7 Geochemistry (Posters)

Monday, 21 March 2016
8:00 AM - 12:00 PM
Convention Hall

INFLUENCE OF H2S ON THE ANALYSIS OF CO2 USING THE VOLUMETRIC EXPANSION METHOD IN WELL WATERS ASSOCIATED WITH CO2-ENHANCED OIL RECOVERY

Paper number: 7-4
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

Carbon dioxide-enhanced oil recovery (EOR) is a method used to supplement conventional water flooding approaches and flush residual crude oil from subsurface rock formations towards production wells for recovery. CO2 is injected along with water under pressure and it moves through the pore spaces of the rock, mixes with and lowers the viscosity of the oil, and helps displace oil from the rock formation. The concentration of CO2 in production water is needed to determine CO2 breakthrough rates at the production well, as well as identify potential paths of CO2 leakage into groundwater reservoirs. The CarboQC carbonation meter is used to measure the concentration of CO2 in water under field conditions by monitoring the temperature and pressure changes during the multiple expansion of a sealed volume of water and calculating the PCO2 from the ideal gas law. This method is effective using carbonated beverages and most natural waters because the solubility of potentially interfering common gases such as O2 and N2 is more than 50 times lower in water than it is for CO2. Hydrogen sulfide (H2S), which is even more soluble than CO2 in water, is sometimes encountered in very high concentrations in water associated with high-sulfur petroleum deposits or natural gas production, and this directly interferes with CO2 analysis by volumetric expansion. In this study, we examined the effects of H2S on CO2 measurements in saline produced waters from EOR wells in Texas. Two methods were tested as ways to subtract H2S from the dissolved gas fraction. Sulfide was oxidized with hydrogen peroxide, which produced elemental sulfur or sulfate as a reaction product depending on the pH of the water sample, but this generated gas pressure due to peroxide reaction with other organics. Copper sulfate was added to eliminate the dissolved sulfide via precipitation of highly insoluble copper sulfides. Copper sulfides were rapidly precipitated in EOR well samples, but the reaction simultaneously lowered the pH relative to the amount of sulfide present. This resulted in a variable increase in the measured CO2 due to the conversion of bicarbonate ion to carbonic acid. The potential for this analytical approach to be effective in such waters is further discussed relative to dissolved inorganic carbon content in water and the potential interactions between CO2 and H2S.

Geological Society of America Abstracts with Programs. Vol. 48, No. 1

doi: 10.1130/abs/2016NE-272496

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