In conventional oil and gas reservoirs, the use of prefrac pump-in tests, in conjunction with analysis of the shut-in pressure response, has been a tremendous asset in Improving fracture stimulation designs. Since its introduction in 1979, many modifications and improved analysis techniques have evolved to increase the value of "minifrac" tests. In recent years, the popularity of completing wells in coal formations has led to the use of minifrac applications in these wells as operators attempt to better understand how coals respond to hydraulic fracturing. Although some operators have enjoyed success with minifracs, the usefulness of these types of prefrac tests has been limited as compared to applications in conventional gas reservoirs.

In fracture stimulation of coalbed methane wells, the use of minifrac tests and other pump-in tests has sometimes resulted in abnormally high injection pressures during the subsequent fracturing treatment. Many times the result has been an early screenout during the proppant placement. Some operators have abandoned the use of minifrac type pump-in tests for fear of creating pressure problems that would jeopardize the stimulation treatment.

In this paper, problems attributed to minifrac tests are described, along with explanations for many of these occurrences. Also included are successful applications of pump-in tests and a modification to improve fluid loss calculations. Recommended procedures to minimize the possibility of creating high Injection pressures are given. Field examples from the San Juan Basin, Piceance Basin, Black Warrior Basin and the Central Appalachian Basin are used to illustrate problems and support the recommended procedures presented.

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