Characterization of fluid and heat flow during mud loss and its application in lost circulation management

Failure to manage and minimize lost circulation can greatly increase the cost of drilling and increase the risk of well abandonment. Many remedial procedures are not working as planned because information in loss zone locations is lacking, preventing treatment from being applied directly to the points of losses and, thus, resulting in low efficiency and extended non-productive time (NPT). This dissertation presents an innovative approach for identifying the location of loss zone using distributed temperature measurement while drilling. A transient thermal model for predicting the temperature profile in the wellbore and formation during mud loss is developed as a forward calculation procedure of the loss zone mapping approach. Numerical solutions under different lost circulation conditions, when used together with the distributed temperature measurement, can identify the location of mud loss. For a deep well with moderate to severe loss, there is a significant change in the temperature profile in the wellbore as mud loss proceeds. The characteristics of wellbore thermal behavior over time are evaluated and identified as good indicators of loss zone location. The distributed temperature measurement while drilling was facilitated by using drilling microchip technology, which was recently developed and validated by successful field tests. The work also details the development and field testing of the drilling microchip systems.;By matching the simulated results with the distributed temperature measurements at different timestamps, the depth of the loss zone can be accurately identified. Case studies are given to show the practical applications of the method. The results from these case studies are important in applying expandable tubular systems, setting cement plugs and spotting lost circulation material (LCM) pills. Additional uses of loss zone mapping approach include identifying highly permeable zones for reservoir or formation evaluation purposes.;In addition, time dependent temperature profiles of annular mud and near-wellbore formations under different lost circulation conditions and types of muds (oil based mud/water based mud) are presented to evaluate the effects from different parameters. The effects of changes on equivalent circulating density during mud loss are also evaluated in this study. These results allow for a better estimate of subsurface pressure and temperature conditions during lost circulation. Since the thermal regime of a formation in the vicinity of a wellbore affects the stability of the well significantly during drilling operations, the lost circulation management can be improved by having more realistic wellbore temperature and pressure profiles.