Application of Underbalanced Coiled Tubing Drilling Technology to Enhance Gas Production in Deep Carbonate Reservoirs

Heterogeneus deep carbonate reservoirs require enhanced development strategies to maximize reservoir contact and ultimately to increase the recovery factor. In some complex carbonate reservoirs, conventional strategies for reservoir development are not always the best choice and new technologies have to be applied to optimize the reservoir development. In such cases, underbalanced coiled tubing drilling (UBCTD) has proven to be a suitable approach to exploit more complex reservoir areas, where conventional drilling and stimulation techniques no always meet well productivity expectations. The UBCTD technology consists of drilling a well with a drilling fluid pressure lower than the reservoir pressure, which tends to minimize the formation damage. Due to the underbalanced condition imposed in the wellbore, the well is allowed to flow naturally during drilling, while its productivity is measured. Another technique that accompanies this strategy is called bio-steering, in which cuttings are inspected while drilling to detect micro-fossils from the reservoir. Based on the real-time well productivity and the micro-fossils appearance, the well trajectory can be adjusted and corrected during drilling to chase the good wellbore productivity layers. A number of wells has been drilled using this strategy with encouraging results so far, which opens a great window to continue exploiting the reservoirs under development. With this technology, multilateral placement is possible with a high degree of accuracy across thin reservoir layers, which maximize the reservoir contact and increases the well productivity. This work presents a general description of this technology as well as present a successful field case including all stages from well planning to well execution and testing.