Different Rates Of Injection Research Articles

Simulation of hydraulic fracturing and Darcy fluid flow in a porous medium using a coupled Discrete Element Method with fluid flow

Studying fluid penetration of the rock matrix during fracture propagation is one of the most difficult technical challenges of hydraulic fracture engineering. To deal with this issue, a coupled hydraulic-mechanical model was performed to simulate fracture propagation during hydraulic fracturing. For this purpose, a new discrete elements approach with a force-displacement law was used for simulating the fracturing process in a flow-coupled Discrete Element Method (DEM). A series of cases was simulated to evaluate the effect of different rates of injection and permeability. Good agreement was obtained between the numerical results of this study and the reported experimental results. The results of hydraulic fracture modeling indicated that a low fluid viscosity led to wider fluid penetration and simultaneous occurrence of failure phenomenon and penetration. In the case of high viscosity, the fracture is propagated beyond the fluid penetration zone, and higher fluid pressure for fracture creation was needed than was the case for a low viscosity fluid. The results of the simulations with different permeability and low viscosity of fluid revealed that when the permeability was high, the fluid penetration was faster relative to the case with low permeability. The growth pattern of fracture in low permeability is straight and branching, but in the case of high permeability, the fracture pathway was straight and thick. The pressurization rate affected the number of cracks and the geometry of the fracture in the hydraulic fracturing model. Finally, an increase in pressurization rate resulted in an increase in the number of tensile cracks.

The effect of rate of injection on injection pressure profiles measured using in-line and needle-tip sensors: an in-vitro study.

Alongside ultrasonic visualisation, measurement of injection pressure is an effective tool for reducing the risk of intraneural injection during peripheral nerve block. The aim of this study was to compare injection pressure profiles when measured along the injection line with the pressure measured directly at the needle tip using different rates of injection. A syringe pump delivered a 5-ml injection of saline into silicone gel at three different speeds (5ml.min-1 , 10ml.min-1 and 15ml.min-1 ). Fibreoptic pressure sensors recorded real-time pressure profiles of the injection pressure directly at the needle tip and along the injection line. A total of 15 injections were successfully performed, five for each injection rate, totalling 30 recorded pressure profiles. More rapid rates of injection caused peak pressure measured in-line to increase, whereas pressure measured at the needle tip remained constant (mean (SD) pressure in-line 30.76 (3.45) kPa vs. 72.25 (1.55) kPa and mean (SD) pressure at needle tip 19.92 (1.22) kPa vs. 20.93 (2.66) kPa at 5ml.min-1 and 15ml.min-1 , respectively). Injection pressure profiles showed that in-line pressure measurement failed to record precise real-time pressure changes occurring at the needle tip (mean (95%CI) pressure difference 10.8 (6.98-14.70) kPa vs. 51.2 (47.52-54.89) kPa for in-line and needle-tip measures, respectively). We conclude that, in order to accurately monitor the true injection pressure generated, independent from operator and injection parameters, measurement at the needle tip is necessary, as injection pressure measured along the injection line is an unreliable surrogate.

Decreasing the Pain of Finger Block Injection: Level II Evidence

There is level II evidence that volunteers prefer the single subcutaneous injection in the midline of the proximal phalanx with lidocaine and epinephrine (SIMPLE) finger block over the classic two dorsal injection block technique. The purpose of this study was to possibly further decrease the pain of digital block injection by examining the effect of the duration of injection on the pain felt by volunteers receiving the SIMPLE block at two different injection rates. Forty healthy blinded volunteers were injected 2mL of lidocaine 1% and epinephrine 1/100,000 in the digital palmar crease of both long fingers, one at a time. Two different rates of injection were used: 8 and 60s. Pain scores were measured using a visual analogue scale and the volunteers were asked which of injection techniques they preferred. The visual analogue scale results revealed less pain with the slow injection (p < 0.001). Thirty three out of 40 volunteers preferred the slow injection rate. No difference could be attributed to sex of participants or to the first hand injected. Blinded volunteers preferred digital blocks injected over 60s to the more rapid 8s. Decreasing the pain of injection only takes a minute of our valuable time for finger blocks.

Migration and Storage Mechanisms of CO&lt;sub&gt;2&lt;/sub&gt; with Different Injection Rates

Geological sequestration of CO2 in deep saline formations has been considered as an effective way to mitigate the greenhouse effect. With different rates of injection to a storage formation, the migration and storage mechanisms of CO2 are different. In this paper, we simulated the migration of CO2 based on a generic geological reservoir under simplified conditions. The results show that higher injection rate will lead to higher migration velocity and farther distance from the injection well, while it has no influence on dissolution amount when the total amounts of injected CO2 are equal.

HCl/Formic In-Situ-Gelled Acids as Diverting Agents for Carbonate Acidizing

Summary In highly heterogeneous carbonate reservoirs, several acid systems have been used to enhance acid diversion during matrix acidizing such as surfactant-based acids and in-situ-gelled acids. In-situ-gelled acids are also used to reduce leakoff rate in acid fracturing. The main acid used in this system is hydrochloric acid (HCl). However, high reaction rates and severity of corrosion problems, especially for wells completed with Cr-based tubulars, limit the use of HCl at high temperatures. On the other hand, mixing organic acids with HCl either increases the acid penetration or reduces the necessary strength of HCl and the necessary load of the corrosion inhibitors. A few studies addressed the systems that use both advantages. The objective of this work is to investigate the behavior and the performance of different in-situ-gelled HCl/formic acid blends as diverting agents by conducting viscosity measurements, reaction-rate measurements using the rotating-disk apparatus, and through coreflood study. Formic acid was blended with HCl, and four in-situ-gelled acids were examined. Formic acid concentration varied from 0 to 6.31 wt%, and HCl concentration ranged from 0 to 5 wt%. Pink Desert limestone was used for reaction-rate and coreflood experiments. The rotating-disk apparatus was used to measure the reaction rate at 250°F at disk rotational speeds of 100 and 1,000 rev/min. The effect of formic acid concentration and zirconium crosslinking on the reaction rate was examined. Coreflood experiments were conducted at 250°F using two different rates of injection (2 and 10 cm3/min), and the core samples were imaged using a computed-tomography (CT) scan technique after each coreflood experiment. Increasing formic acid concentration decreased the reaction rate of in-situ-gelled HCl/formic acid with calcite at both low and high disk rotational speeds. This was confirmed by viscosity measurements, which showed that increasing formic acid concentration increased the viscosity of the live acids and decreased the viscosity of the spent acids. Coreflood results showed that increasing formic acid concentration in HCl/formic acid blends reduced acid ability for diversion. In the selected range of acid concentration and for the type of polymer and crosslinking agent used, the in-situ HCl/formic acid behaved more like gelled acid and reached a breakthrough in all coreflood experiments. The higher the formic acid concentration, the higher the pore volume of the acid required to break through.

Gerry's Real World Guide to Pharmacokinetics and Other Things

Gerry's Real World Guide to Pharmacokinetics and Other Things, G. M. Woerlee, Troubador Publishing Ltd: Leicester, UK, 142 pp; indexed, illustrated ISBN: 1-905237-16-2; Price £9.95 Pharmacokinetics is perhaps not the best loved topic in the anaesthetic curriculum. Multi-compartment models can seem a long way from clinical practice and those without a mathematical bent find the formulae and equations of pharmacokinetic modelling daunting. Most clinical anaesthetists do not think about time constants and volumes of distribution at all during the course of the average working day. Despite this, pharmacokinetics is important. If anaesthetists do not think explicitly about pharmacokinetic modelling it is because they have a good understanding of, and feeling for, the time course of action of the drugs that they use and how this may vary in different circumstances. This instinctive understanding does not exist in a vacuum. It rests upon a body of knowledge about pharmacokinetic properties of each drug. Unlike practitioners in many other specialties, anaesthetists work with many drugs that act in seconds or minutes rather than in days or weeks. To practice with insight the anaesthetist must have an understanding of pharmacokinetics and its application in the real world. This little monograph delivers the necessary understanding. This is a little book. Excluding the preface, references and appendices there are only 126 pages of text. The book is designed to be read from cover to cover. It takes the form of a series of dialogues between Dr Gerry, an infinitely wise and well informed, if somewhat acerbic, Consultant Anaesthetist with a deep knowledge of pharmacokinetics and his young trainee Dr Bob. The British reader may think of Dr Bob as being an experienced senior health officer (SHO). He is able to give a safe anaesthetic and is keen to learn and develop. However, he is still building up both his knowledge base and clinical experience and is prey to many of the common pitfalls of the everyday practice of the clinical anaesthesia. The chapters describe short vignettes in which Dr Gerry and Dr Bob deal with a series of challenging clinical cases and often challenging surgeons. In each chapter the pharmacokinetic problem to be addressed is presented in a clinical context. The topics covered include the pharmacokinetics of anaesthetic induction, multi-compartment models and drug redistribution, the impact of renal failure, haemorrhage and obesity on drug handling, drug elimination in breast milk and the pharmacokinetics of drug infusions. In each case the relevant pharmacokinetic models and equations are presented but Dr Bob and the reader are encouraged to do real calculations with real numbers using these equations and to work out what these models might represent in terms of real life processes. In one example this is as simple as working out how propofol is diluted as it is injected into an arm vein, passes through the venous circulation to the right heart, on through the pulmonary circulation, through the left heart and on to the brain and how this dilution is affected by two different rates of injection. It may fairly be argued that what the reader is asked to imagine is a considerable over simplification of a complex process. However, it is a useful mental working model and the lessons drawn about the impacts of different rates of injection on the concentration of drug arriving at the heart and the consequent myocardial depression are undoubtedly valuable. The characters in situations in this book are drawn larger than life. Dr Gerry has a coffee addiction that could earn him an implantable defibrillator. The surgeons revel in names such as Mr Hawley Crippen and Dr Sam Pickwick, a rotund junk food eating obesity surgeon, and have personality traits to match. The interactions between Dr Gerry and his surgical colleagues would probably lead to them being suspended in a modern National Health Service (NHS) hospital and I would emphasise that this book is a tutor in pharmacokinetics not in anaesthesia and operating list management. It is nevertheless a very good read. The book does lack an index and I feel that this is a major shortcoming. Nevertheless this is a delightful and well-written book which succeeds in its aim of teaching pharmacokinetics and will be a welcome relief to any trainee studying for professional examinations. It deserves a place in any trainees pre-examination reading list and should be saved up as a treat for the dark days when exam preparation is becoming almost unbearably tedious but the exam is still some time away.

Specificity of Lumbar Medial Branch and L5 Dorsal Ramus Blocks

A cross-sectional study. To determine the face validity of lumbar medial branch blocks. Lumbar medial branch blocks have been used increasingly to diagnose zygapophysial joint pain. The course and relations of the medial branches of the dorsal rami have been demonstrated in previous anatomic studies. What is not known is whether blocks of the medial branches anesthetize these nerves exclusively or whether they anesthetize other structures that are potential sources of pain. In a cadaveric study, the branches of the dorsal rami were exposed. Spinal needles were placed over the nerves, and plain radiographs were taken to demonstrate the precise radiographic locations of the nerves. In the second phase of the study, healthy volunteers underwent injections of radiographic contrast over the nerves, and plain radiographs and computed tomographic images were taken. Injections were performed using different rates of injection and in two positions for each nerve. Radiographic contrast incorporated the medial branches of the dorsal rami in every injection. When injections were performed using the upper position, aberrant flow of contrast medium was demonstrated with extension into the epidural space or intervertebral foramina. When a position lower on the transverse process was selected, aberrant flow was very uncommon. Eight percent of injections were found to be intravenous. When the appropriate technique is used, medial branch blocks are target specific. To guard against false-negative responses due to intravenous up-take, contrast medium must be used before the injection of local anaesthetic.

Comparison of Infusion Rates of Three I.V. Anaesthetic Agents for Induction in Elderly Patients

BERTHOUD, M. C.; McLAUGHLAN, G. A.; BROOME, I. J.; HENDERSON, P. D.; PEACOCK, J. E.; REILLY, C. S. Author Information

COMPARISON OF INFUSION RATES OF THREE I.V. ANAESTHETIC AGENTS FOR INDUCTION IN ELDERLY PATIENTS

We have compared the effect of different rates of injection of 2.5% thiopentone, 0.5% methohexitone and 0.2% etomidate for induction of anaesthesia in 90 premedicated, elderly patients. The agents were administered by infusion pump at rates of 1200 ml h-1, 600 ml h-1 and 300 ml h-1, respectively until anaesthesia was induced as judged by loss of verbal contact with the patient. The times for induction were significantly greater with the slower infusion rates (thiopentone 41 s, 57 s and 91 s (P < 0.001); methohexitone 44 s, 62 s and 84 s (P < 0.01); etomidate 48 s, 59 s and 87 s (P < 0.001)). The doses were significantly smaller (P < 0.001) with the slower infusion rates for all three agents (thiopentone 5.0, 3.7 and 2.8 mg kg-1; methohexitone 1.00, 0.75 and 0.56 mg kg-1; etomidate 0.26, 0.15 and 0.11 mg kg-1). For each drug there was no significant difference in induction characteristics, oxygen saturation, heart rate or mean arterial pressure, at the different infusion rates.

Reversal of neuromuscular block

The effect on heart rate of different rates of injection (10 seconds, 1, 3 and 5 minutes) of a fixed dose (neostigmine 2.5 mg and atropine 1.2 mg) and a weight-related dose (neostigmine 50 micrograms/kg and atropine 25 micrograms/kg) of neostigmine-atropine mixture given for the reversal of residual competitive neuromuscular block was studied in 196 healthy adult patients. In both series slow injection lessened and delayed the initial rise in heart rate. The subsequent fall in heart rate was less when the drugs were injected over 3 min compared with the 10 seconds and 1 minute injection groups but when given over 5 minutes there was a steady fall in heart rate, more so with the weight-related dose. It is recommended that a neostigmine and atropine mixture should be administered over 3 min.

PHARMACOKINETIC EVALUATION OF ICI 35 868 IN MAN: Single induction doses with different rates of injection

Blood concentrations of ICI 35 868 have been measured in patients following a single bolus dose of 2 mg kg-1. Three different rates of injection of the anaesthetic agent (3-5s, 20s and 40 or 50s) were examined. Pharmacokinetic indices, derived from blood concentrations of ICI 35 868, were independent of the speed of injection. The blood profiles could be described by a two-compartment open model with a mean alpha-phase half-life of 2.5 min and a mean beta-phase half-life of 54.5 min. The mean total body clearance was 3454 ml min-1. Similar data were obtained from a 4-mg kg-1 dose. The mean recovery time (4.4 min) and concentration of ICI 35 868 at awakening (1.05 micrograms ml-1) were also independent of the rate of injection. Using the derived pharmacokinetic model, predictions of drug concentrations have been made for repeated bolus doses, or infusions, of ICI 35 868.

Cardiopulmonary effects of intravenous gas embolism; with special reference to fate of intravascular gas bubbles.

To determine the graded cardiopulmonary effects and fate of pulmonary gas embolism, 11 sheep (with chronically implanted Doppler ultrasonic flow probes on pulmonary and brachiocephalic arteries) were subjected to experimental intravenous injection of nitrogen, oxygen and carbon dioxide. Three different rates of injection of each gas (0.03, 0.09 and 0.15ml/kg/min) were used for 30 minutes. Doppler ultrasonic flow probes were found to be very sensitive to the injected intravascular gas and produced characteristic chirps. The electromagnetic blood flowmeter was insensitive to the passage of these gases. Cardiopulmonary responses include elevation of pulmonary arterial pressure, diminished cardiac output and arterial hypoxemia. Nitrogen produced the greatest response and carbon dioxide the least, correlating with differences in solubility and diffusion rates. These responses developed with a one-half time of 15-20 minutes, with recovery, following cessation of injection, at the same rate. No statistically significant changes occurred in heart rate, systemic arterial pressure, pH or Pco2. Passage of intravenous gas through the pulmonary vasculature to the systemic circulation occurred only at the 0.15ml/kg/min dosage hate. The opening of the intrapulmonary arteriovenous shunts was primarily responsible for the decrease in arterial oxygen tension and passage of gas through the lung.

Evaluation of Fractured Reservoirs

Abstract Efforts were made to find improved means for locating fractures penetrated by a wellbore and for estimating fracture reservoir volume. The four approaches to the problem utilized acoustic logs, porosity estimates from different sources, transient pressure and fluid flow data, and resistivity logs. Acoustic amplitude attenuation and acoustic variable-intensity interference patterns have been used to locate fractures. Although amplitude logs have often proved useful for fracture detection, they are frequently inconclusive when used alone. This is due partially to variations in amplitude caused by factors other than fracturing. The variable-intensity interference patterns produced by borehole discontinuities in casing and in open-hole fractured sections were found to be quite useful in detecting fractures; but, like amplitude logs, they are not definitive by themselves. A technique has been developed that uses porosity estimate comparisons to evaluate fractured reservoirs. If this technique is used with acoustic variable-intensity interference patterns, it may be helpful for delineating fractured zones and for estimating fracture porosity. Transient pressure behavior observed for a fractured reservoir was found to be in agreement with that theoretically predicted for linear flow systems. Since this behavior is markedly different from that of a homogeneous reservoir, interpretation of transient pressures may provide a means of recognizing fractures. Other helpful techniques employing pressure and fluid flow data are comparison of calculated kh's for injection and withdrawal of fluids, comparison of calculated kh's for different rates of injection, and calculation of k/phi's from pressure and log data, where k is permeability, h is producing thickness, and phi is porosity. Some of these techniques also present possibilities for calculation of reservoir volumes. The fourth approach to fracture detection showed that, under certain conditions, an induction log can be used to detect a resistivity anomaly opposite a fractured zone. Although some of the techniques discussed show promise of being helpful, further study will be required before evaluations of fractured reservoirs become as satisfactory as evaluations of "normal" porosity reservoirs. Introduction Experience has shown that the presence of a fractured system can improve the productivity of hydrocarbon reservoirs. In some cases, fracture void space also supplies a significant portion of the total porosity. However, quantitative determination of the contribution of fracture systems to production from petroleum reservoirs has proven difficult. This is due in part to lack of consistently successful techniques for locating and usefully describing fracture systems penetrated by a wellbore. This paper presents the initial results of a research program on the use of borehole measurements for evaluation of fractured reservoirs. The objectives of this research are to find improved means forlocating fractures penetrated by a wellbore, andestimating in-situ reservoir volume contained within fracture systems in communication with the wellbore. This progress report will describe our attempts to date to use four types of data for fractured reservoir evaluation:acoustic logs,porosity estimates from different sources,transient pressure and fluid flow data, andresistivity logs. ACOUSTIC LOGS Amplitude Logs The acoustic amplitude log is one of the most widely used measurements in attempts to detect fractures. SPEJ P. 28ˆ

Acute intracranial hypertension, cerebral blood flow, and the EEG

Rapid expansion of an extradural balloon is a form of compression concussion and results in decreased EEG amplitude and profound alterations in the animal's vital signs. The latter consist of bradycardia, hypotension and bradypnea or respiratory arrest. When intracranial pressure is suddenly increased by this method, large pressure differentials are established throughout the intracranial space resulting in movement of the brain. This displacement, particularly of the brain-stem, could then account for the observed changes in both the EEG and vital signs. However, by expanding the balloon at many different rates of injection it has been demonstrated that the signs of compression concussion can occur when intracranial pressure is minimally elevated and movement of the brain is insignificant. We believe that the EEG changes observed at this time are due to local stress and that the alterations in vital signs result from electrophysiological excitation or inhibition of medullary centers, not direct physical involvement of the brain-stem. With more gradual expansion of the balloon the EEG remains normal until the intracranial pressure approaches the systemic arterial pressure, and the changes which occur at this time are due to cerebral ischemia.