SCEC Award Number 16062 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Borehole-derived Constraints on the SCEC Community Stress Model
Name Organization
Joann Stock California Institute of Technology Patricia Persaud California Institute of Technology
Other Participants Deborah Smith, USGS, no-cost collaborator
SCEC Priorities 2d SCEC Groups SDOT
Report Due Date 03/15/2017 Date Report Submitted 03/15/2017
Project Abstract
We use borehole breakouts to determine principal stress directions (SH and Sh) in wells in oil fields in Los Angeles and Ventura Counties. Analyses are complete for the onshore Long Beach and Inglewood, and the offshore Wilmington and Huntington Beach oil fields down to depths of 3 km. In Inglewood, NE SH orientations occur in most wells south of a NW-striking thrust fault, which are oriented sub-perpendicular to the thrust fault rather than at a consistent angle to the Newport-Inglewood Fault (NIF) zone. An E-W SH direction in two wells likely reflects the stress state of the flower structure in the gra-ben just west of the Inglewood fault. In Long Beach, SH varies substantially in the topmost 1 km due to a shallow structure influenced by overthrusting across the Pickler Fault, and merging of the NE Flank Fault and Cherry Hill faults. The large variations in SH in the northern flank of the anticline appear to be related to the N-NW-striking faults that merge with the NIF-Cherry Hill Fault near the anticlinal crest. Relative changes in the principal stress magnitudes are observed in Huntington Beach. The observed short-length-scale variations in SH direction are attributed to the proximity to faults, fault segmentation, or fault overlap. They indicate the likely complexity that may be found in stress fields near other active faults. Analyses continue on newer data obtained from offshore wells in the Santa Barbara Basin.
Intellectual Merit We are working with borehole breakout data to constrain the SCEC Community Stress Model. This provides a useful complement to the various scales of models being derived from seismicity and geodynamics. We are working with new types of well logs and have updated the methods needed to analyze these. We are expanding our area of study to include wells from offshore oil platforms in Ventura county and Kern county as data become available. Our results show stress field variations over short spatial scales, which need to be taken into account in understanding dynamic linkages between active faults and expected triggering of adjacent faults.
Broader Impacts As a result of this study we have made contact with other researchers who have access to offshore Santa Barbara data sets. We started analysis of these data sets. We have established partnerships with more oil field operators and service providers who are learning about what SCEC does, and the importance of their data to the SCEC CSM efforts. We are broadening the participation of underrepresented groups with the involvement of Dr. Patricia Persaud, who is an ethnic minority female scientist. Dr. Persaud is supervising a masters student at LSU who is now working on analyses of the recently acquired data sets.
Exemplary Figure Figure 4.
Caption: Top: SH orientations in the Long Beach oil field. Data for some wells are not shown to avoid over-lap. Orange and blue circles mark wells with greater than 3 m and 5 m total breakout length respectively. Gray contours at 200-ft interval are modified from Chavez (2015) and represent the top of the Alamitos zone. Black faults are modified from Chavez (2015) and Wright (1991). Map symbols as in Figure 1 except well symbols are not keyed to number of observations; black lines are other faults known from more de-tailed studies (see Persaud et al., 2015a, 2015b). Gray lines: structure contours. Bottom: Rose diagram of SH directions. Red = all measurements. Yellow = measurements from depths > 900 m.
Credits: Figure produced by Patricia Persaud.