Decreasing Injection Rate Research Articles

A resolved CFD-DEM coupling method to simulate proppant transport in narrow rough fractures

A proppant transport model was proposed to simulate the fluid-granular interactions in rough narrow fractures. The Computational Fluid Dynamic (CFD) was used to describe the fluid flow, while the Discrete Element Method (DEM) was adopted to describe the particle motion. Considering the roughness characteristics of narrow fractures, the resolved CFD-DEM coupling method was employed to simulate the fluid-granular interactions. Firstly, the resolved CFD-DEM coupling method was validated by previous simulation/experimental results. Then, simulations of proppant transport in synthetic rough fractures with different fractal dimensions and random number seeds were conducted. The results showed that roughness characteristics increased the possibility of proppant settling at a location with a large roughness height. A fracture with a higher fractal dimension had a higher proppant coverage ratio, leading to a better fracture propping effect. The proppant coverage ratio in rough fractures increased with increasing proppant size and decreasing injection rate.

Earthquakes Induced by Wastewater Injection, Part I: Model Development and Hindcasting

ABSTRACTIn the past decade, several parts of central United States, including Oklahoma, have experienced unprecedented seismicity rates, following an increase in the volumes of wastewater fluids that are being disposed underground. In this article, we present a semi-empirical model to hindcast the observed seismicity given the injection time history. Our proposed recurrence model is a modified version of the Gutenberg–Richter relation, building upon the seismogenic index model, which predicts a linear relationship between the number of induced events and the injected volume. Our methodology accounts for the effects of spatiotemporal pore-pressure diffusion, the stressing-rate dependency of the time lag between injection and seismicity rate changes, and the rapid cessation of seismicity upon unloading. We also introduced a novel multiscale regression, which enabled us to produce grid-independent results of increased spatial resolution. Although the model is generic to be applicable in any region and has essentially only two free parameters for spatial calibration, it matches the earthquake time history of Oklahoma well across various scales, for both increasing and decreasing injection rates. In the companion paper (Grigoratos, Rathje, et al., 2020), we employ the model to distinguish the disposal-induced seismicity from the expected tectonic seismicity and test its forecasting potential.

Temporal response of magnitude distribution to fluid injection rates in The Geysers geothermal field

The influence of fluid injection rates on the magnitude distribution of the seismicity which occurred in the NW part of The Geysers geothermal site is studied here. A direct comparison between injection rate changes and b value response is attempted after appropriate selection of data subsets. Due to the relatively small sample (1121 events, corresponding to an average rate of ~ 0.45 events/day), we also aggregated seismic activity into two families corresponding to increasing and decreasing injection rates, respectively. The b values were calculated as a function of time lag related to the injection activity. In agreement with previous studies, we found a statistically significant direct relation between b values and injection rate changes, which occurred at a zero or very short time lag (from 0 to ~ 15 days). However, the b value changes are related to the slope (i.e., the second derivative of injection volume), instead of the absolute values of injection rates. The increasing injection rates correspond to b = 1.18 ± 0.06, whereas the decreasing injection rates correspond to b = 1.10 ± 0.05. The corresponding values estimated by the repeated medians technique are b = 1.97 ± 0.20 and b = 1.50 ± 0.13. Both differences are significant at 0.05 level.

Fluid Injection and Time‐Dependent Seismic Hazard in the Barnett Shale, Texas

AbstractThe Barnett Shale in Texas experienced an increase in seismicity since 2008, coinciding with high‐volume deep fluid injection. Despite the spatial proximity, the lack of a first‐order correlation between seismic records and the total volume of injected fluid requires more comprehensive geomechanical analysis, which accounts for local hydrogeology. Using time‐varying injections at 96 wells and employing a coupled linear poroelastic model, we simulate the spatiotemporal evolution of pore pressure and poroelastic stresses during 2007–2015. The overall contribution of poroelastic stresses to Coulomb failure stress change is ~10% of that of pore pressure; however, both can explain the spatiotemporal distribution of earthquakes. We use a seismicity rate model to calculate earthquake magnitude exceedance probability due to stress changes. The obtained time‐dependent seismic hazard is heterogeneous in space and time. Decreasing injection rates does not necessarily reduce probabilities immediately.

Study of Hepatic Artery Cone-beam Imaging by Low-rate Injection in Iodinated Contrast Agent.

CT during hepatic arteriography (CTHA) of cone-beam computed tomography (CBCT) provides valid information in performing transcatheter arterial chemo-embolization (TACE). The usefulness of CTHA with the diluted contrast medium has been reported in some medical conferences. However, the operation becomes somehow complicated for the medical institutions that have angiography injectors with a single head. In this study, we aimed to investigate the clinical equivalence of low-rate injection method and diluted injection method. The relationship between the injection rate and transit time of contrast medium was tested. Then, we measured the signal values of CBCT and CT values both in varying injection rates and in the case of doubling dilution. The transit time of contrast medium became delayed with decreasing injection rate. The signal values of CBCT in the case of doubling dilution showed almost the same as those at a half of injection rate without dilution. We also obtained the same finding from the comparative investigation of CT values. ROC analysis of digital subtraction angiography (DSA) and CBCT was carried out, and the area under the curve (AUC) of CBCT showed a significantly higher value. It is suggested that CTHA with low-rate injection method offers diagnostic image similar in some degree to the diluted injection method.

Numerical Modeling of Variable Fluid Injection-Rate Modes on Fracturing Network Evolution in Naturally Fractured Formations

In this study, variable injection-rate technology was numerically investigated in a pre-existing discrete fracture network (DFN) formation, the Tarim Basin in China. A flow-stress-damage (FSD) coupling model has been used in an initial attempt towards how reservoir response to variable injection-rates at different hydraulic fracturing stages. The established numerical model simultaneously considered the macroscopic and microscopic heterogeneity characteristics. Eight numerical cases were studied. Four cases were used to study the variable injection-rate technology, and the other four cases were applied for a constant injection-rate in order to compare with the variable injection-rate technology. The simulation results show that the variable injection-rate technology is a potentially good method to a form complex fracturing networks. The hydraulic fracturing effectiveness when increasing the injection-rate at each stage is the best, also, the total injected fluid is at a minimum. At the initial stage, many under-fracturing points appear around the wellbore with a relatively low injection-rate; the sudden increase of injection rate drives the dynamic propagation of hydraulic fractures along many branching fracturing points. However, the case with decreasing injection rate is the worst. By comparing with constant injection-rate cases, the hydraulic fracturing effectiveness with variable flow rate technology is generally better than those with constant injection-rate technology. This work strongly links the production technology and hydraulic fracturing effectiveness evaluation and aids in the understanding and optimization of hydraulic fracturing simulations in naturally fractured reservoirs.

Velocity‐saturation relation in partially saturated rocks: Modelling the effect of injection rate changes

ABSTRACTThe relationship between P‐wave velocity and fluid saturation in a porous medium is of importance for reservoir rock characterization. Forced imbibition experiments in the laboratory reveal rather complicated velocity–saturation relations, including rollover‐like patterns induced by injection rate changes. Poroelasticity theory‐based patchy saturation models using a constant fluid patch size are not able to describe these velocity–saturation relations. Therefore, we incorporate a saturation‐dependent patch size function into two models for patchy saturation. This recipe allows us to model observed velocity–saturation relations obtained for different and variable injection rates. The results reveal an increase in patch size with fluid saturation and show a reduction in the patch size for decreasing injection rate. This indicates that there can exist a distinct relation between patch size and injection rate. We assess the relative importance of capillarity on velocity–saturation relations and find that capillarity stiffening impairs the impact of patch size changes. Capillarity stiffening appears to be a plausible explanation when a decrease in the injection rate is expected to boost the importance of capillarity.

Laboratory study of the influence of changing the injection rate on P-wave velocities and water saturation in a Limestone

SummaryForced imbibition was performed in a Limestone Savonnieres by injecting water into a dry sample. The injection was monitored with X-ray Computed Tomography (CT) and active ultrasonic measurements so that the time-space distribution of the invading fluid could be simultaneously observed in CT images and quantified through measuring P-wave velocities and water saturation.The CT scans allowed us to observe a water front advancing away from the area of injection and estimate saturation. Through the evolution of P-wave velocities, we observed a strong influence on the acoustic response with the presence of water and with the changing of injection rates. The approaching of the water front to the monitored position decreased P-wave velocities while the saturation increased continuously. The P-wave velocities decrease occurred for a short period of time and was followed by a sharp increase which happens when the fluid front crossed the monitored position. Decreasing injection rate decreased P-wave velocities and saturation. Increasing injection rate, increased P-wave velocities and saturation, sharply and for a short period of time followed by a slight decrease for P-wave velocities and a continuous increase.Our experimental data confirms how sensitive acoustic waves are to the presence of water and that changing injection rates promote considerable fluid distribution that is drastically reflected in the acoustic velocities.

Mathematical model for calculating the dispersion coefficient of super critical CO 2 from the results of laboratory experiments on enhanced gas recovery

A straightforward method is presented for calculating the dispersion coefficient of super-critical carbon dioxide (SCO 2) displacing methane in a linear porous reservoir. The dispersivity of SCO 2 was identified to be a function of injected pressure, in-situ gas composition and injection rate. It was found to vary proportionally to changes in purity of the displaced phase and injection rate, while inversely varying with injected pressure. The aim of this study was to investigate the impact of injection rates and various test conditions (pressure and temperature) on recovery efficiency. Experimental results revealed methane recovery is improved with increasing pore pressure and composition of the in-situ gas, while poor recovery efficiency resulted with decreasing injection rates below 10 cm/h. All experiments were carried out on the same core plug from a single gas field. The dimension of the core was measured as 19.41 cm in length and 12.255 cm in diameter. Preliminary tests indicated air permeability of 92.5 md and porosity of 0.143.

Two models for the formation of magma reservoirs by small increments

It is now clear that magma reservoirs develop over long time intervals out of a large number of individual intrusions. Evidence from some large volcanic deposits, including those of the Bishop Tuff, California, and Fish Canyon Tuff, Colorado, indicates that such reservoirs may experience pervasive and rapid heating before catastrophic eruptions. Injection of hot primitive melt in the reservoir is often invoked to explain these observations, but this requires the rapid emplacement of a large magma volume (at least 25 km 3 in less than 100 years for the Bishop Tuff) and efficient heat transfer through a thick cumulate pile. Within a magma body that grows incrementally, temperatures rise progressively and may eventually lead to a permanent volume of melt. Temperature and crystallization follow two completely different paths depending on the thickness of individual intrusive sheets. In one limit, corresponding to thick sheets, crystallization proceeds at equilibrium. Initial magma batches crystallize completely and a permanent body of melt develops progressively once ambient temperatures in the complex rise above the solidus. In the other limit, corresponding to thin sheets, crystallization is kinetically-controlled, such that initial intrusions do not crystallize completely and preserve a glassy residue. Once temperatures within the growing magma pile reach a certain threshold value, nucleation and growth of crystals get reactivated in the residual glass. Crystallization then proceeds catastrophically in a positive feedback loop involving latent heat release and temperature rise. Thus, an initial phase with no evolved melt present ends with the sudden formation of a large volume of evolved melt in a crystal mush. After this initial phase, new intrusions get emplaced in heated surroundings and follow a thermal path similar to that of the equilibrium case, with melts that become increasingly more primitive with time. Evidence for kinetic controls on crystallization in the natural environment is provided by the significant amounts of glass (up to 40%) that are found in thin isolated basaltic sills and dykes. Owing to sluggish crystallization kinetics, more glass should be generated in andesitic and dacitic magmas emplaced in similar conditions. Devitrification of such quantities of glass accounts for the rapid heating of a thick sill complex. The two models of magma reservoir formation involve different requirements: the intrusion thickness must be smaller than a critical value in the kinetic model and the average magma input rate must exceed a threshold value in the equilibrium model. For a given injection rate, a permanent magma reservoir forms in a shorter time interval and over a smaller cumulative magma thickness in the kinetic model than in the equilibrium one. The kinetic model is such that the amount of evolved melt generated increases with decreasing injection rate, in contrast to the equilibrium model for which the opposite relationship holds.

Methods for estimating CO2 storage in saline reservoirs

Abstract Methods for estimating subsurface volumes in porous and permeable geologic formations are routinely applied in oil and gas, ground water, underground natural gas storage, and UIC disposal evaluations. In general, these methods can be divided into two categories: static and dynamic. The static models require only rock and fluid properties, while the dynamic methods require information about active injection, e.g. injection volumes and reservoir pressures. The static models are volumetric and compressibility; the dynamic models are decline curve analyses, mass (or volumetric) balance, and reservoir simulation. The volumetric method requires a simple geometric description of the formation that includes formation height and area, porosity, and some type of factor that reflects the pore volume that CO2 can occupy. The compressibility method relates the change in pore pressure to the change in water and pore volume. Pore pressure will increase as CO2 is injected. This causes a decrease in water volume and an increase in pore volume. The sum of these changes can accommodate space for CO2 storage. This is primarily an issue for closed reservoirs. For active CO2 injection, in addition to the static methods, dynamic methods can be used. Some geologic formations will incur flat or constant injection rates with variable injection pressure, while other formations will have decreasing injection rate with constant injection pressure. This is primarily due to surface operations and the outer boundary condition of the reservoir (closed or open). A decreasing injection rate trend can be analyzed and extrapolated to an uneconomic injection rate to infer the ultimate storage capacity of an active injection well. Mass or volumetric balance can be used to estimate subsurface injected volumes using cumulative injection volume as a function of pore pressure. Based on the geologic unit, combinations of parameters are used to allow straight line projections of the observed trends to make forecasts of the ultimate storage capacity. Injection zone flow simulation models can be used pre- or post injection, require the most input data and can accommodate a very rigorously defined geologic model. Storage estimates can be made readily from simulation for various development scenarios that include completion interval, well-type, injection rates, and multiple injection well spacing. The data requirements, assumptions and limitations for each of these methods are reviewed. Advantages and disadvantages of applying each method to basin-scale and specific site-scale storage estimates are discussed.

Prediction model of bottom hole temperature and pressure at deep injector for CO2 sequestration to recover injection rate

Abstract The field test of CO 2 -ECBM was carried during 2003 to 2007 in order to evaluate technical feasibility of injecting CO 2 into the coal seam while producing CH 4 at Yubari City, Hokkaido, Japan. It aims to resolve global warming and to develop a system for injection and sequestration of CO 2 into coal seams. The targeted coal seam is located about 900 m below the surface. The absolute pressure at the bottom hole is approximately 15.5 MPa and the CO 2 temperature is about 28 ∘ C before the injecting into the coal seam. Thus, CO 2 is injected in liquid phase to the coal seam and supercritical condition of CO 2 has not been satisfied due to heat loss along the deep injection well. Replacements of usual tubing pipes with thermal insulated tubings were applied, however the temperature at the bottom hole was still lower than the CO 2 critical temperature. The project had a problem about decreasing injection rate after starting injection CO 2 . It was evaluated by analysing the field test data that the maximu m decreasing ratio of the coal seam permeability was 0.065 and permeability around injection well was became 6 times larger than the original one. We assumed that its reason is caused with swelling of the coal seam around the injection well by liquid CO 2 injection. Present study has focused on the keeping supercritical CO 2 in the tubing because viscosity of supercritical CO 2 that is 40% smaller than that of liquid CO 2 . The CO 2 temperature has been successfully predicted in order to keep CO 2 in supercritical condition from the surface to the bottom for various CO 2 injection rates and electric heater power. The minimum injection rate has been presented in order to keep CO 2 in the supercritical condition at the bottom hole of the injection tubing. Injected CO 2 is expected to be super critical over 12 ton/day of injection rate without any heating in the tubing.

Delayed gelation in corefloods using Cr(III)-malonate as a crosslinker

Flow experiments have been conducted using a hydrolysed polyacrylamide (HPAM) or an acrylamide-AMPS copolymer crosslinked with chromium malonate. Retention of the chemicals prior to gelation has been studied at different temperatures and injection rates. The retention of the polymer was independent of the crosslinker concentration. The two polymers gave different results; the acrylamide-AMPS copolymer showed very low retention; the HPAM gave quite high retention values. At low temperatures, malonate with a ratio 1:3 (CrMa 3) and 1:4 (CrMa 4) protected the chromium against precipitation in Berea cores. At high temperatures, chromium precipitation was observed; retention increased with decreasing injection rate. An excess of malonate has some protecting effects on retention. Reducing the initial pH from 7 to 5 lowered the retention. In quartz sand and Bentheim sandstone the retention of CrMa 3 was very low even at high temperatures; no precipitation was observed before gelation. After a shut-in period, gel formed at pH less than 7 in the sand and the Bentheim cores. However, no gel formed in the Berea cores.

Phase morphology of injection‐molded blends of nylon‐6 and polyethylene and comparison with compression molding

AbstractAn experimental study is presented of the development of phase morphology in injection and compression molding of 80/20 and 60/40 nylon‐6/polyethylene blends and its evolution during annealing. The phase morphology of the compression‐molded part is isotropic, while that of both screw and ram injection‐molded parts is both heterogeneous and anisotropic through the cross section. In the injection‐molded parts, the morphology exhibits its greatest level of isotropy in the core and becomes increasingly anisotropic approaching the mold wall (through the thinnest cross section); i.e., the 2 direction. There is an intermediate position of maximum anisotropy. Sections made in various directions indicate that the dispersed phase forms platelets oriented in the plane of the machine and width directions. The position of maximum anisotropy seems to represent a frozen layer thickness that increases with decreasing mold temperature and with decreasing injection rate into the mold. Annealing studies show coalescence in both compression‐ and injection‐molded bars. The greatest coalescence occurs in the injection‐molded parts near the positions of greatest anisotropy of morphology. This suggests that coalescence is associated with collisions between dispersed phase globules as their sphericity increases.

Injection molding in disk‐shaped cavities

AbstractExperimental results together with predictions based on a numerical simulation are reported for the filling by injection molding of a center gated, disk‐shaped cavity with acrylonitrile‐butadiene‐styrene terpolymer (Lustran ABS Q714) and with polypropylene (Pro‐fax 6523). At a specified fractional fill, the output of a pressure transducer (Δπzz) near the sprue was measured and the clamp force (F) was obtained by. integrating the output of four pressure transducers over the projected area. A systematic study was made to determine the effect of the (1) material properties, (2) cavity thickness, (3) melt temperature in the barrel, and (4) injection rate on the measured and simulated values for the pressure transducer output and clamp force. For a given barrel temperature, cavity thickness and intermediate‐to‐high injection rates, the pressure transducer output and clamp force were found to be nearly independent of injection rate for ABS and to increase with increasing injection rate for polypropylene. As the injection rate approached zero, the pressure transducer output and clamp force increased because of the long time available for cooling the flowing melt. For ABS the simulated results were about 5‐25 percent higher than experiment, whereas for polypropylene they were about 10 percent lower than experiment when the viscosity model included solidification Flow instabilities were observed to occur at conditions where the pressure transducer output curve showed a marked upturn with decreasing injection rate.