10.30632/PJV65N4-2024a10 What Causes Mud-Logging Mud Gas Response to Vary and Two Techniques to Quantify Mud Gas

Mud logging, a crucial tool for determining overpressured zones, balancing mud weight to formation pressure, and monitoring gas in formations, is hindered by the widely varying mud gas response the causes of which remain poorly understood. It’s not uncommon to observe a ten-fold variation in mud gas response while drilling formations with similar log characteristics. Furthermore, cumulative production shows a weak correlation with mud-logging mud gas response in horizontal wells. By comprehending and accounting for these mud gas variations, we can significantly enhance the effectiveness of mud logging. In the past, mud gas has been normalized using the drilling rate, hole size, and mud pump rate, yet these factors do not fully explain the mud gas response. Proper lagging of mud gas to its depth, drilling mud flushing in front of the bit, gas solubility in drilling mud, surface losses, gas trap, and sampling design will be discussed and quantified. Two innovative techniques will be introduced to quantify the gas in the formation under varying drilling parameters and conditions. These techniques, namely gas markers and normalization techniques, not only enhance overpressure detection and help determine the balanced mud weight but also provide a quantitative measure of gas in the formation. By using these techniques, mud gas can be a predictor variable in data mining applications, paving the way for enhanced well drilling performance and improved well productivity.