Tracer flow model for naturally fractured geothermal reservoirs

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The model proposed has been developed to study the flow of tracers through naturally fractured geothermal reservoirs. The reservoir is treated as being composed of two regions: a mobile region where diffusion and convection take place and a stagnant or immobile region where only diffusion and adsorption are allowed. Solutions to the basic equations in the Laplace space were derived for tracer injection and were numerically inverted using the Stehfest algorithm. Even though numerical dispersion is present in these solutions, starting at moderate dimensionless time values, a definite trend was found as to infer the behavior of the system under ... continued below

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281-289

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Ramirez, Jetzabeth; Rivera, Jesus & Rodriquez, Fernando January 1, 1988.

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Description

The model proposed has been developed to study the flow of tracers through naturally fractured geothermal reservoirs. The reservoir is treated as being composed of two regions: a mobile region where diffusion and convection take place and a stagnant or immobile region where only diffusion and adsorption are allowed. Solutions to the basic equations in the Laplace space were derived for tracer injection and were numerically inverted using the Stehfest algorithm. Even though numerical dispersion is present in these solutions, starting at moderate dimensionless time values, a definite trend was found as to infer the behavior of the system under different flow conditions. For practical purposes, it was found that he size of the matrix blocks does not seem to affect the tracer concentration reponse and the solution became equivalent to that previously presented by Tang et al. Under these conditions, the behavior of the system can be described by two dimensionless parameters: the Peclet number for the fractures, P{sub e{sup 1}}, and a parameter {alpha} ({alpha} = {xi}{sqrt}P{sub e{sup 2}}), where {xi} is {xi} = {phi}{sub e} D{sub e}/v(w-{delta}) and P{sub e{sup 2}} is the Peclet number for the matrix. Tracer response for spike injection was also derived in this work. A limiting analytical solution was found for the case of {alpha} approaching zero and a given P{sub e{sup 1}}, which corresponds to the case of a homogeneous system. It is shown that this limiting solution is valid for {alpha} < 10{sup -2}. For the case of continuous injection this solution reduces to that previously presented by Coats and Smith. For the spike solution it was found that the breakthrough time for maximum tracer concentration is directly related to the dimensionless group ({sqrt}(9 + (X{sub D}){sup 2}(P{sub e{sup 1}}){sup 2}) -3)/P{sub e{sup 1}}. Therefore it is possible to obtain the value of P{sub e{sup 1}} or X{sub D}. A set of graphs of dimensionless concentration in the fracture vs. dimensionless time for tracer response were developed. It was found that if P{sub e{sup 1}} is held constant while {alpha} is changing, the limiting solution becomes a limiting curve for a family of curves in a plot of C{sub D} vs. t{sub D}. In this graph P{sub e{sup 1}} fixes the range in which the family of curves evolves. It was also found that the breakthrough time for a given concentration is a strong function of {alpha}.

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281-289

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  • Proceedings, thirteenth workshop on geothermal reservoir engineering, Stanford University, Stanford, CA, January 19-21, 1988

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  • Report No.: SGP-TR-113-40
  • Grant Number: AS07-84ID12529
  • Office of Scientific & Technical Information Report Number: 887295
  • Archival Resource Key: ark:/67531/metadc886117

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Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • January 1, 1988

Added to The UNT Digital Library

  • Sept. 21, 2016, 2:29 a.m.

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  • Dec. 7, 2016, 11:17 p.m.

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Ramirez, Jetzabeth; Rivera, Jesus & Rodriquez, Fernando. Tracer flow model for naturally fractured geothermal reservoirs, article, January 1, 1988; United States. (digital.library.unt.edu/ark:/67531/metadc886117/: accessed October 20, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.