The project goal is to develop second-generation materials with sufficient structure and mechanical integrity to allow application as proppant or gravel pack materials.

Idaho National Laboratory
Idaho Falls, ID

University of Tulsa
Tulsa, OK

Haliburton Energy Services
Duncan, OK

Since its introduction, hydraulic fracturing has been the prime engineering tool for improving well productivity either through bypassing near-wellbore damage or by actually stimulating performance by increasing the effective wellbore radius to flow. Intrinsic to the application of fracturing technology is the use of proppants. In a general sense, proppants can be viewed as a physical means to "prop" the fracture open. Critical issues associated with the application of proppants include placement, collapse, flow-back, and clean-up of viscous carriers following placement, while problems continue to exist in scale build-up, fines migration, and paraffin deposition. With respect to those issues that impact fracture conductivity, the application of small-volume chemical treatments or squeeze/workover jobs has been the industry standard practice when remedial action is necessary.

Despite the recent developments in hydraulic fracture technology, high fracture conductivity is frequently not realized due to the inability to effectively remove carrier additives (gels, fluid loss additives) or maintain proppant pack flow integrity over time (scale and paraffin build-up or fines migration).

Project Results
This project is expected to develop proppant materials with the ability to selectively release or activate materials to either maintain or improve fracture conductivity through the use of bio-catalytic systems.

Project researchers have accomplished the following tasks:

• Selectively tested a promising spore. A guar-degrading organism, Geobacillus kaustophilus, was successfully isolated and reproduced in concentrations required for laboratory testing. Geobacillus kaustophilus is an aerobic, spore-forming rod that can grow at temperatures up to 70° C., has a salt tolerance to 20% (w/v), and expresses an enzymatic system that can degrade a variety of guar gums. The culture is stable.
• Through laboratory experimentation determined the bacillus envelope of activity (pH, temperature, salinity, etc.) in likely oilfield conditions.
• Demonstrated bead competency at desired conditions for inclusion in proppant packs.

Benefits
The success of the "smart" proppant technology development project will improve clean-up and maintenance of fracture conductivity following fracture jobs. With respect to issues that impact fracture conductivity, application of small-volume chemical treatments has been an industry standard practice when remedial action is required. Unfortunately, these treatments have low success rates; ineffective delivery of chemicals to the damaged area is often the cause of failure. Incorporation of the chemical treatment with proppant placement has the potential to provide a cost-effective solution to a significant problem in the oil and gas industry.

Project Summary
A smart proppant is composed of materials that are designed to interact with the physical or chemical properties of their surroundings to produce a predetermined, favorable effect. Specifically, porous materials with structural characteristics similar to those of existing proppants are being engineered with selective coating and membrane materials to offer predetermined release or activation of desirable compounds that affect or remedy fracture conductivity. The engineered systems are conceptually based on existing technology that is simplistically described as a porous particle encapsulated by a nomex membrane.

Inherent in the structure of the developed materials is the ability to selectively release or activate materials of interest to maintain or improve fracture conductivity. Materials of interest include scale inhibitors, frac gel breakers, paraffin inhibitors, acids, etc. Selective release or activation is achieved by engineering both the internal solid phase as well as the encapsulating membrane. Because the remedial agent will be incorporated within the proppant, effective and uniform delivery is not an issue. Engineered features include chemical derivitization of the porous solid surface, incorporation of solid reactants/absorbents/adsorbents (e.g. activated carbon), and membrane thickness and nominal pore size distribution and density.

Numerous technologies have been described for the encapsulation of viscosity breakers. These include utilization of impermeable membranes that are designed to crush, dissolve, or rupture (on osmotic swelling), as well as permeable membranes that allow slow release through dissolution. Additionally, granular formulations with low dissolution rates have been used, as have “porous grain” technologies, dissolvable coatings, microemulsions, and macroemulsions.

This novel effort represents a composite approach utilizing unique technology to encapsulate finely divided solid materials within a porous nomex matrix to produce porous beads or to produce porous membranes or coatings on larger particles that are thermally stable to 350° C. The encapsulated, finely divided, solid material can be selected to give the membrane specific properties in terms of the permeability of the membrane, adsorption and desorption of target compounds, catalysis, and chemical reactions. The effort is expected to yield a robust polymeric carrier system for active agents with favorable release rates, activity profile, and appropriate longevity. A variety of materials (including chemical, biological, or physical) can be included in the porous matrix during the manufacturing process.

The application of chemical (e.g., oxidizers) technology is readily accepted as appropriate, with the only issue being controlled release. Biocatalysts, however, does not have this general utility or acceptance for several reasons. Biocatalytic (specifically enzymatic) systems have been evaluated in the past for application as visbreakers and were found to have an insufficient half-life for application. Although the enzyme(s) have insufficient thermostability, the organisms that produce the enzymes are extremely robust and are not limited by this restriction. This effort highlights the inclusion of active biomass in engineered systems for the continued supply of catalytic materials at the expense of the viscosifying agent. This approach potentially will 1) mitigate thermostability issues of isolated enzymes, 2) provide a dynamic source of catalysis, and 3) allow for the induction of additional enzyme systems and provision of required co-factors.

(June 2006)
This project was completed in April. The Final Report should be available by October.

$469,000

$43,000 (8% of total)

NETL - Jim Barnes (jim.barnes@netl.doe.gov or 918-699-2076)
INL - Gregory Bala (gb3@inl.gov or 208-526-8178)