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New hard rock drilling simulator could enhance shale gas drilling techniques

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Curtin University petroleum engineering researchers are using a high-speed drilling simulator to replicate the increasingly popular industry method of drilling deep boreholes in tight gas formations and shales.

Professor Vamegh Rasouli of Curtin’s Department of Petroleum Engineering said the research was being undertaken with the aim of improving efficiency in hard rock drilling but could be extended for shale gas drilling and fracturing.

Professor Rasouli said the simulator was capable of performing normal, over-balanced and under-balanced drilling, as well as simulating the use of different mud types and drilling through hard rock using diamond-impregnated bits.

“Simulation of drilling practices in the laboratory will be very beneficial for field operations as we can study the effects of different parameters on drilling efficiency,” Professor Rasouli said.

“There are various issues to overcome during the drilling and production phases of gas wells, including wellbore instability during drilling and hydraulic fracturing for enhanced recovery.”

The drilling simulator has been designed with a drilling lid mounted on a True Triaxial Stress Cell (TTSC), which is capable of simulating drilling at typical bottom hole conditions.

The TTSC has been successfully used in hydraulic fracturing experiments on samples as small as 50 millimetres to understand the response of tight sandstones and gas shale formations to drilling.

Professor Rasouli said the TTSC could monitor the magnitude of stress and strains on the sample and measure torque and drag systems, two important drilling operation parameters.

“During testing, three independent stresses can be applied to the sample to simulate real in-situ field stress conditions,” Professor Rasouli said.

“A significant feature of the rig is its ultra-high speed rotation which can move at up to 10,000 revolutions per minute (rpm) to simulate hard rock drilling in tight sandstones.

“A drilling fluid of any type can be circulated in the simulated borehole, similar to a field situation, to study its effect on drilling performance.”

It has been observed that drill speeds above 5,000 rpm can improve the rate of penetration by using water pressure to fracture the rock, rather than direct contact. The Curtin researchers refer to this technique as “drill bit surfing”.

Researchers will further investigate this aspect of the simulation.

Notes to editor:

A stress magnitude of up to 20 megapascals (MPa) (4,500 pounds per square inch (psi) in each direction) can be applied on a 100 millimetre cube sample and the pore pressure can be independently raised up to 21 MPa (4,600 psi).

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