Geothermal Gas Compositions: Review of Sampling and Analysis Method

Jeremiah Kipngok, Timothy Kinara, Evans Gichuhi
Geothermal Development Company


Geothermal gases provide crucial information on geothermal reservoirs and processes affecting reservoir fluid chemistry, potential environmental effects of the gases and quality of steam that is critical in power plant design. Accurate gas data is extremely important in these endeavors. Notably, geothermal gases are sensitive to external interferences hence the need for extra caution during sampling and analysis. Examination of gas results for wells, fumaroles and dry gas emanations revealed significant fluctuations and inconsistencies which led to the conclusion that it is critical to review the procedure of gas analysis in order to obtain representative gas results. The current gas sampling and analysis procedure is prone to error inherent in the process. In the current procedure, two gas sampling flasks prepared with 50 ml NaOH solution are used to collect gas samples with one flask used for analysis of CO2 and H2S trapped by the NaOH solution and the other for dry gas analysis using the gas chromatograph (GC). However, variations may occur due to conditions during sampling, amount of condensate collected and possible contamination of either of the samples, all of which may significantly influence the final result. In order to control these uncertainties and potential sources of error, it is proposed that the gas sampling and analysis procedure be modified to use only one sampling flask for the entire gas sample collection and analysis. Additionally, the proposed setup minimizes effects of injection of samples into the GC during analysis hence potentially reducing its down time. The one-off cost of modifying the current setup is approximately 8,900 USD (KSh. 969,000). It is viewed that the benefits far outweigh the cost. This research proposal therefore presents a review of processes affecting gas results and subsequent proposed changes to the gas analysis method/procedure.

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