Gas Condesate

EVALUATION OF SOLVENTS EFFICIENCY IN CONDENSATE BANKING REMOVAL EVALUACION DE LA EFICIENCIA DE SOLVENTES EN LA REMOCION DEL BANCO DE CONDENSADO
TOMAS CORREA
Msc. en Gas Natural y Gerencia de Energía, Instituto Tecnológico Metropolitano ITM, tomascorrea@itm.edu.co

DJEBBAR TIAB
Dr. en Ingeniería de Petróleos, Universidad de Oklahoma, USA, dtiab@ou.edu

DORA PATRICIA RESTREPO
Dr. enIngeniería de Petróleos, Universidad Nacional de Colombia, dprestre@ou.edu Recibido para revisar septiembre 14 de 2008, aceptado noviembre 4 de 2008, versión final noviembre 11 de 2008

ABSTRACT: This work describes experimental design and tests performed to simulate gas condensate reservoir conditions below dew point in the laboratory using three different compositions of synthetic gas condensate.Methanol, propanol and methylene chloride are the solvents used to remove the condensate banking and improve the gas effective permeability near to the wellbore. Solvents are injected in Berea sandstone rock with similar petrophysical properties in order to compare the efficiency at removing the condensate banking. It was observed that all of the solvents improved the gas effective permeability afterremoving banking condensate; however, methanol was the more efficient solvent to remove it while methylene chloride had the lowest values of gas effective permeability after removing the banking condensate. KEY WORDS: Gas condensate reservoir, miscible displacement, experimental work, enhanced recovery, gas effective permeability, condensate banking removal. RESUMEN: Este estudio describe elmontaje experimental y las pruebas realizadas en el laboratorio para simular las condiciones de un yacimiento de gas condensado por debajo del punto de burbuja usando tres diferentes composiciones sintéticas de gas condensado. Metanol, Propanol y cloruro de metileno son los solventes usados para remover el banco de condensado y mejorar la permeabilidad efectiva al gas en la cara del núcleo. Ellos soninyectados en areniscas Berea con propiedades petrofísicas similares con el fin de comparar el grado de eficiencia en la remoción del banco de condensado. Los experimentos muestran que los tres solventes mejoraron la permeabilidad efectiva al gas después de remover el banco de condensado; sin embargo el metanol fue el solvente más eficiente para remover el banco de condensado, mientras el clorurode metileno mostró los valores más bajos de permeabilidad efectiva al gas indicando menor eficiencia en la remoción el banco de condensado. PALABRAS CLAVE: Yacimientos de gas condensado, desplazamiento miscible, trabajo experimental, recobro mejorado, permeabilidad efectiva al gas, remoción del banco de condensado.

Dyna, Año 76, Nro. 157, pp. 163-171. Medellín, Marzo de 2009. ISSN 0012-7353164

Correa et al

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INTRODUCCION

Many of the largest natural gas reservoirs (3035%) have reservoir conditions which result in retrograde condensation due to pressure decreases during the production of gas. During depletion of these gas condensate reservoirs, as the pressure drop below the dew point pressure, liquid drops out of the gas phase and forms condensate banking near thewellbore, reducing the gas productivity significantly. The condensate continues accumulating in portions of the pore space that otherwise would be available for gas flow, thus blocking the gas flow. Once the condensate saturation exceeds the residual saturation, the condensate continuously forms and flows towards the wellbore. Liquid saturations near the wells can reach 50 to 60% under pseudo steadystate flow of gas and condensate. Productivity reductions of 40-80% have been reported for some fields. Reductions in relative permeability greater than 95% in laboratory cores at low capillary number have been reported for both low and high permeability rocks. The degree of condensate banking depends indirectly on a combination of several factors including fluids properties (interfacial tension,...