Downhole Viewing Distance: How far can you see?

Often I have been asked by prospective clients "how far can you see?" when they are considering monitoring their frac. Their concerns are obvious, spending 10s to 100s of thousands on fracture monitoring only to find they have a limited view of the project, an unknown recording bias, or worse no data can cause obvious hesitation (who wants to be responsible for approving a project with little to know data?).

As expected there are many factors which can contribute to the successful recording of hydraulic fracturing events (microseisms). The dominant factors is the rock's brittleness. Areas such as the Barnett shale and Montney were critical to the success of microseismic monitoring due to their brittleness and the number of events which were often recorded. As the technique was applied to different fields, the success has been more limited creating some apprehension in operators to spend money on this technique. Monitoring well offset and location relative to SHmax can also have a large influence as the frac might be propagating AWAY from the monitoring well limiting the effectiveness of the project. Similarly, too close, and the fracture may propagate to the monitor well and result in a cloud of events near the monitor well.

The downhole equipment is also a factor as some have clear advantages due to the well coupling and number of phones within each tool (sonde). The ability to join tools for stacking was a selling point but with little establish benefit in real world applications. The length of the toolstring (geophone sonde array) position of the geophones within the array have some effect as well. Often overlooked is the condition of the wellbore where CBL logs can be important as a tool coupled in an uncemented section can result in a noisy instrument(s).

Completions design is another important factor in viewing distance. Low Pressure/pumping rate can reduce the number of microseisms recorded in addition to how the fluid is injected via perforation ports or sleeves, as the events are not as focused between packers and reduce the orthogonal propagation when compared to perforation shots.

In the coming months I will be posting a color contour map overlay where one can obtain an estimate of viewing distances based on my experience in that field. My success rate in predicting viewing distances for clients has been within 200 feet, and I tend to conservatively estimate the value.