Research on Rapid Identification and Evaluation Technology for Gas Formation during Underbalanced Drilling

The underbalanced drilling (UBD) technology has been widely implemented due to its advantages in drilling efficiency improvement and cost reduction. However, this advanced technology requires very special equipment and operational mechanism, which raises multiple challenges to traditional well logging techniques. In this study, a real-time logging system (MWD/LWD and mud logging) was developed and utilized during underbalanced drilling, to quickly identify and evaluate gas formation. This advanced system enables fast detection of gas formation and determining the formation type while drilling, by monitoring the changes in gas production. This real-time logging system provides a powerful technical support to the gas reservoir drilling and development. A case study has clearly shown that the interpretation and evaluation results based on the real-time logging data agree well with the results of conventional well logging. Therefore, this advanced real-time logging technique can be utilized as an effective guidance for field operation.