Designed to complement the Sonic Dual Tube 6 in. (SDT60) system for sonic applications, the SDT60 Weighted Wireline (WWL) system from Geoprobe® adds yet another innovative tool to the Geoprobe® sonic tool box. While conventional wireline systems with various latching mechanisms have proven themselves in the coring world, their adaptation to sonic applications has not been without its challenges.
Jed Davis, lead engineer for the new system, said that conventional wireline systems utilize a mechanical latch to hold a core barrel in place inside of the core rod at the bottom of the tool string. “The tool string (core barrel and core rod) is advanced through the sampling interval,” Davis explained. “A release tool (overshot) is then lowered down to release the mechanical latch so the core barrel can be retracted.”
The ‘secret’ behind the SDT60 Weighted Wireline design is ... Mass. The core barrel uses a simple weight system to hold it in place at the bottom of the tool string rather than a mechanical latch. In other words, the latching mechanism is replaced by a weight system.
Davis explained: “The weight system is modular in design and is comprised of 150 lb. weight segments that can be coupled together depending on sampling conditions. In most cases two, 150 lb. weight segments are sufficient to sample consolidated formations,” he said.
According to Davis, one critical design feature of this system is the adaptation of the modular weight system to the Geoprobe® rod handler. “Once the weight system is initially put into the tool string, it’s not handled by us again until after the last sample has been retrieved from the borehole,” he said. During every sample extraction at ground surface, the weight system is easily handled by the rod handler and never by the driller or driller’s helper. “Coming from someone who spends their days outside working with tools, that’s a great thing!” Davis added.
The SDT60 Weighted Wireline system is designed to complement the standard SDT60 tooling. Davis recommends using standard SDT60 tooling with 2.25-in. center rods in softer, shallower formations. When deeper intervals (50 feet plus) or consolidated formations are encountered, “the weighted wireline system can easily be implemented without pulling the casing,” Davis added.
The SDT45 and SDT60 and the SDT45 and SDT60 Weighted Wireline systems are designed by and available exclusively through Geoprobe Systems®, and can be used under most sonic rigs.