Fracture Sealing Research Articles

Cathodoluminescence as a tracing technique for quartz precipitation in low velocity shear experiments

Two simulated gouges (a pure quartz and a quartz-muscovite mixture) were experimentally deformed in a ring shear apparatus at a constant low velocity under hydrothermal conditions favourable for dissolution–precipitation processes. Microstructural analysis using scanning electron microscope cathodoluminescence imaging and cathodoluminescence spectroscopy combined with chemical analysis showed that quartz dissolution and precipitation occurred in both experiments. The starting materials and deformation conditions were chosen so that dissolution–precipitation microstructures could be unambiguously identified from their cathodoluminescence signal. Precipitated quartz was observed as blue luminescent fracture fills and overgrowths with increased Al content relative to the original quartz. In the pure quartz gouge, most of the shear deformation was localized on a boundary-parallel slip surface. Sealing of fractures in a pulverized zone directly adjacent to the slip surface may have helped keeping the deformation localized. In the quartz-muscovite mixture, some evidence was observed of shear-accommodating precipitation of quartz in strain shadows, but predominantly in fractures, elongating the original grains. Precipitation of quartz in fractures implies that the length scale of diffusive mass transfer in frictional-viscous flow is shorter than the length of the quartz domains. Additionally, fracturing might play a more important role than generally assumed. Our results show that cathodoluminescence, especially combined with chemical analysis, is a powerful tool in microstructural analyses of experimentally deformed quartz-bearing material and visualizing quartz precipitation.

Sealing of fractures in a representative CO2 reservoir caprock by migration of fines

AbstractThe impact of fines migration on fracture transmissivity reduction was investigated by injecting a brine solution containing a suspension of 0.1 wt.% kaolinite particles with a mean particle size distribution of 9.6 μm through fractured shale core samples. The fractures had apertures estimated to be approximately 100 μm. A mass balance approach was used to determine the quantity of kaolinite that was deposited within the fractures (influent – effluent = amount deposited in fractures). Large fractions (44–90%) of the suspended kaolinite pumped through the fractures were deposited within the fractures. Based on fracture volumes estimated with X‐ray computed tomography, it was determined that approximately 10 to 17% of the fracture volume was filled with kaolinite at the point when flow was completely restricted. These results indicate that 100 μm fractures in CO2 reservoir caprocks could be sealed within hours if the brines passing through the fractures contain a proportional volume of particulates to the tests performed in this laboratory study. © 2021 Battelle Memorial Institute. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Simulating Fracture Sealing by Granular LCM Particles in Geothermal Drilling

Lost circulation occurs when the returned fluid is less than what is pumped into the well due to loss of fluid to pores or fractures. A lost-circulation event is a common occurrence in a geothermal well. Typical geothermal reservoirs are often under-pressured and have larger fracture apertures. A severe lost-circulation event is costly and may lead to stuck pipe, well instability, and well abandonment. One typical treatment is adding lost-circulation materials (LCMs) to seal fractures. Conventional LCMs fail to properly seal fractures because their mechanical limit is exceeded at elevated temperatures. In this paper, parametric studies in numerical simulations are conducted to better understand different thermal effects on the sealing mechanisms of LCMs. The computational fluid dynamics (CFDs) and the discrete element method (DEM) are coupled to accurately capture the true physics of sealing by granular materials. Due to computational limits, the traditional Eulerian–Eulerian approach treats solid particles as a group of continuum matter. With the advance of modern computational power, particle bridging is achievable with DEM to track individual particles by modeling their interactive forces between each other. Particle–fluid interactions can be modeled by coupling CFD algorithms. Fracture sealing capability is investigated by studying the effect of four individual properties including fluid viscosity, particle size, friction coefficient, and Young’s modulus. It is found that thermally degraded properties lead to inefficient fracture sealing.

Experimental study of the impact of filter cakes on the evaluation of LCMs for improved lost circulation preventive treatments

Methods to prevent the losses of drilling fluids involve approaches to prevent the initiation of fractures and to inhibit the growth of any pre-existing or drilling-induced microfractures. The inclusion of lost circulation materials (LCMs) in drilling fluids is a common method for managing these microfractures. Recent studies have indicated the critical role of filter cakes in continually strengthening the wellbore; however, most of the current LCM design and evaluation methods neglect the effects of filter cakes. In this study, experimental investigations were conducted to understand the effects of LCMs on the creation of filter cakes and the facilitation of fracture sealing. The processes of filter cake rupture and fracture sealing were investigated by changing and monitoring the differential pressure across the filter cakes. The performance of the filter cakes and LCMs in preventing and reducing fluid losses was evaluated based on the maximum sealing pressure, sealing structure stability, and total fluid loss upon the formation of an effective fracture seal. The effects of the filter-cake thickness, shear yield stress, as well as the type, concentration, and particle size distribution of LCM on the filter cake rupture and fracture-sealing processes were investigated.The test results show that filter cakes accelerate the sealing of microfractures, thus facilitating preventive treatments for lost circulation. The properties and effectiveness of filter cakes for these processes are affected by the particle size distribution of the LCMs in the drilling fluids. Therefore, it is recommended to evaluate the performance of LCMs considering the effects of the filter cakes. The results of this study can be used as a reference to develop more realistic evaluations and improved design of LCMs in lost circulation preventive treatments.

An Experimental Evaluation of the Effects of Filtercake in Wellbore Strengthening: Filtercake Rupture Resistance and Fracture Sealing Time

Abstract Recent research studies have indicated that filtercakes play a role in preventing fracture initiation, blocking pre-existing narrow fractures, and isolating drilling-induced fractures at the initiation stage. The ability of the filtercakes to effectively strengthen the wellbore expectedly depends on its capability in maintaining its integrity and providing the barrier to isolate pressure and fluid transmission between the wellbore and fractures. In this research, a modified permeability apparatus was used to evaluate the quality of drilling fluid filtercakes. A new criterion defined as filtercake rupture resistance is proposed to characterize the filtercake quality regarding its ability to sustain pressure over an open fracture. Experimental tests were conducted to investigate how filtercake thickness and filtercake yield strength affect the rupture resistance. The mechanism of filtercake in sealing the narrow fractures is explored, and it was observed that solid's plugging/bridging plays the vital role in this mechanism. A thicker and stronger filtercake also contributes to a faster establishment of complete fracture seal. The results of this research can be utilized as a reference that guides the optimization of drilling fluid for continuously strengthening the wellbore.

Bayesian inference for heterogeneous caprock permeability based on above zone pressure monitoring

The presence of faults/fractures or highly permeable zones in the primary sealing caprock of a CO2 storage reservoir can result in leakage of CO2. Monitoring of leakage requires the capability to detect and resolve the onset, location, and volume of leakage in a systematic and timely manner. Pressure-based monitoring possesses such capabilities. This study demonstrates a basis for monitoring network design based on the characterization of CO2 leakage scenarios through an assessment of the integrity and permeability of the caprock inferred from above zone pressure measurements. Four representative heterogeneous fractured seal types are characterized to demonstrate seal permeability ranging from highly permeable to impermeable. Based on Bayesian classification theory, the probability of each fractured caprock scenario given above zone pressure measurements with measurement error is inferred. The sensitivity to injection rate and caprock thickness is also evaluated and the probability of proper classification is calculated. The time required to distinguish between above zone pressure outcomes and the associated leakage scenarios is also computed.

Fracture Sealing with Microbially-Induced Calcium Carbonate Precipitation: A Field Study

A primary environmental risk from unconventional oil and gas development or carbon sequestration is subsurface fluid leakage in the near wellbore environment. A potential solution to remediate leakage pathways is to promote microbially induced calcium carbonate precipitation (MICP) to plug fractures and reduce permeability in porous materials. The advantage of microbially induced calcium carbonate precipitation (MICP) over cement-based sealants is that the solutions used to promote MICP are aqueous. MICP solutions have low viscosities compared to cement, facilitating fluid transport into the formation. In this study, MICP was promoted in a fractured sandstone layer within the Fayette Sandstone Formation 340.8 m below ground surface using conventional oil field subsurface fluid delivery technologies (packer and bailer). After 24 urea/calcium solution and 6 microbial (Sporosarcina pasteurii) suspension injections, the injectivity was decreased (flow rate decreased from 1.9 to 0.47 L/min) and a reduction in the in-well pressure falloff (>30% before and 7% after treatment) was observed. In addition, during refracturing an increase in the fracture extension pressure was measured as compared to before MICP treatment. This study suggests MICP is a promising tool for sealing subsurface fractures in the near wellbore environment.

Sealing of fractures in claystone

The sealing behavior of fractures in clay rocks for deep disposal of radioactive waste has been comprehensively investigated at the GRS laboratory. Various sealing experiments were performed on strongly cracked samples of different sizes from the Callovo-Oxfordian argillite and the Opalinus clay under relevant repository conditions. The fractured samples were compacted and flowed through with gas or synthetic pore-water under confining stresses up to 18MPa and elevated temperatures from 20°C to 90°C. Sealing of fractures was quantified by measurements of their closure and permeability. Under the applied thermo-hydro-mechanical (THM) conditions, significant fracture closure and permeability decrease to very low levels of 10−19 to 10−21m2 were observed within time periods of months to years. The properties of the resealed claystones are comparable with those of the intact rock mass. All test results suggest high sealing potentials of the studied claystones.

Experimental Examination of Fluid Flow in Fractured Carbon Storage Sealing Formations

This report describes a series of experiments where CO2-saturated-brine flow through fractured seal rocks from three sites within the continental United States that are being considered, or are actively being used, for CCUS pilot studies were examined. The experiments were performed over multiple weeks by injecting CO2 saturated brine through fractured samples, and were scanned with a computed tomography scanner at regular intervals over the course of the experiment while kept at representative reservoir pressures. The goal was to evaluate the change in the fracture flow that would result from a CO2 leakage event so that accurate relationships can be implemented in numerical models to assess risk. Of the three different formations studied in this series of fractured seal formation CO2-saturated-brine flow through experiments, only one formation had a reaction that was greater than the noise in the system. Reactions within the Tuscaloosa claystone sample appeared to reduce the transmissivity of the fracture slightly over the 39 day experiment. The change in the geometry of the fracture was not great enough to view with the medical CT images that were captured during the experiment. All other tests showed a minimal amount of change in the fracture and fracture flow properties.

Particulate-Based Loss-Prevention Material—The Secrets of Fracture Sealing Revealed!

Summary Owing to the narrow drilling margin that exists between the pore-pressure and the fracture-pressure gradient, drilling in depleted-reservoir, high-pressure/high-temperature, and deepwater environments is universally recognized as being technically challenging. A number of field techniques are available for mitigating many of the drilling problems encountered. Included among these are specialized fluid engineering that involves the use of chemical- and particulate-based treatments for minimizing or preventing losses. In many instances, these techniques can be used to strengthen or stabilize the wellbore when drilling at or near the fracture gradient, thereby potentially eliminating the need for intermediate casing strings. This paper discusses particulate-based-treatments design for sealing fractures. Substantial experience gained from innovative laboratory testing has highlighted the mechanisms and many factors that determine the effectiveness of the fracture seal. The particle-size distribution (PSD) relative to the fracture aperture, particle morphology, volumetric concentration, rheological properties of the fluid, and fluid-loss control influence whether the seal is established within the fracture or at the fracture mouth. Understanding this distinction is important with respect to selecting the optimum treatment and its application for given field conditions. Parameters critical for optimizing the treatment have been identified and are discussed in the context of laboratory and field experience.

State of the hydrothermal activity of Soufrière of Guadeloupe volcano inferred by VLF surveys

La Soufrière (1467 m) is the active island arc volcano of Guadeloupe Island in the Lesser Antilles arc. Its historical eruptions are more or less violent phreatic outbursts the last of which, in 1976–1977, led to the evacuation of nearly 70 000 persons. The subsurface structure of the volcano consists of calderas, craters, and avalanche amphitheatres nested within the composite pile of eruptive products. Since the last magmatic eruption, dated ca. 1440 AD, the four phreatic eruptions have developed radial fractures on Soufrière dome favouring the development of a huge active hydrothermal system emphasized by a tropical environment. After the eruptions, the thermal state and the stable ground water flow are completely disorganised during several years during which the slow mineralization of rocks is becoming again preponderant. Sealing of fractures and decay of rocks permeability act as a cap for upward thermal transfers. Therefore Soufrière dome operates as a valve, resealing the hydrothermal system underlying the volcano thus providing over pressurization that could lead to the next phreatic eruption. In 1992 new small seismic swarms have appeared. Several of them are recorded every year while the emission of acid gas slowly increases. In order to recognise the superficial electrical resistive and conductive zones (less than 100 m depth) as well as the cavities on Soufrière volcano, we have made Very Low Frequency (VLF) surveys in 2000. Electrical conductive zones are clearly associated with major radial faults starting from the summit in which the hydrothermal activity takes place. In the continuation of these active hydrothermal fractures hot springs are located down slope. Conversely some of the resistive zones are associated with inactive clayed and sealed or opened faults. The distribution of the conductive zones allows detailing the state of the superficial part of the hydrothermal system of La Soufrière. The distribution of vertical clayed zones associated with major faults supposes Soufrière dome constituted of more or less consolidated blocks joined side by side and lying on the hydrothermally floor of crater Amic.

Bench-scale testing of molten food-grade paraffin wax and high density polyethylene as injectable grouts

Molten, food-grade paraffin wax and molten high density polyethylene (HDPE) plastic were tested for use as injectable grouts. The food-grade wax was tested under both saturated and unsaturated conditions, and the HDPE was tested for unsaturated conditions. The grouted medium was fractured shale. The paraffin wax sealed well under both saturated and unsaturated conditions with no shrinkage upon cooling. The HDPE suffered significant shrinkage during cooling, which adversely affected its sealing potential. Our bench-scale tests suggest that molten wax grout may be useful to shut off mine water influx in fractured rock and/or seal mine tailings piles to prevent the development of acid mine drainage and/or leaching of metals and mineral processing chemicals.

Sealing of narrow fractures in hard rock

Sealing of narrow fractures in hard rock

Multicomponent reactive transport in discrete fractures: II: Infiltration of hyperalkaline groundwater at Maqarin, Jordan, a natural analogue site

A numerical multicomponent reactive transport model described fully in Steefel and Lichtner (1998)[Steefel, C.I., Lichtner, P.C., 1998. Multicomponent reactive transport in discrete fractures, I. Controls on reaction front geometry. J. Hydrol. (in press)] is used to simulate the infiltration of hyperalkaline groundwater along discrete fractures at Maqarin, Jordan, a site considered as a natural analogue to cement-bearing nuclear waste repositories. In the Eastern Springs area at Maqarin, two prominent sets of sub-parallel fractures trending NW–SE are approximately perpendicular to the local water table contours, with the slope of the water table indicating north-westward flow. Extensive mineralogic investigations [Alexander W.R. (Ed.), 1992. A natural analogue study of cement-buffered, hyperalkaline groundwaters and their interaction with a sedimentary host rock. NAgrA Technical Report (NTB 91-10), Wettingen, Switzerland; Milodowski, A.E., Hyslop, E.K., Pearce, J.M., Wetton, P.D., Kemp, S.J., Longworth, G., Hodginson, E., and Hughes, C.R., 1998. Mineralogy and geochemistry of the western springs area. In: Smellie, J.A.T. (ed.), 1998: Maqarin Natural Analogue Study: Phase III. SKB Technical Report TR98-04, Stockholm, Sweden] indicate that the width of intense rock alteration zone bordering the fractures changes from about 4 mm at one locality (the M1 sampling site) to approximately 1 mm 100 m to the north-west in the flow direction (the M2 site), suggesting a lessening of alteration intensity in that direction. Using this information, the dimensionless parameter δ v/φ D′ (φ=porosity, D′=effective diffusion coefficient in rock matrix, δ=fracture aperture, and v=fluid velocity in the fracture) and measurements of the local hydraulic head gradient and effective diffusion coefficient in the rock matrix, a mean fracture aperture of 0.194 mm is calculated assuming the cubic law applies. This information, in combination with measured groundwater compositions at the Maqarin site, is used as input for numerical simulations of the hyperalkaline groundwater infiltration along fractures. The width of the alteration zones in the rock matrix bordering fractures is also used to constrain mineral dissolution rates in the field. The simulations predict that ettringite [Ca 6Al 2(SO 4) 3(OH) 12·26H 2O] with lesser amounts of hillebrandite and tobermorite (hydrated calcium silicates or CSH phases) will be the dominant alteration products forming at the expense of the primary silicates in the rock matrix and fracture, in agreement with observations at the Maqarin site. The simulations also come close to matching the pH of water samples collected along fractures at the M1 and M2 sites, with a fracture aperture of 0.22 mm giving the closest match with the pH data (within 13% of the value indicated by the rock matrix alteration widths). The simulations suggest two possible scenarios for the time evolution of the fracture–rock matrix system. Where rate constants for secondary mineral precipitation reactions are the same in both the rock matrix and fracture, the rock matrix tends to become completely cemented before the fracture. This results in a downstream migration of the hyperalkaline plume. In contrast, if rates are as little as one order of magnitude higher in the fracture than in the rock matrix, it is possible to seal the fracture first, thus causing the mineral zones to collapse upstream as a result of the reduction in fracture permeability. Sealing of fractures is observed at Maqarin and the simulations predict a mineral paragenesis in the fracture resulting from this scenario which is broadly compatible with field observations.

Fracture sealing in zircon as evaluated by electron microprobe analyses and back-scattered electron imaging

The internal structure of zircon is commonly revealed by back-scattered electron (BSE) images. Grains from a 750-700 Ma old talc-alkaline mafic metatonalite from southernmost Brazil show relict igneous faces, irregular and diffuse metamorphic overgrowths, and fracture sealing. Sealing of fractures is observed as light grey patches in BSE images. EPMA profiles show strong but differential increases in Hf and U in the sealed fractures, unlike the common assertion in the literature that fractures are only pathways of leaching. Sealing of fractures occurs near borders of grains as well as in their cores and is not visible during standard petrographic examination; thus careful BSE image evaluation is needed before either in situ or whole grain isotopic determinations are made.

Episodic fluid expulsion from geopressured sediments

Numerical simulation of fluid explusion from geopressured sediments using a one-dimensional finite difference model shows that large volumes of fluid can be transported through a fractured seal during short-lived (<100 year) expulsion events. In this model, abnormal fluid pressures are maintained by an impermeable seal. When the fluid pressure exceeds 85% of the lithostatic pressure, a vertical fracture opens in the seal, providing a permeable pathway from the geopressured sediments into the overlying section. Fluid pressure in the seal decreases as fluid flows through the fracture, closing the fracture as sediments in the seal compact. Once the fracture closes, the seal remains impermeable until fluid flowing from deeper in the section increases fluid pressure to the fracture criteria, a process that takes 10 000–500 000 years. Fractures emplaced in relatively incompressible seals, such as compacted and/or cemented sediments, remain open for 20–50 years; fluid fluxes through the seal integrated over the life of these events are 1−5×107 kg/m2, and temperatures in the overlying sediments are increased by 5–20°C. These temperature anomalies decay to less than half their original value in 300 years, suggesting that the thermal anomalies observed in wells that are attributed to fluid expulsion formed in response to a very recent or currently active event.

Water Circulations on La Soufriere Volcano Inferred by Self-Potential Surveys (Guadeloupe, Lesser Antilles). Renew of Volcanic Activity?

Soufriere volcano is an andesite explosive volcano located in Guadeloupe in the lesser Antilles arc. Since the last magmatic eruption dated 1440 ± 40 AD several violent phreatic eruptions have occurred. The two last 1956 and 1976-1977 phreatic/phreato magmatic eruptions were preceded by several decades of quietness. During these quiet periods, hydrothermalization and argillization are expanding due to high tropical rainfalls (10 to 12 m per year). Sealing of fractures yields more and more difficult the release of thermal stresses developed by the magmatic body supposed to be at 6 km depth. Overpressures are increasing in confined superficial water tables. Renew of seismic activity started in May 1992. About 1400 earthquakes were recorded between May and December 1992. The onset of activity was preceded, one year before, by a slight increase of vapor emission inside South crater located on Soufriere dome at the upper end of August 30, 1976 fault, by the reactivation of the small Tarade hot spring dried up since the 1976-1977 eruption, and by the appearance of a new, low flow rate, hot spring called Pas du Roy (about 30°C). A Self Potential (S.P.) survey has been performed in July 1992 on Soufriere massif. The S.P. anomalies evidence structural heterogeneities and ground waters flowing within the massif. A large, smooth, positive S.P. anomaly, composed of two localized and pronounced anomalous zones, is spreading on the south-west-south-east sector of the dome basis. The larger anomalous zone is located on Morne Mitan in the axis of the regional Ty and August, 30, 1976 faults. This zone is extending along the contact zone between Soufriere dome and Carmichael cone. The 1992 survey is compared with 1987 survey. Soufriere dome is now submitted to a ring of positive S.P. anomalies which are lying along the inner part of Amic crater. The positive anomalous zone located on Morne Mitan has developed since 1987. The second anomalous zone, located on the south-west part of the dome, was not observed in 1987. The amplitude reaches 200 mV. The S.P. mapping points out that warm ground water beneath the south part of the volcano summit, along clayey beds, could generate the collapse of the south-west-south-east sector of Soufriere dome.

Ohio plant blast costs BASF $1.1 million fine

BASF has agreed to pay the Occupational Safety & Health Administration $1.1 million in fines for 133 safety and health violations, as a result of an explosion and fire at its Cincinnati, Ohio, coatings plant in July that killed two workers and injured 80 others, and caused considerable damage in the neighborhood. BASF says that it will not resume manufacturing operations at the 80- year-old plant. It has established a $400,000 fund to retrain 96 displaced workers, and will expand resin production at Greenville, Ohio, to make up for lost production. It will continue to maintain 85 administrative, laboratory, and R&D personnel at the Cincinnati site. OSHA area director William Murphy confirms Cincinnati fire chief William A. Miller's original assessment that the fire and explosion occurred because of a pressure seal failure during solvent cleaning of a resin reactor (C&EN, July 30, page 8). The fractured seal filled the atmosphere with a flammable vapor. Murphy ...

Structural and fluid-chemical properties of seismogenic normal faults

Abstract Structures in extensional fault zones can be classified using the configuration of fault branch lines and tip lines. Important classes include the segment bend, segment termination, segment branch, cross-fault intersection, and segment offset. The effect of these structures on rupture history is not necessarily consistent, neither between individual earthquakes nor between different fault zones. Rupture behavior is dependent on several other factors including loading conditions (regional and localized rupture tip stress fields), fluid-mechanical processes, and chemical processes. Fracture toughness is partly controlled by the angular discordance between slip directions on adjacent fault segments. Greater discordance between slip directions and intersection lines of fault segments results in greater strain incompatibility. An internal fracture network generally evolves within a segment boundary to maintain compatibility and transfer slip between the segments. The dimensions and structure of this fracture network may also partly control rupture propagation. Presumably, activation of a fault network with large angular discordances between slip directions and intersection lines will generate numerous asperities as the subsidiary faults mutually interact and offset each other. The geometry of a segment boundary may change with depth and the three-dimensional nature of the structure may be important in controlling rupture history. Fluids influence rupturing via fluid-pressure effects and time-dependent chemical processes. Fracture propagation by stress corrosion may favor instability, and chemical alteration may produce minerals of lower strengths, allowing time-dependent creep. Sealing and healing of fractures, however, may remove damage and increase strength. Elementary computations indicate that representative times for sealing and chemical alteration are between 1 and 1000 years for reasonable physical conditions, well within the recurrence intervals of most large earthquakes. Time to failure for stress corrosion cracking is more highly variable and strongly sensitive to applied stress and fluid pressure.