Use of Nanoparticles for Reducing the Permeability of Fine-Grained Rocks Such as Shales
Physical Sciences : Petroleum
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- Mukul Sharma, Ph.D. , Petroleum and Geosystems Engineering
- Martin Chenevert, Ph.D. , Petroleum and Geosystems Engineering
When drilling wellbores into the earth, certain types of low-permeability formations such as shale are encountered, become weakened, and often collapse into the wellbore. Shale instability has been estimated to result in drilling costs of over $1 billion per year, especially due to the increasing complexity of today’s wells. Companies cannot afford to suffer further consequences from shale instability.
Studies have shown that the cause of these failures can be traced to the invasion of the low permeability clay-containing rocks by water and other components in the drilling fluids. The invasion increases the pore pressure of the rock, develops swelling pressures, and reduces its strength. It is then easy for external stresses to crush the shale and thereby produce a borehole collapse.
Inventors at The University of Texas at Austin have developed a novel solution for reducing the permeability of shale formations using specific nanoparticles in the drilling fluids. By identifying the pore throat radii of shale samples, the investigators were able to select fine particles that would fit into the pore throats during the drilling process and create a non-permeable shale surface. Tests have shown reduction of 80% to 95% in permeability of the shale, which results in drastic reduction of absorbed water and potential for collapse.
- Extremely high fluid blockage or permeability reduction (80% to 100%)
- Eliminates need for using saline muds and chemicals during the drilling process
- Improved wellbore stability
- Silica particles are environmentally friendly
- Silica nanoparticles ranging from 5 to 20 nm in diameter
- Reduces permeability by blocking pore throats in shale
- Reduces flow by 80% to 95%, as opposed to a mere 7% by saline muds and chemicals
Shale formations are becoming increasingly popular targets for oil and gas companies in the search for natural gas and oil within the United States, as they constitute over 75% of the nation’s drilled formations. As it is estimated that 90% of wellbore problems are attributed to the collapse of shale, there is considerable need for increasing stability in these types of formations.
Proof of concept