Frac Signals: Using microseismic monitoring to optimize fracture stimulation
Courtesy of: New Technology Magazine
June 4 2015
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SPARSE NETWORKS A Nanometrics field engineer works with a broadband seismometer. By installing continuously monitoring, permanent networks, Nanometrics can provide immediate, real-time feedback on seismicity and the environment in which operators are producing.
A SPARTAN APPROACH
Nanometrics is opting for a sparse network long-term monitoring strategy to provide insight on the natural seismicity of an area, thus illuminating many natural faults, enabling companies to assess or quantify the existing subterranean stress field and therefore run better frac completions.
“If you have a good understanding of the broader geology, stress field and seismicity, then you are better placed to operate in an area,” says Neil Spriggs, co-chief executive officer of global operations for the Kanata, Ont.–based company, which has an Oil & Gas Division in Calgary.
Traditional surface microseismic involves 5,000–7,000 geophones measuring actual frac completion during the brief two- to three-week treatment process, he notes, while Nanometrics typically uses 10–15 stations and continuously monitors the subject environment long term.
“What that allows us to do is capture a lot of the seismic activity over a period of time, which provides a lot of insight into the environment in which we are working. A sparse network is lower cost, requires fewer stations and is less intrusive on the environment.”
According to Spriggs, typical surface frac monitoring requires a lot of equipment densely instrumenting an area, which can be disruptive and may require line cutting. His company requires less obtrusive technologybecause it is only trying to answer a few key questions about the fracturing network.
“We provide our customers with a broader understanding of the environment in which they are operating, and we look for potentially larger events associated with natural seismicity and frac completions. With just a few of those events, we could drill down into the data and then tell a customer whether [he or she] found an existing fault and if the fracturing completion is moving out of zone.”
Nanometrics installs continuously monitoring, permanent networks, which provides immediate, real-time feedback on seismicity and the environment in which operators are producing. Using a smaller subset of data over a longer period of time, the network can answer broader questions such as whether a company is fracturing in expected volumes, or whether proppant and fractures could move out of zone along a pre-existing fault.
“On the list of 20 questions [companies] want answered, you have to bring a big, dense network in order to answer all 20,” Spriggs says. “However, if you only need answers to the top five or six questions, then we can do that with a sparse network. The beauty is we can then do that on many, many more completions.”
Nanometrics takes many noise measurements in an area and models the whole environment, ascertaining key locations at which to place stations to meet objectives. Since the company is not placing its array randomly, it can design that array for the specific environment, yielding significant gains in signal-to-noise ratios.
The stations themselves use high-end, more sensitive seismometers as opposed to geophones. By placing such sensitive stations in quieter locations and at shallow depths, Spriggs says, Nanometrics achieves significant signal-to-nose ratio gains before monitoring even begins.
“We can use fewer [stations] because we use higher-quality instrumentation and a different approach to sampling the data. To answer the very detailed questions, we wouldn’t need thousands of geophones. Rather, we would use hundreds of seismometers. There is an advantage there.”
He adds, “There is real value in giving customers real-time and immediate feedback on what is going on, but I think what we are looking to do and what we are investing is in the signal processing in order to basically define smaller and smaller events from sparse networks. We are investing in mining a sparse network for the richest catalogue we can get.”
Jul 13, 2015