Active Fault Detection by an Automatic Breakout Geometry Characterization Algorithm from Ultrasonic Borehole Imager

Abstract

An underground stress state might be disturbed in an area, particularly adjusting to an active shear zone. Borehole breakouts (BOs) that appeared in a circular hole excavated in an inhomogeneous stress field might be tracked to identify the active shear zone. The present study aims to develop the breakout morphology analysis (BMA) algorithm to exploit the valuable attributes of borehole BOs including azimuth, width, and intensity (depth of elongation) of failure from wellbore ultrasonic imaging tools. In the current study, the extracted azimuthal information was surveyed to detect the active shear zone along the well. Ultrasonic data from five wells drilled in the doubly plunging Ahvaz Anticline located in Iran were collected for the purpose of algorithm verification. The multiwell correlation of the BOs’ azimuth generated by the algorithm in the Ahvaz Anticline suggests a shear plan dipping southwest-northeast direction is possibly active in the deep vertical wells. Similarly, the seismic reflection profile of the Ahvaz Anticline shows a track of detachment faulting system in the mid-Cretaceous sediments. The finding confirms that the raw ultrasonic traveling time is more applicable than other borehole image data, such as static and dynamic images of ultrasonic amplitude, in BO characterization.