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Improvement of Fracturing for Gas Shales
Project Number
07122-38
Goal

The goal of this project is to develop non-damaging, productivity enhancing, low environmental impact fracturing techniques for gas shale reservoirs and demonstrate their performance through field tests.

Performer

University of Texas (UT), Austin, TX 77204-4004
Daneshy Consultants Int’l, Houston, TX 77079
BJ Services, Tomball, TX 77375

Background

The reliability of hydraulic fracturing as a means for enabling the economic viability of wells completed in the Barnett shale and other more recently developed unconventional shale gas reservoirs need to be improved. Permeability reduction caused by the fracturing fluid and limited fracture length apparently limit productivity in new plays. Non-damaging fracturing fluids and ultra-light weight proppants that minimize the volume of water that must be utilized and disposed of are needed. Ultra-light weight proppants and foam fluids could be combined to meet this need.

This project will be carried out in two phases: fluid development and field demonstration. The first phase will include: determination of physical/mechanical properties of ultra-low density proppants developed by BJ Services at different closure stress and temperature environments; development of new conventional and foam fracturing fluids with an emphasis on low liquid content, environmental sensitivity and reduced use of polymers; and development of an engineering methodology utilizing these new systems for fracture treatments in Barnett Shale gas wells. The second phase will include a field demonstration of these new fracture treatment systems and post-fracture treatment evaluation.

Impact

The impact of this project could be a significant improvement in the productivity of the typical Barnett shale gas well. This would result in accelerated gas production and increased reserves per well across the remaining undeveloped areas of the Barnett play. To the degree that the methodology could be applied to other shale gas plays, it would result in accelerated production and increased reserves in those plays as well. It might also have applicability to tight gas sands. There may also be economic enhancement and environmental benefits through a reduction in the volume of water required for fracturing treatments (up to an order of magnitude lower than conventional slick water treatments).

Accomplishments (most recent listed first)

The Technology Status Assessment has been completed. The task to determine proppant properties has been completed.

The researchers have designed a plunger to measure the strength of single particles. Thus far, strength has been measured in this way for three proppants. The mechanical properties of proppant packs and single proppents have also been measured for three proppants. Proppants that produce fines have been identified. A report has been written on proppant property determination. An API conductivity cell has been obtained and assembled. Foams have been formulated that can potentially be used as proppant-carrying fluids. Stability of foams has been studied.

A presentation titled, “Fracturing with Light Weight Proppants” was presented at the RPSEA Unconventional Gas Conference, April 6-7, 2010, in Golden, CO.

A website has been created for the project for technology transfer.http://www.cpge.utexas.edu/?q=People [external site]

Current Status

The key tasks are outlined below.

Determining proppant properties. The research team at the University of Texas will determine the physical and mechanical properties of ultra low density proppant developed by BJ Services and its chemical compatibility with existing fracturing fluids. These properties include sphericity, size distribution, and density. The mechanical properties will also be determined, including crush strength and deformability. Tests will be repeated at various temperatures and closure stress regimes and the chemical properties and compatibility of the proppants will be determined. The purpose of these tests is to ensure that there are no undesirable reactions among the fracturing fluids, additives and proppants. This task is complete.

Determining flow capacity. The proppant bed flow capacity will be determined under multiple closure stress and temperature environments. This task consists of determining the flow capacity of the new proppant (with slick water and foams) under several different combinations of temperature, closure stress, and proppant concentration. These tests may require development of new testing procedures and equipment. The outcome will be tables of data for use in the design of actual hydraulic fracture treatments. To date, an API conductivity cell has been acquired and assembled.

Formulating foam fluids. Foam fracturing fluids will be formulated with an emphasis on low liquid content, environmental sensitivity, and reduced use of polymers. The work done under this task will consist of the determination of rheological properties of various quality foams, selection of a suitable polymer content to yield a foam with suitable rheological properties, and determination of the foam bubble size and its relationship to viscosity and rheological properties at different shear rates and foam qualities. This is needed for optimization of foam properties. Thus far, stability of foam columns has been measured and proppant transport through foam columns is being studied.

Collecting fracturing data. The engineering data for the use of combined fluid-proppant systems will be collected, including fluid leak-off coefficients (at various foam qualities and temperatures) and friction pressure for flow in tubing and fracture. The collection of some of this data may require the development of special testing equipment and algorithms, since foam quality will be a dynamic property that will be changing during flow and because of it.

Designing fracture treatments. Engineering methodologies will be developed for fracture treatments in Barnett Shale gas fields. Effective field use of the new materials requires a step-by-step procedure, including guidelines for fluid selection and formulation to match formation properties, selection of proper pad volume, selection of proppant concentration and volumes of slurry containing the proppant, and a basic pumping schedule. The formation characterization will be obtained from a field operator research partner. Also included will be computations of expected surface pressures. Since the main purpose of the fracturing treatment is to create a long propped fracture, the computations must include a relationship between treatment design and created fracture geometry, as well as an estimation of the production increase that will result from the treatment.

Performing field test. In Phase II, several treatments will be designed and executed in Barnett Shale gas reservoirs and their outcome compared with other existing methods. Two to five treatments (depending on cost) will be designed for a single field with wells already stimulated in a traditional way (for comparison). This phase will require close collaboration among The University of Texas, BJ Services, and the field operator. It is anticipated that the engineering work will be done at UT, equipment selection and mobilization will be carried out by BJ Services, and the operator will supervise the actual field execution.

Evaluating fracture treatments. The fracture treatments performed during the field tests will be evaluated from several different perspectives: simplicity and ease of fracturing fluid preparation and mixing, ease of proppant handling and pumping, ease of CO2 use, reduction of fracturing fluid volume, treatment clean-up, and productivity improvements. Production data will be analyzed before and after the stimulation to establish the effectiveness of the new technology.

Project Start
Project End
DOE Contribution

$691,821 (includes both Phase I and Phase II)

Performer Contribution

$411,663 (includes both Phase I and Phase II)

Contact Information

RPSEA – Charlotte Schroeder (cschroeder@rpsea.org or 281-690-5506)
NETL – Virginia Weyland (Virginia.Weyland@netl.doe.gov or 281-494-2517) 
University of Texas – Dr. Kishore K. Mohanty (kishore.mohanty@engr.utexas.edu or 512-471-3077)

Additional Information

Topical Report [PDF] - November, 2009