Vertical, Angled and Horizontal Wells in Shallow Aquifers—Drawing Lemonade from Lemons

George Losonsky, PhD, PG, 4207 Rhoda Dr, Baton Rouge, LA 70816: glosonsky@cox.net, Scott M. Bergeron, PE, PO Box 3414, Baton Rouge, LA 70821: smbergeron@envirodepot.com

As regulatory agencies across the USA have become increasingly focused on rationing quality groundwater from high-yield regional drinking water aquifers, industry has come under pressure to reduce their dependence on such aquifers by augmenting their supply with groundwater from less desirable, low-yield aquifers. Common characteristics of such aquifers include strongly heterogeneous distribution of clay lenses with low hydraulic conductivity, high degree of stratification, and total dissolved solids levels unacceptable for drinking water or industrial use. Water management professionals traditionally ignore such units, as they drill deeper into more productive aquifers; hydrogeologists often refer to them as water-bearing units instead of aquifers. Unpredictable, widely variable hydrogeologic characteristics and generally low yield of this class of shallow aquifers challenge conventional means of production. While the default solution is placement of a dense network of vertical, fully penetrating wells, more cost-effective production scenarios can be derived using partially penetrating wells, angled wells, and horizontal wells—alone or in combination. Drill rigs conventionally used to install vertical water wells can by adjusted to drill straight bores at an angle in order to place longer screen sections through thin aquifers, or to side-step inaccessible terrain, such as infrastructure or wetlands, immediately above the targeted section of aquifer. Utility bore technology or oilfield downhole steerable drilling tools can be adapted to install a long horizontal well that can replace tens or even hundreds of vertical wellheads, mimic and overcome aquifer heterogeneity, and generate considerable operation and maintenance savings. Alternative means of production can be used to supply groundwater from shallow, non-drinking water aquifers for a range of industrial uses including cooling water, process water, firewater, dust control water, and emergency water supply. Expanded availability of drilling methods for angled and horizontal wells has even led to consideration of low-yield aquifers suitable for drinking water at municipalities or commercial developments with limited water demand. No single drilling method is the panacea for all the challenges posed by shallow, low-yield aquifers. Vertical wells are the least expensive to install, but their rigid geometry limits the possibilities for recovery system optimization. Angled bores are less costly than directional bores, but only add limited additional screen length compared to vertical ones. Horizontal wells afford maximum flexibility of screen and wellhead placement, but costs vary widely and subsurface utilities pose a number of potential hurdles or barriers to successful well installation.