The pilot appraisal of acid fracturing of coalbed methane reservoir in southeast Qinshui Basin, China

Abstract

The reserves of Coalbed Methane (CBM) in Qinshui Basin are quite promising, but the outputs from CBM wells are quite small even after massive hydraulic fracturing. Herein the fracture system with #3 and #15 coal seams in Qinshui basin was analyzed, and it was found that both of the macro-scale fractures and micro-scale fractures are filled with clay and carbonate minerals, which explains the low productivity of CBM wells after conventional hydraulic fracturing. Acid fracturing has long been an effective method for carbonate gas reservoir to improve the gas well production. However, there were few reports about the application of acid fracturing in coal bed methane field. Based on the mineral identification and acid sensitivity test, the feasibility of acid fracturing demonstrated that the acid does more help than damage to increase the permeability of coal seams in Qinshui basin. Onsite operations have shown that acid fracturing is applicable for the CBM wells in Jincheng Mining Area. It was also observed from the microseismic survey that when applying the acid fracturing treatment, the stimulated reservoir area depends on the acid volume pumped in the first stage, which is crucial to the success of the stimulation. Las reservas de gas metano de carbón (CBM, del inglés Coalbed Methane) en la cuenca Qinshui son más que prometedoras, pero la producción en los pozos es muy pequeña, incluso después de fracturas hidráulicas masivas. En este trabajo se analizaron los sistemas de fractura de las vetas de carbón #3 y #15 de la cuenca Qinshui y se encontró que tanto las fracturas a macroescala como aquellas a microescala están cubiertas con arcillas y minerales carbonatos, lo que explica la baja productividad de los pozos de gas metano de carbón después de la fractura hidráulica convencional. La fractura ácida ha sido un método efectivo en los depósitos de gas carbonato para mejorar la producción en el pozo de gas. Sin embargo, existen pocos informes sobre la aplicación de la fractura ácida en el campo del gas metano de carbón. De acuerdo con la identificación mineral y las pruebas de sensibilidad ácida, la factibilidad de la fractura ácida demostró que el ácido es reparador en el incremento de la permeabilidad en las vetas de carbón de la cuenca Qinshui. Las operaciones in situ han demostrado que la fractura ácida es aplicable para los pozos de gas metano de carbón en el área minera de Jincheng. También se observó en el sondeo microsísmico que cuando se aplica un tratamiento de fractura ácida, el área del depósito estimulada depende del volumen de ácido bombeado en primera instancia, lo que es determinante en el éxito de la estimulación. ABSTRACT RESUMENPalabras clave: Gas metano de carbón, fractura ácida, pruebas de sensibilidad ácida, área del reservorio estimulada.Record Manuscript

Controls on Hydrogen Sulfide Formation and Techniques for Its Treatment in the Binchang Xiaozhuang Coal Mine, China

“…By measuring hydrogen sulfide and pyrite δ 34 S abundances, Liu et al demonstrated that the δ 34 S of mine produced by BSR was commonly negative and even reached −50‰. In contrast, the δ 34 S of mine produced by thermal sulfate reduction (TSR) was commonly greater than +10‰, which is similar to the δ 34 S of sulfides in the field. , Liu et al and Machel found that anaerobic environments with the temperature of 60–80 °C had an effect on the type of sulfate-reducing bacteria (SRB) present. , Yan et al and Jiang et al noted that the ash index can indicate the trend of the reducing capacity for sedimentary environments hosting coal seams containing hydrogen sulfide. , After Deng et al used the acid–base index of the coal, the salinity index, and the retention index to determine the hydrodynamic condition of the coal’s formation, their studies further revealed the effects of the reducing sedimentary environment on the formation of hydrogen sulfide . Fu et al studied the excess sulfur in the Zaozhuang Bayi coal mine, China, and reached the conclusion that magmatic heat led to abnormal enrichment of hydrogen sulfide…”

A Thermo-Hydro-Mechanical-Chemical Coupling Model and Its Application in Acid Fracturing Enhanced Coalbed Methane Recovery Simulation

“…Therefore, the permeability of coal reservoirs is the key parameter that dominates gas and water migration [3]. Most coal reservoirs in China are characterized by low permeability (~0.001-~0.1 mD), which has largely restricted coal seam degassing processes, especially when the mining moves towards deeper depths [4][5][6][7]. In order to guarantee safe mining and CBM production, the reservoir permeability should be further improved to increase the efficiency of coalbed methane extraction.…”

Underground microseismic monitoring of a hydraulic fracturing operation for CBM reservoirs in a coal mine

“…The length and width of the fracture network can be estimated by analyzing the MS locations. 31,32 And the characteristic of MS responses to the evolution of hydraulic pressure (HP) is significant, which can reveal the fracture occurrence mechanism. 31,32 And the characteristic of MS responses to the evolution of hydraulic pressure (HP) is significant, which can reveal the fracture occurrence mechanism.…”

“…30 A number of application tests of MS monitoring for subsurface HF have been performed to estimate the stimulated area. 31,32 And the characteristic of MS responses to the evolution of hydraulic pressure (HP) is significant, which can reveal the fracture occurrence mechanism. 33 However, the mechanism of MS responses to HF is rarely expressed in the complicated subsurface field.…”