Mass scanning of drill cuttings indicator of hydrocarbon migration

Quadrupole mass spectrometer [54,383 bytes] A rapid drill cuttings evaluation process developed originally by Amoco, when used over a wide area, can reveal a great deal about fluid migration patterns in subsurface reservoirs. The process could conceivably provide the equivalent of a road map to untapped oil and gas reserves.

Western US Gulf of Mexico first to see wide use of technology

William Furlow
Contributing Editor
A rapid drill cuttings evaluation process developed originally by Amoco, when used over a wide area, can reveal a great deal about fluid migration patterns in subsurface reservoirs. The process could conceivably provide the equivalent of a road map to untapped oil and gas reserves.

Petroleum Geo-Services, no stranger to the art of the spin off, was quick to move when Amoco spun off its proprietary fluid inclusion technologies into a separate company, known as FIT (Fluid Inclusions Technology). PGS Reservoir has established an alliance with this cuttings company. While the agreement is not referred to as exclusive, Geoscience Manager Allen Bertagne said his company has enough work to keep FIT technicians busy for years. PGS Reservoir is the consulting arm of PGS.

Bertagne said FIT surveys do not include any seismic work, but add another level to the understanding of formations. "We immediately understood the fit between our technology and this technology," he said.

Analysis process

FIT is able to go beyond traditional methods of physically examining slivers of rock under a microscope or classical organic geochemical techniques, which use a solvent to lift and analyze the solvent chemical stain of these fluids from the surface of rocks.

Don Hall, President of FIT said these techniques are irreplaceable, but FIT allows for a faster, broader, and complementary system of analysis that goes to the core of the issue.

FIT tests the fluids physically trapped in the rocks they retrieve as drill cuttings or corings. The pockets of fluids, ranging in size from sub-micronic to 20-30 microns, tell the story of fluid migrations in subsurface formations, when taken on a whole. The trick is to possess the technology to process a large number of these samples in a short amount of time.

Hall said the FIT process uses trays of 575 samples, each about the size of a pebble. The location of each sample is also stored in the computer. These samples are washed and baked in a vacuum oven to clean their surface prior to analysis. The samples are pummeled by pneumatic hammer into the consistency of fine powder, and the molecular volatile stream released from the micron-sized fluid-filled cavities is pumped through four quadrupole mass spectrometers.

Within the mass spectrometers, volatiles are ionized into a collection of charged particles. By filtering these particles through an applied voltage and radio frequency potential, the machine can scan the samples for different organic and inorganic compounds, telling which of these species is present and in what quantity.

A detector amplifies this signal, which is interpreted by the signal processor and translated into a printout that looks similar to a wireline log, listing the different species of molecules as a function of atomic mass and quantity. By comparing these results to a baseline taken from known formations, FIT technicians can determine a lot about a well.

Nearby hydrocarbons

Hall said the large number of samples the machine can handle, 2 trays of 575 samples every 14 hours, allows the FIT team to not only map the past movement of hydrocarbons through a formation, but infer the presence of nearby undiscovered petroleum accumulations based on the presence of water-soluble hydrocarbons in a sample.

The process will also indicate bypassed pay zones and information about the type and quality of the pay.

Hall said the ability to analyze thousands of cuttings from different wells in an area will help in mapping where hydrocarbons have migrated to and also help in establishing seal perspectives for a specific horizon.

Western Gulf sale

The PGS-FIT alliance was formed at a propitious time, just before the August Western Gulf of Mexico Lease Sale. According to Bertagne, FIT and PGS Reservoirs worked night and day to prepare a comprehensive study of 179 wells in the Western Gulf. Once complete, this study was unveiled for potential clients on the eve of the sale.

Bertagne said there were other actors that led to the selection of the Western Gulf for this first survey. One was, of course the availability of open leases, but he also said the availability of cuttings was another consideration.

For the Gulf of Mexico study, the FIT technology was used to analyze cuttings taken at 60 ft. intervals from 179 wells in the Gulf. Wagner said a technician, using traditional methods, would be lucky to complete a study such as the one they prepared before the lease sale in a life time. Wagner said the study covered 24,000 cuttings to give an idea of where hydrocarbons were located in relation to existing wells.

While the alliance was pushing to have the study done in time to advise clients on the Western lease sale, Bertagne said the applications go far beyond bidding on open leases. Clients armed with this detailed information will be at an advantage when negotiating farm-in contracts on existing leases. By having a clearer understanding of what a field's potential might be these companies can put a more informed offer on the table and have a dependable recompletion plan.

PGS and FIT plan to license this Western Gulf of Mexico survey to the industry. Bertagne said the survey shows a much clearer picture of just what is left to discover in the Gulf of Mexico. Gesturing to a Western Gulf map on the wall of his PGS office (no photos please) Bertagne points out the broad spread of large and small red sundials indicating prospective untapped reserves of gas and condensate. Bertagne said he has identified 20 strong leads in federal and state waters off the Texas coast, with "hydrocarbon potential" identified in 37 of the 179 wells surveyed. "We're finding potential where there are existing fields and where there are no fields," Bertagne said.

PGS and FIT have several other projects already on the table to identify other hidden potential in the GOM and other offshore regions. "We're actually considering some international projects," he said. Bertagne said he could not comment on some of the surveys under consideration, but did say his team is looking at the waters offshore Louisiana and the deepwater Gulf.

Wagner and Bertagne admit this new technology is in its infancy, but the potential exists not only for farm-in of existing fields and new wells in established regions, but for better targeting of wells in relatively unexplored areas.

Copyright 1997 Oil & Gas Journal. All Rights Reserved.

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