Characterization of non-matrix type and flow potential using lost circulation information

Abstract Lost circulation zones (LCZs) provide valuable information about the properties of non-matrix features – i.e., fractures and karst – intersected by wells during conventional drilling, including information about the type, size, connectivity and flow potential. The magnitude of the loss rate and lost volume should reflect the nature of the non-matrix feature responsible for losses. For example, the total volume lost in each of these zones provides a minimum volume of connected pore space, whereas the instantaneous rate of loss suggests whether the LCZ is due to drilling into a cave (high rate of loss) versus a fracture (low rate of loss). We define and quantify each LCZ from information recorded in the drilling reports including top and base of the LCZ, maximum loss rate, and cumulative volume lost to the zone. Once each LCZ has been identified from the drilling reports, we evaluate wellbore images and caliper logs across each anomalous zone to determine the cause of the loss event – e.g., caves or fractures. Results suggest that caves are typically characterized by high lost rates (>50 m 3 /h or 315 bbl/h), while fractures and touching vugs are characterized by lower rates ( 3 /h or 315 bbl/h). Low rates and volumes in excess of 160 m 3 (1006 bbl) appear to be related to fractures, while volumes below this threshold can be attributed to either fractures or touching vugs. This natural breakout between karst and fractures in particular, allows us to work in data challenged environments and use drilling data as a screening tool to evaluate whether the main non-matrix flow elements are fracture or karst dominated. A key product of this work is a volume versus rate (VvR) plot that typifies loss characteristics for specific non-matrix features, so that in the absence of image logs, it can be used to infer the causes of each LCZ event.