Complex reservoir drilling fluid solutions for reservoir drilling
Andrzej Szczygieł
Vol. 36, no. 1 (2019), pp. 45-58, [1]
Drilling into a pay zone with a conventional fluid can introduce a host of previously undefined risks, all of which diminish reservoir connectivity with the wellbore or reduce formation permeability. This is particularly true in horizontal wells, where the pay zone can be exposed to the drilling fluid over a long interval. Selecting the most suitable fluid system for drilling into the pay zone requires an understanding of the reservoir. Using data generated by lab testing on core plugs from carefully selected pay zone cores, a reservoir-fluid-sensitivity study should be conducted to determine the morphological and mineralogical composition of the reservoir rock. Natural reservoir fluids should be analyzed to establish their chemical makeup. The degree of damage that could be caused by anticipated problems can be modeled, as the effectiveness of possible solutions for mitigating the risks. In addition to being safe and economical for the application, a Reservoir Drill-In Fluid should be compatible with the reservoir's native fluids to avoid causing precipitation of salts or emulsions production. A suitable nondamaging fluid should establish a filter cake on the face of the formation and shouldn't penetrate too far into the formation pore pattern. The fluid filtrate should inhibit or prevent swelling of reactive clay particles within the pore throats. Formation damage commonly is caused by: – Pay zone invasion and plugging by fine particles. – Formation clay swelling. – Commingling of incompatible fluids. – Movement of dislodged formation pore-filling particles. – Changes in reservoir-rock wettability. – Formation of emulsions or water blocks. Once a damage mechanism has diminished the permeability of a reservoir, it seldom is possible to restore the reservoir to its original condition.