The mud losses events in the reservoir phase at Castilla field (Colombia – South America) during drilling campaign of 77 wells in 2015 represented an overrun close to $20 MMUS and an accumulated volume of 160.000 bbls of drilling mud lost in the hole. The main reason of these events are associated to crossing structural lineaments during drilling such as faults and set of natural fractures together with the already depleted reservoir sandstone, which results in a drop of the magnitude of the minimum horizontal stress also known as closure pressure of such natural fractures. As a result of the decreased magnitude of the minimum horizontal stress, the natural fractures are considered to be in a critical state of stress increasing the risk of having mud losses through the opened natural fractures. Ecopetrol's geomechanics team has led the visualization and conceptualization of such mud losses events from ant-tracking models got from seismic data and plotted on the prospects wells surveys. A total of 18 wells scattered in the field were analyzed using the proposed methodology in this paper showing 78% of effectiveness of the prediction mud losses during drilling.
Based on the analysis of the drilling history of 442 wells drilled from 2005 to 2015 it was possible to point that 17.5% of the time was associated to non-productive time (NPT) and 18% of it was due to mud losses events. In Ecopetrol's oil fields seismic attributes have never been used before to perform root cause analysis of mud losses events in reservoirs with high fracture density. Detailed seismic structural interpretations have been developed in order to improve the root cause analysis of the mud losses events in the reservoir phase using seismic attributes such as ant-tracking having in mind that these attributes are specific measurements of geometrical, cinematic, dynamic or static features that come from seismic data and are mainly used to quantify the amplitude and geomorphological features seen in seismic data.
