Research uses mud pulses for pore pressure prediction

Engineers at the Idaho National Engineering and Environmental Laboratory are studying the use of hydraulic power pulses through a drilling rig's mud circulating system to provide an enhanced 'look' ahead of the bit in seismic-while-drilling operations.


DALLAS�Engineers at the Idaho National Engineering and Environmental Laboratory are studying the use of hydraulic power pulses through a drilling rig's mud circulating system to provide an enhanced "look" ahead of the bit in seismic-while-drilling operations.

It's part of an ongoing program at the lab, funded partly by the US Energy Department, to develop a downhole seismic source for look-ahead-of-the-bit technology.

The goal is to provide accurate predictions of formation pore pressures to optimize both casing and drilling fluids programs for over-pressured zones and to avoid well control problems. Possible economic benefits include elimination of casing strings, maintenance of optimum hole size to total depth, and reduction of non-productive time while drilling, officials said Wednesday at the close of the annual meeting of the Society of Petroleum Engineers.

Currently, no drilling system reliably provides that capability, officials said.

The experimental program was outlined Wednesday in a technical paper prepared by staff members of the Idaho laboratory, the Lawrence Berkley National Laboratory, and TerraTek, a research firm based in Salt Lake City.

Deeper oil and gas reservoirs with complex geologies will be the first targets for the technology, researchers said. Prime candidates for pore pressure prediction are deepwater blocks in the Gulf of Mexico with substantial subsalt coverage.

A high percentage of oil and gas reserves in more than 5,000 ft of water have significant sections of salt and subsalt transition zones. Operations in those areas are characterized by expensive wells, uncertain pore pressures, and potentially serious loss zones while drilling.

The objective of current testing is to characterize compressional wave coupling of single pressure pulses of hydraulic power into rock under a range of conditions. Accelerations of pressure are measured at different distances into the rock and up the drill string, along with average pressure and strain resulting from hydraulic pulsations through the mud circulating system.

Tests were conducted in a drilling test stand using a 15.5-by-36-in. core of Mancos shale from central Utah�a cretaceous shaly siltstone with a clay content of 15-20%.

Five accelerometers were installed in the core. Other measurement instruments also were used, including a pressure transducer about 6 ft. above the core sample, and a hydrophone installed on top of the core.

A series of six hydraulic coupling tests were performed to develop an experimental methodology for evaluating prototype downhole seismic sources, officials said.

The tests were done under differential pressures of 6,000-8,000 psi. Coupling tests were performed at 2,000-10,000 psi.

Initial results suggest that additional accelerometers will be needed in future rock samples for increased reliability and validation of the modeling, said officials.

Researchers hope to benchmark seismic sources in the lab before deploying the tools in expensive offshore operations.

About 9,500 persons attended the 3-day SPE meeting in Dallas. That was down from 12,000 last year in Houston, which always draws a bigger turnout because of the large number of oil and gas engineers there.

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