On October 31st, former Cascade subject matter expert, Michael Jordan, presented the webinar, “Tired of DPT Refusal? How to Achieve Deep Site Characterization.” In the webinar, he discussed solutions for overcoming many DPT refusal scenarios in order to gather the high-resolution site characterization data for optimal conceptual site models (CSMs).
If you missed the webinar, you can still watch the recording. Update your email preferences to ensure you receive future webinar-related communications.
This blog provides an in-depth response to questions posed by the webinar audience.
Q: Does the sonic profiler heat the groundwater like sonic heats the soil?
A: The sonic drill-based samplers discussed are not typically advanced with sonic resonant energy. They are pushed ahead of the outer override casing. In fact, it was originally known as the “push-ahead” sampler. The sampler can be advanced past the parts of the formation that have been impacted by drilling operations to assist in collecting representative formation samples.
Q: Not so much a question but more of an observation based on my experience. Anytime there are borehole logs available specific to the site you are going to, it can be a huge help to review them and what was encountered. I'm a firm believer in "knowing before going."
A: This is very true. Often Cascade will ask for logs or look into past projects that we have completed in the area to get a better understanding of the subsurface conditions prior to mobilization to the site. A significant change that has happened over time is the move to both sonic and percussion-based drilling. With these methods, geotechnical information is more limited. Standard Penetration Test (SPT) log information is very useful in understanding soil density but is not collected as much now.
Q: What do the acronyms MIP, MIHPT, and APS stand for?
A: The membrane interface hydraulic profiling tool (MIHPT) is the membrane interface probe (MIP) with the hydraulic profiling tool (HPT). It heats up the subsurface as it is advanced and allows vapor to diffuse across a permeable membrane and be swept to the surface with a carrier gas, which is then analyzed. With this tool, you can get a relative understanding of the concentrations at depth. At the same time, it is pushing water out at a known pressure and flow on the HPT side, so you can get an idea of hydraulic conductivity for the zone you are in.
Similarly, with the Waterloo Advanced Profiling System (APS) tool, as it is being advanced it’s injecting water out and you are recording flow and pressure - so again you’re getting an idea of the hydraulic conductivity, with each specific unit. But you can stop that tool and collect a representative groundwater sample in a very discrete interval. Those are two of the ways we characterize sites for HRSC investigations.
- MIP = Membrane Interface Probe
- MIHPT = Membrane interface hydraulic profiling tool
- Cone penetrometer testing with electrical conductivity
- APS = Advanced Profiling System. There was an original profiler developed (Waterloo), and subsequently, we took that and increased the productivity of it quite substantially (WaterlooAPS).
Q: What are the angle capabilities for hybrid sonic/DPT with Waterloo?
A: Our sonic rigs are capable of advancing tooling at angles down to 23 degrees - that is, 67 degrees off vertical.
Q: What are the issues with the use of water for sonic interfering with Waterloo?
A: That is a big concern that we think about quite a bit and comes into play in our pre-planning talks. We prioritize two things in those talks:
- Trying to minimize the water usage as much as possible. We do need to use some water with sonic advancement, but we try to minimize it.
- Being able to advance past the interval that is impacted by drilling action. We’ve been doing this for quite some time with Waterloo (originally with mud rotary), and we recognized that if we are able to get five to eight feet below the drilling interface, we are outside of its impact in most cases. The Waterloo system includes the use of a multimeter, so we can actually understand if there are impacts because we’re monitoring Dissolved Oxygen (DO), Reduction Oxidation Potential (REDOX), and pH. In some cases, with the ISOFLOW and push-ahead we can add fluorescein dye or another reference indicator and purge the interval until we see that it is gone. That way we understand we are not having impacts from our drilling fluids.
Q: Are there limitations to using hybrid technologies in running/flowing sands?
A: No. The biggest concern is where to stop the outside casing. Typically, when we are in flowing sand conditions the DPT operations move along quite well. Those are fairly soft formations and we can wiggle through those with the injection of water from the Waterloo tip or the HTP tip. The biggest problem is knowing where to end the casing runs. If we were to end in the middle of a flowing sand unit this would be affected by the heaving conditions. If there is a bottom unit of a silt or a clay, we can key into that to prevent the sand from entering the casing. In addition, we also will mix up traditional muds to keep heave out of sonic casing as we are advancing the DPT equipment.
Again, if you missed Michael’s webinar, watch the recording today.
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