An Offshore Subsidence Monitoring Program (OSMP) was designed for Macpherson Oil Company to detect early stages of oil production related subsidence. The OSMP program included:

1. Collection and analysis of pre-production background subsidence data
2. Installation of offshore bench marks
3. Baseline measurements of onshore and offshore benchmarks
4. Long-term monitoring during production. The purpose of the program was to detect early stages of a regional reduction in ground surface elevation due directly to oil production. The primary objective was to determine the origin and rate of vertical elevation changes in the study area.

The critical issues included:

1. Criteria or test to determine the origin of offshore, vertical elevation changes
2. Risk or pattern of elevation change as a reliable indicator of potential nearshore or onshore problems. The postulates were oil production, without fluid injection, can potentially result in measurable regional subsidence; also the elevation of the ground surface is not static.

Mitigation of suspected oil production subsidence will commence when the following are observed:

1. A regional increase in rate of subsidence at several adjoining bench marks that are not attributed to other processes
2. Change in subsidence rate conforming to a pattern of concentrated rate change above the zone of maximum fluid withdrawal and/or fluid pressure drop and a reduction in subsidence rate as a function of increasing distance from the reservoir
3. Nearshore change in slope gradient.

Coastal Environments obtained the first permit for tideland oil production in California in the last 30 years for the Macpherson Oil Company.

Macpherson Oil Company
2716 Ocean Park Blvd., Ste. 3080
Santa Monica, CA 90405

Data Analysis & Numerical Modeling

Marine Geology