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This article discusses the results of a study on the benefits of automation in general, and improved instrumentation and control capabilities in particular, to the drilling efficiency in the pre-salt. The industry is facing certain obstacles in improving the drilling efficiency in the pre-salt. These include, amongst others, limited or low-quality data measurements, and non-systematic practices for controlling the operating parameters. The end result is sub-optimal control of the operating parameters (rotary speed, weight-on-bit, and flow), which can directly affect the rate of penetration (ROP). The first phase of a joint research project between a service company and operator has the objective of producing a software simulator of the drilling process, capable of capturing the first order dynamics of the entire process, including bit-rock interaction, axial, torsional and lateral dynamics of the bottom-hole assembly (BHA) and the drill-string, as well as the dynamics of the rig equipment (pumps, top-drive, draw-works). The purpose of this simulator is to study the transient behavior of drilling parameters - weigth on bit (WOB), pressures, rotary speed (RPM), etc. both at the surface as well as down hole, as a result of formation changes, or changes in the surface operating parameters. The objective of this study is to evaluate how an improved (automatic) control of the surface operating parameters can result in better, more accurate control of all the variables that affect the drilling process and its efficiency. The parameters studied were the hole cleaning, equivalent circulating density (ECD), pressure transients (surge/swab), stick & slip. This study also considers the effect of availability of down hole measurements can have on the models calibration used in this simulator, so it can more accurately capture the true dynamics of the drilling process. Once the simulator is calibrated (with or without down hole data), the next step is to use it to evaluate various control strategies, and ultimately decide what is the right set of operating parameters that will optimize a composite cost function: a linear combination of ROP, drilling efficiency, hole cleaning, or any other metric that is considered when optimizing the drilling process. A trade-off that had to be made early on in this project was between the real-time capability of this simulator, and the computational complexity of the underlying models. The models created were specifically built in order to run fast, allowing this real-time calibration and evaluation of the various control strategies. With further development and validation of this simulator, in a condition of running in parallel with actual drilling operations, such a system, along with other automation tools, has the potential to become a product that can be deployed and act as an "advisor" to drilling personnel, to help support their decision making process. Ultimately these control decisions can be made using an increasing level of automation. |
