Ingenuity Helps Keep Cities Over Oil Field From Sinking
Like a tiny elevator, the metal cylinder descends through 4,000 feet of pipe into the loose, oil-rich sands that make up the Wilmington Oil Field.
Its cargo: radioactive bullets.
At the earth’s surface, an engineer touches an electronic trigger. The cylinder--a specialized kind of gun--fires one bullet, then another, then another through the thin walls of the pipe. They lodge precisely 50 feet apart, like signposts in a downward tunnel.
The radioactive bullets, a key tool in charting underground surveys, are just one of the high-tech tools engineers are using to prevent geologic disaster in Wilmington and Long Beach. They are weapons in a double-barreled campaign: to prevent the ground from sinking as the field gives up its yearly bonanza of crude oil and to boost production at the state’s biggest oil field.
After 48 years of drilling, the Wilmington Oil Field has produced more than 2.1 billion barrels of oil, making it easily the largest ever discovered in California. The aging reserve yielded more than 38 million barrels in 1983 alone, generating revenues of nearly $300 million for the state, $8 million for Long Beach and $3 million for the Los Angeles Harbor Department.
Yield by Year 2014
Its ultimate yield is expected to exceed 2.5 billion barrels by the time production stops in the year 2014.
But oil extraction is no longer a simple matter of drilling and pumping. For the past 30 years, unusual geologic conditions have plagued production at the oil field. Its huge size and relatively young, soft sediments--unhardened by the setting of earth’s natural concretes--have left the field with little structural support as the great pockets of oil have been removed.
“As you produce from these underground reservoirs, you reduce the pressures,” explained Xenophon Colazas, director of oil properties for Long Beach. “Then this overburden--this 4,000 feet of dirt you have above it--pushes down on the sediments. It’s like pushing down on a sponge. As you push down on the sponge, you compact it . . . (and) you see a sinkage of the ground above.”
The problem, called subsidence, has created a legacy of property damage in Long Beach and eastern Wilmington. In the early 1950s, before engineers began high-pressure water injections into the field, portions of the area sank by as much as 29 feet--a drop that cracked buildings, bridges and roads and sheared off hundreds of underground oil lines.
The case brought a first taste of international exposure to Long Beach in 1952, when Time magazine labeled it the nation’s “sinking city.”
The Wilmington Oil Field “is the worst case in the world as far as oil subsidence is concerned,” said Don Lande, a petroleum engineer for the state Division of Oil and Gas, which regulates efforts to control subsidence. Coincidence placed the geologically vulnerable oil field at the edge of a populous waterfront area, where small changes in elevation can create huge problems, Lande said.
The field’s geologic structure and location are different, for example, than those at the Torrance Oil Field to the west, where fears of subsidence are not nearly so great.
“In the old days, in the 1950s, there were periods of flooding during high tides,” Lande said, recalling coastal portions of Long Beach and Terminal Island. “Extensive dikes had to be built to keep out the water. Buildings had to be replaced. . . . A lot of others were damaged.”
Today, engineers control subsidence with an arsenal of water wells, injection pumps, water separation tanks, geologic survey points, charts, graphs, meters and underground monitoring devices.
Radioactive bullets are just part of the ammunition. Buried deep in the oil sands, they offer one way to gauge the shifts, or compactions, of loose sediments, a tip-off that land is sinking. Engineers periodically measure the distance between the bullets, using gamma-ray detectors lowered deep into the oil lines.
“We may shoot one bullet, say, at 3,900 feet, and then another at 3,950 feet,” Colazas said. “Then, years later, we go back into the hole with our radioactive instruments and see at what depths we find them.” In theory, bullets found deeper, shallower or closer together show evidence of compaction. Those found at the same depths are signals that the ground is stable.
But there is far more to it than that, Colazas said. The whole task of keeping the land afloat becomes a massive Rubik’s Cube of oil pockets, fault blocks, fluid pressures and piping systems. It involves the complex ebb and flow of more than 23,000 oil wells, more than 800 water-injection wells and nearly 100 underground oil reservoirs. That means additional coordination between government agencies that oversee the field and private oil companies that do the drilling, sharing in the profits.
Originally, many oil operators resisted water injection, fearing that cooperative production methods would jeopardize their business interests and require huge equipment costs. But now, in an era of escalated oil prices and dwindling reserves, the technology not only keeps the field from sinking, it also plays a critical role in bringing hard-to-recover oil to the surface.
Drillers employ the water like a giant underground squeegee, forcing low-grade oil toward production wells. Without the practice, engineers agree, production at Wilmington and many other older fields would slow to a trickle--even without the threat of subsidence.
“As it turned out, it was a real benefit to oil operations,” Colazas said. “It has improved oil operations by 100%.”
In his second-floor office at Long Beach City Hall, directly over eastern portions of the Wilmington field, Xen Colazas runs a sort of commando headquarters in the battle to control subsidence. His charts, maps and oversized diagrams present a detailed anatomical picture of the oil pool and twisting well lines that pierce its surface.
In an aerial view, the oil field lies like an irregular oval bubble over the south-coast harbor areas, extending southeastward from Wilmington through downtown Long Beach and into the ocean floor south of Belmont Shore and Seal Beach. A small dip in sedimentary layers separates it from the Torrance Oil Field, an older, much smaller field stretching northwestward from Wilmington into Redondo Beach.
Measuring 11 miles long and three miles wide, the field represents part of a geologic “anticline,” an uplift in the earth’s crust, where oil became trapped under thin layers of shale and sandstone. The field is relatively shallow, by oil-field standards, lying at depths of 2,200 to 5,800 feet. Its seven sand layers were laid down during latter Miocene Era--26 million to 19 million years ago.
100 Oil Reservoirs
Complicating the field’s structure, Colazas said, are thin rock layers that separate the oil sands and at least 15 vertical fault blocks that cut the sand layers into sections, like slices of a layer cake. Thus, there are at least 100 different oil reservoirs--each with its own sand densities and fluid pressures.
“When you go back in there to inject water, you have to tailor your injection methods to the reservoirs,” Colazas said. “You may have a well producing from one (underground) reservoir, which decreases the pressure in that reservoir, and you may believe that’s causing a loss in elevation at the surface. So you have to go back in and repressure that particular reservoir.
“We’re actually tailoring our water-injection system to about 30 or 40" reservoirs.
Water injection had been used in other fields dating back into the 1940s, primarily to increase oil production, according to Lande. But never has it involved such an overhaul of drilling operations, such a mammoth coordination effort and such an important regional problem as at the Wilmington Oil Field.
To tailor the water injections, engineers have to record exactly where, when and how much water is forced into the field, then chronicle how that affects--or does not affect--surface elevations. Monitoring the effects involves a variety of underground tests as well as surface measurements throughout Long Beach, Wilmington and the Los Angeles Harbor area.
“Semiannually, we check about 1,700 elevation benchmarks” in Long Beach alone, Colazas said.
The City of Long Beach, the largest operator of the oil field, plays the lead role in tracking ground-level changes and in coordinating water injection with private oil drillers. Additional survey work is carried out by the City of Los Angeles and the Los Angeles Harbor Department, which keep a running history of elevations at 450 benchmarks in western parts of the oil field.
Small elevation changes occur constantly as the earth’s surface “breathes,” according to Colazas.
“We use the information to prepare our maps,” he said. “We try to coordinate the ups and downs of the elevation with our water injections. . . . We have found there is a direct correlation.”
A trend in the changes--as much as five one-hundredths of an inch for several successive measurements, a minuscule fraction of the huge subsidence rates of the 1950s--is enough to create concern, according to Lawrence Olson, a subsidence engineer for the city of Long Beach. Engineers react to the movements by adjusting the huge water flow in appropriate underground oil reservoirs.
“We’re injecting about 1.4 million barrels of water per day, which means about 59 million gallons,” Colazas said. The amount, slightly more than the volumes of fluid pumped from the ground, creates another technological challenge, because the ocean water that is used can corrode pumping equipment and damage layers of the oil field.
Injection water, which must be free of contaminants, has to come partly from shallow reservoirs lying 200 to 400 feet below the ocean floor. Water there is naturally filtered and replenished as it seeps down through the sandy ocean bottom; it is drawn to the surface by water wells, Colazas said.
Larger volumes of the water come from deep in the oil zones. That water comes to the surface mixed with the oil--at almost 10 parts to 1--and must be drawn off in separation tanks before it is pumped back down.
In both cases, the water must be filtered to remove corrosion-causing oxygen and sulfates, then treated with chemicals to kill bacteria that could grow in the oil sands.
“Bacteria will plug up” the reservoirs, Olson said. “The water and oil flow through little pores in the sand. If those pores are plugged in any way . . . that can make it impermeable.”
Cost per Barrel
At 3,000 to 5,000 pounds of pressure, the water is injected by modified oil pumps at a cost of about $1.40 for every barrel of oil that is produced. Today’s high oil prices, about $22.80 per barrel, enable oil operators to take good advantage of water injection even in areas, such as the Torrance Oil Field, where subsidence is a negligible threat, oil officials said.
At the Torrance field, which opened in the 1920s, total subsidence has measured only about a foot, Colazas said. Private drillers use 77 injection wells there to produce about 2 million barrels of oil per year and to prevent additional subsidence.
At the Wilmington Oil Field, dotted by 813 injection wells, a number of production wells have been reopened in recent years because of water injection, said George Horeczko, an engineer with the Los Angeles Harbor Department. More than 70% of the field’s current production is attributable to water injection, a 1983 state oil report said.
In designing the injection systems, engineers like to align the injection wells deep within an oil reservoir, Olson said. Several are placed beneath rows of production lines, enabling a bank of water to force the oil toward several collection points at once--like a long pool irrigating a row of corn stalks.
“The objective is to inject the water below the oil,” Olson said. “The oil floats on the water . . . and moves toward an area of less pressure. It floats up toward the well bores.”
The first hint of disaster surfaced at the Long Beach Naval Shipyard. During the busy 1940s, when the world was at war, portions of the yard began to flood at high tide. At first, some baffled observers blamed the problem on construction work for a new dry dock--the Navy had been pumping water from the marshy ground.
But the dry dock went in, the war ended, and the land kept sinking, Colazas said. Consultants were hired. A series of surveys began. Evidence mounted as the tides crept higher.
By 1952, parts of Terminal Island, originally at 14 feet, had sunk below sea level--and were dropping at the alarming rate of 2.5 feet a year. A bowl-shaped depression fanned out across downtown Long Beach and eastern Wilmington, causing extensive damage and forcing seaside property owners to build long dikes. Most of them reached heights of 20 feet or more.
“At the time subsidence occurred here it was a major disaster,” Colazas said.
Before it was over, land elevations at the bottom of the bowl would be nearly 15 feet below sea level. Horizontal earth movement, caused by the sinkage, measured 10 feet in places. Streets were cracked and broken. Water lines were severed and building foundations cracked. About 1,000 oil wells were damaged, many of their production lines cut by moving sediments. Five minor earthquakes rumbled out of the fault blocks of the oil field.
The Commodore Heim Bridge, a drawbridge connecting Terminal Island to the mainland, was pushed out of kilter, rendering it inoperable.
“Surface structure such as warehouses, piers, docks, pipelines and streets have been damaged by loss of elevation or stresses to the extent of possibly $30 million,” a UCLA geologist, U.S. Grant, told a meeting of petroleum engineers in 1958.
At the time, sinkage was at 24 feet--and no one was sure how far it would go. Some estimates suggested as far as 72 feet, Colazas said. The sea would have gobbled up huge chunks of the coastline.
“Oh, my God, it would have been terrible,” Colazas said.
Water injections, first tried in 1953, seemed to offer hope of halting the problem. But first there was the matter of consolidating several hundred private oil producers, many of whom were stiffly opposed to cooperative drilling efforts.
A 1958 state law, written especially for the Wilmington field, forced drillers to consolidate, placing control of the oil field into the hands of three large operators. Those operators--the city of Long Beach, the Champlin Petroleum Co. and Mobil Oil Corp.--now divide the field along major fault blocks, coordinating water injections and sharing oil profits among the land owners.
“People did not want to give up their individual operating rights,” recalled Art Spaulding, a former Los Angeles oil administrator who now is general manager of the Western Oil and Gas Assn., a trade group representing about 100 oil companies. “There were thousands of individual properties involved, hundreds of oil producers. . . . They did not want to fool around with major (oil) operators.”
Reasons for Balking
Some may have feared that water injection would drive oil from beneath their land to other parts of the oil field, where it would have been collected by other producers, Spaulding said. Others balked at contributing big money toward water lines and injection pumps, knowing they might have to wait 10 years before the money flowed back in the form of greater oil production.
“You had to drill a whole bunch of injection wells--and they don’t come cheap,” Spaulding said. He estimated the cost of overhauling the field at hundreds of millions of dollars. “It was a monumental project--that’s why it took so long. But the handwriting was on the wall . . . subsidence was endangering all kinds of property, and even lives . . . and eventually it did succeed.”
A formal water-injection plan for the entire Wilmington Oil Field won state approval in 1959, six years after the technology was first tried. And the measures worked. By 1966, the graph lines charting subsidence had leveled.
In the meantime, other problems had to be solved. The federal government had filed suit over property damage at the naval shipyard, involving claims against Long Beach, the state and 39 private oil companies. A $6-million settlement in 1963 also guaranteed that Long Beach would continue injection measures.
In addition, the city of Long Beach had enacted an ordinance in the 1950s that banned drilling in the east end of the oil field. In 1962, reassured by the efforts to control subsidence, Long Beach voters overturned the ban, enabling drillers to tap offshore reserves with an estimated ultimate yield of about 1 billion barrels, Colazas said.
Although dikes still protect sunken parts of Terminal Island, some parts of the subsidence bowl have rebounded slightly because of the water injections--although engineers say there is no hope of repressuring compacted oil sands. Most rebounding areas are like a section of Wilmington near Pacific Coast Highway and the Harbor Freeway, where elevations rose about 18 inches in a period of seven years, surveys by the City of Los Angeles show.
Meanwhile, the increasing use of water injection for oil recovery has prompted many producers to begin experimenting with newer technologies--including injections of hot steam and chemical polymers--to squeeze additional life out of the oil field. Jeff Druyun, the petroleum coordinator for the City Administrative Office in Los Angeles, speculated that better technologies could help oil producers get at huge volumes of oil that cannot be tapped even by water injection--as much as 2 billion barrels at the Wilmington Oil Field.
“So the field, even though it’s old, is not forgotten,” Druyun said. “Everybody’s trying to get that last oink out of the pig.”