Pressure signature of gas influx

Increasing demands for oil and gas and depleting conventional reservoirs during the past century have led the petroleum industry to drill more offshore wells. One of the most important concerns in any drilling operation is safety, early gas influx detection and well control challenges. This concern is highlighted in offshore drilling due to a narrower mud window and lower influx tolerance. Even though significant enhancements have been made in offshore drilling, still conventional well control procedures are applied in most of the wells. Conventional indicators to detect a gas influx are rudimentary and unreliable for drilling costly deep offshore wells.;Having access to continuous real-time annular pressure data, offered by mounting distributed pressure sensors along the wired drill pipe, can be very helpful in early detection and handling of an influx. However, pressure variations at the sensor should be precisely predicted before applying this technology. Most of the annular pressure prediction methods rely on simplifying assumptions such as the single bubble model that can cause significant error and a faulty design.;This study presents a transient two-phase model for precise prediction of annular pressure profile during gas influx entrance to the wellbore. The model is developed based on the conservation equations and it takes the solubility of gas in synthetic based mud into account. The model is validated with the available two-phase experimental data for three different annular geometries.;Methodologies are developed for early gas influx detection and determining the location during conventional drilling and Constant Bottom-Hole Pressure (CBHP) technique of Managed Pressure Drilling (MPD). These methodologies indicate that early influx detection and determining its type and location can be conducted by monitoring variations in the annular pressure profile and return mud flow rate (flow out). This can reduce influx detection time to less than half. Pit gain and variations in pump pressure are used for final verification and not as primary indicators anymore. A chart methodology is proposed to select the best response to an influx in CBHP technique of MPD. The chart methodology is prompt, convenient and requires no calculations. Applying new technologies, such as wired drillpipe and accurate flow meters, in advanced well control operations results in significant enhancements in safety, improving MPD design, enhancements in real-time decision-making and reducing non-productive time in costly offshore wells.