Method for Prevention of Shale Fracture Hydration During Well Stimulation by Hydraulic Fracturing
Physical Sciences : Petroleum
Available for licensing
- Eric van Oort , Petroleum and Geosystems Engineering
- John Downs , Formate Brine Ltd.
Hydraulic fracturing is the main technique for unlocking hydrocarbons present in shales. Fracturing is accomplished with water-based fluids which are pumped at high pressures into hydrocarbon-bearing shale formations to create large fractures and associated permeability for hydrocarbon production. Prior to production, an attempt is made to back-produce water that is used for fracturing. A problem, however, is that usually only a fraction of the original quantity of fracturing water is back-produced. The water that is left behind can and does interfere with hydrocarbon production by keeping fractures effectively water-locked. Clay swellings and associated closure of fractures reduce the conduits for production. Inefficient back-production of water also causes embedding of proppant in the fractures. There are currently no effective technologies that prevent water from remaining in fractures after hydraulic fracturing and that actively shield the shale from water absorption.
Researchers at The University of Texas at Austin developed a method to protect the water-sensitive clay fabric and maximize back-production of water during hydraulic fracturing of hydrocarbon-bearing shales. The invention exploits the reverse solubility characteristics of cloud-point glycols (CPGs), which become insoluble and form a separate non-polar phase when temperature is increased. CPG polymers are mixed with fracturing water, remaining in solution until the fluids invade deeper into shale pores. When exposed to higher in-situ temperatures, the CPG polymers separate from the solution to form an emulsion block in the shale pores which inhibits hydration of the clay fabric. Clay swelling and proppant embedding are prevented, which in turn improves hydrocarbon production rates and ultimate hydrocarbon recovery.
Because the shale is protected, more water will be recovered upon flowing back the well, which will minimize water-locking of small fractures and open up the fracture networks for production. The higher water recovery will aid in the re-use of water for subsequent fracturing jobs.
The CPG emulsion blocks are oleophilic, allowing the polymers to rapidly mix with and dissolve in hydrocarbons. When the well is brought on production, the flow of hydrocarbons from the clay fabric to the fracture clears the CPG emulsion blocks and allows production to carry on in an unrestricted manner.
- Improved shale protection
- Improved hydrocarbon production rates and ultimate hydrocarbon recovery
- Enhanced water recovery aids in re-use of water for subsequent fracturing jobs
- Simple clearing of CPG emulsion blocks allows for unrestricted hydrocarbon production
- Reduces the necessary hydraulic pressure required for fracturing
- Reduces required hardware/pump capacity to deliver hydraulic pressure
- Reduces amount of freshwater, a limited resource, required for fracturing
- Exploits the reverse solubility characteristics of cloud-point glycol (CPG) polymers
- CPG polymers remain in solution until exposed to higher in-situ temperatures
- CPG polymers react to higher in-situ temperatures to form emulsion blocks
- Inhibits hydration of the clay/shale fabric
- Prevents clay swelling and proppant embedding
- Minimizes water-locking of small fractures
- Opens up fracture networks for hydrocarbon production
- Oleophilic emulsion blocks can be cleared by the flow of hydrocarbons
- Dual function of CPG polymers as lubricants and friction reducers
- Increased backflow of fracturing water
Markets and Markets Research reports that the global hydraulic fracturing market is expected to grow to $72.6 billion at a compound annual growth rate (CAGR) of over 11.8% by 2019. Hydraulic fracturing is essential for producing the most oil and gas possible from shale formations, in which the necessity for drilling unconventional shale formations is driven by the depletion of onshore oil fields. As of 2014, North America is the largest and most influential market in hydraulic fracturing due to its abundance of available shale reserves.
Proof of concept
- 1 U.S. patent issued: 9,957,439