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Invert emulsion drilling fluids designed with an optimised range of pre-determined sized particulates have been used successfully to eliminate or minimise losses to the formation while drilling depleted reservoirs. Sands can be penetrated with up to 600 bar overbalance without encountering losses or differential sticking. Further, the wells have been drilled at pressures above their natural gradient. Selectively designing these fluids has also made it possible to successfully drill high-angle step-out sections through mature, depleted reservoirs.This paper describes the development and implementation of this technology.Fluid Design Phase – The selection and optimization of type, size and amount of particulates required takes place during the planning stage of the well based on the rock mechanics of the formations to be drilled, drilling fluid properties and the practicalities at the rig site. Execution Phase – Once the fluid design has been finalized, processes and procedures are developed to help ensure that during the project the fluid functions are designed taking account of the practicalities of the actual drilling phase.Recent case histories of the application of this technology are discussed in detail: the first case highlights a severely depleted reservoir in an extreme high-pressure, high-temperature (HPHT) field and the second case relates to extended reach wells drilled through mature reservoirs which can be segmentally depleted. |
