|Clean Harbors surveyors work in areas that challenge their GNSS equipment.|
As oil and gas production continues to increase in North America, the need for geophysical exploration grows with it. Seismic surveyors are adapting to meet the challenges posed by increased demand, cost constrains and environmental concern.
The news is good: In the past five years, the U.S. has made great strides toward reducing imports of petroleum products. While conservation and increases in fuel efficiency have played an important role, production of oil and gas has increased as well. Since 2006, oil production in the U.S. and Canada has gone up by 16 percent to nearly 16 million barrels per day. In the U.S. alone, natural gas production grew by nearly three trillion cubic feet per year, an increase of 15 percent. The work has paid off. According to the U.S. Energy Information Agency, American dependence on foreign oil has declined significantly. In 2005, the U.S. imported 60 percent of the oil it consumed; the number dropped to 45 percent in 2011. By 2017, the U.S. is predicted to surpass Saudi Arabia in oil production.
The production increases have opened new sources for oil and gas, and triggered booms in the U.S. and Canada. And while credit is due to new technologies such as precision drilling and hydraulic fracturing (fracking), improvements in geophysical exploration have also played a central role.
|Use of GNSS speeds fieldwork and reduces the amount of clearing for survey lines.|
Working ahead of the drilling rigs, geophysical (often referred to as “seismic”) exploration teams conduct large, data-intensive surveys of the land and underlying geology to locate the hidden resources. Over the past 15 years, advances in positioning, mapping and computing technologies have enabled seismic surveying to keep pace with market demands.
Seismic geophysical exploration (often referred to as “reflection seismology”) is a primary tool for oil and gas production companies. It works by introducing kinetic energy into the Earth’s crust at designated locations, typically by dynamite blasts in drillholes or by large truck-mounted vibrators. The waves of energy reflect off the various subsurface layers and return to the surface, where they are detected and recorded by arrays of sensors. The data is compiled to create 3D geologic models of the area, which are used by exploration geophysicists to plan drilling and production activities. The models require accurate location of the energy sources and sensors that capture the reflected waves. While seismic exploration is costly, it is quickly paid back by the results of production wells and fields.
The decision to initiate a seismic exploration project unleashes a flood of activity in positioning and information management. In Canada, Calgary-based Clean Harbors Exploration Services provides services for geophysical exploration project management throughout Canada and the U.S. At the start of a project, Clean Harbors receives information on the geographic area and data required. The client’s geophysicists or seismic program designers provide a layout for the arrays of seismic sources and receivers. Source points are locations where energy will be injected into the ground; receiver points are locations for geophones or other sensors that capture the reflected seismic waves. The arrays are based on the type and depth of material. Shallow targets, such as oil sands, require tightly spaced points. Deeper targets, including the Barnett and Marcellus shale formations, call for wider spacing.
|A preplot in GPSeismic shows locations for receiver points. Point numbers are related to layout schemes for geophysical data.|
The challenge comes in fitting the seismic program design into the reality of terrain and obstacles in the field, explains Joe Pilieci, Clean Harbors vice president for geomatics and locating. “The first step is to set up an Esri GIS and collect and compile all digital information that we can find. That includes aerial photography, satellite imagery, LiDAR and any kind of infrastructure mapping that has already been done. We then go out and map anything that we don’t have information for--water wells, houses, fence lines, roads, power lines, buried utilities and sometimes cadastral information.” Clean Harbors trains its crews to recognize and locate items of interest, collecting field data using Trimble Pathfinder ProXH handheld GPS receivers.
The field locations and attribute details are added to the GIS, along with the seismic design points. Clean Harbors GIS Operations Manager Sean Wilson inspects the maps and proposed layout (known as the “preplot”) for the seismic points. He identifies regions called exclusion zones that--for physical or other reasons--restrict the placement of seismic sources or receivers. Design points are usually moved or offset to new locations that will provide the same geophysical results. Clean Harbors uses GPSeismic software to manage the survey points and information, including uploading preplot data to the field and exporting final results to the clients’ formats.
The quantity and quality of pre-survey information is important, and it represents a big advance in seismic surveys. “We use georeferenced maps to identify features that affect the exclusion zones,” Wilson says. “It’s much more productive to create a redesigned preplot in the office than to discover a problem while in the field and have to change it on the fly.”
The rich data helps in planning project execution as well. Using a combination of LiDAR and aerial imagery, Clean Harbors can model the landscape where teams will be working. They can then plan the type of equipment needed and simulate the movement of vehicles and machinery through the terrain.
With the preplot complete, survey teams go into the field to mark the locations for the source and receiver points, typically using RTK GNSS. Clean Harbors crews use Trimble R8 GNSS rovers, with Trimble R7 GNSS receivers set up as RTK base stations on local geodetic control marks. As each survey point is set, the crew records additional GNSS data to measure its final location. Depending on conditions, the data may be collected as RTK vectors or in a longer-duration dataset.
Pilieci says that a typical job can have 10 or more survey teams, with each team setting 100 to 200 points in a day. The data are post processed to provide checks on the RTK work; Clean Harbors technicians process thousands of GNSS vectors each day. Because the vertical component is crucial for modeling the subsurface layers, the review pays special attention to the confirming accuracy in elevations. In many cases, technicians use LiDAR or other elevation data to provide a check on the GNSS elevations. After an internal review, coordinates and quality control information go to the client for use in processing the data from the geophysical sensors.
|Clean Harbors drill rigs await guidance from survey crews. A single crew can set more than 100 points in a day.|
While the basic concepts of reflection seismology are well established, seismic surveying has experienced significant improvements both in technology and project management.
Today’s projects cover more ground with more points, and do it in less time, compared to geophysical exploration in the 1990s. One of the primary drivers is the increased capability of the software and computing hardware used for geophysical modeling. While bigger, more sophisticated models produce better results, they demand more data on the front end. “A large job used to be 100 square miles,” said Cliff Harris, a geophysicist turned software developer who founded Dynamic Survey Solutions, Inc. in the early 1990s to develop GPSeismic software. “Today, that size is commonplace, and 300 square miles is not unusual in some parts of the world. The old jobs would have a few hundred channels (receiver points); now they can go to 10,000 or more.”
It could not have happened without GNSS. In the 1990s, seismic teams used static GPS for control, but most stakeout took place with total stations and traversing. Field computing was more intensive on optical surveys, and the interlinked nature of the traverse points meant that an error at one location could affect an entire line. By the early 2000s, satellite-based surveying had replaced optical methods on many projects. Today, seismic survey crews use RTK GNSS almost exclusively, reverting to optical methods only in the most difficult forest canopy. But that’s not the only difference GNSS has made in the forest.
In addition to being much slower than the satellite-based surveys, optical methods require extensive clearing to create lines of sight. That’s not necessary with GNSS. Instead of following straight lines, surveyors can use GNSS to take a meandering path to reach points more efficiently, and multiple crews can work simultaneously on different sections of the same line. The impact from the mechanical equipment has been reduced as well. In the mid 1990s, cut lines were often 16 feet wide; now they are 10 to 11 feet wide. Over a large project, the modern methods result in significantly less ground disturbance and fewer trees cut down. But even with the advances in the field, seismic survey managers still face challenges.
The ability to manage multiple projects is a key requirement. Working from Calgary, Clean Harbors Survey Operations Manager Jeff Plourde manages the day-to-day operations of the Canadian survey crews. In the winter of 2012, Plourde coordinated roughly 60 different projects in Canada, with as many as 16 projects running at one time. (Winter is the busy season in Canada, with seismic crews taking advantage of the frozen ground.) As part of project planning, Plourde determines the quantity and type of GNSS equipment that will be needed.
|A survey team prepares for a day in the field. Clean Harbors crews use single-base RTK for most of their work.|
In 2010, Clean Harbors upgraded its fleet of GNSS equipment, replacing old hardware with its current Trimble GNSS systems. With an inventory of more than 200 receivers, the company is meticulous in managing its gear. When a survey project is completed, the field equipment returns to the Calgary warehouse where it is cleaned and checked. The firm utilizes Trimble AllTrack asset management software to track the usage, status and maintenance records of the equipment, including software and firmware versions. As part of the checkout routine, the GNSS receivers and data collectors (Clean Harbors operates Trimble TSC3 controllers and Trimble Access software) receive any needed updates to firmware and software.
Once on a project, crews will not receive any new firmware or software. “When a pack goes out, it is up to date including survey styles and templates, code libraries, batteries, cables and accessories,” Plourde says. “We lock the units to prevent the field guys from trying to install new software.”
Although the mapping and survey crews use different hardware in the field, all crews run the same code library, and point descriptions and attributes are consistent throughout a project. When necessary, however, the crews can define new codes to describe features in the field. “With so many different people, it’s important to have a set of consistent standards,” Wilson says. “We’re able to operate a system for field coding that is controlled, yet flexible enough to handle unique situations.”
What’s next for firms like Clean Harbors that are on the leading edge? With an eye on the bottom line, Pilieci keeps detailed statistics on performance. “In 2010, we saw a 10 percent increase in productivity over our previous systems,” he says. “The new GNSS equipment was responding more quickly, the real-time component behaved better and we achieved better results in the high-noise, tree-cover conditions where we frequently operate.”
While the GNSS performance is impressive, the company’s office processes have also improved field productivity. In order to achieve the desired geophysical results, technicians need to design exclusion zones that preserve the original design geometry of sensors and receivers. In the field, unexpected obstacles can require new exclusion zones, which introduces delays and rework. By using GIS for preplot design, Clean Harbors has reduced the occurrence of in-field changes to survey plans.
Modern GNSS also helps Clean Harbors manage labor costs. The company has reduced the size of its field crews, and Pilieci notes that GNSS crews require less training and expertise than the teams using optical surveying. In the coming season, Clean Harbors will implement the Land Seismic application in its Trimble Access field software. By using field software tailored to seismic work, Plourde expects to reap additional productivity in field and office processes.
Harris notes a change coming from the client side as well. “There’s a better dialog between surveyors and geophysicists,” he says. “The older specifications were filled with survey requirements based on old technologies and capabilities. Geophysical clients used to specify the instrumentation and procedures, but now many project specifications trend toward simply the results and accuracy.” This shift gives the surveyors more independence, but they still must meet the requirements and document the results.
“We don’t just go out and lay out points anymore,” Plourde says. “We assist other phases of the operation and deliver a higher level of integrity of the geophysical survey.” For example, every data collector has a camera that can capture georeferenced snapshots. Part of project requirements is to report wildlife activity or unusual environmental conditions. If the crew encounters a bear or a moose, they can snap a picture of it and automatically capture the location of the incident.
With constraints coming from two directions--cost and environmental concerns--oil and gas exploration continues to evolve. “I think that the general public still thinks that exploration companies are not as environmentally aware as they are,” says Pilieci. “Even though the big spills hit the media, the oil companies really do care about the environment. The exploration part of that has changed to help the environment.” As integration deepens between GNSS field systems, geophysical analysis, LiDAR and GIS, seismic surveyors will see further improvements in productivity, costs and environmental impact.