September 25th, 2018
As some of us may be aware groundwater is a precious natural resource contained in aquifers which needs to be protected as well as managed sustainably. An aquifer’s primary functions are to store and transmit water. The aquifers reserve or storage is primarily dependent on the pore space available in the rock/soil medium (effective porosity in % volume). Bigger aquifers with more effective porosity can store more water but the ratio (Storage Coefficient) between volume released and the change in “hydraulic drive” needed to sustain flow controls the accessibility of the stored water. The resource of an aquifer combines the element of volume with time to define the total quantity that can be extracted over a given period. It may not however be the sustainable limit of extraction if the rate of replenishment (recharge) from surface cannot keep up with the rate of extraction from water producing wells.
A meteorological drought can lead to a hydrological drought when the accumulated shortfall of aquifer recharge causes a drop in the groundwater level. For unconfined aquifers (overlain with permeable layers), a drop of water level from a summer drought can quickly be remedied if following average winter rainfall occurs. This is not the case for confined aquifers (contained within impermeable layers) as their area of surface recharge may be much smaller and distant from the area of storage and potential extraction. Increases in population water demand can easily lead to unsustainable extraction rates if the resource of confined aquifers is not managed properly.
Another major concern is the protection of confined aquifers from pollution through well bores, as the potential exists for contaminants to persist for long periods and spread over wide areas. To limit this happening, strict well construction standards are applied and the selection and use of chemicals in drilling wells for the Public Water Supply is controlled by the Drinking Water Inspectorate (DWI). DWI Regulation 31 restricts materials that could potentially enter and contaminate aquifers which could put the public health at risk as well as increase the costs of water treatment. Pure-Bore® polymer is currently the only drilling product for viscosity and fluid loss control on the list of “Approved Products For Public Water Supply in the UK”. Pure-Bore® allows water wells to be successfully drilled through the impermeable overburden above aquifers by controlling the reactivity of clay and silt rocks before casings are grouted to the top of the reservoir formation. Once drilling below the water table, Pure-Bore® protects the aquifer from well bore contaminant invasion with its unique filter cake. This filter cake can also support unconsolidated sands (often found in high yield aquifers) allowing a greater amount of water bearing formation to be produced. Since Pure- Bore® is easily degraded by products normally used in the disinfection of well production screens and gravel packs, the filter cake will not have any residual effect on the initial pumping test or productivity of the well.
While drilling oil and gas wells onshore in the UK and Europe, the well usually passes through the water table in the upper most drilling section. In view of the risk of contamination to aquifers, Pure-Bore® use in sections they are drilled through is essential for their protection, along with isolation from surface contamination by effective casing grouting.