion,and complex geological structures.Additionally,it addresses challenges in equipment selection and durability,system stability and operation safety,environmental impact,and sustainable development.Finally,the paper explores future directions for mid-deep geothermal reinjection technology,highlighting key areas for further research and potential pathways for technological innovation.This comprehensive analysis aims to accelerate the advancement of geothermal reinjection technology,offering essential guidance for the efficient reinjection and sustainable development of geothermal resources.

Study on the geothermal production and reinjection mode in Xiong County

The large karst geothermal field of Xiong County,which is located to the south of geothermal field in Niutuozhen,features huge geothermal resources and favorable condition for development and utilization.Because of the long-term extensive production,the pressure of geothermal reservoir continues to decline and some geothermal wells even face the danger of scrapping.To relieve the fall in pressure of geothermal reservoir and achieve the sustainable development and utilization of geothermal field in the long run,reinjection experiment is conducted in the geothermal field of Xiong County and a three-dimensional hydrothermal coupled numerical model was constructed.The reinjection experiment showed that the mode of one production well and one reinjection well can be achieved in this geothermal field.The numerical simulation is used to forecast and compare the change in pressure field and temperature field under different production and reinjection modes and concludes that the most opotimized production and utilization mode is the concentrated production-reinjection mode,and the most opotimized production-reinjection combination mode is the shallow production and shallow reinjection mode which can ensure the sustainable development and utilization of geothermal resources in the long run.

Numerical Analysis of a Spiral-groove Dry-gas Seal Considering Micro-scale Effects

A dry-gas seal system is a non-contact seal technology that is widely used in different industrial applications.Spiral-groove dry-gas seal utilizes fluid dynamic pressure effects to realize the seal and lubrication processes,while forming a high pressure gas film between two sealing faces due to the deceleration of the gas pumped in or out.There is little research into the effects and the influence on seal performance,if the grooves and the gas film are at the micro-scale.This paper investigates the micro-scale effects on spiral-groove dry-gas seal performance in a numerical solution of a corrected Reynolds equation.The Reynolds equation is discretized by means of the finite difference method with the second order scheme and solved by the successive-over-relaxation（SOR） iterative method.The Knudsen number of the flow in the sealing gas film is changed from 0.005 to 0.120 with a variation of film depth and sealing pressure.The numerical results show that the average pressure in the gas film and the sealed gas leakage increase due to micro-scale effects.The open force is enlarged,while the gas film stiffness is significantly decreased due to micro-scale effects.The friction torque and power consumption remain constant,even in low sealing pressure and spin speed conditions.In this paper,the seal performance at different rotor face spin speeds is also described.The proposed research clarifies the micro-scale effects in a spiral-groove dry-gas seal and their influence on seal performance,which is expected to be useful for the improvement of the design of dry-gas seal systems operating in the slip flow regime.

Formation blockage risk analysis of geothermal water reinjection:Rock property analysis,pumping and reinjection tests,and long-term reinjection prediction

The blockage induced by particle migration and deposition is one of the main reasons for the decrease of reinjection capacity in the porous geothermal reservoir with a low and medium temperature.In this paper,a new drilled geothermal well in Xining basin China is taken as an example to investigate the formation blockage risk due to the movable clay and sand particles in pores.The physical properties of the reservoir rocks were analyzed,a series of pumping and reinjection tests were conducted,and the longterm reinjection performance of the well was predicted by numerical simulation based on the test fitting.The results show that the geothermal reservoir rocks are argillaceous and weakly cemented sandstones with a content of movable clay and sand particles up to 0.18–23.42 wt.%.The well presented a high productivity of 935–2186 m3?d-1 at a pressure difference of 0.7–1.62 MPa in the pumping tests associated with a large amount of clay and sand particles produced out,while in the reinjection test,only a low injectivity of 240–480 m3?d-1 was observed at an injection pressure of 0.2–0.6 MPa with the clay and sand particles near the wellbore move into deep.According to the prediction,under conditions of a blockage risk,the injectivity of the well will start to decline after 100 days of injection,and in the third year,it will decrease by 59.00%–77.09%.The influence of invasion of pretreated suspended particles and scale particles can be neglected.Under conditions of a high blockage risk,the injectivity of the well will decrease significantly in the first 20–30 days,with a decline of 75.39%–78.96%.Generally,the higher the injection pressure or rate,the greater the decrease in injectivity of the well caused by particle blockage.Pump lifting is an effective measure to remove the well blockage which can be used regularly.

Clogging mechanism in the process of reinjection of used geothermal water: A simulation research on Xianyang No.2 reinjection well in a super-deep and porous geothermal reservoir

In the process of geothermal exploitation and utilization, the reinjection amount of used geothermal water in super-deep and porous reservoir is small and significantly decreases over time. This has been a worldwide problem, which greatly restricts the exploitation and utilization of geothermal resources. Based on a large amount of experiments and researches, the reinjection research on the tail water of Xianyang No.2 well, which is carried out by combining the application of hydrogeochemical simulation, clogging mechanism research and the reinjection experiment, has achieved breakthrough results. The clogging mechanism and indoor simulation experiment results show: Factors affecting the tail water reinjection of Xianyang No.2 well mainly include chemical clogging, suspended solids clogging, gas clogging, microbial clogging and composite clogging, yet the effect of particle migration on clogging has not been found; in the process of reinjection, chemical clogging was mainly caused by carbonates(mainly calcite), silicates(mainly chalcedony), and a small amount of iron minerals, and the clogging aggravated when the temperature rose; suspended solids clogging also aggravated when the temperature rose, which showed that particles formed by chemical reaction had a certain proportion in suspended solids.

Flow Dynamics of a Spiral-groove Dry-gas Seal

The dry-gas seal has been widely used in different industries. With increased spin speed of the rotator shaft, turbulence occurs in the gas film between the stator and rotor seal faces. For the micro-scale flow in the gas film and grooves, turbulence can change the pressure distribution of the gas film. Hence, the seal performance is influenced. However, turbulence effects and methods for their evaluation are not considered in the existing industrial designs of dry-gas seal. The present paper numerically obtains the turbulent flow fields of a spiral-groove dry-gas seal to analyze turbulence effects on seal performance. The direct numerical simulation （DNS） and Reynolds-averaged Navier-Stokes （RANS） methods are utilized to predict the velocity field properties in the grooves and gas film. The key performance parameter, open force, is obtained by integrating the pressure distribution, and the obtained result is in good agreement with the experimental data of other researchers. Very large velocity gradients are found in the sealing gas film because of the geometrical effects of the grooves. Considering turbulence effects, the calculation results show that both the gas film pressure and open force decrease. The RANS method underestimates the performance, compared with the DNS. The solution of the conventional Reynolds lubrication equation without turbulence effects suffers from significant calculation errors and a small application scope. The present study helps elucidate the physical mechanism of the hydrodynamic effects of grooves for improving and optimizing the industrial design or seal face pattern of a dry-gas seal.

An Experimental Study on Bio-Clogging in Porous Media during Geothermal Water Reinjection

To study the mechanism of bio-clogging in a porous medium during the reinjection of geothermal water and to improve reinjection efficiency, an indoor one-dimensional reinjection experiment was conducted based on the geological model of the geothermal reinjection demonstration project in Dezhou City. The biological process of porous media clogging was investigated by analyzing the variation of permeability within the medium, the main indexes of nutrient salts, and the content of extracellular polymeric substances (EPS). High-throughput sequencing, based on 16S rRNA, was used to analyze the characteristics and succession of microbial communities during the reinjection of geothermal water. The results of the study show that significant bio-clogging occurs during the reinjection of geothermal water, with an increase in the heterogeneity of the thermal reservoir medium, and a decrease in permeability. The extent of clogging gradually reduces with an increase in seepage path. Thus, thermal reservoir clogging is more serious closer to the water inlet. With an increase in the duration of reinjection, the permeability of the porous medium undergoes three stages: “rapid”, “decline-slow”, and “decrease-stable”. The results show that the richness and diversity of the bacterial community increase and decrease, respectively, during the reinjection process. Bacterial community succession occurs, and the bacterial communities mainly include the Proteobacteria and Bacteroidetes phyla. Pseudomonas and Devosia are respectively the dominant bacteria in the early and late stages of geothermal water reinjection.

Reinjection Tests in Bedrock Geothermal Reservoir of Tianjin

By the end of 2002, there are about 219 production wells (including 12 reinjection wells) in Tianjin. The annual production rate is 1.5×10 7 m 3 and the reinjection rate is 1.66×10 6 m 3. The main side effect anticipated from reinjection is the cooling of the reservoir. It is necessary to estimate the thermal breakthrough time in different distances between injection production wells. This paper describes the 2 D mass and heat transfer in the heterogeneous fractured rocks. The equations that arise for each grid block must be linearized. The main reinjection model is simulated by a program of the TOUGH2 to analyze the change of the temperature field and predict the pressure and heat break through. The tracer test is very important for understanding the transportation pathway and transport channel/space in the doublet system, and estimating the possible cooling resulted from the injection processes.

A New Method for the Dynamic Reserves of Gas Condensate Reservoir Using Cyclic Gas Injection Based on the Effects of Reinjection Ratio and Water Influx

As we all know, cyclic gas injection is one of the most effective development methods to improve condensate oil recovery. When dealing with the calculation of the reserves, the injection-production differences and water influx create great influence on the accuracy. Based on the existing research, we proposed a new material balance equation which considered the differences of composition between produced and injected fluids and the effect of water influx, and a solution was provided in this paper. The results of the method are closer to the actual situation because they are built on the law of conservation of mass, and the using of curve fitting method can not only avoid the use of water influx coefficient but also obtain the water influx rate and reserves at the same time. The YH-23 gas condensate reservoir is taking as a typical subject to do the research, which has been exploited by cycle gas injection for 14 years. Three different methods are used to calculate the reserves, and the results show that the method proposed in this paper has minimum error of 2.96%.

基于“深地-井下-地面”联动的煤矿矿井水处理利用模式初探

煤矿矿井水的高效低耗处理有助于推动煤炭资源的安全、高效开采。现有矿井水井下处理工艺选择受限、处理量小,地面处理占地面积大、运行成本高,矿井水处理后外排至地表又会产生高额的排水费。本文在总结分析煤矿矿井水处理技术现状基础上,提出了“深地-井下-地面”联动的煤矿矿井水处理利用模式:对矿井涌水通过“井下-地面”协同的方式进行高效低耗处理,处理后的矿井水部分用于矿区生产和矿区居民生活,其余部分则进行深地回灌或外排。首先介绍了该模式的基本原理;然后从水质、水量、水文、地质、地下建筑结构和回灌工程可行性对矿井水回灌工程的适用性进行评估和分析;最后介绍了不同水质矿井水处理技术和“井下-地面”协同处理技术体系,尤其针对回灌含水层选择、回灌施工作业、回灌试验、回灌水质模拟、回灌安全性分析等进行总结。

海上油田污水回注井高效解堵技术研究与应用

针对污水回注井酸化效果不理想的问题,利用岩心流动实验、悬浮物含量及粒径测试、X射线衍射对堵塞情况进行了分析。在此基础上,利用填砂管流动和岩心溶蚀实验研发了一套兼具污油清洗与高溶蚀率的酸液体系。此外,结合储层特征优化了酸液置放工艺。结果表明,污油和固体悬浮物在近井地带形成的复合堵塞物是造成储层堵塞的主要原因;1%水基清洗剂洗油率达到86.44%,高溶蚀酸对固体悬浮物溶蚀率达到89.77%,二者复配体系能够快速瓦解油泥小球;化学微粒分流剂可对储层形成有效暂堵分流,且酸化后自动溶解。该技术矿场应用8井次,平均视吸水指数提高1.74倍。该技术适用于污水回注井解堵,并为提高海上污水回注井酸化效果提供理论和实践依据。

世界典型高温地热田回灌经验及对谷露热田回灌井部署的启示

地热尾水回灌是地热田开发过程中必不可少的环节,对热田开发具有重要意义。对世界上不同类型高温地热田回灌策略进行系统梳理,发现不同类型地热田常采取不同的回灌策略:气相为主的气液两相地热田常进行内场回灌;液相为主的气液两相地热田和水热型地热田常采用内场回灌与外场回灌相结合的方式。重点分析与谷露地热田相似的美国Brady Hot Spring地热田、Beowawe地热田和中国羊易地热田三个水热型高温地热田在生产过程中的回灌情况,对上述地热田在回灌过程中的回灌距离、回灌深度及回灌后对热田生产的影响进行总结。上述地热田多采用同构造回灌的方式进行回灌;一般无特定的回灌距离,常采用内场回灌与外场回灌相结合的方式进行;回灌目的层常选择渗透性好的断裂构造;回灌深度以大于500 m的深层回灌为主。这些热田在回灌过程中,为了达到良好效果,需要平衡生产区的压力下降和热突破之间的关系。结合谷露地热田实际地质情况,认为谷露地热田应该采取同构造回灌,且采用内场回灌与外场回灌相结合的深层回灌方式。初步在热田生产区1 km以外的位置选择3片回灌区域。其中回灌1区是主要回灌区域,位于热田生产区的北侧约1~1.5 km范围内。为了防止发生热突破,需要在回灌井实施过程中,进行回灌试验,尽早确定回灌井与生产区之间的水力联系。

采灌均衡条件下地热资源潜力评价方法探讨——以雄安新区碳酸盐岩热储为例

回灌是保障地热资源可持续开发利用的关键手段,而采灌均衡条件下地热资源潜力评价方法研究对地热资源的可持续开发利用具有重要意义。本文通过引入热突破和考虑回灌条件下单井开采权益保护半径的概念,提出了回灌条件下地热资源可开采量的评价方法,并以雄安新区雾迷山组碳酸盐岩热储层为例,分别计算了未考虑回灌条件和考虑回灌条件下的地热流体可开采量、可开采热量及折合标煤量。结果显示采用开采系数法计算的未考虑回灌条件下的可开采量要远小于考虑回灌条件下的可开采量;考虑回灌条件下三种方法的结果对比为:热突破法>考虑回灌条件下单井开采权益保护半径(消耗15%)>考虑回灌条件下单井开采权益保护半径(热储温度下降2℃),考虑地热资源的可持续性以及对热储环境严格保护要求,按照考虑回灌条件下单井开采权益保护半径方法计算的雄安新区雾迷山组热储地热开采量更为适宜。目前全国各地陆续出台相关政策要求实施地热回灌,该方法的提出为科学评价各地回灌条件下的地热可开采量提供了技术支撑。

地热井砂岩热储回灌堵塞机理及解堵研究

地热井回灌是制约水热型地热持续开发的“卡脖子”难题,特别是砂岩热储的回灌更为艰难。为揭示制约砂岩热储回灌过程中面临的堵塞难题,以陕西关中渭河盆地某“一采一灌”模式砂岩地热井为例开展试验研究,探究砂岩热储回灌过程中的4类堵塞机理,并提出相应解堵措施。结果表明:碳酸盐类、部分铝硅酸盐类和铁类矿物沉淀受温度影响较大,地层温度的升高会加速其化学堵塞的形成;随温度的上升,悬浮物堵塞和化学堵塞会构成协同效应。同时悬浮物颗粒布朗运动速度也因温度上升而增大,使堵塞更严重;回灌产生气体堵塞的原因主要是:大体积气泡进入储层内部难、气泡直径与底层喉道大小相当;腐生菌和铁细菌是成微生物堵塞的主要微生物。通过加入阻垢剂可有效防止化学堵塞,采取多级过滤可减缓物理堵塞,在回灌系统中加入自动排气装置可防止气体堵塞,对尾水进行灭菌处理降低微生物堵塞风险。经过现场回暖季试验,采取的解堵措施应用于目标地热井后的回灌率达100%,降低了回灌过程中可能发生的堵塞对回灌带来的不良影响。

白洋淀地表水回灌补给深部岩溶地热储层的水化学数值模拟

以雄安新区广泛开发的深部岩溶地热储层为研究对象,利用PHREEQC模拟了采用白洋淀地表水回灌补给主力开采地热储层-蓟县系雾迷山组岩溶地热储层后的水化学组分变化以及矿物溶解沉淀量.结果表明:回灌期内从回灌井向储层内部水化学类型依次为HCO_(3)·Cl-Na·Mg,HCO_(3)·Cl-Na,Cl·HCO_(3)-Na和Cl-Na型水,呈现由补给水向储层本源水过渡的变化趋势,主要受对流弥散影响,但Mg^(2+)、Ca^(2+)、HCO_(3)^(-)还受水岩反应和pH值等因素控制,变化趋势更为复杂;回灌后矿物的溶解沉淀现象主要发生在以回灌井为中心半径为0.5m的范围内,以方解石的沉淀和白云石的溶解最为明显,整体上会引起裂隙率降低,但其变化程度有限.对岩石渗透性影响不明显.基于回灌所引起的地热储层内部变化类型,划分了4种影响带,各影响带的范围大小依次为水化学影响带、渗流影响带、温度影响带和岩石渗透性影响带.

砂岩热储回灌难点识别与应对措施探讨

砂岩热储在我国分布面积广,热储厚度大,资源储量丰富,是我国北方和西部地区地热供暖的主力热储。但砂岩热储回灌量偏小,回灌过程易衰减,难以规模化开发,这些都是现实存在的难题。已有研究成果主要集中在钻井液污染、物理堵塞和化学堵塞方面,这些都是造成砂岩热储回灌困难的常见原因。本文在充分研究油田注水技术、收集砂岩岩心实验测试和野外回灌试验资料的基础上,分析总结了天津、山东、陕西等地砂岩热储生产性回灌实际案例,认为砂岩热储孔隙直径小、孔隙喉道迂曲度大和回灌流体渗流沿程摩阻力(压耗)大是造成回灌量偏小和衰减的根本原因。主要应对措施是精确识别砂岩热储特征,扩大回灌井井径,改造热储以减小近井地带的回灌流速,抑制以速敏为主的水岩作用发生,这是今后解决砂岩热储回灌困难的关键。

尕斯高盐油藏污水配聚阳离子对聚合物溶液黏度影响的主控因素

根据青海油田尕斯区块回注污水矿化度较高的特点,以山东宝莫生产的聚合物为研究目标,系统探讨了从聚合物驱采出水中的Na^(+)、K^(+)、Ca^(2+)、Mg^(^(2+))、Fe^(2+)、Fe^(3+)等6种离子对聚合物溶液的黏度和稳定性影响的变化规律,并提供了回注污水配聚主要研究方法。结果表明:导致聚合物黏度降低的主要控制因素是高价阳离子,其影响顺序从大到小的次序是Fe^(2+)、Fe^(3+)、Mg^(^(2+))、Ca^(2+)、Na+、K+;而高价阳离子对聚合物溶液黏度稳定性影响顺序从大到小的次序则是:Fe^(2+)、Ca^(2+)(Mg^(^(2+)))、Fe^(3+)、Na^(+)(K^(+))。研究结果展示了回注污水配聚中阳离子对聚合物溶液黏度的响应机理,为聚合物驱技术提供了理论指导。

海上平台超临界CO_(2)管道泄漏扩散规律实验研究

CO_(2)封存是实现中国“双碳”目标的有效技术途径之一,海上CO_(2)封存通常依托海上油气平台管道回注,CO_(2)回注过程中可能发生泄漏而严重影响作业人员安全。以恩平15-1海上平台为研究对象,开展超临界CO_(2)泄漏扩散规律实验研究。通过缩比设计,搭建与恩平15-1相应的物理模型实验平台,利用相似理论和量纲分析方法,设计了超临界CO_(2)泄漏扩散参数,开展了海上平台管道CO_(2)在不同泄漏压力(1.5~3.0 MPa)、泄漏孔径(0.5~6.2 mm)、泄漏方向(水平、竖直、斜45°)及环境风速(0~0.5 m/s)下的相似模型实验,研究泄漏CO_(2)在平台上的扩散情况及浓度分布规律。结果表明:压力和环境风速的变化,会影响CO_(2)泄漏后的近场射流,但对其远场扩散的影响较小;CO_(2)浓度会在泄漏约20 s后达到峰值并保持稳定,不会随泄漏时间的增加而增大;泄漏口径会显著影响泄漏口轴向CO_(2)浓度的分布规律。研究结果为海上平台CO_(2)泄漏监测与安全防护设计提供了参考。