Understanding and quantifying clogging and its management during re-injection of CSG water permeates, brines and blends. Final report

[摘要] The coal seam gas (CSG) industry has been rapidly developing in Australia over the past decade. CSG extraction results in the co-production of water to decrease pressure in the coal bed andpermit desorption of methane gas from the coal surface. Management of produced water is a challenge for the CSG industry and re-injection of this water, which may be treated to variousextents, into overlying aquifers, underlying aquifers, and to the coal seams themselves on completion of mining, is a valuable approach allowing new and expanded beneficial use of water resources for the wider community. The re-injection technique may require water treatment in order to ensure compatibility of injected water with the aquifer so as (a) not to clog injection wells and (b) to prevent adverse changes in water quality in the storage zone. The latter issue isaddressed by a related project. Clogging of injection wells has been found to be the single biggest cause of failure in aquifer recharge operations. Well clogging is defined as a reduction in permeability of the formation immediately surrounding the injection well. Clogging assessment, control, and remediation are among the most important issues to be resolved for efficient managed aquifer recharge operation. Well clogging may be caused by physical, chemical, hydrodynamic, mechanical, and biological processes. The rate and extent of clogging is strongly dependent on properties of the aquifer sediment and native groundwater quality, and characteristics of theinjected water.The intended source water for re-injection water into aquifers is a blend of reverse osmosis (RO) treated CSG associated water with micro filtered-CSG associated water (the pore size of the filteris 0.03 micron). Based on an understanding that the potential for biological and physical clogging due to nutrients and colloids present in the source water will be minimised by micro-filtration prior and/or reverse osmosis to injection, the predominant clogging mechanism associated with the use of low salinity treated CSG-associated water is the potential for in situ clay release. Therefore, the objective of this study was to undertake a literature review, extensive series of laboratory experiments and mathematical modelling to assess clogging potential due to dispersion of in situ clay colloids during reinjection of low salinity treated CSG-associated water into the Precipice Sandstone aquifers at Reedy Creek and Condabri in the Surat Basin, Queensland.Initially a literature review was conducted to establish a conceptual framework to investigate the clogging mechanisms near injection wells, modelling approaches and methods to control andremediate clogging, including the strengths and drawbacks of existing approaches. The literature review aim was to identify various clogging processes in injection wells including entrained airand gas binding, deposition of colloidal particles present in the injectate, biological growth, geochemical reactions, and in situ colloid rearrangement, release, and recapture in the porous media. A verified clogging model based on a series of planned laboratory tests was developed to provide scientific guidance and help develop strategies to avoid or minimize clogging.Key findings of this report include:1) In-situ clay particles were rapidly released from grain surfaces when core samples were flushed with high salinity water (CSG brine) followed by reverse osmosis (RO) treated water (i.e CSG water permeates) or low salinity water (20 mM). This mobilisationresulted in a high concentration zone of clay which moved through the core and caused a severe permeability reduction. The critical concentration of NaCl solution which initiated rapid clay release in sandstone samples was found to be in the region of 20 mM at neutralpH.2) Cation exchange processes between clay and the aqueous solution were responsible forinducing the release (dispersion) of in situ clay particles. The rate of cation exc...

[发布机构] CSIRO

[学科分类] 地球科学(综合)