Reducing Uncertainties in Casing Depth and Formation Evaluation Using "Look-Ahead" Logging While Drilling Technology

Deri, Charles (Schlumberger) | Hebert, John (Schlumberger) | Peternell Carballo, Ana Gabriela (Stone Energy Corporation) | Fisher, James (Stone Energy Corporation) | Gibbs, Rudolph (Cornell Petrophysics) | Cornell, Robert (Schlumberger) | Moreno, Javier


Logging while drilling (LWD) technology has been used successfully to overcome the drilling challenges when exploring a caprock hostile environment in the Main Pass area of the Louisiana Gulf Coast. Because of the geological setting, special steps needed to be taken to mitigate the obstacles and uncertainties while drilling. Successful acquisition and application of selected measurements led to achieving the drilling and formation evaluation objectives.

To drill the optimal wellbore, seismic-while-drilling technology was employed to optimize casing depths and minimize drilling risks such as mud losses and potential H2S. Additional techniques were used to help make the decision to set casing and maintain a viable wellbore for logging and completing the well.

For the second challenge, providing formation evaluation without compromising drilling safety and data quality, additional LWD services were applied. A resistivity-at-the-bit laterolog imager and a multifunction formation evaluation platform were employed to satisfy both the drilling demands and the formation evaluation needs. Having drilling mechanics and formation evaluation measurements available provided not only advanced measurements closer to the bit, giving a better chance of reducing invasion effects, but also impacted the drilling time through shorter rathole section. In addition, the laterolog resistivity imaging provided dips and texture information to map the structure and identify different geological features. Using these technologies, 100 ft were drilled into the caprock with enough information to evaluate the economical value of the prospect reservoir. The combination of these technologies and the ability to interpret the data streamed while drilling allowed the operator to successfully set casing at the top of the limestone caprock. In the end, the drilling risks and uncertainties experienced in the past were totally eliminated by the proper use of LWD technology.