Frac outs, inadvertent returns what ever you call it, it's not good. First, if it is severe, you lose returns - the ability to remove cuttings and keep the hole clean. You don't make a successful bore when you lose returns. Second, depending on where drilling fluid decides to venture, you may be creating an environmental nightmare. Of special concern here are waterways and groundwater aquifers. A third concern is threat to subsurface integrity - under roads, rivers and enbankments. HDD has a well-deserved reputation for being non-intrusive and the least disruptive technique for installing cable, pipe and environmental remediation methodology. There is no guarantee with HDD, but the quicker inadvertent returns can be detected, the better.
Every rig has a drilling fluid pressure gauge, which is how operators monitor down hole flows. Experienced drillers will tell you "the (fluid) pressure gauge tells you what's going on down hole. You watch it all the time. Change in pressure is an indicator." It may be a change in soil formation porosity or hardness. It may be a change in cutting actions, and it may be a sign of blocked return path - cuttings lodged around drill pipe and/or cable or pipe being installed.
Finally, I'm getting to the punch line of this article. This Spring I heard of a new device that was developed specifically for down hole drilling fluid monitoring. Horizontal Technologies (Houston) has designed a "Downhole Pressure Sonde" which monitors fluid pressures around the down hole drilling assembly. That area called the "annular space" has its own set of characteristics. The Downhole Pressure Sonde with an OD of 1.750 is housed in a separate assembly attached behind the steering tool, separated by a non-magnetic section. It transmits the annular space pressure and inside drill pipe fluid pressure to the surface using independent telemetry. In addition, the Downhole Pressure Sonde collects drill pipe temperature and annular drilling fluid temperature. Data is collected and integrated on a commuter-based program at the surface in an independent computer.
Without getting too technical here, the operator can select the sample rate, which can be as often as two distinct update samples per second. Computer, printer, gauges can be custom-integrated depending on circumstances. Get the picture? No, that's what the Downhole Pressure Sonde is supposed to do, give the operator a "picture" of what is going on down hole.
Horizontal Technologies is in the business of HDD steering tool provisioning including field steering hand out-sourcing. They contract with HDD contractors worldwide. Their life is HDD. And they are the first to say the Downhole Pressure Sonde is not a cure all. In fact, the tool has not caught on like wild fire because it still doesn't eliminate the frac-outs, I mean inadvertent returns.
Does it work? Yes. This Spring two HDD jobs involved the Corps of Engineers who specified real-time monitoring of downhole pressures. The HDD operators said, "It was a lot of extra detail work and it really didn't tell you much more than a good set of pressure gauge and torque & thrust gauges." But it does generate additional data, which is great. On both bores, there were no irregularities and obviously no inadvertent returns.
My, conclusion? If the client is willing to pay the extra cost incurred from logging, tool shipment and tool assembly, I think it's a win-win. Until next time.