Hydraulic Fracturing Operations Research Articles

Coupled Poroelastic Modeling of Hydraulic Fracturing‐Induced Seismicity: Implications for Understanding the Post Shut‐In ML 2.9 Earthquake at the Preston New Road, UK

AbstractPost‐injection seismicity associated with hydraulic stimulation has posed great challenges to hydraulic fracturing operations. This work aims to identify the causal mechanism of the post shut‐in ML 2.9 earthquake in August 2019 at the Preston New Road, UK, amongst three plausible mechanisms, that is, the post shut‐in pore pressure diffusion, poroelastic stressing on a non‐overpressurized fault, and poroelastic stressing on an overpressurized fault. A 3D fully coupled poroelastic model that considers the poroelastic solid deformation, fluid flow in both porous rocks and fracture structures, and hydrofracturing‐induced pressure perturbations was developed to simulate the hydromechanical response of the shale reservoir formation to hydraulic fracturing operations at the site. Based on the model results, Coulomb stress changes and seismicity rate were further evaluated on the PNR‐2 fault responsible for the earthquake. Model results have shown that increased pore pressure plays a dominant role in triggering the fault slippage, although the poroelastic stress may have acted to promote the slippage. Amongst the three plausible mechanisms, the post shut‐in pore pressure diffusion is the most favored in terms of Coulomb stress change, seismicity rate, timing of fault slippage and rupture area. The coupled modeling results suggested that the occurrence of the post shut‐in ML 2.9 earthquake was a three‐staged process, involving first propagation of fracture tips that stimulated surrounding reservoir formations, then hydraulic connection with and subsequent pore pressure diffusion to the conductive PNR‐2 fault, and eventually fault activation primarily under the direct impact of increased pore pressure.

Effective Stress Factor Analysis of Proppant for Multi-stage Fracturing in Horizontal Wells

In order to determine the effective stress factor of proppants during the multi-stage hydraulic fracturing operation in horizontal wells and select the appropriate proppant type, the analysis of the effective stress characteristics of proppants is carried out. This analysis considers the geomechanics and long-term production characteristics of multi-stage fractured horizontal wells in reservoirs like Xinjiang Mahu shale oil and Southwest China shale gas. The analysis of influencing factors is also carried out. The results show that, during the multi-stage hydraulic fracturing operation in horizontal wells, the stress on proppants is not only related to geological factors such as reservoir closure stress, but also closely related to total injection volume, cluster spacing, liquid type, injection displacement and post fracture management. First, increasing injection intensity, reducing fracture spacing, using low viscosity fracturing fluid, adopting high injection displacement and utilizing reasonable flowback system can effectively supplement reservoir energy, postpone the effective stress peak of proppants, and increase the effective conductivity of proppants. Second, the production performance analysis results of nearly 300 horizontal wells (from Xinjiang oil field, Erdos tight oil reservoir, Sichuan shale gas reservoir, etc.) shows that: the effective stress of proppants in horizontal wells is only 50–60% of that in vertical wells, which results in a different proppant selection criterion in the volume stimulation of horizontal wells and provides the geomechanics basis of replacing ceramsite proppant with quartz sand to reduce cost and increase efficiency. Based on the above conclusions, the field test of replacing ceramsite proppant with quartz sand was carried out. The proportion of quartz sand increased from less than 30% in 2014 to 69% in 2019. Without any impact on production, the annual investment cost was decreased by more than 1 billion yuan, which set a great example for the promoted low-cost development of unconventional oil and gas reservoirs under low oil price background.

Draft Genome Sequencing of Three Glutaraldehyde-Tolerant Bacteria from Produced Water from Hydraulic Fracturing.

ABSTRACTHere, we report the draft genome sequence of three glutaraldehyde-resistant isolates from produced water from hydraulic fracturing operations. The three strains were identified as Marinobacter sp. strain G11, Halomonas sp. strain G15, and Bacillus sp. strain G16. The genome sequences of these isolates will provide insights into biocide resistance in hydraulic fracturing operations.

Damage Model for Reservoirs with Multisets of Natural Fractures and Its Application in the Simulation of Hydraulic Fracturing

The presence of natural fractures can significantly affect the quality of hydraulic fracturing operations in tightsand and shale or oil/gas formations. This paper describes the procedure used to model natural fractures with continuum damage tensor and the resulting orthotropic permeability tensor. A damage model that uses damage variable in tensor form is presented. In the procedure presented, a nonnegligible angle is assumed to exist between directions of principal stresses in the formation and in the natural-fractures-related damage tensor, and this difference in orientation is modeled by introducing local directions in the model. A damage-dependent permeability tensor in tabular form is then proposed. A second case scenario when the directions of principal stresses and natural fractures align is also analyzed. Numerical results of fracture distribution are presented for both cases, and differences can be seen from the computed contour of the damage variable. The results indicate that the model can effectively simulate the fracture propagation phenomena during hydraulic fracturing.

High strength glass beads coated with CNT/rGO incorporated urethane coating for improved crush resistance for effective hydraulic fracturing

Hydraulic fracturing is a widely employed well stimulation technique in which a synthesized fracking fluid is pumped into the well bore at high pressures to propagate fractures in rock formation matrix for hydrocarbon production. Proppant being one of the essential component of fracturing fluid is used to keep the hydraulically induced fractures open and conductive by acting as a mechanically strong support particle. Hydraulic fracturing operations are gradually shifting into deeper and low permeability (tight) formation at elevated temperature and pressure conditions at which conventionally used silica sand is becoming unviable as proppant due to its crushing. For resin-coated sand (RCS), temperatures greater than 60°C under high pressures, the glass transition temperature (Tg) threshold limit of polyurethane-based resin coating is reached at which this applied coating tends to soften that results reduction in the mechanical strength of the coated sand pack. Glass beads are also considered as good contestant for proppant that were selected in this study due to their high roundness and sphericity. They were drip coated with urethane resin incorporated with three different concentrations of 0.1 wt%, 0.5 wt% and 1 wt% carbon nanotubes (CNTs) and reduced graphene oxide (rGO) nanofillers, respectively. Crush test analysis by means of Universal Testing Machine (UTM) revealed significant improvement in the mechanical strength of coated glass bead proppants. 0.5 wt% loading of CNTs into urethane resin proved to be the best optimum concentration at which the mechanical strength of the coated glass bead improved by 84% along with 40% reduction in fines generation due to its containment within the applied coating. Crush test results also further revealed that nanofillers concentration loadings greater than the optimum threshold limit into urethane resin promoted their mutual agglomeration that resulted in profound reduction in mechanical strength of coated glass beads therefore resulting in more crushing and higher generation of undesired and detrimental fine particles.

InSAR data reveal that the largest hydraulic fracturing-induced earthquake in Canada, to date, is a slow-slip event

For tectonic earthquakes, slip rate spans a continuum from creep to supershear earthquakes, where slow slip events (SSEs) are important in releasing stress without radiating damaging seismic energy. Industrial-scale subsurface fluid injection has caused induced earthquakes, but the role of SSEs in fault activation is currently unclear. Ground-deformation observations, measured by satellite radar, show that SSEs up to magnitude 5.0 occurred during hydraulic fracturing (HF) operations in northwestern Canada, corroborated by reported deformation of the steel well casing. Although the magnitude 5.0 SSE exceeded the magnitude of the largest induced earthquake in this region (magnitude 4.55), it was undetected by seismograph networks. The observed SSEs occurred within a buried thrust belt and their magnitude and duration are consistent with scaling behavior of SSEs in unbounded natural systems, e.g. slab interfaces in subduction zones.

Preparation and identification of carboxymethyl cellulose-degrading enzyme candidates for oilfield applications

Carboxymethyl cellulose (CMC) is often used during hydraulic fracturing (fracking) operations as a fluid viscosifier to facilitate proppant delivery. However, the accumulation of residual CMC at fracture faces can result in formation damage, thereby impeding oil and gas recovery. Whereas harsh chemical oxidizers are typically added to disrupt these polymer accumulations, there is now industrial interest in developing clean, biological approaches for the degradation of CMC under fracking conditions. Using a methanogenic culture known to utilize CMC under conditions typically found in oil fields, we developed an efficient method to isolate and purify CMC-degrading enzymes. Initial purification and concentration of cellular components produced an increase in exo-ß-(1,4)-exoglucanase and ß-(1,4)-glucosidase activities by 9-fold and 26-fold, respectively. Partially purified extracts provided substantial degradation of CMC as monitored by viscosity reduction within three hours at 50 °C, an improvement over the untreated cell-free extract which required 48 h to achieve similar viscosity values, outperforming a commercially-available cellulase preparation. Putative cellulases were identified within the isolated enzyme population, with endo-ß-(1,4)-xylanase from Caldicoprobacter faecalis hypothesized to be an important contributor to CMC degradation. This study demonstrates that enzyme technology holds great promise as a viable approach to degrade CMC accumulations under field conditions.

A model to describe hydraulic fracture conductivity decline curve in 3-stages –focus on Longmaxi formation

This study focuses on modeling fracture conductivity decline curve in 3-stages of slope. In the past few decades, advancement in hydraulic fracturing stimulation technology has greatly helped in the exploitation of hydrocarbon resources from unconventional shale formations. However, applying this technology to deeper shale gas formation (3500–4,500 m) requires a better understanding of deep unconventional formations due to their downhole conditions (high temperature and high pressure). During hydraulic fracturing, micro fractures are often unpropped due to their micro width and complexity. The micro fractures create their own conductivity via sheared displacement (2.5 mm average) of the surfaces in contact. Thus, a reason to investigate the effect of shear displacement in fracture conductivity. Several researchers have investigated shale rock for effect of rough fracture surface on fracture conductivity, however less research have investigated effect of shear-displaced rough fracture on conductivity (Longmaxi formation). Therefore, Longmaxi formation of Sichuan basin, China, was taken as a case study to analyze the characteristic effect of shear failure of rough fracture surface on fracture conductivity.XRD and FESEM tests were done and a 3D laser scanner was used to analyze the fracture surface roughness and a shear displacement of 2.5 mm was allowed before fracture conductivity test was performed (using API RP 61 standard procedure with nitrogen as test medium). JRC correlation was done for the root-mean square of the fracture surface asperity height using Yu/Vayssade and Tatton/Grasselli method.The fracture conductivity curve showed a 3-stage decline pattern. From the 3D laser scan, it was observed that the fracture perpendicular to the bedding plane was mainly rough in the lateral direction, and therefore the fluid flow channel was mainly a lateral groove perpendicular to the flow direction, so the fracture flow ability was poor. JRC result showed roughness for all samples. The 3-stage fracture conductivity model obtained from this work could assist researchers/engineers in the design of hydraulic fracturing operations for deep depth of Longmaxi formation of Sichuan basin.

ENHANCING PERFORMANCE OF MECHANICALLY OPERATED PACKER

During hydraulic fracturing operations of low-permeability reservoirs, packers are the key component to ensure the success of multistage fracturing. Packers enable sections of the wellbore to be sealed of and separately fractured by hydraulic pressure, one at a time, while the remainder of the wellbore is not afected. However, reliable sealing properties of the packer rubber are required to meet the high-pressure and high-temperature (HPHT) conditions of reservoirs (such as 70 MPa and 170 °C). In this study, the structures of the packer rubber with two diferent materials are optimized numerically by ABAQUS and validated by experiments. The optimization process starts from the packer rubber with a conventional structure, and then, the weakest spots are identifed by ABAQUS and improved by slightly varying its structure. This process is iterative, and the fnal optimized structure of a single rubber barrel with expanding back-up rings is achieved. For the structure of three rubber barrels with metallic protective covers, both HNBR and AFLAS fail under HPHT conditions. For the fnal optimized structure, the packer rubber made of AFLAS can work better under HPHT than that made of HNBR which ruptures after setting. The results show that the optimized structure of a single rubber barrel with expanding back-up rings and the material AFLAS are a good combination for the packer rubber playing an excellent sealing performance in multistage fracturing in horizontal wells. Keywords: packer rubber, sealing property, structure optimization, hydrogenated nitrile–butadiene rubber (HNBR), AFLAS rubber.

Strategic Planning for Optimal Management of Different Types of Shale Gas Wastewater

This paper presents a mathematical programming approach for the strategic planning of managing wastewater generated by hydraulic fracturing operations in shale gas production. The proposed approach aims to achieve optimal selection of treatment, storage, and reuse activities. The approach also accounts for the variability of wastewater characteristics including the short-term flowback and transition water as well as the longer-term produced water. Because of the different compositions of the pollutants in the various types of wastewater, stream segregation is considered as an option. Furthermore, the model accounts for seasonal variabilities in freshwater availability. Economic and environmental objectives are considered. The economic objective function aims to determine the minimum total cost, which is composed of freshwater, treatment, storage, and transport costs. Credit is given for reused water. The environmental objective focuses on the reduction of freshwater requirements needed for the fracturing step. The proposed model determines trade-offs between cost and water consumption. A case study is presented, and the results show that it is possible to reduce up to 32.43% of freshwater consumed and to reuse up to 12.26% of the total wastewater from wells for fracturing needs.

Appraisal of groundwater contamination from surface spills of fluids associated with hydraulic fracturing operations

Contaminated groundwater is a priority issue on the environmental agendas of developed countries. Therefore, there is an obvious need to develop instruments and decision-making mechanisms that allow the estimation of the risk to human health due to the presence of contaminants in soils and groundwater, in a fast and reliable manner. Thus, this study aims to assess whether the spilling of hydraulic fracturing fluids prior to injection has a potential risk to groundwater quality in the Kern County Sub-basin, California, by identifying the hydrological factors and solute transport characteristics that control these risks while taking into consideration the temperature rises due to climate change. The approach uses the concept of the groundwater pollution risk based on comparing the concentration of pollutants within the water table by using a predetermined permissible level. The current average annual temperature and that by the end of the 21st century was used to estimate the diffusion of benzene through three types of soil by using HYDRUS-1D software. The software was used to predict the contaminant concentration profile of benzene in the water table with special reference to the impact of surface temperatures. The results showed that an expected rise of the surface temperature by 4.3 °C led to an increase in the concentration of benzene by 2.3 μg/l in sandy loam soil, 6.8 μg/l in silt loam soil, and finally, 2.6 μg/l in loam soil. The results show that climate change can substantially affect soil properties and their chemical constituents, which then play a major role in absorbing pollutants.

Effects of salinity on the leaching of ionic species from hydrocarbon target formations during hydraulic fracturing

The combination of hydraulic fracturing with horizontal drilling has revolutionized oil and gas production. However, most of our understanding of the subsurface mechanisms and chemical interactions that occur during the process come from analyses of flowback and produced water (FPW). While the chemical composition of FPW can provide some information to understand water-rock interactions in the subsurface, the mechanisms by which dissolved species, including potentially toxic heavy metals (PTHM), are mobilized remain poorly constrained. In this study, we used stirred benchtop reactors to simulate the geochemical processes that occur when injected hydraulic fracturing fluid (HFF) interacts with reservoir rock formations of the Upper Devonian Duvernay Formation, a mudstone formation that is an important hydraulic fracturing target in west-central Alberta, Canada. Our aims were to: (1) assess whether our laboratory methods can be used to predict the inorganic chemistry of FPW, including concentrations of PTHM, and (2) to ascertain the reaction kinetics and mechanisms of the release of inorganic components from reservoir rocks. Our results indicate that elemental concentration data from reactor experiments coupled with saturation indices modelling can be used to predict the assemblage of solid phases that precipitates downhole, such as barite + celestine + gypsum. High salinity experiments (0.5 M NaCl), simulating FPW reuse, showed increased concentrations of many dissolved species with increasing salinity. Our findings were corroborated with geochemical modelling of FPW samples collected from operating unconventional wells in the Duvernay Formation. FPW from wells using a mixture of recycled produced water (RPW) and fresh source water to make up the injected HFF had higher concentrations of many elements, including the PTHM, Ba, Sr, and As. Our work illustrates the potential environmental risks of using RPW in hydraulic fracturing operations in the event of a spill and it provides a robust benchtop approach to predict the leaching of elements from the host rock during hydraulic fracturing.

Application of softening-coagulation-flocculation-UF hybrid process for internal reuse of shale gas fracturing flowback water: performance and fouling analysis

Shale gas fracturing flowback water (SGFFW) recycling for another fracking is currently the dominant option but is subject to certain restrictions, including the declined performance of hydraulic fracturing due to divalent metal ions, organics and particles. In this study, we investigated the performance of softening-coagulation-flocculation-ultrafiltration (S-C-F-UF) process in treating Changning SGFFW and membrane foulings. The results indicated that (1) the S-C-F process could achieve better water quality than S-C process, the 99.3% of turbidity, 34% of total organic carbon (TOC) and 85.9% of hardness can be removed under the optimal pretreatment condition (pH = 10, 500 mg/L polyaluminum chloride [PAC], 0.2 mg/L polyacrylamide [PAM]); (2) under the optimal condition, the normalized water flux decline was minimum and the membrane life was the longest; (3) with increase dosage of PAC, the fouling mechanism changed from complete blocking to standard blocking model, while the standard blocking changed to cake blocking model with increase dosage of PAM; (4) the performances of slick water prepared by the effluent treated by the S-C-F-UF hybrid process met the performance requirements of slick water. The results of this paper demonstrated that the hybrid process was an effective technology for internal reuse of SGFFW in shale plays.

Hydrofracture plugging mechanisms and evaluation methods during temporary plugging and diverting fracturing

AbstractTemporary plugging and diverting fracturing (TPDF) technique shows great advantages in stimulating unconventional oil and gas reserves. Revealing the fracture plugging mechanism and establishing the evaluation method are beneficial for revealing the mechanism of forming multiple fractures during TPDF. This work revealed the processes of plugging the fractures based on the typical injection pressure curve of hydraulic fracturing operation and then applied the stress cage model, the fracture closure stress model, and the fracture propagation resistance model to reveal the fracture plugging mechanisms. Moreover, this paper establishes a 2D XFEM model to evaluate the fracture plugging effect, and the reliability of the model is verified against the finite element model. Based on the XFEM model, this work investigates the fracture plugging effects influenced by the uneven distribution of net pressure within the fracture. The results prove that fracture mouth plugging of TPF mainly enhances the wellbore circumferential stress, in‐fracture plugging mainly enhances fracture closure pressure, fracture tip plugging mainly hinders fracturing fluids flowing toward fracture tips, all of them aim at enhancing the reopen pressure of the existing fractures and prevent the propagation of the existing fracture. Diverter bridging and plugging can change the distribution of fracture net pressure and dramatically reduce the fracture tip stress factor, and thus, the existing fracture propagation can be efficiently stopped.

Performance evaluation of analytical methods in linear flow data for hydraulically-fractured gas wells

Hydraulically fractured wells drilled in unconventional gas reservoirs are often produced with significantly high fixed drawdown to increase production. However, such unconventional gas wells exhibit extended periods of linear flow regime which could last for several years. Linear flow regime results from the fluid flow throughout Infinite-Conductivity Hydraulic Fractures (ICHFs) and Finite-Conductivity Hydraulic Fractures (FCHFs). This makes the analysis of linear flow regime of great importance to estimate parameters like fracture half-length, fracture width, fracture permeability and other parameters. Since the fracture half-length is an essential parameter for history matching and forecasting, it should be properly estimated and predicted. In this study, two analytical methods for analyzing linear flow were used to estimate the fracture half-length in hydraulically fractured gas wells producing from ICHFs and FCHFs under constant pressure conditions (fixed drawdown). The analytical methods compared are square root time and inverse production method. The investigated two analytical methods were compared along with the use of five different correction methods. The correction methods applied on the analytical solutions are those proposed by Ibrahim and Wattenbarger (2006), Nobakht and Clarkson (2012), Behmanesh et al. (2017), Chen and Raghavan (2013) and mean pressure. The comparison was done by conducting sensitivity analysis in term of initial pressure, flowing bottom hole pressure, reservoir temperature, permeability and dimensionless fracture conductivity. The study demonstrated that for ICHFs, both analytical methods provide close estimates of fracture half-length with the best results coming from the use of correction techniques of Nobakht and Clarkson (2012) and Behmanesh et al. (2017). For FCHFs, the inverse production method performed better than the square root time technique with the use of Chen and Raghavan (2013) and Ibrahim and Wattenbarger (2006) corrections. However, the inverse production methodology seems to be more sensitive than square root time to the change level in initial pressure and permeability. Moreover, it is shown that the square root time methodology generally overestimates the value of fracture half-length for FCHFs except some of the cases where the mean pressure is used. The results of this study provide general guidelines on the most accurate methods with their correction ways that can help to better analyze linear flow data in fractured gas wells. Also, this research can serve as selection criteria to choose the best analytical production methods to evaluate the performance of hydraulic fractures according to the well and reservoir properties. • This study showed that the square root time methodology can be used for both ICHF and FCHF. • Behmanesh et al. (2017) correction method was recommended due to its straight forward application. • If the inverse solution method is used, Behmanesh et al. (2017) correction is recommended for the ICHF cases. • Chen and Raghavan (2013) correction should be applied for the FCHF cases if the inverse solution method is used. • The square root time method tends to overestimate the value of fracture half-length in some conditions.

Ultra-lightweight Nanosand/Polymer Nanocomposite Materials for Hydraulic Fracturing Operations

Ultra-lightweight Nanosand/Polymer Nanocomposite Materials for Hydraulic Fracturing Operations

Spatiotemporal changes in seismic velocity associated with hydraulic fracturing-induced earthquakes near Fox Creek, Alberta, Canada

To characterize the subsurface geomechanical response to hydraulic fracturing (HF) activities, we study the spatiotemporal changes of seismic velocity during the completion of four HF wells in the Fox Creek area, Alberta, Canada. We estimate temporal velocity changes (dv/v) from ambient seismic noise recorded during the Tony Creek Dual Microseismic Experiment (ToC2ME) by comparing a 5-day stacked noise correlation function with a reference noise correlation function stacked over the deployment period. In the frequency band (0.1–0.4 Hz) most sensitive to the injection depths (~3.4 km), we observe daily dv/v that revealed alternating gradual velocity decreases and increases with magnitudes in the range of ±0.9%. We found a strong temporal correlation between the onset of velocity decreases and periods of intense seismicity, suggesting that the observed dv/v reductions are likely caused by stress-induced subsurface deformation due to elevated pore pressures, increased crack density, and ground shaking. A period of dv/v increase observed between the beginning and end of different well stimulation is attributed to crustal healing. Comparing the dv/v time series with injection parameters, we observed a 272.66% increase in induced seismicity and 50% more reduction in dv/v during the second injection phase that are correlated with 90.53%, 169.64%, and 4.34% increase in the injection volume, rate, and pressure, respectively. Our study provides valuable new information on the changes in reservoir elastic properties within the Western Canadian Sedimentary Basin. It also demonstrates that coda wave interferometry using data from dense seismic arrays near injection sites can be an additional tool for monitoring hydraulic fracturing operations.

Особенности проведения гидроразрыва пласта в отложениях с трудноизвлекаемыми запасами

Introduction. When developing productive deposits containing hard-to-recover oil reserves, the main difficulty is associated with low values of the reservoir properties of the reservoirs and their significant heterogeneity. The use of hydraulic fracturing technology allows solving these problems by increasing the well drainage area, and also as a means of intensifying production. Materials and methods of research. The study of the process of hydraulic fracture development in the deposits of the Bazhenov formation in a vertical well showed that when water is injected, long narrow fractures are formed in the formation, their filling with subsequent supply of a fracturing fluid with proppant leads to an increase in the width and height of the created fracture. Due to the hydrophobic properties and increased brittleness of the rocks of the Bazhenov formation, an effect similar to hydraulic fracturing is also possible during the injection of water into the formation at high pressures, for example, when organizing a waterflooding system. Another direction is multi-zone hydraulic fracturing. The advantage of this method is the greater distribution of fractures over the area compared to point hydraulic fracturing operations. Results and Discussion. On the deposits of the Bazhenov formation, pilot work was carried out to create artificial fracturing by pumping water. The positive effect was expressed in a twofold increase in oil recovery in the pilot area. As a negative side effect, a sharp increase in water cut was noted. The experience of using multi-zone hydraulic fracturing in the conditions of the Bazhenov formation was considered on the example of the deposits of the Surgut arch. The dynamics of flow rates and cumulative oil production by wells during operation is presented. Also, a comparison was made of the main performance indicators of wells with multi-stage hydraulic fracturing with the average indicators of directional wells of the same fields. Conclusion. The pilot work conducted on water injection into the Bazhenov formation deposits unambiguously showed that additional fracturing is formed in the reservoir and the volume of additional fractured capacity is directly proportional to the volume of injected water. The experience of using multi-zone hydraulic fracturing revealed the advantages of this technology compared to directional wells. Under conditions of reservoir reservoir properties uncertainty, the creation of artificial conductivity using hydraulic fracturing may be the only way to ensure well productivity. MSHF in horizontal wells forms a system of fractures in a large volume and seems to be more effective in such conditions compared to conventional hydraulic fracturing.

The Rise, Peak and Decline of the Seismic Hazard Related to Hydraulic Fracturing Activities in the Duvernay Play, Fox Creek Area, Alberta

AbstractWe analyze the temporal evolution of the induced seismicity related to hydraulic fracturing activities in the Duvernay Formation, near Fox Creek, Alberta, Canada. For this analysis, we estimate annual Gutenberg‐Richter parameters, ‐ and ‐ values, and then calculate the annual likelihood of earthquakes greater than magnitude from 2014 to 2020. The seismic hazard near Fox Creek has consistently decreased since 2015, from a 95% probability of an earthquake greater than magnitude in 2015 to 4% in 2019 and less than 1% probability in 2020. The induced seismicity in Fox Creek is characterized by two actively seismic regions with distinctive features: (a) an Eastern region (∼220 events ) with lower b‐values and higher hazard; (b) a Western region (∼210 events ) with higher b‐values and lower seismic hazard. In contrast, extensive regions where hydraulic fracturing is performed, particularly East of the seismic cluster, remain non‐seismogenic. The overall decreasing seismic hazard, which contrasts with increasing operator activity, can be associated with (a) the intensification of hydraulic fracturing operations toward areas less susceptible to induced seismicity and (b) the reduction of seismic activity in the Eastern region, which exhibits the highest seismic hazard. We also find evidence of a minimum annual injection volume required to trigger induced seismicity in both the Western and Eastern regions. The minimum injection threshold increases over the years, implying increasingly successful mitigation strategies, likely due to regulatory implementations in the area, which has led the operators to exercise precaution in regions with significant seismic hazard and adapt treatment strategies to avoid triggering moderate magnitude size events during hydraulic fracturing stimulations.

Proppant transport in hydraulic fractures by creating a capillary suspension

Slick water fracturing fluids with high viscosity and minimal friction pressure losses are commonly employed in hydraulic fracturing technology. The conventional method of conducting hydraulic fracturing operations using high-viscosity fluids is not always suitable in complex geological conditions because hydraulic fracturing in low-productive formations creates fractures that resemble radial fractures, lowering the impact’s efficiency and profitability due to inefficient use of materials and reagents. As such, the goal is to limit the height of the fracture development and increase their length. In this work, we developed a low viscosity fracturing fluid with high proppant transport ability in order to minimize the specific pressure in the fracture and control its height. The hydrophobizing effect of surfactant was investigated, and criteria for employing it in hydraulic fracturing fluid formulation were created. We also developed a fracture model that we used to run simulation experiments in order to determine the nature of the fracturing fluid dispersion. Model simulations of hydraulic fracturing were performed utilizing proppant mesh sizes of 30/60, 20/40, and 16/20. Our experimental results have demonstrated that utilizing a capillary suspension, it is possible to generate a stable formulation of hydraulic fracturing fluid with an effective settling capacity by adding PLA fibers as a reinforcing filler to the formulation.