Produced Water Quality based on Thermal Recovery Processes and after Interaction with Shale
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Management of produced water has always been an issue in the oil and gas industry. As the amount of water injected to produce from unconventional (heavy oil and source rock) resources increases, proper management and treatment of produced water has become increasingly important. The objective is to develop a thorough understanding of the expected quality of produced water originating from different hydrocarbon recovery processes and shale reservoirs to aid the development of plans to manage produced water. The produced water quality can greatly vary depending on water injection processes employed and rock and fluid composition of the formation injected. Produced water originating from steam flooding (SF), steam assisted gravity drainage (SAGD), expanding solventSAGD (ESSAGD), and hot water injection (HWI) processes were characterized. Furthermore, watershale interaction was investigated for Eagle Ford, Marcellus, Barnett, and Green River. The anion and cation concentration were analyzed with ion chromatography. Total dissolved solids (TDS), conductivity, pH, total organic carbon (TOC), and average particle sizes of colloids were measured. The colloids were characterized with zeta potential. The analysis of the ions in the water samples after the shale water interaction indicated a high concentration of sulfate, magnesium and calcium. The concentration of sulfate in the water was discovered to correlate with well with the amount of pyrite and gypsum in the Marcellus, Eagle Ford, and the Green River. However, in the water sample which interacted with the Barnett, there was abundance of sulfate in the water although the amount of pyrite and gypsum was low. This was attributed to the calcium in water samples which interacted with the Marcellus and Eagle Ford causing a reversible reaction during the dissolution of gypsum. Calcium and Magnesium concentrations in the water were correlated with their respective minerals. Water which interacted with the Green River sample did not have a significant amount of calcium and magnesium even though it contained a high amount of magnesium and calcium minerals. This was attributed to both the low solubility constant of dolomite and the high CEC of the Green River sample. Zeta potential and the ionic strength due to cations correlated well for the water samples after the interaction with the shale. However, a similar correlation for the water samples from the EOR experiments could not be achieved due to variation of pH of the samples as well as the variability of the exposed pressure and temperatures which the produced water was subjected to. The analysis of the produced water originating from the EOR processes indicated the ion concentration decreased as the stage at which the water was collected increased. The produced water from the ISC processes contained the largest amount of impurities due to bitumen cracking and therefore, would require the most treatment. Management options for produced water from shale reservoirs traditionally involves treating the water and reusing it for water injection based methods, however, disposal to Class II injection wells is also a possibility.
Ali, Maaz (2015). Produced Water Quality based on Thermal Recovery Processes and after Interaction with Shale. Master's thesis, Texas A & M University. Available electronically from