Drilling wells in mature fields normally entails the integration of multidisciplinary teams to increase the likelihood of a successful drilling and completion program. Maximizing wellbore productivity requires thoughtful planning involving analysis, studies, and risk assessment of the best alternative solutions for well drilling and completion.

Selecting reservoir drilling and completion fluid to minimize rock formation damage requires a high level of consideration. Selecting an appropriate fluid strategy becomes more significant when the reservoir section involves horizontal drilling and an openhole completion design. This paper details the design criteria and final application of a nondamaging drill-in fluid to drill a horizontal well completed as open hole in a mature field (first of its kind in the field).

The fluid design strategy was driven based on analysis of reservoir rock samples, reservoir fluid chemistry analysis, and the natural permeability of selected core samples. The fluid selected was a monovalent brine system using highly clarified and acid-soluble biopolymers as filtrate reducer and viscosity control, respectively, and an engineered and tested bridging package based on sized calcium carbonate. The fluid also contained an amphoteric amine to control clay swelling and dispersion. The nature of the well completion used an in-situ acid-generating filter-cake breaker system for removal of filter cake and damage encountered during reservoir drilling or completion. The filter-cake breaker system also affected fluid design (e.g., compatibility between the two systems), which was incorporated into the design strategy. Additionally, the nature of certain details of the completion architecture affected the breaker system application and was necessary to redesign the filter-cake breaker system to achieve optimal wellbore cleanup while accommodating constraints in the completion design and operation.

Finally, application of the fluid program used with the drilling and completion design and architecture rendered a successful project resulting in higher than expected hydrocarbon output.

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