Reinjection and injection of fluids in geothermal operations (state of the art)

A summary of the problems (encountered as well as anticipated) associated with reinjection of heat-depleted brines and injection of other fluids such as imported brines and gases is presented. Covered are only injection and reinjection problems which are related to the exploitation of liquid-dominated resources by flash-cycle power plants. Suggestions (proven as well as probable) which may offer solutions to many of the identified problems are also covered. In addition, some ideas that should or could be implemented in planning of implementing and/or executing any new geothermal injection operation are described

High-resolution intravascular magnetic resonance quantification of atherosclerotic plaque at 3T

<p>Abstract</p> <p>Background</p> <p>The thickness of fibrous caps (FCT) of atherosclerotic lesions is a critical factor affecting plaque vulnerability to rupture. This study tests whether 3 Tesla high-resolution intravascular cardiovascular magnetic resonance (CMR) employing tiny loopless detectors can identify lesions and accurately measure FCT in human arterial specimens, and whether such an approach is feasible <it>in vivo </it>using animal models.</p> <p>Methods</p> <p>Receive-only 2.2 mm and 0.8 mm diameter intravascular loopless CMR detectors were fabricated for a clinical 3 Tesla MR scanner, and the absolute signal-to-noise ratio determined. The detectors were applied in a two-step protocol comprised of CMR angiography to identify atherosclerotic lesions, followed by high-resolution CMR to characterize FCT, lesion size, and/or vessel wall thickness. The protocol was applied in fresh human iliac and carotid artery specimens in a human-equivalent saline bath. Mean FCT measured by 80 μm intravascular CMR was compared with histology of the same sections. <it>In vivo </it>studies compared aortic wall thickness and plaque size in healthy and hyperlipidemic rabbit models, with post-mortem histology.</p> <p>Results</p> <p>Histology confirmed plaques in human specimens, with calcifications appearing as signal voids. Mean FCT agreed with histological measurements within 13% on average (correlation coefficient, <it>R </it>= 0.98; Bland-Altman analysis, -1.3 ± 68.9 μm). <it>In vivo </it>aortic wall and plaque size measured by 80 μm intravascular CMR agreed with histology.</p> <p>Conclusion</p> <p>Intravascular 3T CMR with loopless detectors can both locate atherosclerotic lesions, and accurately measure FCT at high-resolution in a strategy that appears feasible <it>in vivo</it>. The approach shows promise for quantifying vulnerable plaque for evaluating experimental therapies.</p

Occupational Radiation Protection in Interventional Radiology: A Joint Guideline of the Cardiovascular and Interventional Radiology Society of Europe and the Society of Interventional Radiology

No Abstract

Scale formation at various locations in a geothermal operation due to injection of imported waters

The injection of waters that are not native to a geothermal formation generates various physical and chemical problems. The major chemical problem resulting from such injections is the formation of sulfate scales (particularly CaSO4, BaSO4 and SrSO4) at various locations starting from the injection well through the production well to the surface facilities of any geothermal operation. One of the ways to prevent this type of scale formation is by reducing the sulfate concentration of the injection waters. The effect of sulfate deionization on scale formation at various locations of the geothermal operations is studied. Some experimental results on the CaSO4 scale formation in porous media upon heating an injection water with and without addition of scale inhibitors are also given

Chemical damage due to drilling operations

The drilling of geothermal wells can result in near wellbore damage of both the injection wells and production wells if proper precautions are not taken. Very little specific information on the chemical causes for drilling damage that can directly be applied to the drilling of a geothermal well in a given situation is available in the literature. As part of the present work, the sparse literature references related to the chemical aspects of drilling damage are reviewed. The various sources of chemically induced drilling damages that are related to drilling operations are summarized. Various means of minimizing these chemical damages during and after the drilling of a geothermal well are suggested also

Radiolabelling of chemicals. [Chemical additives used in geothermal operations]

Labeling of chemical additives with radioactive isotopes can solve numerous problems in geothermal operations. The physical and chemical behavior of many chemicals slated for geothermal operations can be studied with the required detail at the extremely low concentration of the commercially available (non-labeled) compounds. The problems of labeling and the basics of these radioactively labeled chemicals are described in this report. Conclusions of this study are: (1) chemicals labeled with radioactive isotopes can be used to investigate the chemical and physical behavior of chemical additives used in geothermal operations. The high detection limits make this technology superior to conventional analytical and monitoring methods; (2) severe difficulties exist for utilizing of radioactively labeled chemicals in geothermal operations. The labeling itself can cause technical problems. Another host of problems is caused by the reluctance of chemical manufacturers to release the necessary proprietary information on their chemicals required for proper labeling; and (3) previous attempts to manufacture radioactively labeled flocculants and to utilize them in a geothermal operation were prematurely abandoned for a number of reasons

Enhancement of heat production through selective scaling

The heat-depleted brine has to be reinjected whether it is for technical, economical, environmental and/or legal purposes. However, there are many problems related to injectivity and injectability in a geothermal field. The major drawback is the dread of an early breakthrough of the heat depleted brine at the production wells. It is believed that this drawback may be overcome through selective scaling. The results of investigation into the feasibility of selective scaling are summarized. Selective scaling is defined here as the process of intentionally precipitating large quantities of chemical compounds at selected locations, such as high permeability streaks or fractures, for the purpose of retarding the flow of injection fluids through these flow channels. Such flow retardation will increase the residence time of the injected fluids in the reservoir by a more suitable heat sweep thereby enhancing the heat extraction from the geothermal reservoir. Three different methods of selective scaling are discussed. These methods are: the injection of a thermodynamically unstable brine; injection of a slug of dirty brine or other thermodynamically unstable brine into selective locations of the reservoir; and mixing of an injection brine which is incompatible with a reservoir brine. The basis of these methods and their impact on the permeability characteristics of the reservoir are discussed through a precipitation model and through simple flow models. The application of these models are illustrated using Salton Sea brine and Currier 2 brine

Flow of particle suspensions through porous media

A new attempt is made to study the mechanisms of particle invasions into porous media. The following subjects are described: A critical survey of the literature indicating that the mechanism of particle invasions is not known in sufficient detail. The pros and cons of existing particle measuring devices are briefly described. Results from a new laboratory study on particle characterizations are given. The results of the laboratory studies on the flow of particle suspensions through porous media (up to 200 md) are discussed. The effects of flow rate and particle concentrations on the amount of damage (i.e., permeability impairment) and depth of penetration (from core inlet towards outlet) are particularly emphasized. Filter methods (e.g., using millipore filter) cannot be used to determine particle invasions into porous medium. Any predictions of the injection problems based on millipore (or any other filter) measurements are useless and should be discarded

Technique to Adjust Adaptive Digital Filter Coefficients in Residue Number System Based Filters

The paper discusses adaptive filtering using Least Mean Square (LMS) and Recursive Least Square (RLS) algorithms. An algorithm for adjusting the coefficients of an adaptive digital filter in the Residue Number System and a procedure of developed algorithm applying depending on filter length and signal length are proposed. Mathematical modeling of the considered algorithms is performed. Examples are presented to demonstrate how the proposed technique can help the designer in the adjustment of the filter coefficients without the need for extensive trial-and-error procedures. The analysis of the denoising quality and computational complexity is made. Synthetic and real data (earthquake recording) were used while testing. The proposed algorithm surpasses the existing ones like LMS and RLS, and their modifications in a number of parameters: adaptation (denoising) quality, ease of implementation, execution time. The main difference between the developed algorithm is the sequential adaptation of each coefficient with zero error. In the known algorithms, the entire vector of coefficients is iteratively adapted, with some specified accuracy. The iterations (steps) number is determined by the input signal length for all algorithms