An important benefit of drilling automation is the ability to ensure continuous updating of the parameters controlling the drilling process according to the current wellbore conditions. While actively drilling, this means continuously adjusting the weight on bit (WOB), topdrive speed and flowrate according to the current formation properties and drilling system behaviour: ability to transport cuttings, buckling or exceeding the geo-pressure margins. We present here the main principles used to design and develop such an adaptive drilling optimization system, and the first results obtained both in a simulated environment and in real operations.
The system achieves adaptability by combining two separate processes. Firstly, it maintains an updated estimate of the bit-rock interaction mechanism using a stochastic approach coupled with a physical model. This is used to predict the system's response to changes in parameters (WOB, topdrive speed or flowrate), including the possible presence of a founder point, i.e. a WOB threshold above which no gain in rate of penetration (ROP) is achieved, and also to detect changes in formation properties. Then, the second process ensures that the effects of the same drilling parameters are evaluated with respect to their ability to ensure safe drilling: cuttings transport and drillstring mechanical stability are the main constraints here, evaluated in a probabilistic framework. The combination of these two processes provides the generation of both safe and optimum drilling parameters.
The system can be used in two contexts: firstly, as an advisory module which provides set-point recommendations to the driller; secondly, as an integrated module into a drilling automation system. In the latter configuration, the generated set-points are used to actively control the drilling process. Note that the bit-rock interaction prognoses enable quick automated detection of – and therefore reaction to- sudden changes in formation properties. Both modes facilitate real-time monitoring of the bit-rock interaction process, including the estimated formation properties, bit aggressiveness and founder point. Results from active tests in a simulated environment and advisory mode against real field data are presented and discussed.