Abstract

The U.S. Department of Energy, Petroleum Consulting Services, Universal Well Services, and Canadian Fracmaster have recently performed eight CO2/sand stimulations on four Devonian Shale gas wells in the Appalachian Basin. Four two-stage CO2/sand stimulations were executed with two operators in the Pike and Martin County, Kentucky area. All stimulations involved 120 tons of carbon dioxide (CO2) and up to 47,500 pounds of sand. In addition, there are eleven existing control wells stimulated with four two-stage foam fracs and seven two-stage nitrogen fracs. Production results from these fifteen wells are compared After nine months of production, CO2/sand fractured wells in the Pike County, Kentucky study area are nearly twice as productive as nitrogen gas fraced wells and nearly five times better than the foam fraced wells in the study group. The per well incremental gas production after nine months ranged from 13.5-22.2 MMcf per well for nitrogen gas and foam fraced wells, respectively. Discussion of the CO2/sand treatment parameters, job execution, and a representative pressure/injection response are discussed in detail. As the operators begin to utilize the CO2/sand frac process on more wells, the new stimulation process will become commercially available on a routine basis.

Background/History

The first publicly documented use of the CO2/sand stimulation process was in 1982. Early field testing of the stimulation process proved highly successful for gas well applications. Laboratory testing and numerical modeling continued to evaluate proppants and fluid rheology. Advantages and limitations had been identified by Lancaster and Sinal as early as 1986. By 1987, more than 450 jobs had been executed in Canada. The CO2/sand frac technology has widespread commercial acceptance by operators in Canada. The technology has yet to be fully demonstrated in the U.S. beyond some early testing in the mid 80's. Hence, the U.S. Department of Energy's Morgantown Energy Technology Center initiated a research and development testing and demonstration program to introduce the CO2/sand frac process to gas well operators in the U.S. The stimulation testing was initiated with a 24-well stimulations planned in the eastern U.S. This paper focuses on the results of four 2-stage stimulations. Future plans include the testing and introduction of the CO2/sand frac process to the western U.S. gas well operators beginning this fall with an 18-well test program in the Rockies. Early results of the first five CO2/sand stimulations ever performed in the eastern U.S. show up to an 4.8 fold increase in production in the Pike County, Kentucky, study area. Gas well operators in eastern Kentucky recognized the production benefits of the CO2 process and are considering stimulation of additional wells. Recent technological advances in the job execution procedures and design and operation of the closed system blender have recently been documented. Industry advances in density measurements and blender equipment modification for higher sand concentrations have improved delivery of CO2 and improved overall efficiency. Recent data from Canadian Fracmaster indicate that approximately 1,000 stimulations have been performed on oil and gas wells in Canada since 1982.

Introduction

The U.S. Department of Energy's Morgantown Energy Technology Center is responsible for implementation of a national natural gas research and development program. The key focus of the program is on product development through the introduction, development and demonstration of new technology. The carbon dioxide/sand stimulation process is a good example. These new products must not only be demonstrated but a commercial service must be made available. This project involved the introduction of the CO2/sand stimulation process to gas well operators in a fifteen well study area of candidate and control wells in Pike and Martin County, Kentucky (Figure 1). Two gas well operators offered four candidate wells drilled, cased, perforated, and ready for two-stage CO2/sand stimulations. In addition, they had previously stimulated eleven control wells consisting of seven two-stage stimulations using nitrogen gas and four two-stage stimulations using nitrogen foam.

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