Impact Of Injection Rate Research Articles

Impact of injection rate on smooth and rough fracture activation in granite: Laboratory-scale acoustic emission analysis

This study aims to understand the effect of injection rate on injection-induced fracture activation in granite. We performed water injection-induced slip tests on samples containing either a smooth or a rough fracture at four different injection rates under undrained conditions and monitored the acoustic emission (AE) signals during the tests. Experimental results reveal that the critical activation fluid pressure is related to the injection rate, pressure diffusion rate, stress state, and fracture roughness. For the smooth fracture, as the injection rate increases, the critical activation fluid pressure increases significantly, while the injection rate has little effect on the critical activation fluid pressure of the rough fracture. The quasi-static slip distance of fractures decreases as the injection rate increases, with rough fractures exhibiting a greater overall slip distance compared to smooth fractures. The number of AE events per unit sliding distance increases with the injection rate, while the global b value decreases. These results indicate that higher injection rates produce more large-magnitude AE events and more severe slip instability and asperity damage. We established a linkage between fluid injection volume, injection rate, and AE events using the seismogenic index (Σ). The smooth fracture exhibits a steadily increasing Σ with the elapse of injection time, and the rate of increase is higher at higher injection rates; while the rough fracture is featured by a fluctuating Σ, signifying the intermittent occurrence of large-magnitude AE events associated with the damage of larger fracture asperities. Our results highlight the importance of fracture surface heterogeneity on injection-induced fracture activation and slip.

Impact of Injection Rate on Flow Mixing during the Refining Stage in an Electric Arc Furnace

During the refining stage of electric arc furnace (EAF) operation, molten steel is stirred to facilitate gas/steel/slag reactions and the removal of impurities, which determines the quality of the steel. The stirring process can be driven by the injection of oxygen, which is carried out by burners operating in lance mode. In this study, a computational fluid dynamics (CFD) platform is used to simulate the liquid steel flow dynamics in an industrial-scale scrap-based EAF. The CFD platform simulates the three-dimensional, transient, non-reacting flow of the liquid steel bath stirred by oxygen injection to analyze the mixing process. In particular, the CFD study simulates liquid steel flow in an industrial-scale EAF with three asymmetric coherent jets, which impacts the liquid steel mixing under different injection conditions. The liquid steel mixing is quantified by defining two variables: the mixing time and the standard deviation of the flow velocity. The results indicate that the mixing rate of the bath is determined by flow dynamics near the injection cavities and that the formation of very low-velocity regions or ‘dead zones’ at the center of the furnace and the balcony regions prevents flow mixing. This study includes a baseline case, where oxygen is injected at 1000 SCFM in all the burners. Two sets of cases are also included: The first set considers cases where oxygen is injected at a reduced and at an increased uniform flow rate, 750 and 1250 SCFM, respectively. The second set considers cases with non-uniform injection rates in each burner, which keep the same total flow rate of the baseline case, 3000 SCFM. Comparison between the two sets of simulations against the baseline case shows that by increasing the uniform flow rate from 1000 to 1250 SCFM, the mixing time is reduced by 10.9%. Moreover, all the non-uniform injection cases reduce the mixing time obtained in the baseline case. However, the reduction in mixing times in these cases is accompanied by an increase in the standard deviations of the flow field. Among the non-uniform injection cases, the largest reduction in mixing time compared to the baseline case is 10.2%, which is obtained when the largest flow rates are assigned to coherent jets located opposite each other across the furnace.

Numerical modeling for CO2 storage with impurities associated with enhanced gas recovery in depleted gas reservoirs

Carbon capture and storage (CCS) in depleted gas reservoirs is an important strategy to mitigate the CO2 emissions, whereas the lack of financial incentives limits its application in large-scale. In order to reduce the costs and get potential financial benefits, CO2 with impurities (N2 and O2) were applied for CCS and CO2 storage with enhanced gas recovery (CSEGR). The impacts of the key properties of the depleted gas reservoir, including the gas recovery, reservoir temperature, residual water saturation, and the injection rate on the performance of CCS and CSEGR were analyzed systematically. The results showed that the CO2 storage capacity decreases proportionally to the impurity concentration. The reservoir with a temperature of 75 °C is favorable for the CO2 storage capacity compared with that of 114 °C. The impact of injection rate on the CO2 storage capacity is minor, whereas a high injection rate (10 kg/s) is advantageous for CSEGR, with a short project duration of 10.5 years compared with that of 20.1 years for the injection rage of 2.5 kg/s. The depleted gas reservoir with a primary gas recovery of 70% is favorable for CSEGR compared with that of 90%, while the order is reverse for CCS. It is suggested to produce the CH4 as possible before the operation of CCS and CSEGR. The N2 and O2 can be detected approximately 0.5 years before CO2 at the determined location, which can be regarded as a signal of potential CO2 leakage due to the chromatographic partitioning. In addition to the solubility and concentration of impurities would affect the partitioning, the residual water saturation is very crucial for the occurrence of significant chromatographic partitioning phenomenon.

Experimental Investigation on the Initiation of Hydraulic Fractures from a Simulated Wellbore in Laminated Shale

Abstract Understanding the formation mechanisms of complex fracture networks is vitally important for hydraulic fracturing operations in shale formation. For this purpose, a hydraulic fracturing experiment under a core-plunger scale is conducted to investigate the impact of the bedding plane angle, borehole size, and injection rate on fracture initiation behaviors of laminated shale rock. The results on rock properties demonstrate that the anisotropic characteristics of shale rock are reflected not only in elastic modulus but also in tensile strength. The results of fracturing experiments show that the bedding plane dip angle and borehole size have significant effects on fracture initiation behaviors, in that fracture initiation pressure (FIP) decreases with the increase of those two factors. The impact of injection rate, by contrast, has no obvious variety regulation. The above data is further used to validate our previously proposed fully anisotropic FIP model, which shows better agreement with experimental results than those using other models under various parameter combinations. Finally, a postfracturing analysis is performed to identify the fracture growth patterns and the microstructures on the fracture surfaces. The results show that the hydraulic fractures (HFs) always grow along mechanically favorable directions, and the potential interaction between HFs and bedding planes mainly manifests as fracture arrest. Meanwhile, the roughness of fracture surfaces is physically different from each other, which in turn results in the difficulties of fluid flow and proppant migration. The findings of this study can help for a better understanding of the fracture initiation behavior of laminated shale rock and the corresponding fracture morphology.

Impact of injection rate on transient oil recovery under mixed-wet conditions: a microfluidic study

Lab-on-a-chip methods were used to visualize the pore-scale distribution of oil within a mixed-wet, quasi-monolayer of marble grains packed in a microfluidic channel as the oil was displaced by water. Water injection rates corresponding to microscopic capillary numbers between Ca = 5 × 10-8 and 2 × 10-4 (Darcy velocities between 0.3 and 1100 ft/d) were considered. As expected, early-time water invasion transitions from stable displacement to capillary fingering with decreasing Ca, with capillary fingering observed at Ca ≤ 10-5. End-point oil saturation decreases with Ca over the entire range of Ca considered, consistent with the canonical capillary desaturation curve. In contrast, Sor derived from approximate numerical simulations using reasonable Pc(Sw) do not display a strong dependence on Ca. These results suggest that the Ca dependence of end-point oil saturation is largely due to capillary end effects which, under conditions considered presently, affect the entire length of the packed bed.

Coupled thermal−gas−mechanical (TGM) model of tight sandstone gas wells

The mechanism of CO2 fracturing under coupled thermal−gas−mechanical (TGM) conditions is important for gas production in tight sandstone gas wells. In this study, a coupled TGM model was proposed on the basis of the elastic damage principal, and the coupling relationships were expressed by the governing equations. The proposed model was then tested through comparison between the numerical uniaxial compressive test and the laboratory test. COMSOL MULTIPHYSICS was adopted to calculate the coupled numerical model; the impact of injection rate and injection gas temperature was fully investigated. The research results showed that the initiation pressure stayed stable with the increase of the breakdown pressure and injection rate over a certain range (0.106 m3 s−1–0.848 m3 s−1). The seepage area under the injection rate of 0.848 m3 s−1 was 3.45 times that under the injection rate of 0.106 m3 s−1, which resulted from the gradual destruction of the samples and the formation of new fractures at higher injection rate. The initiation pressure and the breakdown pressure decreased, since tensile cracks tended to form with the increase of injection temperature. Shear cracks formed around the hole—the crush area. The tensile cracks propagated much deeper into the surrounding rock under the higher injection temperature. This research provides a study of unconventional oil and gas extraction for reference.

Thermodynamic analysis of heat transfer in a wellbore combining compressed air energy storage

Compressed air energy storage (CAES) is a potential energy storage technology. The gas phase and short cycle period are two key factors affecting heat transfer loss in the wellbore of CAES. A semi-analytical solution was developed by using the convolution method considering gas movement in this study to describe the transient behavior of heat transfer with a short cycle period. The comparative analysis of the presented solution with two published solutions showed that the solution matched well with the previous solutions under steady state. Parametric studies were carried out to investigate the impact of injection rate, overall heat transfer coefficient and thermal diffusivity of the formation on heat loss in the wellbore. The results indicated that a low overall heat transfer coefficient and thermal diffusivity of the formation with an appropriate injection rate can efficiently reduce the heat loss. A hypothetical case study with a short cycle period of injection and production was conducted to demonstrate the applicability of the developed solution in CAES. The results suggest that the semi-analytical solution is applicable for heat transfer in the wellbore of CAES.

Filtration in Frac Packs and Its Impact on Injector Performance

SummaryThe filtration of solids in the injection water in a frac pack is the primary factor controlling the injectivity decline in frac-packed water-injection-well completions. The injectivity may decline rapidly or much more slowly, depending on the degree of frac-pack filtration. The widening and lengthening of frac packs and the associated loss of sand control are affected also. However, there are no experimental data available for the filtration coefficient at high velocities that are typical in frac packs. In this research, the filtration coefficients were measured experimentally in high-velocity flows encountered in frac packs. The solid concentrations and pressure drops across proppant-pack sections were measured and correlated with earlier filtration theory and permeability-decline models. The filtration coefficients were measured at various flow rates and for different proppant sizes. Our experiments show that at high fluid velocities, the filtration coefficient is significantly lower than that estimated from prior correlations that are based on low-velocity filtration.We have developed new empirical correlations for filtration coefficients at high flow rates in frac packs. The improved filtration coefficients were used as the primary input into a well-injectivity model. The proper estimation of the filtration enabled us to more accurately analyze the impact of injection rates and proppant selection on injector performance (i.e., predict long-term injection-well behavior). The effect of particle filtration in the frac pack, and its effect on injector performance, was captured accurately for the first time. The newly presented empirical correlations coupled with a model for frac-pack growth in the injection well allowed us to estimate accurately the fracture dimensions and the long-term water injectivity of frac-packed injectors. These results can be used for frac-pack design, proppant selection, and specification of injection-water quality.

A New Approach for Evaluating Migration of Nano Particles in Porous Media

Inter-particle and molecular forces are of most important forces affecting fines migration. Investigating the impact of these types of forces requires information about electrical properties of constitutive component and Nano-sized solids. Surface potential is a well-known parameter, which can be used to measure aforementioned forces. The force balance among electrical, gravity, drag and buoyance forces tracing on a particle can be estimated using fluid properties and physical properties of reservoir such as surface potential, pore size distribution and fine size distribution. The task is to set these forces at conditions that fine migration does not take place. This paper investigates the impact of several parameters that could influence pertinent forces. Effect of ionic strength of flowing fluid is taken into account to evaluate Debye length that determines double layer forces. The impact of injection rate on a parameter named erosion number also studied. The results of this study show that how introducing salts and injection rate can affect stability of fines on their locations.

Multiphase Flow Fields in In-situ Air Sparging and its Effect on Remediation

In-situ air sparging (IAS) is used for the clean-up of soil and groundwater that are contaminated with volatile organic compounds in relatively permeable subsurface environments. In this study, we investigated the secondary groundwater and gas flow fields that develop in the vicinity of single and multiple air sparging wells. The purpose is to evaluate their effects on contaminant plume migration and thus, remediation. Governing equations describing multiphase flow and contaminant transport in a three-dimensional domain were formulated and solved using the Galerkin finite element technique. Trichloroethylene was selected as a target contaminant. The increase in air injection contributed to an increase in the size of the IAS cone of influence and the gas saturation levels within the cone. This reduced the groundwater velocity within the cone and increased the zone of detour of groundwater around the air sparging wells. This outcome was quantified and compared under several IAS operations. Different soil permeability characteristics also affected the groundwater and gas flow patterns, and this impacted the remedial performance of the IAS system. Under high ambient groundwater velocity, an air sparging system that uses a single injection well caused the detour of contaminant plumes around injection wells, regardless of air injection rates, and failed to meet the remedial goal specified here. This system was successful for relatively low ambient groundwater velocity environments used here. An IAS system with multiple injection wells was effective in capturing and remediating the detoured contaminant plume, and showed superior performance when compared to a single injection well IAS system. Using IAS simulation, we also analyzed the impact of injection rates on site remediation using single or multiple wells. Design criteria that are based on the results of this study would be useful in enhancing the performance of the IAS systems.