Horizontal Principal Stress Orientations Near Long Beach, California from Borehole Breakouts

Justin O. Kain, Patricia Persaud, & Joann M. Stock

Submitted August 12, 2019, SCEC Contribution #9465, 2019 SCEC Annual Meeting Poster #TBD

We present new results on crustal stress in the Wilmington oil field near Long Beach, California. The Wilmington field is bordered by major fault systems such as the THUMS-Huntington Beach and the Palos Verdes faults, and is a target of our investigation because no in situ stress constraints currently exists for this region in the Southern California Earthquake Center Community Stress Model. Using oriented 4-arm and 6-arm caliper data obtained from industry, we determine the orientations of borehole breakouts or compressive shear failures in wellbore walls. Our stress analysis will contribute to understanding the conditions under which faults slip by defining the stress tensor that in part controls the likelihood of a particular fault slipping in a particular direction. The data set comprises 36 wells in the Wilmington oil field that are distributed in an ~12 x 3 km2 area and sample a depth up to ~3140 m. This dense dataset yields ~400 breakouts comprising ~1300 m in total length. Our preliminary results in near-vertical wellbore sections deviated less than 10° yield a mean orientation of N5°E ± 19° for SHmax. We also conducted a preliminary misfit calculation for 8 wells from a single platform, comprising ~650 m total length of breakouts. To verify the consistency of the results, the data were bootstrap resampled 100 times. The misfit was then calculated between the bootstrapped data and theoretical stress orientations to obtain a high confidence model of the stress state. Our analysis shows relative stress magnitudes of SHmax=2, Shmin=1.9, and Sv=1 and a median SHmax orientation of N3°E. Initial results show a reverse faulting stress regime for the platform. Further analysis will assess if the full dataset shows changes in the stress regime with depth, area, or across fault blocks. Final results will be provided to the World Stress Map and the Southern California Earthquake Center Community Stress Model.



Key Words
Stress, Crust, Wilmington, Southern California

Citation
Kain, J. O., Persaud, P., & Stock, J. M. (2019, 08). Horizontal Principal Stress Orientations Near Long Beach, California from Borehole Breakouts. Poster Presentation at 2019 SCEC Annual Meeting.


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