Borehole Breakout Determined Stress Regime in the Southern Los Angeles Basin, California

Justin O. Kain, Patricia Persaud, & Edward H. Pritchard

Published August 14, 2018, SCEC Contribution #8494, 2018 SCEC Annual Meeting Poster #154

The Los Angeles basin began its principal phase of opening with subsidence between the Palos Verde and Whittier fault zones and the Santa Monica fault systems. The basin then underwent early Pliocene NW-directed extension followed by transpression, which allowed for the complex structural setting of the Wilmington oil field in the basin’s southwestern margin. The Wilmington oil field has little or no surface expression. Its general structure is that of an asymmetrical anticline crosscut by normal and oblique normal faults. The oil field has a complex history of multiple destructive earthquakes that caused millions of dollars in damage as a result of shifting boreholes and lost holes. These movements are frequently thought to result from compressive forces as a result of subsidence of the field and of the state. The Wilmington field is bounded to the south by two major fault systems, the THUMS-Huntington Beach fault and the right-oblique Palos Verdes fault. The THUMS-Huntington Beach fault parallels the southwest portion of the anticline and various interpretations of its dip and sense of slip exist.
As part of the effort to provide direct constraints on the in-situ stress field in Southern California, we use oriented 4-arm and 6-arm caliper data obtained from industry to determine the orientations of borehole breakouts or compressive shear failures along wellbore walls. The 36 wells in the Wilmington field are distributed in a ~12 x 3 km2 area and sample a depth up to ~3140 m. Wells were assigned a group of I-V based on their bottom hole locations and breakouts were used to determine a best estimate of SHmax orientations and the in-situ stress regime. We present preliminary results that are based on breakouts obtained in 14 wells. Further analysis of the stress data will allow for the estimation of slip potential on local faults.

Key Words
Breakouts, Stress, Southern California

Citation
Kain, J. O., Persaud, P., & Pritchard, E. H. (2018, 08). Borehole Breakout Determined Stress Regime in the Southern Los Angeles Basin, California. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)