Subsidence in Long Beach basin

At the lowest point of the Long Beach basin, the ground has sunk 29 feet, approximately 9 meters, the height of a three-story building. The depression covers more than 20 square miles, more than 50 km², about half the area of Paris intra-muros.

Cause of the subsidence

The subsidence was caused by oil extraction under a port, not by an earthquake or natural disaster. The Wilmington field, discovered in 1932, is the source of this subsidence. It quickly became one of the largest in the United States in terms of cumulative production.

Mechanism of subsidence

Starting in 1940, subsidence became visible, and the mechanism was known: by removing oil and fluids, the pressure in the reservoir drops, and the sandy rocks that make it up compact. The ground on the surface follows the movement.

Rate of subsidence

The pace was surprising. According to Long Beach City services, the Terminal Island shipyard area had already lost more than 4 feet by 1945, and by 1951 the subsidence rate exceeded 2 feet per year. A reference technical study even places the maximum at the center of the basin at 71 centimeters in a single year, in 1951.

Impact on infrastructure

In the streets, this translates into very concrete damage. Dams and protective walls had to be built around port areas to contain water, as flooding became a permanent risk. As far as the city center, about 5 miles from the port, Pine Avenue, then the main commercial artery, was already 2 feet lower in 1950.

Legal actions

In 1958, the United States sued all producers of the field for damages suffered by this naval base. The damage claim was the largest in American history for subsidence caused by fluid pumping. The case was eventually settled amicably, without a verdict.

California Subsidence Act

The same year, California passed its own law. This text, known as the California Subsidence Act, requires producers to unite and repressurize the reservoir by injecting water. The blocking point was the fragmentation of the field's ownership.

Coordination of operations

On the same reservoir, hundreds of operators (about 400 operators, plus dozens of landowners) had no individual interest in injecting water, while the effect was only visible if everyone did it at the same time. To act in a coordinated manner, the different fault blocks were grouped into four units.

Early water injections

The first injections intended to maintain pressure date back to 1953, well before the general agreement of 1958. Experiments, therefore, but not yet a full-scale campaign. It took the threat of a huge federal lawsuit and a state law for the operation to change scale.

Effect of water injection

With hundreds of millions of gallons of seawater pumped into the oil field, the result surprised even the engineers: in 1966, the subsidence was stabilized. The reference study cited earlier notes that the rate of vertical movement dropped to 0 centimeters per year at the center of the basin as early as 1968.

Economic benefits

Even more astonishing, the injection also benefited the companies. Engineers from the city of Long Beach showed in the 1950s that it increased oil recovery, which turned a regulatory constraint into an economic argument.

Ground rebound

After stabilization, the ground slightly rose in some places, a rebound measured in inches only. A technical industry publication speaks of a rise of 8 or 9 inches, about 20 centimeters, to be compared to the 9 meters lost. The landscape, however, has not returned to its original state.

Long-term changes

Some parts of the port area remain several feet below their pre-extraction altitude, and concerned industries left the area during the subsidence years. The field was not, however, abandoned, and the episode changed the rules of the game in Long Beach.

Future development

According to the city, the oil companies had long known that the fields extended eastward, under the city and offshore, but the development of this area did not begin until 1965, after a vote by residents lifted the drilling ban. The condition set by voters: that this extension be unified before exploitation and that water injection begin immediately.