Low Injection Rates Research Articles

Detecting Low-Rate Replay-Based Injection Attacks on In-Vehicle Networks

The lack of security in today’s in-vehicle network make connected vehicles vulnerable to many types of cyber-attacks. Replay-based injection attacks are one of the easiest type of denial-of-service attacks where the attacker floods the in-vehicle network with malicious traffic with intent to alter the vehicle’s normal behavior. The attacker may exploit this vulnerability to launch targeted low-rate injection attacks which are difficult to detect because the network traffic during attacks looks like regular network traffic. In this paper, we propose a sequence mining approach to detect low-rate injection attacks in Control Area Network (CAN). We discuss four different types of replay attacks that can be used by the adversary, and evaluate the effectiveness of proposed method for varying attack characteristics and computational performance for each of the attacks. We observe that the proposed sequence-based anomaly detection achieves over 99% f-score, and outperforms existing dictionary based and multi-variate Markov chain based approach. Given that the proposed technique only uses CAN identifiers, the techniques could be adaptable to any type of vehicle manufacturer.

Fault Reactivation and Induced Seismicity During Multistage Hydraulic Fracturing: Microseismic Analysis and Geomechanical Modeling

SummaryThis paper presents a case study of fault reactivation and induced seismicity during multistage hydraulic fracturing in Sichuan Basin, China. The field microseismicity data delineate a fault activated near the toe of the horizontal well. The spatio-temporal characteristics of the microseismicity indicate that the seismic activity on the fault during the first three stages is directly related to the fluid injection, while after Stage 3, the seismic activity is possibly due to the relaxation of the fault. The fault-related events have larger magnitudes and different frequency-magnitude characteristics compared to the fracturing-related events. Three-dimensional (3D) fully coupled distinct element geomechanical modeling for the first two hydraulic fracturing stages and a shut-in stage between them is performed. The modeling result generates features of microseismicity similar to that of the field data. The energy budget analysis indicates that the aseismic deformation consumes a major part of the energy. The simulated fault shear displacement is also consistent with the casing deformation measured in the field. The model is also used to investigate the impact of possible operational changes on expected seismic responses. The results show that lower injection rate and lower fluid viscosity would be helpful in reducing casing deformation but not in mitigating seismicity. Decreasing the total fluid injection volume is an effective way to mitigate the seismicity, but it may hinder the stimulation of the reservoir formation and the production of the well.

Experimental study of hydraulic fracture initiation and propagation in unconsolidated sand with the injection of temporary plugging agent

High fluid leak-off rate and low pressurization rate are great challenges for hydraulic fracturing in unconsolidated sands. In this paper, the design of an injection plugging agent as a pad for fracture initiation aid in unconsolidated sands is presented. We have carried out tri-axial hydraulic fracturing tests, focusing on super-high- and high-permeability unconsolidated sands with AE (acoustic emission) monitoring. Powdered oil-soluble materials are used as temporary plugging agents. The laboratory tests demonstrated that three types of fracture geometry, multiple fracture, bi-wing fracture and single-wing fracture, are created. Furthermore, there are continuous AE energy signals with the increase of plugging agent injection, which is a good match with the fluctuated pressure. Moreover, multiple peak fracture points can be observed due to intense grains interaction. In addition, the breakdown pressure has positive relationships with the pump rate and concentration of injection of plugging agents. Multiple fractures only exist for super-high-permeability unconsolidated sands with high pumping rate and low plugging agent concentration, which is primarily due to the plugging agent seal for both hydraulic fracture and the rock matrix. A low injection rate with low plugging agent concentration led to single-wing fracture for high-permeability unconsolidated sands, whereas a high injection rate with high plugging agent concentration led to single-wing fracture for low-permeability unconsolidated sands. Low plugging agent concentration is beneficial for aiding hydraulic fracture propagation along the maximum horizontal stress direction. In addition, the high-pump-rate and low-plugging-agent-concentration scenario and low-pump-rate and high-plugging-agent-concentration scenario have a greater chance of creating bi-wing fracture for super-high-permeability unconsolidated sands, whereas low pump rate and high plugging agent concentration are beneficial for bi-wing fracture for high-permeability unconsolidated sands. Local tortuous fracture path indicate tensile and fracture both exist during unconsolidated sands fracturing. With respect to sand control and large contact area, these treatments should be the better fracturing scenario for unconsolidated sand fracturing design with injection of a plugging agent. The findings of this study can help for better understanding of the fracturing mechanism and optimizing treatment parameters in unconsolidated sands fracturing.

Numerical solutions of heat transfer problems in gas production from seabed gas hydrates

The natural gas in gas hydrates is considered as a major resource of future clean energy. Producing natural gas from gas hydrates at seafloor presents a great challenge to the engineers due to low efficiency in heat transfer processes. A numerical model was developed in this study to investigate the temperature profiles along the hose assembly in the MRM for harvesting the natural gas from hydrates at the seafloor. Sensitivity analyses were carried out to find major factors affecting the delivering water temperature to the gas hydrate deposits. The result shows that decreasing the temperature of the injected water at surface will cause drop in the delivery temperature of water in the pipe. The drop in the surface temperature is transferred almost by the same amount to the drop in the delivering temperature with the pipe insulation used. The temperature of the water delivered to the gas hydrates drops slowly and linearly with water depth at high water injection rate, and sharply and non-linearly with water depth at low water injection rate. The delivery water temperature is strongly controlled by the pipe insulation but insensitive to it when the thermal conductivity of the insulation material is less than 0.0245 W/m-oC. The temperature in the riser annulus is not essentially affected by any of the invested parameters. A comparison between the numerical model and analytical model under the condition of homogeneous mixture flow was performed. The result shows a good agreement between them, which verified the numerical model.

Experimental Investigation on Hydraulic Fractures in the Layered Shale Formation

Multistage fracturing of horizontal wells to form a complex fracture network is an essential technology in the exploitation of shale gas. Different from the conventional reservoirs, the mechanical characteristics of shale rock have significant heterogeneity due to the existence of beddings, which makes it difficult to predict the fracture geometry in the shale reservoir. Based on the laboratory experiments, the factors that affect fracture propagation were analyzed. The experimental results revealed that the hydraulic fracture would cross the beddings under the high vertical stress difference, while it would propagate along with the bedding under the low vertical stress difference; besides, the low injection rate and viscosity of the fracturing fluid were beneficial to generate a complex fracture network. Under the high injection rate and viscosity, a planar fracture was created, while a nonplanar fracture was observed under the low injection rate and viscosity, and branch fracture was created. According to the acoustic emission events, the shear events were the main events that occurred during the hydraulic fracturing process, and the acoustic emission events could be adopted to describe the fracture network. Lastly, the supercritical carbon dioxide fracturing was more effective compared with the hydraulic fracturing because the fracture network was more complex.

The propagation research of hydraulically created fractures in coal seams based on discrete element method

Coalbed methane (CBM) is clean unconventional energy that can be exploited with stimulation treatment to realize commercial value, and hydraulic fracturing is the key technology for increasing CBM production. The simulation of hydraulic fractures is an important research content that can guide the engineering practice to achieve the purpose of increasing production. Based on the distribution characteristic of cleats in coal, the research on the propagation of hydraulic fractures is carried out via Discrete element method (DEM). The simulated results show that: hydraulic fractures mainly propagate along the cleats towards the maximum principal stress. The fracture network can be formed due to the intersection of face cleats and butt cleats that can propagate at certain pressure. During the injection process of fracturing fluid, the pressure at injection point decreases with the fracture propagation until the pressure tends to be stable. With the increase of injection rate and fracturing fluid viscosity at the same condition, the maximum aperture of hydraulic fracture increases, while the length of principal hydraulic fracture shortens. Therefore, to achieve the purpose of forming hydraulic fracture network in coal seams with cleats, low viscosity fracturing fluid and low injection rate need be applied to the fracturing technology. As the cleat density increases, the number of branch fractures increases, but the length of principal hydraulic fracture becomes short. Long and narrow hydraulic fractures are easily formed in coal seams with lower cleat density.

Determining Characteristic Relative Permeability From Coreflooding Experiments: A Simplified Model Approach

AbstractRelative permeability measurements from drainage coreflooding experiments are effective properties that vary with injection rate when capillary heterogeneity effects are present. It is therefore important to estimate the fine‐scale characteristic relative permeability ( ), which is independent of flow rate and can be used for accurate reservoir simulation and numerical modeling of coreflooding. Previous methods for estimation are based on two‐phase flow simulations with fine‐scale heterogeneous permeability and capillary pressure. These are computationally complex and prone to error. This work presents a reduced method, based on a simplified model, requiring only solutions of steady state single‐phase flow equations. The simplified model is used to study a number of synthetic 2‐D permeability realizations and 3‐D core models constructed based on experimental data from previous literature. The estimation method is tested on these examples and shown to be generally accurate. Cases where estimation error is significant are characterized by low injection rates, large nonwetting phase fractional flow, strong capillary heterogeneity, and small capillary number (ratio between core average pressure drop and capillary pressure drop). The estimation error is believed to be related to errors in the full‐model (two‐phase flow) simulations; that is, we find that for low injection rates, our simulator presents significantly different results compared to a commercial simulator. This could explain the source of mismatch between full and simplified methods and calls for further investigation of inaccuracy in numerical simulations at low flow rates, which could have implications for coreflood modeling and low rate reservoir simulation.

A spatially resolved fluid-solid interaction model for dense granular packs/soft-sand

Fluid flow through dense granular packs or soft sands can be described as a Darcy’ s flow for low injection rates, as the friction between grain-grain and grain-walls dominate the solid system behaviour. For high injection rates, fluid forces can generate grain displacement forming flow channels or “fractures”, which in turn modify local properties within the system, such as permeability and stress distribution. Due to this kind of “self organized” behaviour, a spatially resolved model for these interactions is required to capture the dynamics of these systems. In this work, we present a resolved model based on the approach taken by the CFDEM open source project which uses LIGGGHTS – a discrete elements method (DEM)– to model the granular behaviour and OpenFoam finite volume library for computational fluid dynamics (CFD), to simulate the fluid behaviour. The capabilities provided by the DEM engine allows the properties of the solid phase, such as inter-grain cohesion and solid confinement stress to be controlled. In this work the original solver provided by the CFDEM project was modified so as to deal with dense granular packs more effectively. Advantages of the approach presented are that it does not require external “scaling parameters” to reproduce well known properties of porous materials and that it inherits the performance provided by the CFDEM project. The model is validated by reproducing the well-known properties of static porous materials, such as its permeability as a function of the system porosity, and by calculating the drag coefficient for a sphere resting inside a uniform flow. Finally, we present fracture patterns obtained when modelling water injection into a Hele-Shaw cell, filled with a dense granular pack.

Improving acid fracture design in dolomite formations utilizing a fully integrated acid fracture model

Acid reactivity with dolomite is more sensitive to temperature as compared to calcite formations, resulting in different dissolution profile. Acid fracture fluids are heated inside the fracture, as it flows away from the wellbore, due to the reservoir heat flux. This causes a sharp increase in dolomite reactivity, resulting in a bell-shaped conductivity profile along the fracture half-length. The productivity of such conductivity distributions will be wrongly estimated if a single average conductivity value is used. In the present research, a reservoir simulator that includes variable fracture conductivity was coupled with an integrated acid fracture model. Also, design guidelines for acid fractures in dolomite formations have been proposed.Case studies are presented, showing that in conventional acid fracture designs, the maximum dissolution in dolomite usually occurs away from the wellbore. This negatively affects productivity, as maximum conductivity is desired near the wellbore. This effect is especially significant for fracturing candidate wells in higher permeability reservoirs. This study shows that in good permeability formations, productivity can be improved by acid fractures designed at a lower injection rate. In cases where the desired injection rate is not sufficient to propagate the fracture, good productivity can be obtained by using two acid stages with different injection rates. A higher injection rate is employed to create the desired fracture dimensions, and a smaller rate used to obtain good conductivity in the near-wellbore region. In low permeability reservoirs, it is desirable to alternate injections of retarded acid systems with pad fluid to create longer acid penetration distances. The results show that, in certain conditions, designs following the proposed guidelines can result in substantial productivity improvement compared to the conventional approach.

Optimization of geothermal energy extraction from abandoned oil well with a novel well bottom curvature design utilizing Taguchi method

Abandoned oil wells have a great potential to be converted into geothermal energy extraction wells. However, these wells have low energy conversion rates as compared to conventional geothermal open loop wells. Therefore, increasing the heat transfer is one of the major concerns in the utilization of abandoned oil well for geothermal energy extraction. This study is conducted to evaluate the heat transfer enhancement of a novel well bottom curvature design installed inside the wellbore using a computational fluid dynamics approach. Various well bottom curvature designs were evaluated, along with the effects of working fluid inlet temperature and flow rate. For optimization, Taguchi Statistical Method was adopted to determine the optimum parameter combination and their interactions. From the study, it is found that 0.5 m well bottom curvature is preferred for higher output temperature and heat transfer rate, whereas 0.8 m well bottom curvature is recommended for lowering pressure drop and producing higher CoP. On the other hand, lower injection temperature (288K) and lower injection rate (10 m3/h) produces better overall wellbore performance, except for higher outlet temperature purposes, where a higher injection temperature (298K) is favoured and higher heat transfer rate applications, where a higher injection rate (30 m3/h) is preferred.

Cyclic hydraulic fracturing of pocheon granite cores and its impact on breakdown pressure, acoustic emission amplitudes and injectivity

Cyclic hydraulic fracturing, which employs cyclic injection with alternating high and low injection rates or pressurization, is suggested to assist in reducing induced seismicity. Our laboratory work demonstrates the impact of cyclic hydraulic fracturing on tensile-dominated fracturing of intact Pocheon granite core specimens. Cyclic injection of water reduces the breakdown pressure by up to ∼20% and the maximum acoustic emission amplitude is reduced by ∼14 dB on average. We observe hydraulic fractures in granite specimens through using computed tomography. Cyclic hydraulic fracturing creates complex fractures with more branches and smaller apertures compared with those created by continuous injection. The average injectivity of the fractured specimens by cyclic injection is smaller than the injectivity measured on specimens fractured by continuous injection.

Should Cerebral Angiography Be Avoided within Three Hours after Subarachnoid Hemorrhage?

ObjectiveWhile the risk of aneurysmal rebleeding induced by catheter cerebral angiography is a serious concern and can delay angiography for a few hours after a subarachnoid hemorrhage (SAH), current angiographic technology and techniques have been much improved. Therefore, this study investigated the risk of aneurysmal rebleeding when using a recent angiographic technique immediately after SAH. MethodsPatients with acute SAH underwent immediate catheter angiography on admission. A four-vessel examination was conducted using a biplane digital subtraction angiography (DSA) system that applied a low injection rate and small volume of a diluted contrast, along with appropriate control of hypertension. Intra-angiographic aneurysmal rebleeding was diagnosed in cases of extravasation of the contrast medium during angiography or increased intracranial bleeding evident in flat-panel detector computed tomography scans. ResultsIn-hospital recurrent hemorrhages before definitive treatment to obliterate the ruptured aneurysm occurred in 11 of 266 patients (4.1%). Following a univariate analysis, a multivariate analysis using a logistic regression analysis revealed that modified Fisher grade 4 was a statistically significant risk factor for an in-hospital recurrent hemorrhage (p =0.032). Cerebral angiography after SAH was performed on 88 patients ≤3 hours, 74 patients between 3–6 hours, and 104 patients >6 hours. None of the time intervals showed any cases of intra-angiographic rebleeding. Moreover, even though the DSA ≤3 hours group included more patients with a poor clinical grade and modified Fisher grade 4, no case of aneurysmal rebleeding occurred during erebral angiography. ConclusionDespite the high risk of aneurysmal rebleeding within a few hours after SAH, emergency cerebral angiography after SAH can be acceptable without increasing the risk of intra-angiographic rebleeding when using current angiographic techniques and equipment.

Numerical Modeling of Discrete Fractures in a Field-Scale FORGE EGS Reservoir

The response of the Fallon FORGE geothermal reservoir to hydraulic stimulation is modeled numerically to aid the conceptual design of the well geometries and completions. The numerical modeling approach is based on (a) a full hydro-mechanical coupling; and (b) explicit representation of a discrete fracture network (DFN). The reservoir-scale model has a core region of 1500 × 1200 × 1200 m3 volume around the positions of conceptual sub-horizontal well designs at the Fallon FORGE site. It contains relevant geological structure and a fracture network constructed and simplified using borehole data. Stimulation was modeled in six stages/zones along the horizontal well using both openhole (low injection rate at 5 kg/s) and cased borehole (combination of high, 80 kg/s, and low injection rates) completions to test the effectiveness of hydraulic fracturing combined with hydro-shearing. The reservoir stimulation in the two models was analyzed and quantitatively assessed. Results indicate that the Fallon FORGE site is well suited for an EGS by multi-staged hydraulic stimulation using sub-horizontal wells. The conclusion is based on the evaluation of potential for fracture slip and aperture increase as functions of induced pressure changes and the orientations of the natural joints relative to the regional principal stresses. Advantages and limitations of explicit representation of the DFN in the numerical models are presented and discussed.

Parametric study of fracture interference effects on fracture geometry for wellbore strengthening

ABSTRACT As one of the most widely used preventive treatment of lost circulation, wellbore strengthening techniques need to be further investigated to improve its efficiency. It is crucial to accurately predict the dynamic propagation of fractures for wellbore strengthening, while most of the numerical simulations neglect the distortion of fracture trajectory affected by fracture interference. Thus, a fully coupled poroelastic model is established by using the extended finite element method (XFEM) – based cohesive zone method (CZM) to investigate the effect of fracture interference. The rock deformation, seepage flow of pore fluid, fluid flow of fracture and leak-off of drilling fluid are coupled by the model. The sensitivity analysis is studied by capturing the change of fracture length, width and deviation angle. The results show that the distortion of the fracture trajectory and the closure extent of fracture surface after bridging can be controlled more easily with lower injection rate and larger spacing. A proper viscosity can balance between the distortion of the fracture trajectory and the tendency of fracture reopening after bridging. The anisotropic stress mainly affects the wellbore strengthening by influencing the propagation direction. Adjusting the inclination and azimuth of the wellbore to increase the effect of stress anisotropy can reduce the effect of stress shadow.

Harmonic Pulse Testing for Well Monitoring: Application to a Fractured Geothermal Reservoir

AbstractHarmonic Pulse Testing (HPT) has been developed as a type of well testing applicable during ongoing field operations because a pulsed signal is superimposed on background pressure trend. Its purpose is to determine well and formation parameters such as wellbore storage, skin, permeability, and boundaries within the investigated volume. Compared to conventional well testing, HPT requires more time to investigate the same reservoir volume. The advantage is that it does not require the interruption of well and reservoir injection/production before and/or during the test because it allows the extraction of an interpretable periodic signal from measured pressure potentially affected by interference. This makes it an ideal monitoring tool. Interpretation is streamlined through diagnostic plots mimicking conventional well test interpretation methods. To this end, analytical solutions in the frequency domain are available. The methodology was applied to monitor stimulation operations performed at an Enhanced Geothermal System site in Pohang, Korea. The activities were divided into two steps: first, a preliminary sequence of tests, injection/fall‐off, and two HPTs, characterized by low injection rates and dedicated to estimate permeability prior to stimulation operations, and then stimulation sequence characterized by a higher injection rate. During the stimulation operations other HPT were performed to monitor formation properties behavior. The interpretation of HPT data through the derivative approach implemented in the frequency domain provided reliable results in agreement with the injection test. Moreover, it provided an estimation of hydraulic properties without cessation of stimulation operations, thus confirming the effectiveness of HPT application for monitoring purposes.

Crack propagation and hydraulic fracturing in different lithologies

We simulated hydraulic fracturing in different lithologic rocks in the horizontal drilling by using the true physical model experiment and large rock specimens, carried out the real-time dynamic monitoring with adding tracer and then did post-fracturing cutting and so on. Based on this monitoring results, we compared and assessed the factors affecting expansion in shale, shell limestone, and tight sandstone and the fracture expansion in these rocks. In shale, the reformed reservoir volume is the highest, fracture network is formed in the process of fracturing. In tight sandstone, the fracture surface boundaries are curved, and the fracture surface area accounts for 25–50% of the entire specimen. In shell limestone, the complexity of the fracture morphology is between shale and tight sandstone, but no fracture network is developed. Brittleness controls the fracture surface area. In highly brittle rocks, the fracture surface area is high. Fracture toughness mainly affects the initiation and propagation of cracks. A fracture network is formed only if bedding planes are present and are more weaker than their corresponding matrix. The horizontal in situ deviatoric stress affects the crack propagation direction, and different lithologies have different horizontal in situ deviatoric stress thresholds. Low fluid injection rate facilitates the formation of complex cracks, whereas high fluid injection rate favors the development of fractures. Fluid injection weakly controls the complexity of hydraulic fracturing in low-brittleness rocks, whereas low-viscosity fracturing fluids favor the formation of complex cracks owing to easy enter microcracks and micro-pore. Displacement has a greater impact on high brittle rocks than low brittle rocks.

Experimental study of the dryout of a 2D heat-generating model porous medium

Dryout experiments are performed in a quasi two-dimensional heat-generating model porous medium, with bottom flooding. The test section is composed of an array of heating cylinders placed between two ceramic plates. It is held vertically and a liquid (HFE-7000) is injected from bottom at a controlled flow rate, pressure and temperature. Dryout incipient power is investigated by applying an increasing thermal power to a bundle of heating cylinders until a dry zone is detected. The liquid inlet mass fluxes range from 1.0kgm-2s-1 to 10.5kgm-2s-1 and the heat fluxes are between 195kWm-2 and 1086kWm-2. Two kinds of dryout phenomenology are observed. First, at low liquid injection rate (below 4.2kgm-2s-1 inlet mass flux), reaching the dryout power results into a liquid front receding from the top of the test section to the upper limit of the heated zone, while downstream the heated zone, the porous medium is vapour-saturated. Second, at higher flow rate (over 5.2kgm-2s-1 inlet mass flux), the boiling crisis happens at the surface of a single heating element, resulting in a local film boiling, whereas a two-phase flow still go through the whole test section. In both cases, high-speed visualizations allow characterizing 8 boiling/flow regimes, depending on the inlet mass flux, the power released by the heated zone, and the location inside the porous medium. In particular, when reaching the dryout incipient power, the existence of a pulsed flow regime is highlighted. Such a characterization of boiling/flow regimes might be helpful in improving dryout models.

Effect of injection parameters on proppant transport in rough vertical fractures: An experimental analysis on visual models

The understanding of proppant flow through fractures is critical in evaluating the performance of hydraulic fracturing operations. As a continuation of our experimental efforts devoted to understanding how proppant flows in rough vertical fractures, in this paper, we examine the effect of injection parameters on the proppant transport in rough vertical fractures. The effects of polymer concentration, injection rate, proppant concentration, and type of proppant were investigated in detail. Experimental results show that, in general, two types of settling patterns can be observed in the proppant transport in a rough fracture: sand-dune settling pattern and tree-like settling pattern. The following conditions tend to suppress the tree-like settling behavior of proppants in the rough fracture: a higher density of the proppants, a lower viscosity of the polymer solution, and a lower injection rate. This is attributed to a higher settling velocity of the proppants in the fracture under these conditions. A sufficiently high polymer concentration is needed to enable effective proppant flow in rough fractures. In general, the relative coverage of proppants increased dramatically as the polymer concentration increased, implying that the higher viscosity of fracturing fluid could enhance the slurry's ability to place more proppant vertically into the fracture and help to maintain a better conductivity after fracturing treatment. A sufficiently high injection rate of the slurry is also needed to enable effective proppant flow in rough fractures. At certain low injection rates, the proppants carried by a low polymer solution might not exhibit a tree-like settling pattern, diminishing the effect of roughness on the proppant transport. This means that even in rough fractures, the tree-like settling pattern of the proppants did not necessarily occur for sure; the injection rate should be properly selected to enable such phenomenon. With other conditions being kept constant, a higher proppant loading led to a higher final relative coverage of the proppants in the rough fractures. But if the injection rate used for delivering the proppants is not sufficiently high, we may encounter injectivity issues; in our lab experiments, this caused the choking of the pump. The heavier proppant (ceramic proppants) in the rough fracture models tended to suppress the tree-like settling pattern that was experienced by the lighter proppant (silica sands). This is attributed to the larger density of the ceramic proppants, leading to a larger settling velocity. In order to maximize the spreading of a given proppant over a rough fracture model, we should determine the proper values of all the essential injection parameters (including polymer solution, injection rate, proppant concentration) by striking a good balance among them. The conclusions obtained in this study shed light on how to optimize slurry injection parameters to achieve an optimal proppant-filling ratio during hydraulic fracturing.

How much water can be captured from flood flows to store in depleted aquifers for mitigating floods and droughts? A case study from Texas, US

Extreme flooding from Hurricane Harvey (∼100 km3, ∼80 million acre feet, maf of rainfall) in Houston, Texas, US co-located with depleted aquifers raises the question of whether we can capture floodwater to reduce flooding impacts and replenish aquifers for droughts. Here we quantified how much water could be captured from high magnitude flows (HMFs) in 10 major rivers discharging to the Gulf of Mexico for potential storage in depleted aquifers along the Texas Gulf Coast. Results show that HMFs (≥95th percentile) from rivers discharging to the Gulf of Mexico total 37 km3 (30 maf) in 2015–2017, similar in capacity to US Lake Mead (32 km3, 26 maf). These flows are less than modeled unappropriated flows that consider appropriated water rights and limited analysis suggests moderate reduction from environmental flows. Similarity in high flow volumes and modeled groundwater depletion in the Gulf Coast Aquifer system (∼25 km3, 20 maf) underscores the potential to partially mitigate flooding using aquifer storage. Interim storage would be required to resolve disconnects between high flood intensities and low aquifer injection rates. Engineering approaches will become increasingly important to manage climate extremes.

A model of cement-formation interface failure length in supercritical CO2-ECBM and storage injection well considering the coal swelling effect under high pressure

The swelling effect of high-pressure carbon dioxide (CO2) in coal seam is obvious. In the restrained deep formation, it is converted to stress acting on the wellbore and the caprock. The action stress is concentrated near the wellbore and poses a threat to the cement-formation interface. Due to interface failure to micro-annulus, wellbore integrity will be lost and this will have an impact on carbon dioxide-enhanced coalbed methane recovery (CO2-ECBM) and storage. In this paper, the pseudo-steady pressure distribution and steady pressure distribution of CO2 injection process were established after considering the change in permeability of coal seam injected with high-pressure supercritical CO2, and the vertical stress distribution model was derived. A one-dimensional radial numerical simulation formed by iterative method was established. A model for calculating the failure length at the cement-formation interface is obtained, and the shear stress and debonding length at the interface at various injection rates and times are calculated. The results show that the shear stress on the cement-formation interface has the maximum magnitude on the height of the interface between coal seam and caprock. The shear stress generated by coal swelling may break the fragile cement-formation interface into a narrow debonding interface. The injection rate has an influence on the interface failure length. For the same total injection amount, low injection rate is beneficial to protect the cement-formation interface integrity. This study provides a reference for the design of maximum injection speed for CO2-ECBM and storage to avoid leakage.