Pressure Transmission Testing Confirms Performance of Aluminum Complex Fluids as Dynamic Borehole Stabilizer

Abstract

Testing the interaction between drilling/completion fluids and the formation is the key critical concept to understand the fundamental mechanism to borehole stability. Unfortunately, most industry tests lack the down-hole conditions to give realistic results. However, there is one advanced testing that can be used to directly and quantitively provide realistic borehole stability interpretations. Specifically, the pore pressure transmission (PPT) test has increasingly gained popularity providing results on how to stabilize troublesome shales by facilitating proper fluid design. In this study, precipitating aluminum chemistry is employed to develop a high-performance water-based mud (HP-WBM) that is tremendously robust and versatile – demonstrating that it can stabilize multiple shale type formations. PPT evaluations on the alumiumum complex HP-WBM was performed at 250°F with a high simulated overbalanced 1000 psi pressure differential, to fully confirm that the system can withstand high pressure influx and prevent pressure transmission into the shale pore matrix, essentially reducing induced borehole instability. PPT testing was performed on two different types of shales, Pierre Type II and Mancos shale exhibit noteworthy differences in physical, chemical, mineralogical, and mechanical properties, making them ideal shales to study the versatility of the aluminum complex drilling fluid. Because of the pore-plugging capabilities, the fluid can establish, an improved semipermeable membrane, allowing for the counterbalance of hydraulic flow into the shale via osmotic backflow. When compared to the base (water-based mud), a significant delay factor is observed using the aluminum complex fluid, indicating significant reduction in pressure transmission into the shale pore matrix. An invert emulsion system was also tested for comparison and showed the Al-HPWBM's was able to perform similarly at stabilizing these shales. Advantages of precipitating aluminum chemistry over other methods will be further discussed.