Pulsed well testing offers an alternative way to determine reservoir properties over a significant area. The benefits that it offers are well to well measurements of transmissibility x thickness and storage terms without having to wait for the definition of a characteristic type curve. Rather the lag and amplitude of pulses related to production from or injection into a well are measured. This has the advantage that it may be applied to a field from which other steady production is occurring.
The technique is also useful in that it can be used as an alternative to interference testing as it provides a well to well, directional value of transmissibility. It is particularly useful when used in multiple hole tests.
In the figure it can be seen that if well P1 is tested alone it yields a value of mean transmissibility. If well P1 is then fitted with a pressure transducer and well P2 is tested then it yields a value of mean transmissibility at that location and a value with directional component between wells P2 and P1. This process can be continued through wells 3 to 5 by leaving a pressure transducer in the previous well and producing or injecting in the well just drilled. Doing this provides a statistically relevant sample of five measurements of mean permeability and ten directional measurements as is shown in the table.
While this is fewer than the total number of permutations that could be tested, it is one where the pressure transducers do not need to be removed until the test process is complete. It thus leaves a five spot pilot test pattern with fairly well known (usually single phase) properties before production commences.
In situations where the principal directions of permeability may be estimated from structural information or stress directions, it is possible to calculate the major and minor permeabilities. Testing wells will yield two measurements of mean transmissibility and one of directional transmissibility. The mean transmissibility is theoretically the square root of the product of the major and minor. Therefore if the mean permeability is known and one principal value is also known then it is possible to calculate the other principal value of transmissibility.
Pulse testing requires very sensitive pressure sensing in the observation wells and negligible well bore storage. Sigra has the pressure sensing technology to achieve this. For normal well spacing it is only suitable for high transmissibility reservoirs but can be used for quite low transmissibilities if the wells are drilled at close spacing.