As new wells are being drilled in more demanding environments, the industry are in some cases facing new challenges or complex operational modes which are absent from available software systems. And no model has yet included the option of distinguishing between the causes behind downhole restrictions. Normally there are several optional causes behind any restriction (any unexpected state or condition). Restrictions manifest themselves in the surface hook-load signal as specific signatures, depending on the downhole conditions. Correct interpretation of a specific cause of the downhole problems in real time represents the ultimate insight into the downhole process. Once implemented, the model will allow for real-time interpretation and for failure diagnosis of complex failure conditions of the downhole process; the proper and optimal treatment of failures can be pointed out. It will lead to increased operational efficiency and avoidance of unplanned cost.
During tripping operations the BHA may accumulate cuttings. The complete material flow behavior may be described by extended granular flow theories (Johansen and Laux 1995; Johansen and Laux 1999; Cloete, Johansen et al. 2012). Since also the fluid flow will be restricted, existing granular flow models will have to be extended to handle the rheology of the drilling fluid and the corresponding lubrication effects as suggested by Sawyer and Tichy (2001). The model should then be able to explain the dynamics of the interaction between drill string and cuttings.
To support the understanding of the complex process and their fingerprints two methods will be used to validate the model.
a) - Field data contain hook load, pump pressure and manipulated variables like sting velocity (block positions) and pump flow rate. Field data of many restrictions are gathered into groups after being analyzed along with information from daily drilling reports, lithology, etc. Downhole restriction in addition to cuttings bed interaction is necessary to understand as well, in order to distinguish them from sought fingerprints. Other interaction can be swellable / creeping wellbore, local dog legs etc. This knowledge can be followed up in greater detail in future projects.
b) - Experimental testing of hypothesis: In existing test facility different wellbore geometries and wellbore materials are combined to create a large number of more or less complex restrictions. Existing test facility will be upgraded to become sufficiently realistic to simulate and study effects of interaction between drill string and cuttings during tripping operations.