Where Is the Fluid? Using Distributed Acoustic Sensing–Based Strain Measurement in Near Real Time

Summary Fiber-optic deployments in offset wells generate multiple data sets, including low-frequency distributed acoustic sensing (DAS) measurements that provide detailed information on the wellbore axial strain during nearby hydraulic fracture treatments. Analysis of strain during a treatment typically consists of magnitude-based detection of fracture hits for location and event time. More detailed post-treatment analysis can tease out at least a few key components of far-field fracture solutions that match the pattern and evolution of measured strain, but the highly nonlinear relationship between fracture growth and measured strain change impedes real-time solutions. This paper introduces a method that linearizes the problem and then applies a Kalman filter-based inversion to determine the proximity of fluid to the offset well as it approaches the fiber during the treatment. The computationally efficient approach enables quick response during a treatment to unexpected fracture growth. The use of a Kalman filter also allows for the incorporation of other data types, such as microseismic locations, into an integrated inversion. Theoretical and field examples demonstrate the technique in action.