Maintained pressure management and fracture network mapping are key issues for successful well construction in fractured carbonate reservoirs. Prediction and characterization of the fracture network prior to drilling is very difficult and challenge optimized well direction and placement in respect to the fractures. Avoiding productivity impairment by loss of drilling fluids is another major challenge.

Later stimulation of a micro-fractured reservoir invaded by drilling mud is extremely difficult or even impossible. Open hole completion is generally preferred in these type of reservoirs. Underbalanced drilling (UBD) is therefore an interesting option for enhanced data acquisition, avoiding reservoir impairment and achieving completion contingency for optimized well production and added value.

Locating and characterizing the natural fractures while drilling is a vital issue for appropriate well placement and selection of completion options during the field development strategy. Depending on the opening and extension of the fractures, the mud loss rates and volumes can differ from low to heavy. The associated fracture network is the main parameter contributing to well production.

Underbalanced drilling is one of the main recommended technologies for further development of fractured carbonate reservoirs in South-West Iran. Flow drilling, allowing the hydrocarbons to flow to surface while drilling, will be advantageous. With sufficient reservoir pressure, this method enables better fracture characterization and a dynamic decision process can be applied for drilling horizontal wells with optimized well trajectory intersecting more fractures. Formation damage can be avoided and dramatically reduce unsuccessfully drilled wells.

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