Recent devastating earthquakes have spurred research into warning systems that can give people a chance to get to higher ground. But their usefulness is limited not only by the speed at which earthquakes and resulting tsunamis occur, but also by the methods by which warnings are transmited, primarily telephone systems and the Internet.

Weir-Jones Engineering Ltd. provides a different kind of early warning system, one that is deployed locally at sites that are susceptible to earthquake damage. In the oil and gas industry, this includes onshore and offshore production facilities and transmission lines, where ground movement can have devastating consequences. According to a USGS report, the 1994 Northridge earthquake in Los Angeles, Calif., caused a gas line to rupture, and the gas was ignited by the ignition system on a nearby truck, causing a massive fire.

The government of British Columbia (BC) judged the Weir-Jones system so effective that it elected to install the system on the George Massey Tunnel south of Vancouver to prevent motorists from being trapped beneath the river during an earthquake.

Workers place equipment to detect earthquakes near the George Massey Tunnel in Vancouver, BC. (Images courtesy of Weir-Jones Engineering Group)

The genesis

Founded in 1971, the Weir-Jones Engineering Group specialized in vibration monitoring, running burst tests on line pipe in northern Alberta. “These tests are destructive and only last a few milliseconds, so you don’t get an opportunity to rerun the test if you don’t get the data the first time around,” said Iain Weir-Jones, company president. “The data acquisition systems have to be super-reliable and very quick.”

Early on, company personnel took measurements, did some engineering work, and turned the data over to their clients. “Most of what we did was tell people like metallurgists or pipeline designers or chemical engineers what their systems were doing so they could modify them and change process parameters,” he said. “It became apparent that, although our expertise was in collecting information, there were a number of areas where it would be useful to collect information for events in an automated manner.”

The goal was to remove the human factor and analyze the data in real time. “We started developing systems which had, for want of a better word, ‘innate’ intelligence,” he explained.

Ultimately, the company began developing systems that could monitor vibration patterns and determine whether or not they were threatening. This became the genesis of the earthquake early warning system (EEWS). Instead of monitoring mechanical vibration, the system listens to vibrations in the earth’s subsurface. It works on a premise that is familiar to geophysicists – the time difference between compressional (P) and shear (S) wave arrivals. The system senses the arrival of P waves, which travel faster than S waves and can be indicative of a major quake.

“If we pick up the P wave reliably, quantify it, and determine whether it is the precursor of a potentially damaging S wave, then we’ve got a time lead before the arrival of the S wave,” he said.

How it works

The subsurface is a noisy place, so redundant sensors are needed to validate the P-wave arrival. Typically these sensors are placed about 1 km (0.6 miles) apart. When two or more sensors pick up a P-wave signature, the P-wave arrival is validated.

The system then studies the amplitude and frequency of the signature. If the signature is determined to be valid and confirms the incoming S wave will cause damage, the system triggers the alarms that have been put in place. In the case of the Massey Tunnel, warning signs are turned on, and the tunnel is closed until the danger is past.

The EEWS also takes into account the design characteristics of the structures being protected. New building codes along the west coast of North America ensure structures can withstand certain ground motion. “The threshold level at a brand new high-rise would not necessarily be the same as a 30-year-old facility,” he said. “We tailor the criteria based on the design characteristics of the structure.”

Weir-Jones said that everything from P-wave detection to estimating damage risk takes about one-third of a second and requires no human intervention. He added that a facility 200 km (120 miles) from the epicenter of an earthquake might have only a 15-second window between the P arrival and the S arrival. “You don’t have a huge amount of time, but it’s enough time to shut down compressors, bring elevators to the lobby, close tunnels, and shut off big natural gas pipelines,” he said.

Weir-Jones emphasized his systems are not to be confused with regional earthquake warning networks. “The facility-specific systems we are building are hardwired and provide instantaneous response with no lost time,” he said.

The George Massey Tunnel is equipped with an earthquake early warning system that will close the tunnel to protect motorists from being trapped under the river.

At the reservoir scale

Not surprisingly, this type of system also is being used to monitor producing fields. “We’re looking at vibrations caused not by massive earthquakes but by small induced earthquakes, microseismic events, and we’re looking for the energy releases caused by strata movement associated with the depletion of the reservoir,” he said. This is helpful in a number of applications:

Delineating production zones;

Fracture monitoring;

EOR techniques;

Heavy oil production-related deformations;

Casing deformation;

Natural gas storage;

Waterflooding;

Carbon sequestration;

Geothermal reservoirs; and

Subsurface waste disposal.

Weir-Jones Engineering provided the equipment and supplies for two of the largest permanent passive micro-seismic monitoring systems in the world, for Imperial Oil at Cold Lake, Alberta, and for Canadian Natural Resources in its cyclic steam stimulation field. The company also developed the world’s first integrated microseismic monitoring system using dedicated radio frequency links between a master and multiple slave stations. The system uses GPS-based time referencing for synchronization across the entire system.

Other installations have included a multichannel, permanently installed system for continuously monitoring the progress of a COsequestration project and an 800-channel permanent passive microseismic monitoring system in Saudi Arabia.

The company also has streamlined its borehole installation, working with Imperial Resources to develop a cost-effective technique for installing custom triaxial packages in deep boreholes using coiled tubing and cement injection and with Encana on a technique to install small-diameter triaxial packages in the annular space between the casing and the wall of the borehole for low-noise installations in producing wells.