Necessity may be the mother of invention, but a simple request from a customer never hurts, either.

Thus it was that when Halliburton unveiled GeoTap, the industry’s first pressure-while-drilling tool, in 2003, its host of industry awards did not keep at least one drilling engineer from asking, “Can it take samples?”

“We were on our third job, very proud of ourselves,” said Jim Wilson, global solutions champion for LWD at Sperry Drilling. “Then a drilling engineer said, ‘We’re pleased with everything you’ve done, but we really want samples.”

So it was back to the drawing board. Six years later, Halliburton introduced the GeoTap IDS, answering that request. “I call it ‘Son of GeoTap,’” Wilson said. Like its dad, GeoTap IDS also has swept awards season, garnering honors from OTC, ONS, World Oil, and E&P.

The new tool is not just a GeoTap with a couple of fluid reservoirs tacked onto the side, Wilson said. Developers considered lessons learned while creating the new tool.

“For one thing, we put the components on the outside of the drill collar,” he said. “It’s like plug and play – you take out one component and put another one in rather than stripping down the entire tool.” It also has a more robust package to withstand while-drilling conditions, he said.

Sampling while drilling

The sensor eliminates the need for wireline operations to obtain multiple samples of oil, water, condensate, or gas. It can acquire samples within hours of drilling the formation.

Wilson explained that a fluid sampler must first remove contaminants – such as drilling fluid –from the formation before it can obtain a sample of the native reservoir fluids. When this operation is performed on wireline, it can be several days before the unit is on site, giving the invasive fluids plenty of time to soak into the formation. When sampling is performed while drilling, the fluids have less time to permeate the formation, which means less time is required to remove them.

The GeoTap IDS sensor identifies fluid and samples while drilling, eliminating the need for wireline operations. (Images courtesy of Halliburton)

Fluids are sampled during short stops in the drilling process using a tool in the LWD assembly. The sensor enables operators to acquire multiple fluid samples within hours of drilling the formation, reducing the likelihood of borehole damage and producing a less contaminated sample.

The GeoTap IDS can be positioned anywhere on the LWD bottomhole assembly (BHA). It extends a probe on command to establish a seal at the borehole wall. Multiple drawdown tests measure formation pressure and calculate fluid mobility for sampling. Then a surface command is sent to begin pump-out operations. In addition to establishing invasion properties, the flushing pump pulls fluids past sensors that measure temperature, pressure, resistivity, capacitance, and density of the fluids, which are monitored continuously until responses stabilize, indicating that cleanup has been achieved.

The fluids are then diverted through a zero shock chamber to a series of conventional 1-liter sample bottles, with up to five bottles in each sensor sample collar. A total of 15 samples can be obtained on one trip.

Samples are available immediately when the BHA returns to the surface.

Quicker decisions

By providing fluid samples much more quickly, it is possible for operators to characterize their reservoirs more closely to real time. In addition, the system also allows for better geosteering, greater ease in avoiding drilling hazards, and reduced rig time. It also can help in early facilities planning.

“You can make decisions about what facilities will be required to process the fluids, whether there are asphaltenes or waxes, and whether H2S poses a safety risk,” Wilson said. “These can be billion-dollar decisions, and it’s critical to get the fluids right as soon as you can.”

The tool also can provide reservoir information for offset wells, indicating whether the fluids in a new well display similar characteristics to an offset or represent a different reservoir.

“We know that reservoirs are not one big old flat pancake extending for miles and miles,” he said. “This tool can help determine whether or not the fluids are the same. Connectivity is a key component. If it’s a new reservoir, you’re getting new information.”

While some of the fluid will be analyzed in laboratories away from the well site, there are analytics tools that can be applied to some of the samples as soon as they have reached the surface. In one situation offshore Angola using a wireline sampler, an oil company paid to fly a unit from the US to run a test at the rig site to determine whether or not it was feasible to run a pipeline from a new discovery to a platform 11 km (7 miles) away. “They found an entire field that they might otherwise have walked away from,” Wilson said. “It was a big win for them.”

A successful LWD application was performed for BG Norge in a Norwegian offshore exploration well. The well was drilled with a conventional LWD string incorporating a standard GeoTap formation tester. Pressure tests identified a thin, mobile sand as a target, but attempts to run wireline tests failed.

An assembly for a wiper trip was configured with the GeoTap IDS tool to take samples in case further wireline tests were not possible even after the hole cleaning. The tool was positioned across the target sand, and a pretest was performed. The data were transmitted to the surface in real time. This information encouraged the operator to take live samples downhole. Pump inlet pressure and fluid sensor data were plotted in real time. The density data were analyzed by specialized software to estimate the amount of contamination. An interim sample was taken 10 minutes into the pump out, and a final sample was taken at 55 minutes..

After the wiper trip with the GeoTap IDS, a wireline trip was performed and successfully obtained samples. These samples required four or more hours to clean up and were compared with the samples of the GeoTap IDS, While contamination levels were high, they were considered acceptable because of the time limits of the testing, and they compared very well to the wireline samples.

The next step

Wilson said there are several of these tools around the world either on location or in the ground. “The acceptance has been good, and we are delivering success in field tests that will be released to the industry soon,” he said.

Improvements to the existing tool include pushing its temperature rating to the 200°C (392°F) mark (currently it is rated at 150°C, or 302°F). Pressure is not as big a hurdle as the tool is rated to 30,000 psi.

The company also is building a comparable tool for larger hole sizes. Current tools can manage holes sizes of 8-1/2 to 11 in.; the hope is to extend that to 17-1/2 in.

But the next step for those hard-to-please drilling engineers is a downhole lab. “You could do a significant amount of cataloging and understanding of the fluids downhole,” Wilson said. To reach this milestone, he said, requires the developers to tiptoe through “an IP minefield.” But the goal has been set, and it will be tested in the wireline environment first, then ruggedized for the LWD environment.

“Six months after the wireline tests, we’ll try it on the LWD side,” he said. “The downhole lab will be our next big step.”