Well performance in relation to design, construction and wellfield operation: a case study from the fossil Ram sandstone aquifer in Southern Jordan

Abstract

The Dubaydib wellfield in Southern Jordan comprises 55 wells up to 600 m in depth, and exploits the fossil Ram sandstone aquifer. It has an average output of 100 MCM a -1 and well yields of 51 - 80 l s -1 . Drilling fluid has affected well performance with lowest specific capacities of 1.56 l s -1 m -1 in bentonite drilled wells, highest ( 5.46 l s -1 m -1 ) in water drilled open hole constructions and in the middle range ( 3.07 l s -1 m -1 ) in polymer drilled wells. Well loss coefficients and skin effect values confirm these results. The productivity of bentonite drilled wells has not improved during production indicating that the damage has been irreversible. Well efficiency evaluations have been found to be sensitive to the method of calculation and not to provide a reliable measure of productivity. During the course of wellfield operation (2013-2021) specific capacities declined from an all well average of 3.78 to 3.13 l s -1 m -1 or c.17 %. The decline reflects the deepening of groundwater levels as a result of aquifer response rather than well deterioration. As groundwater extraction is from storage, specific capacities will continue to fall, tentative estimates suggesting to 2.56 l s -1 m -1  after 25 years and 2.16 l s -1 m -1 after 50 years.