The objective of this project is to research, develop, and test new techniques for creating extensive conductive hydraulic fractures in unconventional tight gas reservoirs. The project has two main components: 1) development and analysis of a database of information from hundreds of fracturing treatments applied in U.S. basins that can be used to relate production performance to stimulation practices, and 2) development and application of a new type of dynamic fracture conductivity test for laboratory investigations of fracturing practices in tight gas reservoirs.

Texas Engineering Experiment Station (TEES), Texas A&M University, College Station, TX

Tight gas reservoirs are found at many depths. The key to economically producing gas from tight gas sand formations is to create long, highly conductive flow paths (hydraulic fractures) to stimulate flow from the reservoir to the wellbore. This project aims to develop better methods for optimizing hydraulic fracture treatments in unconventional tight gas reservoirs by evaluating the productivity achieved in hundreds of completed field treatments and by carrying out laboratory measurements of the conductivity of fractures created with high-rate proppant fracturing techniques.

Laboratory testing will focus on development and application of an entirely new conductivity test—the dynamic fracture conductivity test. In these tests, the laboratory researchers will inject proppant/frac fluid slurries under realistic field conditions, then shut in the conductivity cell to simulate the conditions under which conductivity is actually created. By applying this fresh approach to determining the manner in which proppant is placed and fracture conductivity is created in low-permeability gas wells, the project team hopes to develop novel, systematic treatment design procedures that will inform the next generation of hydraulic fracturing technology for tight sandstone reservoirs.

Results
The project performer has accomplished the following:

• Field treatment. The project team is developing an Access database that contains field treatment data, organized by geographic location, and hydraulic fracture treatment design data, organized by treatment type, for the purpose of building an expert system to determine the optimum completion and stimulation methods for typical tight gas sand reservoirs. The field treatment data will be obtained from over 2,000 published SPE (Society of Petroleum Engineers) papers covering a variety of fracture treatment types in a minimum of three U.S. basins, including the East Texas, West Texas, and Green River basins. This fracture stimulation data, along with publicly available production data, will be used to determine how short-term and long-term production behavior in a particular area has varied as a function of the fracture treatment that was applied. The insights developed from this work, coupled with inputs from industry experts, will be used to design appropriate testing and analysis scenarios for the laboratory work that follows.
• Dynamic fracture conductivity tests. The project team is developing a new experimental protocol for a dynamic fracture conductivity test capable of simulating the proppant placement conditions that occur during an actual frac treatment. Subtasks include modification of an existing American Petroleum Institute (API) fracture conductivity cell, a load frame to apply closure stress, and a flow system with leak off capability, pumps, and a system for blending proppant into a fracture fluid and pumping a proppant/frac fluid slurry. Cores from three or more tight gas provinces in the United States will be used to conduct a series of 30 or more experiments to compare the conductivity measured with dynamic conductivity tests with the results obtained with standard static conductivity tests conducted with the same proppant loading. Significant differences in results between the standard static conductivity tests and the newly developed dynamic conductivity tests will be documented. Researchers have designed and built the experimental apparatus setup as shown in Figure 1 to conduct the dynamic facture conductivity tests. The main components of the apparatus are a mixing tank to prepare slurry, a high-pressure pump to pump the slurry at high-pressure condition (Figure 1.a), a modified API fracture conductivity cell, a load frame to apply closure stress (Figure 1.b), a flow system with leak off capability, and auxiliary equipment. To date, equipment has been assembled and some experiments have been conducted to test the equipment. Pumping a slurry of fracture fluid carrying proppant at high pressure and elevated temperature is a challenging task in the laboratory. Researchers are currently testing the major components in the system, in particular the high-pressure pump, the heaters used to warm the slurry before entering the cell, and the back-pressure regulators used to maintain pressure in the cell. When the equipment shakedown is completed within the next month or two, the project performer will begin a series of experiments aimed at measuring gel damage to the conductivity of a propped fracture.
• Gel damage investigation. The literature on gel damage in tight gas sands is being surveyed and, based on the results, a commonly used polymer system will be selected for gel damage studies. These will include a series of experiments to systematically identify the conditions that lead to gel damage under dynamic conditions. The focus will be on damage in the fracture itself; however, the experimental apparatus includes leak off into the matrix, so an investigation of the effect of unbroken polymer on the matrix can be carried out if it appears to be important. For a given proppant concentration and polymer concentration, a minimum of 50 experiments for a range of temperatures will be conducted. The results will be used to document the occurrence of gel damage and the interplay between proppant concentration and polymer loading and to formulate general guidelines for proppant concentration/polymer loading conditions that lead to minimal gel damage.

Benefits
The proposed work is aimed at improving hydraulic fracturing practices in tight gas reservoirs that cannot be economically developed without the use of hydraulic fracturing. The results from this project will directly impact understanding of the relative effectiveness of various fracturing practices in tight gas basins throughout the United States. This will lead to better treatment designs, higher-productivity completions, lower completion and treatment costs, and additional reserves.

Summary
This project was initiated on April 3, 2006. The project kick-off meeting was held May, 2006. Task 1, preparation of a Research Management Plan, has been completed. For this task, the performer developed a work breakdown structure and supporting material that concisely summarizes the objectives and approach for each task, including detailed schedules and planned expenditures.

(July 2007)
This project does not have funding to continue. The final report is due.

$334,294

$83,574 (20% of total)

NETL – Betty Felber (betty.felber@netl.doe.gov or 918-699-2031)
Texas A&M/TEES – Ding Zhu (ding.zhu@pe.tamu.edu 979-458-4522)