The goal of this project is to develop methods and tools that can enable operators to design, optimize, and implement energized fracture treatments in a systematic way. The simulator that will result from this work would significantly expand the use and cost-effectiveness of energized fracs and improve their design and implementation in tight gas sands.

University of Texas-Austin, Austin, TX

A significant portion of U.S. natural gas production comes from unconventional gas resources such as tight gas sands. Tight gas sands account for 58 percent of the total proved natural gas reserves in the United States.

As many of these tight gas sand basins mature, an increasing number of wells are being drilled or completed into nearly depleted reservoirs. This includes infill wells, recompletions, and field-extension wells. When these activities are carried out, the reservoir pressures encountered are not as high as the initial reservoir pressures. In these situations, where pressure drawdowns can be less than 2,000 psi, significant reductions in well productivity are observed, often due to water blocking and insufficient clean-up of fracture-fluid residues. In addition, many tight gas sand reservoirs display water sensitivity—owing to high clay content—and readily imbibe water due both to very high capillary pressures and low initial water saturations.

This sensitivity to water-based fracturing fluids means that a large proportion of the re-fracs and infill well fracturing operations in many U.S. tight sand basins will most likely be conducted using energized fracture stimulation technology. This approach avoids many of the problems listed above by “energizing” the fracturing fluid through the addition of carbon dioxide or nitrogen. None of the 3-D hydraulic fracture models available today for simulating and designing hydraulic fracture treatments have the capability to adequately simulate energized fracture treatments. These models are not capable of accounting for the changes in fluid composition and phase behavior during injection and flowback after the energized fracture treatments.

By adding thermal and compositional capabilities to 2-D hydraulic fracture models, operators will be able to design and optimize energized fracture stimulation treatments in a systematic way. Such improvements will help operators better develop under-pressurized reservoirs, many of which are water-sensitive and will require energized treatments to be produced effectively. The resulting improvement in development approach will result in fewer unnecessary wells being drilled and fewer completion or recompletion attempts being required to achieve a satisfactory level of natural gas production, reducing costs. In addition to the energy supply and economic benefits flowing from a more cost-effective way to boost domestic energy supply, the reduction in the number of wells and overall activity through improved efficiency also means less impact on the environment.

A new model has been formulated and implemented to simulate fracture growth using energized fluids. The model includes the following salient features:

• It accounts for pressure and temperature changes as the fluid flows in the wellbore and in the fracture
• It solves the component mass balance equations to track the concentration of each species
• It conducts a flash calculation to obtain the composition and properties of each phase
• It accounts for multi-phase leak-off
• It models proppant transport in the fracture
• It is capable of handling injection into different zones and is able to predict fracture size and proppant transport in multiple fractures

The model has been used to simulate the performance of several field treatments in South Texas. The model can be used to history match the net pressure plots and estimates of the fracture geometry have been made. In addition the model has been used to conduct what-if simulations to better design energized fracture treatments. With the simulations of field treatments conducted to date, we feel confident that the model can be used both as a fracture design tool and to history match the net pressure of fracture treatments to estimate fracture dimensions. A pseudo 2-D energized hydraulic fracturing model has been developed. The model has been used to simulate the performance of several field treatments in South Texas. The model can be used to history match the net pressure plots and estimates of the fracture geometry have been made. In addition the model has been used to conduct what-if simulations to better design energized fracture treatments. Publications that summarize the details of this work are listed in the References

(January 2010)
The project is completed. The final report is available below under "Additional Information".

$694,366

$785,414 (53 percent of total)

NETL – Virginia Weyland (virginia.weyland@netl.doe.gov or 281-494-2517)
UT-Austin – Dr. Mukul Sharma (msharma@mail.utexas.edu or 512-471-3257)

Final Project Report [PDF-1.33MB]

Publications
1. “A New Compositional Model for Hydraulic Fracturing With Energized Fluids,” SPE 115750, prepared for presentation at the 2008 SPE Annual Technical Conference and Exhibition held in Denver, Colorado, USA, 21-24 September 2008. K.Friehauf and M.M. Sharma.

2. "Application of a New Compositional Model for Hydraulic Fracturing with Energized Fluids: A South Texas Case Study," SPE 119265, prepared for presentation at the 2009 SPE Hydraulic Fracturing Technology Conference held in The Woodlands, Texas, USA, 19-21 January 2009. K. Friehauf and M. M. Sharma.

3. "A Simple and Accurate Model for Well Productivity for Hydraulically Fractured Wells," SPE 119264, prepared for presentation at the 2009 SPE Hydraulic Fracturing Technology Conference held in The Woodlands, Texas, USA, 19-21 January 2009. K. Friehauf and M. M. Sharma.

4. “A New Solution to Restore Productivity of Gas Wells with Condensate and Water Blocks,” SPE 116711, prepared for presentation at the 2008 SPE Annual Technical Conference and Exhibition held in Denver, Colorado, USA, 21-24 September 2008. V. Bang, G.A. Pope, M.M. Sharma, and J.R. Baran, and M. Ahmadi.

5. “Wettability Alteration to Increase Deliverability of Gas Production Wells,” SPE 117353, prepared for presentation at the 2008 SPE Eastern Regional/AAPG Eastern Section Joint Meeting held in Pittsburgh, Pennsylvania, USA, 11–15 October 2008. X. Xie, U. of Wyoming; Y. Liu,1; M.M. Sharma, U. of Texas at Austin; and W.W. Weiss, Correlations Co.