Pulse Testing: Where do we Stand?

Harmonic pulse testing has long been around as a technique complementary to conventional well testing. It has the advantages of easy employability, applicability during ongoing production and injection, and low cost. Disadvantages are the longer operation times required, the more complicated interpretation methodology, and the limited availability of interpretation tools. The present contribution will summarise history and the principle of harmonic pulse testing, sketch the application possibilities and operational caveats, highlight some of the documented field applications, and discuss the method’s potential and further necessary developments. The application of harmonic pulse testing started with the interference tests measuring pressure responses to injection rate pulses in adjacent wells. This developed into the identification of the pressure response to rate control in the frequency domain. Pulses that are not sinusoidal in shape contain multiple frequency components and when the response is linear, these components can be isolated and interpreted. If the coverage of frequencies is sufficient, an analysis similar to well test analysis can be performed and reservoir properties unveiled. The simplest application of harmonic pulse testing is in a homogeneous reservoir. For an infinite-acting radial flow system, the interpretation will deliver values for reservoir permeability, compressibility, and skin. Wellbore storage can be taken into account as well. Extensions have been formulated to a reservoir with a partially penetrating or horizontal well, a closed reservoir, and a reservoir bounded at one side with a sealing fault. For injection wells in geothermal applications, correlations that include multiple mobility zones are available, which facilitates the identification of the location of a thermal front. A successful analysis depends on the availability of good data. The main factors for the data quality are the accuracy of the operational control and the accuracy of the measurements. It is important that the transition between the pulses occurs fast and reproducibly; suboptimal control quickly reduces the number of useable frequency components. Further, the small variations in pressure that constitute the frequency content require precise determination with downhole measurements. Harmonic pulse testing has great potential in monitoring reservoirs, storages, and geothermal systems, as it is proved by the successful case histories we present. We feel that the development of theory in a more diverse suite of well and reservoir configurations is possible and beneficial. In particular the combination with geomechanics, for instance in reservoirs that are fractured or otherwise stress-sensitive, may have large potential. Further, we see potential in studying the effect of harmonic temperature variations. The application of harmonic pulse testing would be greatly stimulated if tools were available that guide the user through the interpretation and matching steps.