Case Study: Single Well Design Targeting Three Water Bearing Formations

Abstract

Designing an onshore pilot well to be drilled and functioning as water disposal well targeting one of three potential formations to test and evaluate their injectivity. Based on evaluation results, an alternative new and deeper formation will be selected to dispose the unwanted associated produced water, instead of the current shallow formation that is considered as a natural aquifer by authorities. The well is designed to reach the first target in a deviated angle after which evaluation of the barefoot injectivity testing will begin. The decision whether to continue drilling to a secondary target or complete the well depends heavily on the injectivity testing results. The deviated angle of drilling will be dropped to reach a vertical position for the secondary target upon which the last liner will be run and perforated, then the formation testing will be conducted. In case of encounterg failure in the second injectivity testing, drilling to the deepest target will continue and final barefoot testing will be performed. A final optimal design for the pilot disposal well is intended to meet the reservoir and geological team with minimal drilling risks. The distance between this well and the other deep offset wells was the main challenge where the planned total depth was never reached in the disposal location. Also, the design was tailored to accommodate the drilling sections with the separation and long intervals between the targets. Furthermore, the uncertainty of the deepest formation fluid in addition to the uncertainties of formations pressure and formations fracture pressure were a big dispute while preparing the drilling fluids programs particularly across the target in which a water based mud was used as drilling fluid not to damage the formations nor to jeopardize the results of the injectivity tests. The pilot disposal well is drilled successfully penetrating two targets without the need to drill to the third formation. Hence, the new formation that will be used to dispose of the produced but unwanted water is defined after the reservoir team have evaluated the two injectivity tests. The results of the injectivity evaluation also provided the required number of wells that can handle all the expected produced water, and provided the required upgrade for the surface facilities to accommodate the injection pressure. This unique challenging well design, combining slanted and vertical trajectories, can be utilized whenever the budget is limited to one well, while you have multiple different targets to explore. Moreover, a specialized environmental impact study, conducted by independent contractor, confirms that there was no harm from the injected water to the groundwater.