Have You Been Getting That Sinking Feeling?

In recent years the popular press has presented stories describing the process of climate change taking place as the world becomes more industrialized. One of the effects often mentioned is that as atmospheric temperatures rise, polar ice caps melt with increasing rapidity, leading to rises in sea level that can inundate low-lying coastal areas.

Although sea levels can rise at a relatively slow rate due to this phenomenon, another factor can cause much more severe coastal inundation within a considerably compressed time frame. In contrast with sea level rising, the ground can actually sink due to the withdrawal of fluids from the subsurface. This process is known as subsidence, and is a significant geologic hazard in some areas of southern California.

Anyone who has travelled the state has seen oil pumping units scattered across the landscape. In many areas these pumping units are found in tremendous concentrations, particularly in the great oil fields of the southern Central Valley. Another such great oil field is located along the coast of Long Beach and San Pedro, just a few miles from the Twining headquarters in Long Beach.

Discovered in 1932, the Wilmington Oil Field is the third largest oil field in the United States in terms of volume of petroleum produced. Thousands of wells have been drilled to extract petroleum in this field. Production to date is in excess of 3.75 billion barrels of petroleum. Additionally, several times that volume of brine wastewater has been extracted as a by-product of the petroleum production.

Removal of underground fluids from deep formations enabled those formations to compress, thereby causing a drop in the land surface. By 1940, sinking of the land surface in the port area was becoming evident.  By the late 1950s, the port area had developed a bowl of subsidence, which at its most severe point was over 29 feet deep (see Figure 1). Damage to port facilities included inundated wharves and rail lines, sheared pipelines and oil well casings, and distressed roads and buildings.

In order to stem the progression of land sinking, the oil producers instituted a program of reinjecting brine wastewater into the formations from which it came. This technique was highly effective in halting subsidence by the mid-1960s, and even led to eventual rebound of the land surface by up to 2 feet in some areas. The four man-made islands visible in the harbor off of downtown Long Beach are some of the platforms from which this repressurization of the oil sands is performed.

Subsidence issues are not limited to coastal areas, nor to withdrawal of petroleum fluids. The west side of the San Joaquin Valley has experienced severe subsidence due to withdrawal of groundwater used in agriculture.  Figure 2 shows the position of the land surface in 1926, 1952, and 1977 from a farm near Mendota. Subsidence in the Central Valley has accelerated recently as groundwater has been used increasingly to replace irrigation water allocations reduced in response to the ongoing drought. And in the Palm Springs area, large ground cracks associated with groundwater withdrawal and subsidence have appeared in residential areas and elsewhere. These examples illustrate the importance of sound management practices in the development of our precious California petroleum and water resources.