Integration of Drilling History and Borehole Images for Well Completion Improvement
Borehole stability is key for subsurface disciplines to ensure that subsurface data can be acquired with suffcient detail. Our client NAGRA was relying on stable borehole conditions, as due to extensive coring and testing during their multi-well campaign their borehole remained open for a long time.
In few of their wells our client experienced severe circulation losses causing massive delays and even abandonment of the boreholes.
NiMBUC was asked to perform a study to
- identify the zones where circulation losses were likely to occur
- to design safe mud windows
- propose adjusted completion schemes for following boreholes
Methods used
- Drilling history of completed wells reconstructed from drilling reports
- Relevant information, i.e. circulation losses, mud weight, inflow, FIT's, LOT's collected
- Comparison of drilling events with mud program gives insights into the limits of parameters such as fracture gradient or pore pressure
- As some events do not occur directly at bit but later further up in the well, also the timing of events needs consideration
- All events and bounding conditions were noted in drilling history plots
With the help of borehole images zones and geological formations were identified in which mud lossed were likely to occur. Also the mechanisms, by which the mud losses took place, were identified and connected to the data from the drilling reports. The gained results allowed our client to better plan and design the following wells to prevent drilling and circulation loss problems.
