Energy Policy Act of 2005 (Ultra-deepwater and Unconventional Resources Program)
Improved Drilling and Fracturing Fluids for Shale Gas Reservoirs
The University of Texas at Austin
Chevron Energy Tech. Comp.
The development of shale gas plays is largely dependent on the cost of drilling and fracturing horizontal wells. Rapid decline rates require that new wells be drilled just to maintain production. A reduction in the cost and environmental footprint of drilling and fracturing will lead to a significant expansion of shale gas development. This project aims at developing materials and methods for substantially reducing drilling and completion costs and maximizing gas well productivities in shale gas reservoirs. The University of Texas at Austin proposes to accomplish this in two ways:
- Develop nanoparticle based water-based drilling fluids that are compatible with reactive gas shales and cost a lot less than the oil-based fluids being used today, and
- Minimize the amount of frac-fluid trapped in the shale by capillary forces by using fluorocarbon surfactants and energized fluids.
Gas shales often have a high clay content that can cause wellbore stability problems that necessitate the use of oil-based fluids for drilling. This significantly increases drilling costs and the environmental footprint. Recent work conducted in the PIís lab shows that the addition of nanoparticles (in the size range of the pore throats of the shale) to the drilling fluid results in a dramatic reduction in the reactivity of the shale with the drilling fluid. The use of such fluids provides a significant cost savings when drilling water-sensitive shales with water-based fluids without the danger of wellbore collapse.
Fracturing fluids used in gas shales often reduce the permeability of the shale to gas because of trapping of the water in the pore space. This water remains trapped by capillary forces because the pore size in the shale is so small and the capillary pressures are so high. It is proposed to use fluorochemical surfactants in fracturing fluids that adsorb on the shale surface and render the pore surfaces neutrally wet. This significantly reduces the capillary pressure holding the water in the pore space and allows the gas to flow back more easily. The effect of water-blocking on shale gas well productivity is, therefore, minimized resulting in a 2 to 5 fold increase in well productivity.
Finally, in gas shales that contain water sensitive clays, it may be desirable to minimize or eliminate contact with a water based fluid. Energized fracturing fluids, such as CO2 foams, provide a way to accomplish this. The interaction of energized frac fluids with shales will be measured and the potential benefits quantified.
In summary, this project aims at developing novel drilling and fracturing fluids that will provide an operator the following key deliverables:
- Novel, water-based drilling fluids for water sensitive shales that will significantly reduce the cost of drilling horizontal wells in shale gas reservoirs.
- Fluorocarbon additives and energized fracturing fluids to help minimize the impact of water blocking in gas shales during flowback.
- Data and recommendations on the use of these novel drilling and fracturing fluids in gas shales.
Principal Iinvestigators: Mukul M. Sharma, Martin E. Chenevert