Charlie Waltman – Microseismic Technical Advisor
This is the first installment of a two-part series. This article focuses on the benefits of high-density, long-aperture arrays from an operations perspective.
A friend recently suggested I do my homework and gather all the available information before making a large purchase online. I replied “of course, I always do!”. Being a numbers kind of guy, gathering and analyzing all the data seems the right way towards making an informed decision.
This got me thinking about how similar this simple concept is to decide the correct course of action in a field development plan. Why wouldn’t someone want to gather as much of the available seismicity when running a borehole microseismic survey? That’s where having a high-density, long aperture WAVETM Array comes in.
First, a few definitions to set the stage:
“High-density” means a system of closely spaced receivers, commonly referred to as tools. Sigma Cubed typically deploys 40+ tools per monitor well. This is facilitated by using ultra-lightweight 3-C tools deployed on flexible wireline. This contrasts with deploying a much heavier string of rigid interconnects and older, heavier tools. All that extra weight means fewer tools, and more tension on the connections which can cause leakage. This in turn will cause more rig-outs to repair flooded connections – and more importantly missed frac stages! Also, by using a lightweight system and flexible interconnects, the entire network of tools is routinely connected and stays connected before arriving at the wellsite. Therefore, the system can be turned on again at the wellsite and tested before the array is even deployed. That means much faster rig-ins and no downtime, even with significantly more tools.
Let’s also talk about telemetry. Sigma Cubed uses all the available optical fibers within the specialty wireline, and therefore can utilize what’s called an ‘interleaved’ system of communications. That is, every other tool is connected to one of two telemetry systems. Unlike outdated systems, if one tool fails mid-job it doesn’t take down all the tools below it. is You still have a backup system!
It’s easy to see why density counts – it is far better to sample the microseismic data with more and reliable receivers.
Lightweight 3-C microseismic tool
“Long-aperture” simply means an extremely long string of (high density) tools. Sigma Cubed typically deploys 40+ tools with a 2,000’ aperture. The array can be expanded up to 120 tools for VSP applications. We’ve observed that the vast majority of microseismic event arrivals are imaged on the full WAVETM Array. Sampling more of the wavefront leads to more accurate microseismic event locations, but this will be discussed in much greater detail in the second installment of this two-part series.
An industry-standard short aperture array versus Sigma Cubed WAVETM array
Which one would you prefer on your next job??