Thermal analysis in matrix acidization

The present paper addresses the heat transfer that occurs during matrix acidization. The complete process is first approached by separately analyzing two problems: one aiming at the temperature profile down the wellbore and the other looking at the temperature distribution within the reservoir. The wellbore-problem is modeled to consider short-term effects, including energy accumulation during the heat exchange between the wellbore and the surrounding formations. The solution obtained shows the transient behavior in detail, until the consistent collapse to known profiles for the late time periods. The model proposed to the reservoir-problem includes heat generation by the chemical reactions, an essential feature for the proper accounting of the acid-rock interaction. The eventual temperature distribution after the acid penetration into the reservoir, for the complete problem, is then obtained by coupling the solution to the wellbore-problem and the solution to the reservoir-problem. The wellbore-problem and the reservoir-problem are both solved individually via Laplace transforms and the coupled solution is then rendered by convolution in Laplace space. Stehfest's algorithm is used to convert the results to the real domain. Results obtained for typical operational parameters show that the acid temperature is very sensitive to injection flow rate and to fluid volumes injected during the pre-flush operation. Heat accumulation effects are important for injection periods in the order of 10 h. High injection rates result in temperatures, at the formation entrance, yet close to the surface temperature. The effect of heat loss to neighboring formations is rather small. Also, temperatures of the acid in the near-wellbore regions stay at values that are significantly lower than the reservoir initial temperature. The temperature calculation procedures for both specific problems and for the coupled problem are simple to implement and straightforward to use. (c) 2005 Elsevier B.V. All rights reserved.5141671859

DISPERSION IN HEAT AND MASS-TRANSFER NATURAL-CONVECTION ALONG VERTICAL BOUNDARIES IN POROUS-MEDIA

This paper reports an analytical-numerical study on hydrodynamic dispersion in natural convection heat and mass transfer near vertical surfaces embedded in porous media. The study considers the convective flows promoted by the density variation due to the combination of temperature and concentration gradients. Scale analysis is used to determine predominant parameters from a general descriptive form for the diffusive terms in the governing equations. Four classes of flow are possible according to the relative magnitude of the dispersion coefficients. Order of magnitude reasoning is used to obtain the similarity variables and dimensionless parameters, in the search for similarity solutions, An enhanced form of the Runge-Kutta algorithm is applied to solve the system of coupled similarity equations. Results are presented for several cases in each class of flow, covering an extensive range of the governing parameters.3651357136

Analytical solutions for heat flow in multiple pass welding

The purpose of this paper is to present analytical solutions for the heat distribution in the base metal during and after serial hearing in Multiple pass are welding. Recent literature on welding hear transfer has covered extensively numerical models for different aspects of the process. Most of these aspects are nonlinear problems in heat flow, e.g. varying thermal properties, inclusion of radiative transfer in the are, and/or convective flow in the welding pool. The basic analytical models in use were established long ago in classical papers, but these refer to single heat cycles. The present paper addresses the circumstances of multiple cycles. In these cases, depending on the bead length and the interpass time, as shown by the proposed solution, the thermal effects of each successive pass will accumulate. When modelling the hear transfer in each pass, the effects of previous passes enter into the differential equations as nonhomogeneous initial conditions The complexity introduced by these conditions requires special treatment: art analytical solution employing the Green's function method was used. The Main focus in this work is an welding of thin plates. Simple changes to the models take account of the convective heat lass to the surroundings and enable temperature dependent properties to be calculated The solutions were checked against experimental results obtained from a specially designed laboratory setup. Thermal cycles provided by the analytical solutions compare well with temperature histories measured at different locations during thr ee pass gas metal are welding of a 0.5 in (similar to 1 cm) AISI 304 stainless steel plate. Measured data and model results show very good agreement. The analytical solutions are also extended to the geometries of moderately thick plates. (C) 2000 IoM Communications Ltd.52637

ELECTRICAL HEATING OF OIL-RESERVOIRS - NUMERICAL-SIMULATION AND FIELD-TEST RESULTS

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TRANSIENT METHOD FOR MEASURING THERMAL-PROPERTIES OF SATURATED POROUS-MEDIA

This paper describes the development of a transient technique to measure thermal diffusivity and conductivity of porous samples. The method uses the film heat sensor to probe heat flux. Temperature and heat flux are measured dynamically allowing conditions to vary in time at the point of measurement. The data are then treated by a deconvolution algorithm, rendering results proper to simpler models for the same geometry. The numerical treatment in the deconvolution procedure was verified for a hypothetical case. The method was finally tested in the laboratory, with experiments made on samples of natural rock.36102565257

Evaluation of crude oil oxidation by accelerating rate calorimetry Effects of combustion process variables on thermal and kinetic parameters

Accelerating rate calorimetry has been used to study the thermal behavior of the combustion reactions that occur during the in situ combustion process and to estimate key parameters for the numerical simulation studies. This work reports the results from a study on the combustion reactions of heavy oil based on experimental tests using an accelerating rate calorimeter. The temperature settings covered a ramped ranging from 50 to 550 A degrees C. The pressure was kept constant at 20 and 40 bar, and the air flow rates were tested for values of 90 and 120 mL min(-1). An experimental design was built to provide the effects of pressure, air inflow, and oil mass on the main kinetic parameters. Activation energy was 0.6-64 x 10(3) kJ mol(-1), with higher variation in Test-1. LTO region was represented by just one reaction and its activation energy was similar to 10(2) kJ mol(-1) across every tests. Process variables were found to affect the exothermal temperature interval, the activation energy, and the order of reaction. Effects of variables on the kinetic parameters were found to be dependent on specific reaction temperature range, being more pronounced in the range of higher temperatures.113289790

Kinetics of carbonate dissolution and its effects on the porosity and permeability of consolidated porous media

Injection of carbon dioxide into carbonate oil reservoirs is expected to promote chemical dissolution of the rock and alter its petrophysical properties. This work reports an experimental investigation on porosity and permeability alterations of carbonate samples due to the acid action of the carbonated water produced by means of solubilization of carbon dioxide in an aqueous solution. Travertine marble rocks with properties similar to Brazilian pre-salt reservoir rock were used in the tests at 9000 psi and 65 C. Dissolution was carried out in high-pressure vessels during a total period of 240 h. Reaction was stopped at intermediate time intervals to evaluate porosity, permeability and mass loss of the samples. Results showed that the dissolution reaction between the travertine and carbonated water presents a slow kinetic, leading to a small loss of 0.2 g of sample after 240 h of reaction. However, the minor mass loss impacts strongly on the porosity and permeability of the rock. Data show that a variation of 1 wt.% on the sample mass caused by dissolution produces a change of 50% on the sample porosity and of 180% on the sample permeability. The dissolution rate is greatly faster if carbonated water is replaced by HCl aqueous solution and depends on the acid solution concentration. In addition, results lead to an exponential model that allows forecasting the mass loss as a function of time. Knowledge on the dissolution rate of carbonate samples by carbon dioxide solutions is required in EOR and CO2 storage projects to estimate the changes on the flow properties of the porous formation and the damages that can be impinged to the rock. (C) 2013 Elsevier B.V. All rights reserved.112284289Petrobra

COMPARISON OF RESIDUAL OIL SATURATION FOR WATER AND SUPERCRITICAL CO2 FLOODING IN A LONG CORE, WITH LIVE OIL AT RESERVOIR CONDITIONS

The measurement of residual oil saturation (ROS) is of paramount importance in predicting the expected recovery in a producing field. It is also a key factor for reservoir management and for defining possible long-term enhanced oil recovery (EOR) targets. Even though ROS has been known to depend on different factors, such dependence has not been investigated extensively in the laboratory, at reservoir conditions. This paper describes an experimental work focusing on the rock formation and conditions of a very highly productive field that is offshore Brazil. The objective was to compare the recovery efficiency between water and supercritical CO(2) flooding at reservoir conditions in terms of ROS evolution. A careful program of displacement tests was conducted using long real unconsolidated porous media and live reservoir fluid at reservoir pressure and temperature. An improved version of a conventional test apparatus has been implemented successfully to allow high pressure displacements through long cores. A linear x-ray monitoring device permitted us to follow water and CO(2) in situ saturations along the core. A numerical simulation study was developed to scrutinize possible effects from varying conditions. The results obtained in this work led to lower residual oil saturation in the CO(2) flooding than water flooding. Experimental and numerical simulation results are compared.148699708Petrobras-Petroleo Brasileiro S/