Cement Fracture Research Articles

Mix design and characteristics evaluation of high-performance concrete with full aeolian sand based on the packing density theory

• A newly high-performance concrete was prepared by using aeolian sand. • The modified Andreasen & Andersen model was employed to determine the volume fractions of solid powders. • The optimization values of W/C, SP and FA content are 0.19, 1.0 and 25.86 respectively. • The internal pores of developed FAS-HPC are harmless and the pore porosity is 7.3%. • This study further enriches the raw materials for HPC and proposes a fully calculated design method. To solve the shortage issue of high-quality construction aggregates in desert areas and improve the utilization rate of aeolian sand, this study introduces the mix design and characteristics evaluation of high-performance concrete with full aeolian sand (FAS-HPC). The modified Andreasen & Andersen model is employed to determine the volume fractions of solid materials when the mixture system reaches the best packing density. Then the Response Surface Method (RSM) is utilized to conduct the orthogonal design and evaluate the effect of water-cementitious materials (W/C), superplasticizer (SP) and fly ash (FA) content on the flowability, mechanical properties, shrinkage and impermeability of the developed concrete, thus the raw materials proportion of FAS-HPC is optimized. After that, the pore structure and microstructure of the developed concrete are tested and analyzed to verify its durability and compactness. The results show that the volume fractions of AS, silica fume, and cement are determined as 0.482, 0.093, and 0.425 respectively, and the introduction of FA is found to be effective in improving the fluidity and impermeability while reducing the early strength and shrinkage. Under the determined response goals, the optimal values of W/C, SP and FA content are 0.19, 1.0 and 25.86 respectively. While the developed FAS-HPC formed by this ratio has a flowability of 220 mm, 28d flexural strength and compressive strengths of 20.26 MPa and 97.09 MPa respectively, meeting the requirements of HPC. Additionally, the developed FAS-HPC has a porosity of 7.3 % and 76.4 % pores are harmless, which can ensure its superior chloride resistance and durability. This study further enriches the raw materials for HPC and proposes a fully calculated design method, which is of great significance to the sustainable development of HPC.

Proposal of a failure envelope for artificially cemented sand

Soils are particulate materials, which often stand out for their low shear strength. In most cases, this aspect justifies adapting the geotechnical project for this characteristic, which can be even more problematic in the case of soft sands, since it often occurs in superficial layers in various parts of the metropolitan region of Fortaleza. Therefore, the soil improvement procedure with the addition of small cement fractions can be crucial. The content to be adopted should be such as to bring a more economically viable alternative to the geotechnical design of a shallow foundation, for example. The present research aims to propose a modified Mohr-Coulomb envelope for artificially cemented soils. The proposal is based on the development of two functions that relate shear strength parameters (cohesion and friction angle) with the cement content. In order to assess the proposed functions, triaxial shear tests were performed on the sand with different cement contents. The adjustments presented consistent results. In addition, the proposed envelope was validated using published results encountered in literature.

A Three-Parameter Weibull Distribution Method to Determine the Fracture Property of PMMA Bone Cement.

Poly (methyl methacrylate) (PMMA) bone cement is an excellent biological material for anchoring joint replacements. Tensile strength and fracture toughness have a considerable impact on its application and service life. Considering the variability of PMMA bone cement, a three-parameter Weibull distribution method is suggested in the current study to evaluate its tensile strength and fracture toughness distribution. The coefficients of variation for tensile strength and fracture toughness were the minimum when the characteristic crack of PMMA bone cement was . Using the simple equation and fictitious crack length , the mean value (= 43.23 ), minimum value (= 26.29 ), standard deviation (= 6.42 ) of tensile strength, and these values of fracture toughness ( = 1.77 , = 1.02 , = 0.2644 ) were determined simultaneously through experimental data from a wedge splitting test. Based on the statistical analysis, the prediction line between peak load and equivalent area was obtained with 95% reliability. Nearly all experimental data are located within the scope of a 95% confidence interval. Furthermore, relationships were established between tensile strength, fracture toughness, and peak load . Consequently, it was revealed that peak load might be used to easily obtain PMMA bone cement fracture characteristics. Finally, the critical geometric dimension value of the PMMA bone cement sample with a linear elastic fracture was estimated.

Conceptual Framework for Optimizing the Dispersed Composition of Cement Systems

The disadvantage of high-strength multicomponent concretes is the high absolute and specific consumption of the binder per unit of strength. The object of research is multicomponent cement systems. The subject is the composition of multicomponent cement systems in order to significantly increase the concentration of the solid phase per unit volume, as well as strength and durability. The creation of a dense, highly filled solid phase in the form of heterogeneous mineral modifiers of a homogeneous dispersed structure ensures the production of high strength concretes with a low binder content. Theoretical and practical studies have shown that there are only three levels of dispersion of mineral modifiers, functionally related to the spatial and geometric parameters of the clinker component and its own pozzolanic activity, providing strength and other construction and technical properties of multicomponent cement systems at the maximum level. The properties and structure of concrete were studied using two fractions of fine aggregate, granite-gabro crushed stone fr. 5-10 mm, Portland cement class CEM I 42.5N, finely dispersed blast-furnace granular slag, microsilica, highly dispersed fraction of cement, superplasticizer Glenium 430 and high-valence hardening accelerator. Research methods: the shape and size of dispersed particles of the components were determined by a laser analyzer, the mobility of the concrete mixture in accordance with GOST 10181–2014, the strength of concrete in accordance with GOST 10180–2012. The structure of the cement stone was studied using scanning microscopy, thermographic and X-ray phase analysis methods. The strength of concrete with an optimized disperse composition, a superplasticizer and a high-valence hardening accelerator at the age of 28 days after hardening under normal conditions was 128; 137; 163 MPa, with the consumption of multicomponent cement, respectively 650, 700, 750 kg / m3.

Experimental and Mechanistic Characterizations of Oil-Based Cement Slurry Flow Behavior Through Fractures in a Carbonate Reservoir

Abstract In this paper, techniques have been developed to experimentally and mechanistically describe the oil-based cement slurry (OBCS) flow through fractures in carbonate reservoirs when it is co-injected with a pad fluid. Experimentally, a three-dimensional (3D) physical model is used to simulate flow behavior within fractures in carbonate rocks by using the ultra-fine cement and class G cement with or without pad fluids. The injection pressures of an OBCS flow are measured and recorded as a function of time during the experiments at a constant flowrate, while effects of fracture width (i.e., 0.5 mm and 1.0 mm) and cement type (i.e., the class G cement and the ultra-fine cement) on injection pressure are examined and analyzed. Theoretically, the Navier–Stokes (NS) equations are modified and integrated to obtain the explicit velocity equations of visco-plastic materials in a planar fracture, and to further quantify the injection pressure of the slurry flow as a function of viscosity, flowing distance of the injected slurry, fracture width, and flowrate. It is found from the experimental measurements that the fracture width imposes a much larger impact on injection pressure along the fracture than other parameters. Once slurry is made in contact with water, its injection pressure not only increases rapidly with one or two orders of magnitude or even larger but also is changed from its linear to exponential relationship with time after a certain time. During the linear stage, the injection pressure of ultra-fine cement is smaller than that of the class G cement, while an opposite pattern is yielded during the exponential stage, i.e., the exponent of the injection pressure formula pertaining to the ultra-fine cement is found to be about 1.5 times larger than that of the class G cement. By incorporating the experimentally measured patterns of the slurry distribution within the fracture model, the newly developed mechanistic model has been validated by reproducing the experimental pressure measurements, allowing us to perform reliable characterization of the OBCS flow behavior in a fracture and then to efficiently and accurately predict and optimize its water-plugging performance.

Effect of various biochars on physical, mechanical, and microstructural characteristics of cement pastes and mortars

Using waste materials to replace a fraction of cement in concrete is economical and ecologically beneficial. In this work, cement pastes and mortars were fabricated with five different kinds of unsaturated biochars such as bagasse biochar (BB), coconut husk biochar (CHB), peanut husk biochar (PHB), rice husk biochar (RHB), and wheat husk biochar (WHB) at a dosage rate of 1-5 wt% relative to cement. The CO2 adsorption capacity of biochars was estimated to be in the range of 1.25–1.72 mmol/g. The influence of biochar addition on the setting time, water demand for normal consistency, compressive strength, water absorption, and apparent porosity of cement pastes and mortar was assessed. The analytical characterizations such as X-Ray diffraction (XRD), Fourier Transform infrared (FTIR), Scanning electron microscopy (SEM), and Raman spectroscopy analyses were employed for the analysis of biochar-based cement pastes. The results reveal that increasing the biochar dosage in cement pastes reduces setting time and increases the water demand irrespective of biochar type. The best results for water absorption, apparent porosity, and compressive strength were obtained at a dosage of 2 wt% relative to cement for each biochar. The analytical characterizations of biochar-based cement pastes showed the greater formation of hydration products leading to the development of a dense structure. The analytical results corroborated the mechanical performances. The efficacy of biochars in controlling the properties of cement pastes and mortars decreased in the order BB > RHB > PHB > CHB > WHB.

Investigation of steel fiber reinforced high-performance concrete with full aeolian sand: Mix design, characteristics and microstructure

High-performance concrete with full aeolian sand (FA-HPC) has the characteristics of low water binder ratio, large cementitious materials content and no restriction of coarse aggregates, resulting in a high risk of shrinkage cracking. Aiming at reducing the shrinkage of FA-HPC and improving its cracking resistance, mechanical properties and durability, steel fibers with different lengths are employed to reinforce FA-HPC and develop a new type of cement-based composites (FA-HPFRC). For this purpose, the modified Andreasen & Andersen (MAA) model was adopted to determine the volume fractions of aeolian sand (AS), cement, fly ash (FA) and silica fume (SF). Then, the water binder ratio (W/C), superplasticizer (SP) and steel fiber content of FA-HPFRC were optimized through wet packing compactness, flowability, mechanical properties and shrinkage tests. Furthermore, the cracking resistance and microstructure of the developed FA-HPFRC were tested and analyzed from macro-micro perspectives. The results show that the volume fractions of AS, cement, FA and SF are determined as 0.482:0.316: 0.109:0.093 when the powder materials in FA-HPFRC are stacked to the most compact state. The wet packing compactness decreases with a higher W/C ratio while it increases first and then decreases with the increase of SP content. Considering the influences on mechanical properties, the W/C and SP content shall be 19% and 1% of the cementitious material separately. The introduction of steel fibers in FA-HPC reduces the concrete's flowability, destroys its dense packing system and lowers its wet packing compactness. However, the characteristics such as high toughness, and large elastic modulus of steel fibers endow FA-HPFRC with excellent mechanical properties, chloride resistance and shrinkage resistance. Especially steel fibers with 12 mm length perform well in improving the comprehensive performance of FA-HPFRC and increasing the cracking resistance 15.03% higher than that of 6 mm steel fibers. This research further improves FA-HPC's mechanical properties and durability, especially the shrinkage cracking resistance, and provides technical and theoretical support for the application of FA-HPFRC.

Effect of Nano-SiO2/PVA on Corrosion Behavior of Steel Rebar Embedded in High-Volume Fly Ash Mortar under Accelerated Chloride Attack.

In this paper, the influence of Nano-silica (NS) and Polyvinyl alcohol (PVA) fibers on the corrosion behavior of steel rebar embedded in high-volume fly ash cement mortars under accelerated chloride attack was studied by using an impressed voltage technique. The PVA fibers used were 1.0 vol.%, and two mass fractions of cement (50 and 60 wt.%) were replaced by fly ash. Four NS mass fractions (0, 0.5, 1.0, and 1.5 wt.%) were utilized in this paper. In addition, the mono and hybrid effects of NS and PVA on the mechanical properties and water absorption of mortar were also studied. The results showed that the incorporation of PVA and nano-SiO2 can improve the flexural and compressive strengths of high-volume fly ash mortar. Generally, the flexural and compressive strengths increased with the increase of nano-SiO2 content. Moreover, the incorporation NS can also reduce the capillary water–absorption rate of cement mortar. The impressed voltage corrosion test indicated that the composite incorporation of nano-SiO2 and PVA can significantly delay the deterioration process of steel bars in mortar, effectively reducing the steel rebar’s corrosion level and increasing the exposure time of the surface crack. With hybrid-incorporation 1.0 vol.% PVA and 1.0 wt.% nano-SiO2, the steel rebar had the lowest corrosion degree, which exhibited a mass loss of 49% and increased the broken time by 71% as compared to the control mortar.

Science, Medicine, and the Anesthesiologist

Science, Medicine, and the Anesthesiologist

An improved response equation of dual laterolog in dual porosity reservoirs and its solution scheme and applications in fractured reservoirs

Many fractured reservoirs are dual porosity reservoirs including matrix pores and fractures, which both contribute to the porosity. However, previous studies either ignored the effect of pores or fractures on dual laterolog, or had special application conditions. Considering the joint contribution of pores and fractures, a response equation of dual laterolog in dual porosity reservoirs is established. First, based on a borehole model with a vertical fracture in dual porosity reservoirs, fracture porosity equations are established in the investigation depths of deep and shallow laterologs, respectively. Using Archie's equations, the response equations of deep and shallow laterolog resistivities are derived, respectively. Then, the response equation, which is similar to the traditional equation of dual laterolog in fractured tight reservoirs, is established. It contains three unknown parameters, i.e. fracture width, fracture cementation exponent and matrix cementation exponent. To solve the equation, a virtual core model is proposed to estimate the fracture cementation exponent by fracture width. The estimation method of matrix cementation exponents is established by empirical formulas. Then, the response equation can be transformed into a nonlinear equation with one unknown parameter of fracture width, and conventional iterative methods can be employed to solve it and obtain the fracture width. Using the response equation and the solution scheme, the change characteristics of fracture cementation exponents in different fractured reservoirs are first analyzed. It shows that the fracture cementation exponents increase with the fracture widths, and they decrease with the increase of the ratio of formation water resistivity to unfractured reservoir resistivity. The applications indicate that the equation and solution scheme can obtain relatively accurate fracture widths quickly in dual porosity reservoirs, and they are recommended for dual porosity reservoirs with high fracture angel (>70°) and low fracture density (<1/3.78 m-1). The findings of this study can help better understanding of the different contributions of fractures and pores to dual laterolog responses in dual porosity reservoirs, and they can provide an alternative solution for evaluating dual porosity reservoirs.

Nanocontainers Against Biofouling and Corrosion Degradation of Materials: A Short Review With Prospects

The current state of the art in active corrosion prevention is based on the use of macromolecular containers that can store and release corrosion inhibitors particularly to the surface when corrosion develops. These corrosion inhibitor-containing nano- or microcontainers are subsequently infused into coatings, allowing them to self-heal. Especially, nanocontainers for self-healing coatings with controlled corrosion inhibitors, energy storage, cement fracture repair, and antifouling metal protection have recently been developed. Incorporating these nanocontainers into materials in small amounts (e.g., 5–10 wt% in paints) provided anticorrosion protection that was incomparably better than the current approaches. Furthermore, the materials developed had multifunctional properties, including self-healing, antibacterial, and antimicrobial properties. The primary goal of this review was to compile the different research studies that have been published in a variety of publications so that the reader may better understand the potential of these new types of nanotechnology and the prospects for nanocontainers.

Mechanism for the formation of natural fractures and their effects on shale oil accumulation in Junggar Basin, NW China

Despite the importance of natural fractures in shales, few techniques are currently available to examine their formation mechanism and effects on shale oil accumulation directly. The Middle Permian Lucaogou Formation in the Jimsar Sag of the Junggar Basin is a typical fractured shale. The Jimsar Sag has experienced multiple phases of tectonic movement since the Paleozoic Era, forming numerous natural fractures. However, controversy still surrounds the timing of formation, genetic mechanisms, and effects on shale oil accumulation of these fractures. Based on C-O-Nd isotopes, rare earth elements, fluid inclusions, SmNd isochron dating of fracture cements, rock acoustic emission, and triaxial rheological experiment, this study precisely define the fracture formation time, trace the provenances of fluids filling the fractures, elucidate the genetic mechanism of fractures and their effects on shale oil accumulation. The results suggest that these fractures were mainly formed in the Late Permian, Late Jurassic, and Early Cretaceous. Palaeotectonic stress field simulations further show that the tectonic movements in the Late Permian formed nearly N-S-trending fractures due to severe north-south extrusion. High-temperature fluids originating from the post-collision mantle intruded the Lucaogou Formation between ~258.1 Ma and ~ 257.6 Ma. Subsequently, tectonic movements in the Tianshan Mountains during the Late Jurassic resulted in extrusion from southwest to northeast, forming NEE-trending fractures. During this tectonic event, basin fluids intruded the Lucaogou Formation between ~150.2 Ma and ~ 146.5 Ma. The persistent fold rollback that occurred in the Bogda piedmont foreland sag in the Early Cretaceous subjected the Jimsar Sag to severe extrusion, forming NNW-trending fractures. This tectonic event influenced the intrusion of basin fluids into the Lucaogou Formation between ~123.0 Ma and ~ 120.3 Ma. The Late Jurassic and Early Cretaceous fractures coincided with the peak of oil generation and expulsion in the Lucaogou shale and created conduits and reservoir volumes for the migration and accumulation of shale oil. Our study introduces a new approach that integrates geophysical and geochemical data to investigate the formation processes of fracture and their impact on shale oil accumulation.

The Use of Formic Acid and Organic Mud Acid for Stimulation of Volcanic Rocks in Minami-Nagaoka Gas Field, Japan

Summary Unlike acid stimulation in sandstone and carbonate formations, acid stimulation of volcanic formations is not well documented in the literature, and its effectiveness and applicability are not well understood. This study aims to evaluate acidizing of volcanic rocks (especially rhyolite) as a well stimulation technique through a comprehensive experimental and modeling investigation using formation samples from a volcanic reservoir, the Minami-Nagaoka gas field in Japan. The experimental study consists of rock characterization, solubility tests, coreflooding tests, and batch reactor tests. The rock samples are investigated with computed tomography (CT) for textural characteristics and with X-ray diffraction (XRD) analysis for lithological characteristics. With these results, candidate acid systems are selected, and their effectiveness in terms of the capability of dissolving volcanic rocks is evaluated through acid solubility tests. Acid coreflooding tests are performed using undamaged plug cores to evaluate permeability responses caused by acid/rock reactions under high-temperature and high-pressure conditions (300°F and 3,000 psi, respectively). Batch reactor tests are conducted to quantify damage due to secondary/tertiary reactions. The mineralogical and textural characteristics of the rock samples let us select formic acid as the preflush acid and a mixture of formic acid and hydrofluoric acid (HF) called organic mud acid (OMA) as the main treatment acid. The composition of OMA was a mixture of 9% formic acid and 1% HF or 10% formic acid and 0.5% HF in this work. Results of the coreflooding tests with the preflush acid indicated permeability enhancement in all the samples and, especially in cores with cemented fractures filled by carbonate minerals, substantial permeability enhancement was observed. On the other hand, cores treated with OMA after the preflush indicated further permeability enhancement in some cases without cemented fractures, whereas other cases showed permeability impairment after the OMA injection. Furthermore, results of the batch reactor tests with formic acid indicated low precipitation risks, whereas those with OMA suggested higher precipitation risks. Detailed analysis on the thin sections and residuals of the batch reactor tests with OMA highlighted the precipitation of unique fluorides, and the precipitation risk was modeled and quantitatively evaluated with geochemical simulations. Although there is more room to investigate the risks of the usage of OMA for the volcanic rocks, the results in this work suggest the use of formic acid as a main treatment acid, as in carbonate acidizing, for wells with abundant cemented fractures in near-wellbore regions. This paper provides insights on acid stimulation in volcanic rocks (especially rhyolite). The results provide a fundamental understanding on the acid/rock reactions and the potential benefits/risks for productivity enhancement of wells in the subject volcanic reservoir.

Reactive Powder Concrete Microstructure and Particle Packing.

The subject of this study is the dispersed composition of multicomponent cement systems. This study aims to reduce interparticle voids, increasing the strength and concentration of the solid phase. The investigated concrete mixture contained two fine aggregate fractions, granite-gabbro crushed stone of 5–10 mm fraction, Portland cement of CEM I 42.5N class, finely dispersed granular blast furnace slag, microsilica, highly dispersed cement fraction, superplasticizer Glenium 430, and high-valence hardening accelerator. A laser analyzer determined the shape and size of dispersed particles of the components. The structure of the cement stone was studied by scanning microscopy, thermographic, and X-ray phase analysis methods. The strength of concrete with an optimized dispersed composition at the age of 2 days was 52, 63, and 74 MPa, while that at the age of 28 days was 128, 137, and 163 MPa. For this concrete, the consumption of multicomponent cement was 650, 700, and 750 kg/m3, respectively. The high efficiency of the application of bimodal clinker component and granulated blast-furnace slag is shown. It is established that the optimal content of nanoscale additives, including microsilica, should be insignificant and determined experimentally.

ANALISIS PENINGKATAN NILAI CBR LEMPUNG PLASTISITAS TINGGI TERSTABILISASI SEMEN DAN ABU DASAR

Improvement of soft clay with cement, lime, asphalt, and other additives has been done for few decades. Utilization of waste materials i.e gypsum, marble, rubber; rice hush ash, cane hush ash, saw-dust ash etc. The industrial wasted usage from coal burning process as pozzolanic agent has been proven improving the physical and mechanical properties of soil. This study aims to determine effect of bottom ash combined with cement to improve strength and permeability of high plasticity clay. CBR and hydraulic conductivity tests in the laboratory were carried out to study the changes. Several variations fraction of bottom ash (5%/10%/15%) and cement (3%/5%) were determined in this study. curing processes for 7 days and 28 days was carried out before testing the CBR and permeability. The test results of CBR and permeability of clay were 0.78% and 6E-09 m/sec, respectively. The addition of 3% cement and 5% bottom ash does not qualify soil as aggregate of sub-grade because the CBR value is &lt;12%. The best value was at fraction of 5% cement and 15% bottom ash, with CBR value of 38.60% and k=3.99E-08 m/s. The higher content of cement or bottom ash and curing time, soil properties are better. Composition of 5% cement and bottom ash on ranges of 10%-15% can be used as sub-grade. Keywords: bottom ash, curing, hydraulic conductivity, soaked, stabilization, CBR

Cemented or Uncemented Hemiarthroplasty for Intracapsular Hip Fracture

BackgroundControversy exists over the use of bone cement in hip fractures treated with hemiarthroplasty. Only limited data on quality of life after cemented as compared with modern uncemented hemiarthroplasties are available.MethodsWe conducted a multicenter, randomized, controlled trial comparing cemented with uncemented hemiarthroplasty in patients 60 years of age or older with an intracapsular hip fracture. The primary outcome was health-related quality of life measured with the use of utility scores on the EuroQol Group 5-Dimension (EQ-5D) questionnaire at 4 months after randomization (range of scores, −0.594 to 1, with higher scores indicating better quality of life; range for minimal clinically important difference, 0.050 to 0.075).ResultsA total of 610 patients were assigned to undergo cemented hemiarthroplasty and 615 to undergo modern uncemented hemiarthroplasty; follow-up data were available for 71.6% of the patients at 4 months. The mean EQ-5D utility score was 0.371 in patients assigned to the cemented group and 0.315 in those assigned to the uncemented group (adjusted difference, 0.055; 95% confidence interval [CI], 0.009 to 0.101; P=0.02). The between-group difference at 1 month was similar to that at 4 months, but the difference at 12 months was smaller than that at 4 months. Mortality at 12 months was 23.9% in the cemented group and 27.8% in the uncemented group (odds ratio for death, 0.80; 95% CI, 0.62 to 1.05). Periprosthetic fractures occurred in 0.5% and 2.1% of the patients in the respective groups (odds ratio [uncemented vs. cemented], 4.37; 95% CI, 1.19 to 24.00). The incidences of other complications were similar in the two groups.ConclusionsAmong patients 60 years of age or older with an intracapsular hip fracture, cemented hemiarthroplasty resulted in a modestly but significantly better quality of life and a lower risk of periprosthetic fracture than uncemented hemiarthroplasty. (Funded by the National Institute for Health Research; WHiTE 5 ISRCTN number, ISRCTN18393176.)

Evolution of Fault-Zone Hydromechanical Properties in Response to Different Cementation Processes

Abstract Progressive cementation and sealing of fault-localized fractures impact crustal mass transport and the recovery of fault strength following slip events. We use discrete fracture network (DFN) models to examine how fracture sealing during end-member cementation mechanisms (i.e., reaction- versus transported-limited cementation) influences the partitioning of fluid flow through time. DfnWorks was used to generate randomized fracture networks parameterized with fracture orientation data compiled from field studies. Single-phase flow simulations were performed for each network over a series of timesteps, and network parameters were modified to reflect progressive fracture sealing consistent with either reaction- or transport-limited crystal growth. Results show that when fracture cementation is reaction-limited, fluid flow becomes progressively channelized into a smaller number of fractures with larger apertures. When fracture cementation is transport-limited, fluid flow experiences progressive dechannelization, becoming more homogeneously distributed throughout the fracture network. These behaviors are observed regardless of the DFN parameterization, suggesting that the effect is an intrinsic component of all fracture networks subjected to the end-member cementation mechanisms. These results have first-order implications for the spatial distribution of fluid flow in fractured rocks and recovery of permeability and strength during fault/fracture healing in the immediate aftermath of fault slip.

A two‐stage, fault‐controlled paleofluid system at the southern termination of the Gypsum Valley salt wall, Paradox Basin, Colorado, USA

AbstractThis study combines field structural analysis with thin‐section petrography, U‐Pb dating, and strontium, carbon and oxygen isotopic analysis of calcite fracture fills to constrain the evolution of the 2‐5 km scale paleofluid system around the faulted, plunging fold nose comprising the southern termination of the Gypsum Valley salt wall in the Paradox Basin, U.S.A. Brittle deformation in this region began with the formation of a down‐to‐the‐northeast, counter‐regional fault and then progressed into jointing and faulting in a radial pattern, followed by jointing in a concentric pattern. Coupled with increases in fracture abundance toward the faults, multiple stages of mineralization suggest that the faults served as efficient and long‐lived conduits for vertical fluid migration. Although fracture cement textures and calcite colour are variable throughout the area, the distribution of these characteristics does not correlate with fracture orientation, relative age, stratigraphic or structural position. Irrespective of the type of calcite comprising the fracture cements, δ13C values average near −7‰ (VPDB), whereas δ18O values cluster into groups whose averages are roughly 6‰ apart, with the more negative grouping stratigraphically restricted to fracture cements in Jurassic rocks. The stratigraphic segregation of δ18O values suggests the paleofluid system contained two distinct paleofluids, a more recent one comprised of meteoric waters and an older one comprising brine that originated in Pennsylvanian strata. 87Sr/86Sr ratios in fracture‐filling calcite cements indicate that the older fluid underwent fluid‐rock interaction with Permian strata and that this evolved fluid migrated upwards along the faults until the Triassic or Jurassic. Thereafter, fluid migrating along the faults was more meteoric and appears to have migrated downward along the faults, where it interacted with Permian strata. Consistent U‐Pb dates from carbonates precipitated from the older fluid suggest this stage of the paleofluid system was active around 240 Ma. Local burial history models and published temperatures for fracture cements elsewhere in the basin suggest the younger stage of the paleofluid system occurred during the Latest Cretaceous to Oligocene. This study highlights the spatial and temporal complexity of fluid systems in the vicinity of salt structures and emphasises the need to interpret them through careful integration of high resolution stratigraphic and structural data in the context of evolving salt tectonics.

Technology Focus: Well Integrity (January 2022)

Almost every aspect of the upstream industry has been forced to adapt best practices and methodologies in significant ways over the last 2 years, and even the core discipline of assuring well integrity is no exception. Against a backdrop of global uncertainty and challenging economics, well integrity subject-matter experts have continued to prioritize human and environmental safety in production while pivoting their skills toward areas of growing importance such as carbon capture and sequestration. New technologies and simulation methods have allowed the authors of the three SPE papers in this year’s feature to provide a path forward that suggests new possibilities that retain the central goals of safety and productivity. Paper SPE 204385 describes the use of polymer capsules, embedded in cement and with semipermeable shells, that react with antagonistic gases downhole, such as carbon dioxide (CO2), to form a more-benign and -beneficial material. The author writes that, from this reaction with CO2, a mineral precipitate seals fractures in cement and aids in the recovery of wells. Part of the industry emphasis on decarbonization constitutes the repurposing of depleted fields as CO2 storage sites, as the authors of paper SPE 205537 describe in their discussion of such an effort offshore Sarawak. They use leakage-rate modeling to perform the critical task of estimating well integrity and re-entering existing plugged and abandoned wells. The authors of paper SPE 206052 explore various well-construction concepts and analyze the ability of cement to withstand long-term well loads. They write that, while reduction of cement stresses remains a challenge, one viable option is the use of cementless solutions, including a technology based on metal expandable packers that can seal long wellbore sections through metallic-to-rock isolation. No matter the specialized purpose or characteristics of any well, its integrity is the linchpin of production and safety. The SPE papers in this year’s feature display a versatility and willingness to tackle long-standing issues with new technologies and approaches that the upstream industry will always value. Recommended additional reading at OnePetro: www.onepetro.org. SPE 204374 - Epoxy Resin Exhibits Long-Term Durability and Chemical Stability as a Well Sealant by Fred Sabins, Riteks, et al. OTC 30299 - Big Data and Machine Learning: Effective Tools or Ensuring Well Integrity by Marcus Blane Savini, Frank’s International, et al. SPE 206252 - Development of a Digital Twin for Well Integrity Management in Underground Gas Storage Fields by Carlo Busollo, Snam, et al

Novel laboratory setup for realistic wellbore cement and formation integrity studies

Oilfield wellbore integrity relies on a good well cement formulation, placement, and resistance to solicitations when aging, either due to chemical or stress changes. Requirements are that the cement sheath and plugs remain as proper hydraulic barriers for all foreseeable future. Thus, to qualify the cement formulations with respect to various types of stress changes, it is important to carry out these tests in the field relevant conditions in the laboratory. These tests will contribute to improved understanding of the limiting factors influencing the well integrity and assist in design of remediation strategies. Hence, a new experimental setup designed for studying near wellbore systems in field conditions is introduced. The setup comprises of an advanced X-ray cell with the possibility of three independent pressure controls of casing, pore and formation pressures. The experiments are carried out under simultaneous X-ray Micro-CT imaging allowing to monitor the in-situ mechanical changes. Numerical calculations in the finite element domain are carried out for the same test conditions with first results showing the evolution of radial cracks in the cement sheath and the formation rock submitted to excessive well pressures. The test results confirm with the numerical simulation. These results may provide valuable input for near-wellbore integrity assessments. • A unique laboratory set-up with more relevant field conditions for study cement and near wellbore formation integrity. • X-ray imaging system can visualize radial fractures in the annular cement and formation in the laboratorysetup. • Fracture structures are qualitatively and quantitively different, with and without confinement pressure. • Using a finite element tool, OOFEM, to model the obtained experimental results.