Reduction of Energy Consumption for Water Wells Rehabilitation. Technology Optimization

Groundwater wells are widely used in the energy sector, including for drinking water supplies and as water source wells in the oil and gas industry to increase production of natural gas and petroleum. Water well clogging, which can happen to any well for various reasons, is a serious problem that can lead to increased power costs due to a higher head to the pump, a reduction in the flow rate and various drawdown issues. If rehabilitation procedures do not take place in time, this can result in permanent loss of the well, and a new well must be drilled, which is not a sustainable approach. Rehabilitation methods for water wells usually include mechanical and chemical treatments, and even though these methods are well established and have been used for many years we can still observe many abandoned wells which could be rehabilitated. In this study, sets of cavitation generators are developed and used in combination with common conic hydrodynamic nozzles. This combination reduces the pressure in the system and makes the cleaning setup much lighter and more mobile. The designed nozzles were successfully used in hydrodynamic cleaning of four water wells.

Evaluation of NaCl and MgCl2 heat exchange fluids in a deep binary geothermal system in a sedimentary halite formation

Halite formations are attractive geothermal reservoirs due to their high heat conductivity, resulting in higher temperatures than other formations at similar depths. However, halite formations are highly reactive with undersaturated water. An understanding of the geochemical reactions that occur within halite-saturated formation waters can inform decision making regarding well construction, prevention of well clogging, formation dissolution, and thermal short-circuiting. Batch reaction and numerical 3-D flow and equilibrium reactive transport modeling were used to characterize the produced NaCl-brine in a well targeting a halite-saturated formation. The potential for inhibition of precipitation and dissolution using an MgCl2-brine and NaCl + MgCl2-brine were also investigated. Within the injection well, heating of an NaCl-brine from 70 to 120 °C caused the solubility of halite to decrease, resulting in the potential dissolution of 0.479 mol kg−1 halite at the formation. Conversely, cooling from 120 to 100 °C in the production well resulted in potential precipitation of 0.196 mol kg−1 halite. Concurrent precipitation of anhydrite is also expected. Introduction of MgCl2 into the heat exchange brine, which has a common Cl− ion, resulted in a decreased potential for dissolution by 0.290 mol kg−1 halite within the formation, as well as decreased precipitation within the production well, compared to the NaCl-brine. The halite solubility was altered by changes in pressure up to 0.045 mol kg−1. This indicates that designing and monitoring the composition of heat exchange fluids in highly saline environments is an important component in geothermal project design.

Evaluation of NaCl and MgCl2 heat exchange fluids in a deep binary geothermal system in a sedimentary halite formation

Halite formations are attractive geothermal reservoirs due to their high heat conductivity, resulting in higher temperatures than other formations at similar depths. However, halite formations are highly reactive with undersaturated water. An understanding of the geochemical reactions that occur within halite-saturated formation waters can inform decision making regarding well construction, prevention of well clogging, formation dissolution, and thermal short-circuiting. Batch reaction and numerical 3-D flow and equilibrium reactive transport modeling were used to characterize the produced NaCl-brine in a well targeting a halite-saturated formation. The potential for inhibition of precipitation and dissolution using an MgCl2-brine and NaCl+MgCl2-brine were also investigated. Within the injection well for an NaCl-brine, with heating from 70 to 120°C, the solubility of halite decreases resulting in the potential dissolution of 0.479 mol kg-1 halite at the formation. Cooling from 120 to 100°C in the production well results in precipitation of 0.196 mol kg-1 halite as well as anhydrite. Introduction of MgCl2, resulting in a common Cl- ion, into the heat exchange brine resulted in a decreased potential for dissolution by 0.290 mol kg-1 halite within the formation, as well as decreased precipitation within the production well, compared to the NaCl-brine. The halite solubility was altered by changes in pressure up to 0.045 mol kg-1. This indicates that designing and monitoring the composition of heat exchange fluids in highly saline environments is an important component in geothermal project design.

Evaluation of NaCl and MgCl2 heat exchange fluids in a deep binary geothermal system in a sedimentary halite formation

Halite formations are attractive geothermal reservoirs due to their high heat conductivity, resulting in higher temperatures than other formations at similar depths. However, halite formations are highly reactive with undersaturated water. An understanding of the geochemical reactions that occur within halite-saturated formation waters can inform decision making regarding well construction, prevention of well clogging, formation dissolution, and thermal short-circuiting. Batch reaction and numerical 3-D flow and equilibrium reactive transport modeling were used to characterize the produced NaCl-brine in a well targeting a halite-saturated formation. The potential for inhibition of precipitation and dissolution using an MgCl 2 -brine and NaCl+MgCl 2 -brine were also investigated. Within the injection well, with heating from 70 to 120°C, the solubility of halite decreases resulting in the potential dissolution of 0.479 mol kg -1 at the formation. Cooling from 120 to 100°C in the production well results in precipitation of 0.196 mol kg -1 halite as well as anhydrite, brucite, carnallite, goergeyite, gypsum, halite, kieserite and polyhalite. Introduction of MgCl 2 , resulting in a common Cl - ion, into the heat exchange brine resulted in a decreased potential for dissolution by 0.290 mol kg -1 as the heat exchange fluid entered the formation and within the formation itself, as well as decreased precipitation within the production well, compared to the NaCl-brine. The halite solubility was altered by changes in pressure up to 0.045 mol kg -1 . This indicates that designing and monitoring the composition of heat exchange fluids in highly saline environments is an important component in geothermal project design.

Evaluating Treatment Requirements for Recycled Water to Manage Well Clogging during Aquifer Storage and Recovery: A Case Study in the Werribee Formation, Australia

Managed aquifer recharge (MAR) is the intentional recharge of water to suitable aquifers for subsequent beneficial use or to achieve environmental benefits. Well injection techniques for MAR, such as Aquifer Storage and Recovery (ASR), rely on implementing appropriate design and defining the operational parameters to minimise well clogging and maintain sustainable rates of recharge over the long term. The purpose of this study was to develop water quality targets and pre-treatment requirements for recycled water to allow sustained recharge and recovery in a medium-coarse siliceous aquifer. The recharge water is a blend of 40% Class A recycled water and 60% reverse osmosis (RO)-treated Class A recycled water. Four source waters for MAR were evaluated: (1) this blend with no further treatment, and this blend with additional treatment using: (2) a 20 µm sediment cartridge filter, (3) a 5 µm sediment cartridge filter, or (4) a 5 µm granular activated carbon (GAC) cartridge filter. All four treatment options were also further disinfected with chlorine. The four blended and treated recycled waters were used in laboratory columns packed with aquifer material under saturated conditions at constant temperature (20.7 °C) with light excluded for up to 42 days. Substantial differences in the changes in hydraulic conductivity of the columns were observed for the different treatments within 14 days of the experiment, despite low turbidity (<2 NTU) of the blend waters. After 14 days, the GAC-treated water had a 7% decline in hydraulic conductivity, which was very different from the other three blend waters, which had declines of 39–52%. Based on these results and consistent with previous studies, a target biodegradable dissolved organic carbon (BDOC) level of <0.2 mg/L was recommended to ensure a biologically stable source of water to reduce clogging during recharge.

Drinking water treatment and chemical well clogging by iron(II) oxidation and hydrous ferric oxide (HFO) precipitation

Removal of iron(II) from groundwater by aeration and rapid sand filtration (RSF) with the accompanying production of drinking water sludge in the preparation of drinking water from groundwater, and chemical well clogging by accumulation of hydrous ferric oxide (HFO) precipitates and biomass after mixing of oxygen containing and of iron(II) containing groundwater, are identical processes. Iron(II) may precipitate from (ground)water by homogeneous, heterogeneous and/or biological oxidation, where the contribution of these processes, and thus the characteristics of the corresponding HFO precipitates, is a function of pH and process-conditions. Under current conditions in drinking water treatment, homogeneous oxidation dominates above pH ≈ 7.75, and heterogeneous and biological oxidation below this value. In chemical well clogging, this transition occurs at pH ≈ 7.0. This information is relevant for the optimization of removal of iron(II) from groundwater by aeration and RSF and the corresponding quality of the produced drinking water sludge, and for the operation of wells clogging by accumulation of HFO precipitates and biomass.