Nanoemulsions have the potential to efficiently remove oil- based drilling fluids (OBDFs) due to their particular structure and properties. However, the oil phase in nanoemulsions is not compatible with cement slurries. Whether this will cause contamination of cement slurry is an issue worth discussing. In this paper, the potential contamination of cement slurry by nanoemulsions and the corresponding mechanism are discussed. The results show that the addition of nanoemulsion will not cause the thickening of cement slurry but will slightly affect the mechanical properties of hardened cement. When the cement slurry is mixed with 6.375 wt% nanoemulsion, the compressive strength and elastic modulus of hardened cement decrease by 8.9 and 14.9%, while the permeability increases by 11.8%. The mixing of nanoemulsions does not affect the hydration of cement slurry, but the oil droplets in the emulsions will lead to the formation of tiny pores in the hardened cement, which would adversely affect the mechanical properties of hardened cement. The oil droplets in nanoemulsion are coated by surfactants, so it does not affect cement hydration. The oil droplets are small and evenly distributed, which can reduce the influence of nanoemulsion on the microstructure of hardened cement. The stability of emulsion droplet in cement slurry is important but easy to be ignored. The possibility of incompatibility between nanoemulsion and cement slurry can be reduced by reducing the adsorption of surfactants. Nanoemulsions would maintain good stability under the function of surfactant interfacial film and yield stress of cement slurry.

Summary In the full life cycle of a well, thermal and mechanical loads may yield serious issues for the cement sheath integrity. However, the information for the integrity assessment, such as temperature and strain, is difficult to acquire underground. In this study, a full-scale experimental facility is used, allowing us to mimic the casing-cement sheath-formation (CCSF) system of a well. The system is monitored by fiber Bragg grating (FBG), enabling a real-time, high-accuracy, nondestructive measurement of temperature and strain inside the cement sheath in the sequence of setting and completion stage. Our observation reveals that the temperature of the cement sample cured in the mold is 22.3°C higher than the curing temperature; however, this temperature difference is not observed in the cement sheath cured in the CCSF system. This implies that the data obtained from the cement sample may overestimate the early-age performance of the cement sheath. Besides, the FBG measures a free strain of the tested cement during the hydration to be −370 με. This shrinkage can yield an internal stress in the CCSF system, which leads the cement sheath to swell circumferentially during the setting stage. During the completion stage, when the cement sheath is subjected to cyclic loading at three casing pressure levels, (i i.e., 10, 20, and 50 MPa), the maximum increment of circumferential strain reaches 160, 270, and 850 με, respectively. A plastic strain is observed for the 50 MPa pressure level, but not for the two other pressure levels (10 and 20 MPa). Unlike the observations in cyclic loading tests on cement samples, the plastic strain in the CCSF system accumulates linearly in the first 10 cycles and then increases slowly afterward. This difference is suggested to be attributed to the redistribution of internal stress along with the accumulation of plastic strain. Finally, the strains measured by the FBG are validated by the simulation, demonstrating the promising applicability of the FBG technology for monitoring the integrity of cement sheath.

为明确共聚物型油井水泥浆降失水剂的构效关系以及指导新型抗超高温耐盐降失水剂的分子结构设计,通过分子动力学模拟和实验相结合的方法研究了侧链结构对共聚物型降失水剂性能的影响及其抗温耐盐作用机理.实验结果表明,刚性苯环侧基的引入降低了 240℃养护后淡水/饱和盐水水泥浆的API失水量,表现出优异的抗超高温耐盐性能.通过分子动力学模拟结果表明,刚性苯环侧基的引入增大了共聚物链段的回转半径,并减弱大量反离子(Na+和Ca2+)存在时对共聚物功能基团的去水化作用.这有利于降失水剂在水泥颗粒表面的吸附和水化,并充分发挥其原有使用效能.

目的 提高页岩气井多级压裂过程中水泥环界面完整性.方法 针对4种在页岩气井中使用的水泥浆体系,基于水泥环完整性评价装置,开展在循环压力条件下水泥环界面完整性实验.采用高精度流量计、扫描电镜和核磁共振等监测手段,定量检测环空气窜速率,探索水泥环在加载前后的微观结构变化.根据实验装置基础参数,采用有限元方法模拟循环加载过程水泥环界面的损伤演化情况.结果 常规水泥浆、18％(均为质量分数)胶乳剂水泥浆、36％胶乳剂水泥浆、18％胶乳剂加1％增韧剂水泥浆,其环空气窜速率分别为722、300～677、20～45、10～25 mL/min.经循环载荷作用后,常规水泥浆在水泥环本体出现明显径向裂缝和界面微环隙,且水泥浆水化产物较疏松;36％胶乳剂水泥浆仅在水泥环界面产生较小的微环隙,水化产物在界面处较致密,水泥石孔径较小.在循环载荷作用下,水泥环界面孔隙显著增加,界面处产生塑性应变并不断增加.结论 胶乳剂和韧性剂材料可有效填充水泥颗粒之间的间隙,降低水泥石孔径尺寸.胶乳剂通过改善水泥环的微观形态结构,避免在本体产生裂缝,提高了界面密封性能.增韧剂对水泥颗粒产生较强的粘结作用,与胶乳剂的配合使用进一步增强了水泥环界面的密封效果,两者共同作用可显著提升水泥环空密封能力.在循环载荷作用下,水泥环界面易形成微环隙,为环空气体提供了窜流通道,造成环空带压.现场采用添加18％胶乳剂加1％增韧剂的韧性水泥浆体系开展固井施工,水泥石力学性能能够满足水泥石强度大于30 MPa和弹性模量小于7 GPa的性能要求.同时,使用韧性水泥浆的井段固井质量也较好,后续压裂施工过程也未见环空带压问题.通过合理优选韧性水泥浆添加剂含量,能够为环空提供良好的密封效果,提升水泥环的密封完整性.

Abstract Oil well cement additives applied in high-temperature environments play an increasingly important role in well cementing work. In this study, a ternary copolymer LNS-1 consisting of sodium styrene sulfonate (SSS), maleic acid (MA), and N-vinylcaprolactam (NVCL) was designed and synthesized using potassium persulfate as an initiator via free radical aqueous solution copolymerization, which was then used as a retarder additive for oil well cement under high-temperature conditions. The structure and performance of copolymer LNS-1 was assessed via gel permeation chromatography, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance hydrogen spectrum, Thermogravimetric analysis, and scanning electron microscopy analysis. To study the effect of the retarder on cement slurry properties, the performance of the slurry with LNS-1 was tested. The experimental results demonstrate that LNS-1 was successfully synthesized with excellent retarding ability, thermal resistance, and outstanding suspension; thus, the copolymer can serve as an excellent retarder for oil well cement. Through exploration, it is found that the mechanism of the retarder mainly includes adsorption – membrane layer mechanism and chelation – covering mechanism. NVCL exhibits good complexation, adsorption, hydrolysis stability, and thermal stability. It contains three lone pairs of electrons, which allow the NVCL to chelate Ca2+ that in the liquid phase of the cement. The number of calcium ions is therefore reduced in the cement liquid phase, and cement hydration is inhibited to a certain extent, contributing to a longer hydration process. Graphical Abstract

A new scheme for controlling the rheological properties and stability of oil-in-water nanoemulsions is presented based on the polymer-surfactant self-assembly in solution. Specifically, amphiphilic property, hydrophobic association and thermo-responsive behavior is imparted to the polymer by using surfactant as a main function monomer to introduce hydrophilic and hydrophobic groups on the polymer. The polymer can cooperate with the surfactant to form oil-water interfacial film without compromising nanoemulsion formation based on its self assembly properties. And there can be a moderate increase of the association between the hydrophobic groups on different polymers with increasing temperature based on their hydrophobicity. These behaviors will affect the rheological properties and stability of the nanoemulsion. The thermo-association mechanism of polymer, interaction between polymer and surfactant, and the effects of the polymer on nanoemulsions were analyzed. Test results show that, the thermo-association occurs when the polymer concentration is greater than 0.2%, and the association begins to be obvious when the temperature is higher than 50 degrees C, which would increase the viscosity of solution. The thermo-association may be attributed to the fact that the curled side chains of the polymer stretch and the hydrophobically association is intensified under higher temperature. The self-assembly of polymer and surfactant increase the interface film dilational modulus of the emulsions, which is conducive to the stability of nanoemulsion droplets. This polymer and the thermo-association mechanism could be applied in the study of smart emulsion and temperature-resistant emulsion.

Sustained casing pressure (SCP) was an urgent problem to be solved during shale gas exploration and development. To cope with the issue of SCP, a method of establishing gas channeling barrier was proposed, and the location of the barrier was optimized, considering engineering and geological factors. A series of tests, containing uniaxial/triaxial compression tests and cyclic loading-unloading tests, were carried out to evaluate the accumulated plastic strain. Also, a full-scale cement sheath sealing integrity evaluation device was employed to verify the appearance of the micro-annulus. Computed tomography scan and nuclear magnetic resonance tests were performed to measure and analyze the distribution of microcracks and pores in the cement sheath after cyclic loading-unloadings. Numerical models of the wellbore assembly were established, which considered wellbore structures of different intervals of an actual deep shale gas well. Research findings indicated that after loading and unloading a certain number of times, the accumulation of plastic strain showed an increasing trend with the increase of the measured depth in the vertical section, but decreased with the rise of the measured depth in the horizontal section. The method of setting gas channeling barrier was proposed and could be used to avoid SCP by using the cement slurry with low elastic modulus, which could significantly reduce the cost of cementing operation. Many factors, including the non-uniform in-situ stress, wellbore structure, fracturing stage number, casing internal pressure, and formation mechanical properties were considered to establish the optimization method of barrier locations, and this method was verified by using the logging data of an actual well as well as the engineering and geological data.

为实现超深井与复杂井超高温固井水泥浆体系的构建目标,突破常规固井水泥浆降失水剂的超高温控失水瓶颈,研制开发了超高温水泥浆降失水剂F-SHT,并对其进行了结构表征与性能评价.结果表明,F-SHT的数均分子量为21 475 Da,表观黏度低,不影响水泥浆的配制;在温度达到294℃时开始发生明显热失重,表明其分子链热稳定性良好;有效控失水温度可达240℃且可抗饱和盐水,采用水泥浆静态失水量评价方法,测得240℃/6.9 MPa下饱和盐水水泥浆API失水量为38 mL.测试了 F-SHT在水泥浆体系中的综合性能,停开机、稳定性与API失水评价结果均合格.F-SHT在河探1井Φ177.8 mm尾管固井中成功应用,结果表明F-SHT现场适应性良好,固井质量良好,同时为超深层油气资源的勘探开发提供了有力支撑.

Reasonable placement of casing centralizers is the key to control casing eccentricity and ensure displacement efficiency, especially in the highly-deviated wells. Therefore, this paper proposed a casing eccentricity limit model for casing eccentricity control. The calculation method of casing eccentricity limit in the eccentric annulus, which can ensure that all the drilling fluid in eccentric annular can be displaced, was established considering the borehole size, wellbore deviation angle, and the performance of displacement fluid and displaced fluid. And the effect of wellbore deviation angle, dynamic shear of cement slurry, yield value of drilling fluid, and their density difference on eccentricity limit were studied. Results show that the eccentricity limit is controlled by many factors. Increasing the well-deviated angle and yield value of drilling fluid would reduce the eccentricity limit while increasing the dynamic shear force of cement slurry and the density difference between cement slurry and drilling fluid would increase the eccentricity limit. Then, the placement of casing centralizers in highly-deviated well was optimized based on the casing eccentricity limit and bend beam theory. Centralizers can be placed according to specific borehole conditions, and centralizers can be rationally added to ensure casing central degree in the section with large deviation angle. The field tests proved that the eccentricity limit model helped increase the cementing quality in highly-deviated well, indicating that the casing eccentricity was controlled reasonably.

The temperature is as high as 500 °C at the bottom of shale oil wells during in-situ development. During shale oil production, the fluids with high temperature are transmitted to the wellhead, and the wellbore temperature will rise extremely, which greatly affects the cement sheath integrity. In this paper, the linear expansion coefficient of cement stone under the temperature of 500 ℃ were measured. Based on the experimental data and the field data of shale oil well, the stage finite element modeling method was adopted to establish a casing-cement-formation (CCF) model considering the temperature and pressure coupling. The results revealed that the linear expansion coefficient of cement stone decreases linearly with the increase of temperature. When the temperature was less than 250 ℃, the cement stone expanded. However, when the temperature exceeded 250 ℃, it shrank. The maximum shrinkage ratio can be 25 × 10–6/℃ for the temperature of 500 ℃. The circumferential stress of the inner wall of cement sheath first increased rapidly, then slowly decreased to be stable. The larger the cement stone shrink ratio was, the greater the circumferential stress was. The maximum circumferential stress can exceed 10 MPa for the shrink ratio of 25 × 10–6/℃. It can be concluded that the circumferential stress appears in a tensile state under high temperature conditions, which can easily lead to the failure of the cement sheath seal. The strength of the cement stone should be considered when designing the cement slurry property. In addition to the decay performance, the expansion of the cement stone should also be designed to ensure that the cement stone does not shrink when subjected to high temperature conditions.

The viscosity of cement slurry decreases when the temperature rises, resulting in bleeding and sedimentation issues caused by high temperatures. The available viscosity modifying admixtures (VMAs) usually thicken cement slurry under low temperatures but their performances deteriorate under higher temperatures. This study proposes a novel thermo-thickening VMA (i.e., a thermo-thickening polymer with strong hydrophobicity, HTP); its thickening ability will become stronger with an increase in temperature. HTP helps to compensate for the consecutive viscosity reduction of cement slurry due to temperature increases and yields a constant-consistency cement slurry over a wide temperature range (up to 165 degrees C). Most importantly, HTP is able to slash the bleeding water exuded from cement slurry and eliminate the compressive-strength/density differences among the upper-middle-lower hardened cement paste segments, resulting in a significant improvement in the settlement stability of cement slurry. Microscopic observations reveal that the HTP molecules may fully stretch in the cement slurry and integrate with cement hydration products, contributing to the uniform micromorphology of hardened cement paste. The novel thermo-thickening VMA imposes a limited impact on the compressive strength, fluid loss and thickening time of cement slurry and is very compatible with various cement additives. Finally, the high-temperature high-density cement slurry system containing HTP exhibits a constant consistency until rapid setting behavior, which suggests that it has good potential for field applications. (c) 2021 Elsevier Ltd. All rights reserved.

Effective removal of mudcake from the wellbore before cementing is critical to developing an excellent bond between cement and formation. The application of spacer can remove mudcake effectively. The evaluation of mudcake removal efficiency is significant to the design of spacer. The methods proposed by scholars have limits on the development of mudcake and the simulation of the flushing process. For this paper, a novel apparatus used to test mudcake removal efficiency was designed. A novel experimental method for mudcake removal efficiency of spacer was proposed. The influence factors of mudcake removal efficiency are discussed. The method can evaluate the flushing efficiency quantitatively and provide guidance for designing of spacer.

深层超深层已成为中国油气增储上产的重要领域,但油气勘探开发难度加大,尤其是深井超深井超高温复杂工况下固井作业安全和固井质量难以保障,对超高温固井水泥浆技术提出了严峻的挑战.其中,缓凝剂是保障深井超深井固井作业安全的关键材料,直接决定着固井作业的成败.然而,目前国内聚合物缓凝剂耐温能力不超过200℃,无法满足井底循环温度超过200℃的固井需求,超高温缓凝剂仍主要依赖进口.为了给深层超深层油气勘探开发提供技术支撑,通过分子结构优化设计、耐温抗盐基团有效介入,采用自由基水溶液聚合方法制备出超高温固井水泥浆缓凝剂DRH-3L,并对其综合性能进行了评价.研究结果表明:①DRH-3L适用温度范围广(70～220℃),缓凝性能优异,220℃下水泥浆稠化时间在500 min以上;②水泥浆稠化时间与加量、温度呈良好的线性关系;③与常用降失水剂配伍性良好;④在50～120℃大温差条件下,水泥石强度发展迅速且对高温水泥石力学强度发展无不利影响.结论 认为,所研发的新型水泥浆缓凝剂在超高温深井超深井等复杂井固井中具有良好的应用前景.

Fiber Bragg grating (FBG) sensing technology is a new structure monitoring technology. Aiming at the influence of hydration and cyclic casing pressure on cement sheath integrity in real wellbore conditions, firstly, the temperature and strain variation regularities of cement sheath in setting stage are investigated by FBG and a test device for evaluating cement sheath integrity. Then the circumferential strains of cement sheath and casing under cyclic casing pressure are studied. Furthermore, the applicability of FBG technology is verified. The results show that the temperature and strain of cement slurry change rapidly in 5 hours after pouring. In cyclic casing pressure stage, circumferential strains of cement sheath and casing are both tensile strains. In addition, circumferential strain of cement sheath and casing increases with the increase of casing pressure. The FBG sensors have high sensitivity that can reflect the change of casing pressure in time. The FBG technology is a scientific temperature and strain monitoring method for cement sheath. The results of this study are of great significance to the application of FBG technology for cement sheath integrity.

新材料与石油工程技术的融合发展将驱动技术创新,甚至带来颠覆性的技术变革,成为油气勘探开发工程技术新利器,有利于推动油气增储上产、降本增效.新材料在生物医药、航天航空、国防军事、机械设备、油气勘探等领域发挥巨大作用,国内外石油公司和石油工程技术服务公司更加注重技术创新,不断加大新材料、新技术研发和应用力度.当前,石油工程技术逐渐向智能化、实时化、自动化方向发展,亟须新材料提供技术支撑以及多学科、多领域跨界融合.就功能而言着重从智能化、自适应、广谱化3个方面对新材料研究进展进行论述,为石油工程新材料研发提供新思路、新方法.

Excellent physical and chemical properties of halloysite nanotube make it potential to reinforce cement composites. In this study, effects of halloysite nanotube on mechanical properties of oil well cement were investigated. The results showed that the compressive and flexural strength of cement with 3% halloysite nanotube was increased by 40.8% and 49.2%, respectively and the elasticity modulus decreased by 20.01% after curing for 28 days, which demonstrated that halloysite nanotube cement had high strength and good toughness. TG-DTA, SEM, XRD, MIP tests were carried out to study the hydration products and microstructure changes in cement samples after adding halloysite nanotube. Optimized hydration products, lower permeability up to 38.82%, cross-linking and denser microstructure all contributed to excellent mechanical properties of oil well cement with halloysite nanotube. (C) 2020 Elsevier Ltd. All rights reserved.

针对蒸汽驱稠油热采井井筒温度高达350℃,常规加砂水泥在高温下结构疏松,抗压强度低,铝酸盐及磷铝酸盐水泥成本高及与硅酸盐水泥污染严重等问题.通过探索高温增强作用机理,开发出高温特种增强材料,结合配套硅酸盐外加剂,研发出综合性能良好的抗350℃高温硅酸盐基水泥浆,并进行了水泥浆综合性能测试、XRD晶相组分分析、SEM晶相形貌分析,结果表明,抗350℃高温硅酸盐基水泥浆的沉降稳定性小于0.02 g/cm3,游离液量为0,API失水量小于50 mL,流动度大于20 cm,70℃水泥石24 h抗压强度大于14 MPa,且3轮次下350℃高温水泥石强度大于40 MPa,长期强度发展稳定,满足稠油热采井的工程应用需求,突破了超高温下硅酸盐水泥强度低、铝酸盐及磷铝酸盐水泥必用的困境,促进了超高温水泥浆技术进步.

The conventional oil-well cement dispersant has the characteristics of poor dispersion at high temperature, poor compatibility with other additives, and environmental pollution during the production process. In this article, with ultra-early strong polyether monomer, acrylic acid, 2-acrylamine-2-methylpropyl sulfonic acid, sodium methacrylate as copolymer monomers, an environmentally friendly polycarboxylic acid dispersant, DRPC-1L, was prepared by the aqueous solution free-radical polymerization. The chemical composition and thermal stability of the synthetic copolymer were characterized by FTIR and TGA techniques. The evaluation results show that DRPC-1L has a wide temperature range (30~210 °C), good salt-resistance and dispersing effect. It can significantly improve the rheological performance of cement slurry, and it is well matched with oil-well cement additives such as fluid loss agent, retarder and so on. Moreover, it is beneficial to the mechanical strength development of set cement, especially the early compressive strength. It can also inhibit the abnormal gelation phenomenon of cement slurry, flash set, that occurs during high temperature thickening experiments, which plays an important role in enhancing the comprehensive performance of cement slurry. Consequently, the novel polycarboxylic acid dispersant has good application prospects in deep and ultra-deep wells cementing.

Drilling fluid additive is an important factor of contamination between cement paste and drilling fluid, in which PAC is the most significant one. This work investigated the effects of PAC on the hydration process and properties of cement by using X-ray diffraction (XRD), Different scanning thermal analyzer (DSC), Fourier transform infrared spectrometer (FTIR) and Zeta-potential. Based on the results of Environment Scanning Electron Microscopy (ESEM), the evolution of the microstructure of polymer-cement could be well explained by Ohama model. Combining with the rheological and mechanical measurements, it's surmised that H2O could bind with –OH of PAC through hydrogen bond to form cross-linking structure and trapping free water, which lead to the deterioration of rheological properties and inhibit the hydration process, accompanied by reduction of C-S-H content to decrease the compressive strength. Fe3+ and Al3+ released by cement hydration induced PAC to form gel through the formation of dynamic ion bonds and hinder the homogeneous dispersion of cement particles, proving that the deterioration of rheology properties is result of coupling effects of hydrogen and ion bond. According to the mechanism, using Al3+ and Fe3+ metal masking agent or raising pH could mitigate the contact contamination and increase the safety of cementing.

地层类型制约地应力对固井水泥环的力学作用方式,明确地层类型对水泥环应力和结构完整性的影响特征,是建立井筒完整性保障技术的基础.以蠕变、弹性、刚性地层为研究对象,建立套管—水泥环—地层固结体有限元力学模型,分析地层类型、施工项目等对水泥环界面应力的影响.结果表明:蠕变地层中,地应力增加,界面接触压力增大;弹性、刚性地层中,地应力对界面应力无影响.蠕变、弹性地层中,地层弹性模量对界面应力的影响与地层、应力类型有关;刚性地层中,地层弹性模量对界面应力无影响.弹性地层中,加载时,水泥环易发生周向拉伸破坏,危险部位为窄间隙内界面.套管试压施工时,存在水泥环拉伸破坏的危险,危险井段为井口及深部弹性地层井段;储气库井注气施工时,存在的主要危险为加载过程中弹性地层井段水泥环本体拉裂破坏.