Cement Slurry Research Articles

Research and Application of Smart Temporary Plugging Gel for Small Casing Cementing in Changqing Oilfield

Abstract In response to the serious leakage and low productivity recovery rate after cement plugging during the secondary cementing process of repairing small casing in the old wells of Changqing Oilfield, this study draws on the theory of shielding and temporary plugging in the drilling process to propose an adaptive smart temporary plugging gel technology. This technology has developed a weak gel suspension base liquid and synthesized a polymer material with good viscosity, high deformability, high sealing strength, and the ability to automatically hydrate and degrade at a certain temperature. It synergistically cooperates with other auxiliary temporary plugging materials to form an adaptive and self-degrading temporary plugging gel system, which can quickly form a sealing barrier at severely leaking areas such as corroded perforations, effectively preventing cement slurry leakage during subsequent cementing processes, shortening the operation cycle, and protecting the reservoir. Experimental evaluations indicate that the gel system can withstand pressure up to 15MPa, degrades in 7-10 days, and achieves a reservoir recovery rate of over 90%, effectively achieving the goals of plugging, releasing, and minimizing reservoir pollution. It has been applied in 30 wells in the Changqing Oilfield, with a success rate of over 96% in the first plugging operation, and an average production recovery rate of over 95%, significantly protecting the oil reservoir.

Experimental and simulation study of magnesium phosphate cement two-liquid grouting materials

Magnesium phosphate cement (MPC) has a promising application in grouting. This study drew on the traditional cement-waterglass two-liquid grouting model. Creatively, the two main reaction components of MPC, dead-burned magnesium oxide and phosphate, were applied to the grouting field in a two-component liquid form. At the same time, through proportioning adjustment and experimental testing, we obtained A\B liquid components, which can be stabilized. In addition, MPC slurry was compared with the traditional grouting material, silicate cement slurry, to demonstrate its superiority. Finally, we simulated the grout diffusion process of the mixed slurry using the two-phase Darcy's law module of COMSOL Multiphysics subsurface fluids. The results show that the mixed slurry with a magnesium phosphate ratio of 1/3, a magnesium–boron ratio between 5% and 10%, and a water–cement ratio of 0.2–0.5 has better stability and mobility. Under the same fluidity, its strength is much higher than that of common silicate cement slurry and has good injectability. MPC was subjected to two-fluid grouting to take advantage of its fast-hardening and early-strengthening properties, while also improving its stability and fluidity. This study provided a theoretical foundation for the application of MPC.

Development and Evaluation of Insulation Materials for Deepwater Cementing.

Marine oil and gas resources are abundant in deepwater regions, where the shallow seabed harbors natural gas hydrate layers due to the cold temperature and high-pressure environment. Hydrates are prone to thermal decomposition, which can compromise the integrity of cement sealing and even lead to accidents like blowouts. While current low-hydrated heat cement systems mitigate hydrate decomposition from cement hydration heat during the waiting period for cementing, they do not address heat transfer from deep strata to shallow hydrate layers through fluid circulation in the tubing during deep oil and gas development. Rather than utilizing costly pipe insulation technology, adjusting the thermal conductivity of well cement emerges as a cost-effective approach to prevent heat loss in the wellbore to the hydrate layer and thus inhibit hydrate decomposition. The critical aspect lies in utilizing insulation functional materials. This study delves into the functional and structural design of insulation materials suitable for cement slurry systems in well cementing, outlining the preparation methods and processes for two insulation materials (SDBW and SDBW-II) tailored for deepwater well cementing. SDBW and SDBW-II are both nuclear shell structural materials. The core is made of high-strength hollow microspheres, produced by using a reverse suspension polymerization method to form spheres followed by high-temperature sintering. The shell consists of a wear-resistant BPA epoxy resin layer, with the surface of SDBW-II also containing highly reflective glass microspheres. Incorporating 20% of material SDBW into the cement reduces the thermal conductivity of the cement stone from 0.8 to 0.31 W·(m·K)-1 while achieving a compressive strength of 6 MPa after 24 h at 20 °C. Material SDBW-II offers both thermal resistance and reflection functions, increasing reflectivity (R) from 0.3 to 0.5. By adding 20% of this material to the cement, under the same conditions, although the compressive strength decreases to 4.2 MPa, the thermal conductivity can be reduced to 0.27 W·(m·K)-1. Furthermore, there is no significant change within 180 days, demonstrating long-term thermal insulation stability. These developed insulation materials can effectively improve the thermal insulation performance of the cement sheath, thereby maintaining the stability of the upper natural gas hydrate layer in the oil and gas production process of deepwater wells, providing an innovative solution for the long-term operation of deepwater oil and gas wells.

Evaluation of Biosurfactants to Preflush for Offshore Wells.

With the improvement of environmental protection requirements in offshore oil and gas exploration, there is a great demand to find environmentally friendly surfactants for cementing preflush fluids. In the present paper, the application potential of three biosurfactants of rhamnolipid, lipopeptide, and sophorolipid in the preflush fluid was evaluated through a series of experiments. The experiments studied the interfacial tension (IFT) of the biosurfactants, resistance to temperature, salt resistance (sodium chloride and sea salt), and the influences of the studied biosurfactants on the rheological compatibility and capabilities to convert the wettability of the formation from oil-wet to water-wet, mud cake removal efficiency, and to improve the interfacial bonding properties of the preflush fluid. The results showed that rhamnolipid, lipopeptide, and sophorolipid exhibited excellent surface activities in high-temperature and sodium chloride (NaCl) environments. When exposed to sea salt, lipopeptides lost their function due to agglomeration, while rhamnolipids and sophorolipids maintained structural stabilities and high surface activities. When rhamnolipid was mixed with sophorolipid in a ratio of 2:1 at the same concentration, the combined biosurfactant had the best surface activity among the studied surfactants. The combined biosurfactant not only had good rheological compatibility with the drilling fluid and cement slurry but also showed excellent properties in the removal of mud cake. In addition, the effect of the removal of the mud cake was verified by the gas channeling experiment. The experimental results show that the presence of mud cake can reduce the bonding strength. When rhamnolipid was mixed with sophorolipid in a ratio of 2:1 at the same concentration, the removal efficiency of mud cake was the highest, and the interfacial bonding property of the cement sheath can be improved.

Permeable Cement Based on Foamed Cement and Permeable Skeleton Materials

Summary Permeable cement has been widely used in the construction industry. In oil fields, the use of permeable cement to replace screens and reduce the cost of well construction has been attempted. However, the compressive strength of permeable cement is low. Herein, a new method for producing permeable cement using foamed cement and permeable microspheres (PMs) is proposed. A permeable cement slurry system is produced by selecting the foaming agent, foam stabilizer, length and dosage of basalt fibers, and permeable skeleton materials (PSMs). The system formula is Jiahua G-grade cement + 1.3% alpha-olefin sulfonate (AOS) + 0.5% xanthan gum (Xg) + 2% nano-SiO2 + 1% 6-mm basalt fiber + 30% PM. The compressive strength and permeability of the permeable cement were tested using compressive strength and hydraulic permeability tests, respectively. The compressive strength of this system could reach 6.6 MPa when it was cured for 2 days at 50°C. Its liquid permeability could reach 0.06×10−3 μm2 when it was cured for 14 days at 50°C.

Synthesis and performance study of amphoteric polymer suspension stabilizer for cementing slurry at ultra-high temperature

As the number of ultra-deep wells increases, maintaining the suspension stability of cement slurry at ultra-high temperatures becomes increasingly challenging; the development of a suspension stabilizer suitable for ultra-high temperature environments is imperative. Therefore, this study synthesized a temperature-resistant polymer suspension stabilizer (LHAP) using 2-acrylamide-2-methylpropanesulfonic acid (AMPS), N, N-dimethyl acrylamide (DMAA), 4-acryloylmorpholine (ACMO), and quaternary ammonium cationic hydrophobic long-chain monomer hexadecyl dimethylallyl ammonium chloride (DMAAC-16) as raw materials. It was applied to maintain the suspension stability of cement slurry at ultra-high temperatures. The molecular structure and molecular weight of LHAP were characterized and tested using infrared spectroscopy, nuclear magnetic hydrogen spectroscopy, and Ubbelohde viscometer. The thermal stability and viscosity-temperature performance of LHAP were measured using thermogravimetric analysis and rheometer, respectively. Through the segmented density difference testing of cement stone columns, the suspension stability effect of LHAP on cement slurry under high temperature was evaluated. The suspension stabilization mechanism of LHAP was studied through fluorescence probe testing, variable temperature UV visible light testing, variable temperature particle size distribution testing, Zeta potential analysis, Environmental Scanning Electron Microscopy (ESEM) analysis, and scanning electron microscopy (SEM) analysis. The results indicated that the polymer suspension agent LHAP had excellent temperature resistance, and the molecules didn’t undergo significant thermal degradation below 302 ℃. At high temperatures of 220 ℃, LHAP could maintain the suspension stability of cement slurry, and the segmented density difference of cement columns was less than 0.01 g/cm3. Mechanism analysis revealed that in addition to enhancing temperature resistance by introducing sulfonic acid groups and rigid rings, LHAP also effectively maintains the stability of the slurry suspension at ultra-high temperatures by coordinating electrostatic interactions and molecular associations. LHAP can effectively solve the settlement instability problem of cement slurry under ultra-high temperature, which is beneficial for improving the safety and quality of cementing construction in ultra-deep wells.

Nano-enhancing polymer as a fluid loss additive for ultra-high temperature cementing

The exploitation of ultra-deep oil and gas wells is accompanied by technical problems of ultra-high temperature, especially in the cementing process, which will directly deactivate many admixtures. By in-situ polymerization of the monomers and Nano-SiO2 to improve the temperature resistance, the resulting high temperature resistant composite polymer slurry system can show high efficiency in reducing fluid loss under the high temperature environment of 240℃. The synthesis of the high temperature resistant polymer was characterized by IR and 1H NMR, and its physicochemical properties were analyzed by DLS, GPC, TEM and Cryo-SEM. The synergistic mechanism of Nano-SiO2 on the high temperature resistance of the polymer was revealed by TGA. Using DLS, SEM and EDS, a series of cement slurry systems were used to analyze and compare the effect on fluid loss reduction of different adding methods of Nano-SiO2 in cement slurry at high temperature. The results showed that the grafted Nano-SiO2 polymer maintained effective adsorption capacity at high temperature without degradation, and its fluid loss reduction ability was significantly improved at high temperature. The high temperature resistant composite polymer is strongly adsorbed between cement particles to form a dense and robust spatial network structure. The CSH gel structure is optimized by the particle size gradation of the system, so as to obtain a dense cement cake, which is expected to be applied in high temperature cementing.

Increasing the Thermal Resistance of Water-Based Mud for Drilling Geothermal Wells

Energy demand and growing environmental concerns have fueled increased interest in geothermal drilling in recent decades. The high temperature and pressure in the boreholes present significant challenges to drilling, particularly in terms of the selection of suitable drilling mud, cement slurry, and drilling equipment. Drilling mud is regarded as one of the primary factors that affect the cost and success of geothermal drilling. This paper presents experimental studies aimed at assessing the thermal stability of drilling muds for geothermal drilling. Research on the antidegradation of polymers contained in drilling muds is presented. The thermal stability of drilling fluids was evaluated on the basis of changes in rheological and filtration parameters under the influence of a temperature of 160 °C. Attempts were made to increase the thermal resistance of drilling fluids by using antioxidants and glycol compounds. The effectiveness of increasing the thermal resistance of muds by adding synthetic polymers, nanomaterials, and graphite was tested. A new way of increasing the thermal resistance of drilling muds by using fatty amine compounds in combination with the amine agent ‘TEA’ was proposed. Tests showed that the addition of polyglycol and the antioxidant agent sodium ascorbate to the mud did not protect the polymers from decomposition at 160 °C. There was no effect of increasing the thermal conductivity on improving the thermal resistance of the scrubber. Based on the analysis of results from laboratory tests, a composition of a water-based drilling mud without bentonite was developed for drilling geothermal wells. The developed drilling mud is characterized by thermal resistance up to 160 °C, stable rheological parameters, low filtration, and appropriate thermal conductivity characteristics.

Development of cement slurries with additives of nanoclay particles for the construction of oil wells at elevated temperatures

Relevance. Strength decrease is a phenomenon that becomes more pronounced as the temperature rises above 110°C. It is characterized by significant chemical and microstructural changes that Portland cement undergoes at high temperatures. Adding silica particles (SiO2) to cement can significantly increase cement resistance to strength reduction when the temperature exceeds 110°C. Nanoclays are currently used in the cement industry to increase the strength of the cement matrix due to their ability to fill capillary micropores and due to their relatively small particle size. Aim. To investigate the effect of adding nanoparticles (nanoclay) to Saudi grade G cement on compressive and tensile strength, and cement stone permeability under high temperature conditions (300°С). Objects. Six samples of cement mortars with different concentrations of nanoclay, cement stones from, tested after 7 and 28 days of hardening at 25 and 300°C. Methods. Cement chemical composition was evaluated by the X-ray fluorescence method with the WORKSTN-V Olympus Vanta X-ray fluorescence analyzer. Cement physical composition was evaluated by the method of ray diffraction on the Mastersizer 2000 laser particle size analyzer. The test of the grouting stone samples was carried out in accordance with ISO 10426-2:2003 on a hydraulic press 65-L1132. The tensile strength of the samples by the Brazilian method was tested in accordance with ASTM D 3967-08 standard on a hydraulic press 65-L1132. The permeability of the samples was determined by single-phase stationary filtration at a facility for studying the filtration and capacitance properties of the PIK-OFP-UCH core in accordance with ISO 10426-2:2003. Results. The data obtained showed that cement destruction at extremely high temperatures can be avoided by using nanoclay (up to 3% by weight of cement). The microstructure of the cement matrix was significantly affected due to the aggregation of nanoparticles when more than 3% of nanoclay was added. All rheological characteristics of the cement slurry were improved by the addition of nanoclay particles.

Study on the Diffusion Mechanism of Infiltration Grouting in Fault Fracture Zone Considering the Time-Varying Characteristics of Slurry Viscosity Under Seawater Environment

Fault fracture zones are rock formations commonly encountered in submarine tunnels, and the diffusion mechanism of slurry in fault fracture zones has a crucial impact on submarine tunnel reinforcement. Based on the seepage equation of Bingham fluid, the tortuosity parameter, fractal theory, and variable viscosity equation are introduced to establish a spherical permeation grouting model of Bingham fluid considering the slurry diffusion path and viscosity time variability. The viscosity variation law with time of sulfur aluminate cement slurry under different seawater admixture conditions was tested, and the time-varying equation of viscosity of sulfur aluminate cement slurry was obtained by fitting. A set of fault fracture zone permeation grouting test system was developed, and a fault fracture zone grouting simulation test was carried out. The study shows that the diffusion distance calculated without considering the influence of slurry diffusion path and seawater is 1.63–1.91 times of the test value, which obviously overestimates the diffusion distance; the diffusion distance calculated with considering the influence of diffusion path and seawater is 1.06–1.35 times of the test value, which is in good agreement with the test value. The research results can provide some theoretical support for the design of grouting in seawater environment.

Recycling of waste glass powder: Effects on microstructure, mechanical properties and sustainability of seashell powder calcined sludge cement

The massive accumulation of waste seashells, waste sludge and waste glass not only occupies a large amount of land resources, leading to a shortage of land resources, but also causes serious soil-water-air composite pollution over a long period of time with the role of the surrounding environment, which poses a serious hazard to the ecological environment and public health. In this study, the effect patterns of waste glass powder (WGP) on the workability, mechanical properties, microstructure and carbon emission of seashell powder calcined sludge cement (SCSC) slurries prepared using waste sludge and waste seashells as supplementary cementitious materials in place of part of the cement clinker were investigated. The hydration process and microstructure of the materials were characterized by heat of hydration tests, thermogravimetry (TG-DTG), infrared Fourier transform (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the addition of WGP improved the fluidity of SCSC slurries and reduced the shear stress of SCSC slurries without changing the flow pattern of SCSC slurries, and all the slurries conformed to the power law model. The compressive strength of SCSC slurries increased by 25.26 % with 5 % WGP addition. The CO2 emissions per cubic meter of SCSC slurries were reduced by 4.43 %, 8.81 %, 13.5 % and 18.23 % for WGP additions of 5 %, 10 %, 15 % and 20 %, respectively. These results can provide a new way for the efficient resource utilization of waste seashells, waste sludge and waste glass, and reduce the CO2 emission during the cement production process, promoting the clean production of cement.

Cement slurry penetration behavior of swirl grouting technology

Traditional pressure grouting technology operates under steady pressure conditions, causing the grout to easily flow along preferential pathways. This results in uneven grout penetration and increased economic costs. This study proposes swirl grouting technology, which effectively improves this problem. To verify the effectiveness of swirl grouting, a fan-shaped blade tool was also proposed. The grout penetration performance was investigated through experimental studies. The length, width, height, weight, and uniformity of the grouted bodies produced by the swirl grouting method were compared with those produced by the steady pressure grouting method. Then, the mechanisms of swirl grouting were analyzed through transparent disc visualization experiments. The results demonstrated that, at different water–cement ratios, the swirl device increased the penetration length in the X, Y, and Z directions by 43.3%, 27.8%, and 45.8%, respectively, compared to the conventional straight device, and by 57.3%, 39.4%, and 55.6%, respectively, compared to the fan blade device. Moreover, the swirl device increased the weight of the grouted stone body by 54.9% compared to the conventional straight device and by 91.0% compared to the fan blade device, significantly enhancing filling efficiency. The uniformity coefficient of the swirl device permeation decreased by 56.6% and 51.0%, respectively, compared to the conventional straight device and the fan blade device, resulting in a more uniform grout distribution. The transparent disc visualization experiment further revealed the advantage of the swirl device in promoting the migration of fine particles, with a significant increase in average penetration distance and a penetration shape closer to a regular circle. The rotating flow path of the swirl device imparts additional rotational momentum and multidirectional penetration capabilities. The resulting turbulence accelerates the mixing of grout with the soil matrix, facilitating the migration of fine particles, expanding flow channels, and reducing flow resistance. This combination of effects enhances penetration efficiency and reduces energy loss. This study offers significant practical application value for improving engineering quality, construction efficiency, and reducing costs.

Exploring the effect of self-combustion gangue powder particle distribution on rheological behavior and hydration mechanism in cement-based systems

Solid waste-based mineral admixtures are widely employed as a partial replacement for Portland cement due to their superior performance and minimal carbon and environmental footprint. This study involves the production of self-combustion gangue powder (SCGP) with varying particle sizes achieved through crushing, screening, and grinding. The SCGP is subsequently blended with cement to form a self-combustion gangue powder-cement (SCGP-C) system with diverse particle size distribution. Rheological tests and hydration exothermic tests were conducted to investigate the rheological behavior and degree of hydration of the SCGP-C mixed system. The results show that SCGP enhances the plastic viscosity and thixotropy of the mixed slurry. However, when a finer SCGP (d50=1.36 μm) was used to replace 15 % of the cement for the same mass, the yield stress and rheological index of the slurry were reduced by 28.1 % and 15.4 % respectively compared to the control group, while the closed-packing of the SCGP-C system was obtained. When the cement was replaced by 15 % SCGP (mass substitution), the yield stresses of finer and coarser SCGP (d50=18.24 μm) and pure cement slurries were increased by 289.1 %, 67.3 %, and 29.2 %, respectively, at T=60 min compared to T=0 min. This suggests that the fineness of SCGP has a greater effect on the yield stresses of mixed slurries over time. Mixed slurries with different finenesses of SCGP all prolonged the hydration induction period and reduced the total exothermic heat of hydration. Incorporating 15 % finer SCGP extended the induction period of the mixed slurry by 27 min and increased the peak value of the main hydration curve. Appropriate incorporation of SCGP helps to improve the fluidity and early strength of mortar in the SCGP-C system and promotes the physical filling effect and the positive role of SCGP volcanic ash in the cement system.

Effect of Different Concentration of CO2 Gas Injected into Fresh Cement Paste Along with the Addition of Superplasticizer on the Mechanical Properties of Cement

This paper focused on examining the impact of injecting varying concentrations of carbon dioxide (CO2) gas on the mechanical characteristics of both the fresh and hardened states of cement paste. This study also considered the influence of the presence or absence of polycarboxylate superplasticizer in cement mixture on these properties. Many researchers discovered the benefit of CO2 gas utilization in cement mixture to accelerate the early strength of cement or concrete hydration by its carbonation that form calcium carbonate (CaCO3). The application method is to directly inject CO2 gas in a curing chamber for air-curing of precast concrete. Alternatively, carbonated water is mixed with cement during concrete mixing. However, the use of CO2 gas does not significantly improve the 28-day strength of concrete. This study explores how to improve the carbonation impact on mechanical properties of cement paste and apply it to ground improvement. In this study, the method adopted is direct injection of CO2 gas during cement slurry mixing with different injection duration. The influence of CO2 in the presence of superplasticizer (SP) in cement slurry was also studied as SP is generally used for grouting. The results showed that the carbonation of cement paste with additional of superplasticizer significantly affect its flow, viscosity and bleeding properties. Unlike samples with SP addition, the samples without SP addition showed higher compressive strength after 28 days of curing up to certain CO2 injection time. For all CO2 gas injection time, smaller porosity rates were observed for 7-day cured samples with SP addition compared to those without SP addition. This is due to accelerated carbonation due to SP presence in cement mixture. From the results, the optimum of CO2 gas injection time for one liter mixture of cement paste to improve its compressive strength (up to 123% increase) have been discovered. It can be inferred that the addition of superplasticizer in cement slurry reduces the amount of CO32- ions and Ca2+ ions during carbonation process of cement hydration products, which are strongly related to the pH level in pore solution. These ions play a significant roles in determining the mechanical properties of cement slurry.

A novel low molecular weight thermal response suspension stabilizer for oil well cement in high temperature environment: Synthesis, behavior and mechanism research

To solve solid particle sedimentation of cement slurry under high temperatures, a novel low molecular weight thermal-responsive copolymer was synthesized as a suspension stabilizer by free radical polymerization. The structure and performance of the suspension stabilizer were investigated by in-situ infrared spectroscopy, ultraviolet–visible spectroscopy, etc. The results revealed that the suspension stabilizer has thermal-responsive characteristics and excellent thermal stability. After adding 0.1% suspension stabilizer, the solids suspension stability of cement slurry was improved with a density difference ≤0.02 g cm−3 under 200 °C, and cement slurry exhibited limited viscosity increasing at low and high temperatures.

Deposition morphology and mechanical properties of lean cemented gangue backfill material: Laboratory test and field application

Backfilling mining technology provides an efficient and environmentally-friendly solution for treating additional products (such as tailings, coal gangue and other solid waste) in coal mining process, which are filled into the underground goaf area, thus reducing surface subsidence, roof strata damage, and associated geological disasters. In this study, a novel backfill material called lean cemented gangue backfill material (LCGBM) is introduced, and various experiments, including uniaxial compression tests, creep tests, CT-SEM scanning and reconstruction are carried out to evaluate its mechanical properties and engineering practicability. The test results indicate that the strength and volume fraction of self-compacting cement (SCC) slurry and solid waste aggregate jointly control the uniaxial compressive strength and failure mode of LCGBM, reflecting the bucket effect under the influence of two components. Although the volume fraction of aggregate and SCC slurry is intentionally reduced to control the cost, this cemented granular material shows excellent compressive strength, overall stiffness and long-term bearing capacity in laboratory and field tests. In the process of engineering application, the uniaxial compressive strength of the LCGBM reaches 14 MPa, and the initial setting time is 120 s, which reduces the consumption of gangue aggregate by 35 % and greatly reduces the construction time. In addition, a calculation method of the optimal mixing ratio of raw materials is proposed, which can adjust the strength and volume fraction of SCC slurry according to the optimal mixing range, so as to maximize the utilization of the strength of LCGBM, and reduce the construction time and aggregate of backfilling. The research findings emphasize the potential of the LCGBM in promoting clean and sustainable coal mining practice.

Synthesis of suspension stabilizers for isolation fluids by response surface methodology and study of their properties

In order to solve the problem of unstable settling of isolation fluid at high temperatures, high-temperature-resistant suspension stabilizers for isolation fluids were prepared. Using the free radical aqueous solution method with 2-acrylamido-2-methylpropanesulfonic acid (AMPS), YX-1 (a monomer containing an amide group) as the main chain of the molecule, and N-Vinylpyrrolidone (NVP) and DX-2 (monomer containing hydrophobic groups) as the side chains of the molecule. We innovate the suspension stabilizer synthesis process, the synthesis conditions of the suspension stabilizer were optimized by using the one-factor experimental design and response surface analysis. The elemental composition and structure of the polymer suspension stabilizers were tested and analyzed by using X-ray spectroscopy (XPS), infrared spectroscopy (FTIR) and nuclear magnetic resonance hydrogen spectroscopy (H NMR). The hydrophobic aggregation behaviour of the polymer molecular chains was demonstrated from a microscopic point of view using fluorescence spectroscopy tests and size analysis of polymer molecular aggregates. Oscillation experiments on the isolation solution with suspension stabiliser showed that the hydrophobic groups contained in the polymers can undergo the effect of joining and bridging, and can also form a strong spatial network structure at 220°C, leading to the enhanced elasticity of the isolation fluid, which helps to alleviate the sedimentation of barite. Sedimentation stability and compatibility were evaluated for the isolation fluid containing suspension stabilizers. It was found that the isolation solution suspension performance is good under the condition of 90–220℃, its density difference is less than 0.10 g/cm3. It can also effectively prevent the contact contamination of the drilling fluid cement slurry, which is conducive to the improvement of the quality of the deep well cementing.

Mechanisms of near-wellbore fracture growth considering the presence of cement sheath microcracks and their implications on wellbore stability

Placement of intended perforations is usually extensive enough into the reservoir to minimize any near wellbore influence on the expected fracture growth. However, some unplanned fractures do not necessarily originate from the intended shot holes. A sufficient volume of published work exists on the processes of crack growth from the near wellbore regions such as from the cement sheath or from fractures observed on the formation wall surrounding the wellbore. A robust quantification of wellbore stability issues should not detach such fracture development, which can potentially result into issues such as cement sheath damage and unnecessary formation damage in the near-wellbore regions. Such fractures may become fluid injection points during stimulation related wellbore pressurization, leading to pronounced development. In such scenarios, fracture development may become a nuisance if it jeopardises the intended structural support and zonal isolation integrity of the cement sheath around the wellbore, leading to wellbore failure, and a potential abandonment. The pressure transmission across this structural seal affects the zonal isolation integrity and its intended structural support leading to wellbore instability. Understanding crack growth behaviour in such cement-rock structural framework is still illusional yet it poses the wellbore to a risky state of instability. Our study provides insight into mechanical and elastic behavior of a tightly bonded cement-rock framework with presence of initial cracks. It also provides insight into how the acting far-field stresses, applied wellbore pressures, crack length, and orientation angle influence the crack growth morphologies including planar fractures, curved and cyclic fractures. The study is important not only for a proper selection of the cement slurry but also for the definition of allowable pressures during the wellbore lifespan. Inappropriately selected parameters might lead to the loss of wellbore integrity to a point as early as the start of a well’s life.

Synergistic Effects of Magnesium Oxide and SBR Latex Additives on Cement Sheath Stability in Oil Well Operations.

Leaks through cement sheaths remain a complex and challenging issue in the oil industry, representing a persistent obstacle that has endured for decades. The drying shrinkage, an inherent characteristic of Portland cement, substantially exacerbates this problem, driving the formation of microcracks and heightened permeability under variable stress conditions. In this context, additives emerge as significant elements in addressing this issue, offering a pathway to mitigate the adverse effects of leaks. Among these additives, magnesium oxide (MgO) stands out for its ability to reduce drying shrinkage through structural modifications in the cement matrix. Simultaneously, SBR Latex, another important additive, acts to minimize gas migration due to its polymeric microstructure while also strengthening acid resistance and enhancing microstructural cohesion. This study aims to deepen the understanding of the interaction between MgO and SBR Latex additives in cement slurries, employing an experimental design to substantiate and expand upon the analyses conducted. The results reveal a synergistic integration of these additives, with MgO acting as an effective agent in reducing drying shrinkage and gel formation, thereby contributing to the strengthening of shear strength. Conversely, SBR Latex provides elasticity to the slurry, although with a slight compromise in compressive strength, with a relatively limited effect on shear strength. The strategic combination of these additives results in improvements in the mechanical integrity of cement slurries, a positive advancement in the context of petroleum well cementing operations. Thus, this study not only highlights the individual properties of MgO and SBR Latex but also offers valuable perspectives for the careful formulation of cements, with potential applications in challenging operational environments in the oil industry.

Strength characteristics of cement slurry in high geothermal tunnel environment

The early-age strength of grouting material is crucial for tunnel support under high geothermal temperatures. Grouting materials (such as the most commonly used cement slurry) hydrate and solidify under the condition of variable-temperature curing after entering the real stratum. However, the development process of the early strength of cement paste under the condition of variable-temperature curing is still unclear. This aim of this study was to elucidate the environmental effects of high-ground-temperature tunnels on the early strength development of cement stone. Cement slurry was subjected to variable-temperature curing under three different temperatures (T = 40°C, 60°C and 80°C) and two different relative humidities (H = 5% and 95%) through design experiments. Compressive strength tests were conducted, along with microscopic analysis using X-ray diffraction, scanning electron microscopy and nuclear magnetic resonance. The results indicate that the strength of cement stone under variable-temperature curing was lower than that under constant-temperature curing at the same temperature. The influence of variable-temperature curing conditions on the strength variation of samples with a high water/cement ratio at later age was greater for curing at 80°C. The research results are helpful to understand the influence of environmental effects of high-ground-temperature tunnels on the properties of grouting materials.