Analysis of numerous injection/falloff tests in the field, primarily on coalbed methane wells, has led to a better understanding of the requirements for proper injection/falloff testing. Because most of the formations do not flow prior to testing, test design is difficult and many of the testing procedures must be modified during the test itself. If a testing program is not carefully designed and implemented, erroneous results for permeability and skin factor can be obtained, even though the analysis results appear reasonable.
This paper outlines some general guidelines for injection/falloff testing of coalbed methane and other low permeability reservoirs. Using several field-based examples, potential analysis pitfalls are highlighted including 1) injection above fracture pressure, 2) non-stable reservoir pressure prior to testing, and 3) a poor connection between the wellbore and reservoir. Any of these conditions may result in pressure responses which appear analyzable, but which give misleading or erroneous results.