Drilling Mud Sensing for Wellbore Stability

J.O. Alvarez
Aramco Americas - Sensors development,
United States

Keywords: microwave measurements, Permittivity, Drilling Mud Monitoring, Loss Circulation


Reservoir brine invasion and circulation losses are some of the well control problems faced by drilling operations. These events may lead to safety incidents, such as loss of well control, and non-productive time (NPT). Narrow drilling margins are generally to blame, but the lack of reliable real time mud-monitoring systems exacerbates the problem. In particular, there is a lack of commercially available real-time sensing technologies of the oil to brine ratio (OBR). Solutions such as Managed Pressure Drilling (MPD) techniques have proven useful for minimizing the risk of well control incidents. However, it requires accurate, real time measurements of rheological parameters. Without them, the system’s uncertainty increases, and so does the chances of well control problems. A microwave drilling mud analyzer (MDMA), was built and tested with drilling muds with different brine concentrations. The MDMA can perform non-intrusive in-line measurements. It uses a vector network analyzer to measure the reflection (S11) and transmission (S21) coefficients of the circulating drill mud between 1 GHz and 4GHz. It consists of two dielectrically filled waveguides with similar diameter to that of the main pipe. There are also two tapered metallic ridges inside each waveguide and connected directly to the microwave feed. These ridges increase the effective bandwidth of the waveguide by capacitively loading the dominant transmission TE11 mode, and they lower the cutoff frequency of the waveguides. For the present study, the waveguides were filled with glass-filled-Noryl, which provides a better impedance match with the oil-based drill mud. In addition, Noryl is also a low-loss material and has low water absorption, which makes it ideal for laboratory and flow loop testing. Drilling muds with different brine concentrations were tested with MDMA. The concentrations tested were 10% brine (90:10), 20% brine (80:20), and 30% brine (70:30). A sample of Diesel was also tested as a “No-Brine” reference. Results showed a clear high sensitivity to brine content. Indeed, the amplitude and phase of the transmission coefficient provides clearly distinguishable signatures for each OBR. In addition, the phase of the reflection coefficient provides another parameter for OBR monitoring. Additional tests on 80:20 with less salt concentration (90:10 mud diluted in DI water) and 80:20 with additional solids, were conducted. Results showed a clear distinction in transmission amplitude between the new muds and the original 80:20 mud. In conclusion, given its speed, results obtained, and its field readiness, the MDMA is an ideal tool for OBR monitoring during drilling operations.