Alternative Injection Method Research Articles

Enhancing oil recovery and carbon sequestration through alternating injection of methane-rich associated gas and CO2 in deep reservoirs

The direct emission of methane-rich associated gas from oil fields is a significant contributor to the greenhouse effect. Currently, alternative gas flooding predominantly employs CO2 and N2 as displacement phases, with limited research focusing on the alternating injection of methane-rich associated gas and CO2 tailored for oil field production. This study investigates the feasibility of enhancing oil recovery and mitigating the greenhouse effect through the alternating injection of methane-rich associated gas and CO2 into reservoirs using experimental and numerical simulation approaches. Initially, core-scale laboratory experiments were conducted on the alternating injection of methane-rich associated gas and CO2, followed by establishing a corresponding numerical simulation model. The results indicate that, compared to continuous CO2 injection, the alternating injection method results in a 2.48% reduction in oil recovery efficiency. However, this method demonstrates superior control over the mobility of oil, gas, and water. This is because there are two ways to enhance oil recovery efficiency: improve extraction efficiency and increase the swept area. CO2 has a high extraction efficiency but a relatively small swept area. Therefore, we aim to increase the swept area by using an alternating injection method of CO2 and associated gas, where mobility is a key factor in expanding the swept area. Specifically, the mobility ratio between oil and gas decreases from 9.65 to 8.24, and the ratio of oil mobility in the remobilized zone to water mobility in the unswept zone reduces from 0.770 to 0.441, suggesting significant potential for improving the sweep efficiency of heterogeneous reservoirs through alternating injection. Subsequently, numerical simulations were performed at the reservoir scale to investigate the alternating injections of methane-rich associated gas and CO2 with varying slug sizes. At the reservoir scale, compared to continuous CO2 injection, the alternating injection method increases the swept area of injected gas from 4.72 to 7.82 km2, consequently resulting in an additional production of 18 969 m3 of oil and sequestration of 9.0619 × 108 kg CO2 equivalents, representing increases of 15.6% and 460.4%, respectively. Finally, the slug ratio for alternating injection was optimized using the surrogate optimization method in MATLAB. After optimization, the cumulative oil production increased by 31.6% and the carbon sequestration capacity increased by 74.1%, compared to continuous CO2 flooding. This study offers valuable theoretical support for improving oil recovery through gas injection and facilitating carbon sequestration in reservoirs.

A novel measurement approach based on wideband excitation for frequency-coupling admittances of train converter

ABSTRACT In order to assess the high-frequency resonance and stability issue in the electrified railway system, a novel wideband measurement approach based on multi-tone signal is developed for extracting the sampling frequency-coupling admittances (SFCAs) of train converter. By injecting a series of linearly independent wideband excitation signals, the SFCAs of train are obtained simultaneously without affecting the network impedance. Considering the frequency distribution of wideband signal, an alternating injection method based on multi-tone signal is proposed. It aims at eliminating the overlapping effects of various frequency relationships on the target coupling harmonics in the 4QC control system. With unknown network impedance, the SFCAs of train covering all the desired frequencies, even several times sampling frequency, can be captured by the proposed wideband measurement approach. Comprehensive experiments are conducted on a hardware-in-the-loop (HIL) system for validating the measurement results.

Research on profile inversion controlling methods of multi-slug polymer alternative injection

ABSTRACTThe development practice of polymer flooding shows that the injection profile easily inverses during the process of single slug polymer flooding. The low effective or ineffective circulation of abundant injecting water in high permeability layer, low producing degree of low permeability layer and large polymer volume have influenced the sweep efficiency and oil recovery of polymer flooding. In view of these questions, the alternative injection method of various viscosity polymer slugs is studied. This paper explains the theory of enhanced oil recovery of multi-slug polymer alternative injection. The experiment results show that the alternative injection of high and low viscosity polymer slugs has a better effect than single slug polymer flooding. The mobility differences between high-low permeability layers can be effectively reduced. For a multi-layer heterogeneous reservoir, there is an optimal alternative cycle. Reasonable slug size can not only inhibit dominant channel forming in high permeability layer but also can effectively produce low permeability layer and control profile inversion to a certain extent. This provides a technical support for studying the controlling methods of profile inversion.

Examining the Potential of Immiscible CO2 for Gravity-assisted Enhanced Oil Recovery and Storage

This paper investigates the effectiveness of gravity-assisted immiscible CO2 injection for enhanced oil recovery and CO2 storage with three-phase heterogeneous reservoir simulation. Two types of immiscible injection are considered: constant, uninterrupted CO2 injection, and alternating CO2 injection, the latter of which entails interchanging periods of CO2 injection with periods of well inactivity. These injection strategies are applied to four different oil types to evaluate recovery and storage potentials. Enhanced oil recovery is very effective with 40° API oil, achieving ultimate field recoveries of 80.63 percent for constant CO2 injection and 63.77 percent for alternating CO2 injection. CO2 injection is far less effective for heavier oils. Constant CO2 injection generally produces more oil than alternating injection, given the greater amount of CO2 injected. When controlling for total CO2 injected, however, the two injection methods produce oil equally well. The alternating injection method is more efficient at storing CO2 than the constant injection method for the same quantity of CO2 injected across all oil types. For 40° API oil, the alternating method is as high as 16 percent more efficient, the best of all four oils examined. The increased storage efficiency coupled with the lack of additional oil production indicates that CO2 is finding space for storage by displacing water accumulated during an initializing water-flood. Evidence of significant water displacement by CO2 supports the legitimacy of the long term goal of CO2 sequestration into saline aquifers.

Analysis of the Spatial Correlation of Indoor MIMO PLC Channels

In this letter, an analysis of the spatial correlation of multiple-input multiple-output (MIMO) power line communications (PLC) channels in the frequency range 1–80 MHz is provided, where the term spatial correlation refers to the relation between the paths that form the MIMO channel matrix. The study is based on a large set of $2\times 2$ MIMO channels measured in four different countries. The presented statistical analysis of the condition number reveals three important facts. First, the spatial correlation is almost independent of frequency, which has important implications in the development of top-down MIMO PLC channel models. Second, the use of an alternative injection method can notably reduce the spatial correlation and, consequently, increase the system bit-rate. Third, there exist countries whose channels have larger spatial correlation values than others. Since spatial correlation plays a key role in the performance of MIMO PLC systems, a hypothesis relating the type of wiring deployed in the indoor power grid to the spatial correlation is given and supported by simulations.

Impact of wind power plant reactive current injection during asymmetrical grid faults

As more renewable energy sources, especially more wind turbines (WTs) are installed in the power system; grid codes for wind power integration are being generated to sustain stable power system operation with non-synchronous generation. Common to most of the grid codes, wind power plants (WPPs) are requested to stay connected and inject positive-sequence reactive current in order to boost positive-sequence grid voltage during short-circuit grid faults, irrespective of the fault type; symmetrical or asymmetrical. However, as shown in this study, when WPPs inject pure positive-sequence reactive current in case of asymmetrical faults, as a conventional method (CM) in accordance with the grid code requirement, positive-sequence grid voltage is boosted, but also higher negative sequence voltage in the grid and higher overvoltages at the non-faulty phases occur. In this study, an alternative injection method, where WTs are injecting both positive and negative sequence currents during asymmetrical faults, providing improved grid support, is given and compared with the CM. In addition, effect of coupling between positive, negative and zero sequences when WPPs are injecting currents during asymmetrical faults, is investigated, which was not considered in the wind power impact studies before.

The point-touch technique for botulinum toxin injection in adductor spasmodic dysphonia: quality of life assessment

Botulinum toxin injection under electromyographic guidance is the 'gold standard' for adductor spasmodic dysphonia treatment. The point-touch technique, an alternative injection method which relies on anatomical landmarks, is cheaper, quicker and more accessible, but has not yet gained widespread acceptance due to concerns about patient satisfaction. To assess swallowing and voice-related quality of life following point-touch botulinum toxin injection in adductor spasmodic dysphonia patients. Stanford University Voice and Swallowing Center. Prospective case series (evidence level four). Consecutive adductor spasmodic dysphonia patients with a stable botulinum toxin dose-response relationship were recruited prospectively. The Eating Assessment Tool and Voice-Related Quality of Life questionnaires were completed pre-treatment and at 10 and 30 per cent completion of the injection cycle, respectively. Thirty-seven patients completed follow up. The mean total botulinum toxin dose was 0.88 units. Pre-treatment Voice-Related Quality of Life questionnaire results reflected the burden of disease. Post-treatment Eating Assessment Tool and Voice-Related Quality of Life questionnaire results were collected at 2.53 and 7.84 weeks, respectively; the former showed an increase in dysphagia, albeit statistically insignificant, while the latter showed significantly improved scores (both domain and total). The point-touch technique is a viable alternative for botulinum toxin injection in the treatment of adductor spasmodic dysphonia.

An Open-Label Safety Study of Enfuvirtide Injection with a Needle-Free Injection Device or Needle/Syringe: The Biojector 2000 Open-Label Safety Study (BOSS)

Enfuvirtide (ENF) administration by needle/syringe is commonly associated with injection site reactions (ISRs). This study assessed ISRs and participant preference between a needle-free injection device (NFID) and a 27-gauge 1/2-inch needle/syringe (NS). A total of 349 participants with human immunodeficiency virus infection, who had difficulty tolerating long-term administration of ENF by NS, underwent randomization (2:1) to ENF administered twice daily by NFID for 8 weeks, or by NS for 4 weeks followed by NFID for 4 weeks. The objectives of the study were to compare ISRs associated with ENF injection using NFID or NS based on a composite endpoint, ISR incidence/severity, overall ISR scores, and discontinuations. In the NFID group, ISRs improved as the percentage of participants meeting the composite endpoint decreased from baseline (40.1%) to week 4 (25.4%) and remained stable at week 8 (21.2%). In the NS --> NFID group, the percentage meeting the composite endpoint worsened from baseline (36.5%) to week 4 (45.1%), but improved at week 8 (26.1%) after switching. Between-participant comparison showed a statistically significant greater improvement from baseline to week 4 in overall ISR score in the NFID group compared to the NS group. Within-participant comparison of the NS --> NFID group showed a significantly greater decrease in overall ISR score from baseline to week 8. In responses to a questionnaire, 87.2% of the participants surveyed preferred the NFID delivery system over NS. NFID is an alternative injection method that may reduce the incidence and severity of treatment-limiting ISRs associated with ENF administration.

Effects of Injection Therapy using Muscle Derived Stem Cell/ Chitosan/ Hydroapatite Composite Gel in a Rat Model of Urinary Incontinence

Purpose: We investigated whether periurethral injections of musclederived stem cells (MDSC) and chitosan/hydroapatite after denervation of rat's pudendal nerve could increase the leak point pressure over a long time period in a rat model of urinary incontinence. Materials and Methods: Muscle-derived stem cells isolated from the gastrocnemius muscle of normal female rats were purified to obtain a myogenic population by using the preplate technique. The N group was the normal female rats, the D Group was the pudendal nerve transected group and the M Group was the MDSC/chitosan/hydroapatite composite gel injected group after pudendal nerve transection. The MDSC/chitosan/hydroapatite composite gel was injected into the proximal periurethral area. At 2 and 4 weeks, visually identified leak point pressure measurement was done with using the vertical tilt/intravesical pressure clamp model of urinary incontinence. The rats were then sacrificed and the periurethral tissues harvested for histological examination. Results: The leak point pressure was significantly lower in the D group at each time compared with the N group, and the leak point pressure in the N and M groups were significantly higher than those in the D group at both 2 and 4 weeks. The persistence of MDSC over the period of study was verified by histological examination. Conclusions: MDSC/chitosan/hydroapatite injection into the denervated external urethral sphincter in female rats increased the leak point pressure at 2 and 4 weeks. This MDSC/chitosan/hydroapatite composite gel can be an alternative injection method for treating urinary incontinence in the future. (Korean J Urol 2007;48:627-632) 󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏

An improved method for determining the critical energy for interface trap generation of n-MOSFETs under Vg= Vd/2 stress mode

Hot-carrier degradation of n-channel MOSFETs with 4 and 9 nm gate oxides is studied under intermediate gate voltage stress ( V g= V d/2). An alternating injection method is proposed for determining the electron trapping effect on saturated drain current degradation. On this basis, an improved method for determining the critical energy for interface trap generation is developed. It can extract the critical energy more accurately than that through the traditional method. This method is applicable for n-MOSFETs with either thinner or thicker oxides under any stress mode between intermediate ( V g= V d/2) and higher gate voltage ( V g= V d).