2018 Offshore Technology Yearbook

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34 | December 2017 | 2018 OFFSHORE TECHNOLOGY YEARBOOK | DRILLING TECHNOLOGY "I called on different labs to try to correlate my samples to what they were doing for analysis. For example, they can't do the analysis that we are doing at the rig even in the lab as part of a standard analysis. They lump different gases together and give a combination of gases. However the real value is in separating those different isomers so that we can lead to a better understanding of the forma- tion," Bruns explained. The system works by sampling drilling fl uid through a low-maintenance, self-cleaning strainer that removes drill cuttings. The sampling is done in the return line as close to the bell nipple as possible. The sample then goes through a progressive cavity pump and then to an aluminum heater, which is designed to maintain the desired tempera- ture of the mud. From there the mud is measured by a coriolis fl ow meter and then to a constant-vol- ume gas trap where the gas is extracted, explained Rocio Brendle, marketing and commercial man- ager for BHGE. The gas goes to a gas distribution panel and then is analyzed by this high-speed gas chromatograph. Multi-columns and multi-ovens in the chromato- graph allow baseline separation of compounds and isomers, Brendle added. The TRU-Vision gas equipment doesn't take up any additional deck space on the rig. Two people can lift it into place. With most rigs' return fl ow- line being high enough off the deck in the "shaker house" the extraction apparatus fi ts nicely under- neath that, Bruns said. Density data from large-bore holes Until now, the only way to get density data for porosity measurements from sections in 14 1 / 2 -in. to 17 1 / 2 -in. holes was to run a wireline. Of course, that costs operators rig time, and they were look- ing for ways to eliminate that, said Sperry Drill- ing's Parker. "It started off with a major operator in the Gulf of Mexico suggesting we should build a larger ver- sion of the density tool—the azimuthal lithodensity (ALD) tool that measures density while drilling— and we agreed," he continued. Since then the tool has been used by the opera- tor and a number of other customers in the GoM. What the operators wanted was to log zones that are potentially hydrocarbon bearing and eliminate some of the wireline runs. "There's another benefi t from the fact that the tool is azimuthal. The tool is basically measuring all around the wellbore as the tool rotates as part of the drillstring. You can generate an image inside the borehole based on variations in density. From that you can estimate the formation dip angle and orientation," he explained. "There are some areas in the Gulf of Mexico where they drill through salt layers. The seismic data through salt is very poor. When the ALD tool exits below the salt, the issue is understanding the orientation of the bedding. What is the dip angle? Which way are the formations dipping? Having that kind of information in that hole size is import- ant. The ALD tool can give an estimate of the dip angle and a chance immediately to better plan the well and decide which way to drill when they get out of the salt," he said. That approach has been available for much smaller holes for some time. Sperry now has a much larger tool for the bigger bore sizes in the GoM. The ALD tool is built into the drillstring along with other tools. "We have a three-bladed stabi- lizer on the tool. Built into one of the blades are the actual detectors that we're using for the sensor readings for measuring formation density. Because we're in a drilling situation, we use a stabilizer blade The BHGE TRU-Vision system provides a baseline separation of more than 27 gases using a gas chromatograph on the offshore rig for the analysis. (Image courtesy of Baker Hughes, a GE company)

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