Interference testing is a process of injecting or withdrawing reservoir fluid, usually from a single well, while monitoring the effects on fluid pressure in surrounding wells. It is particularly useful in determining the directional nature of permeability. In this case at least three monitoring wells are theoretically required to determine the full directional nature of permeability.
In its simplest form, interference testing involves drilling a central injection or production hole surrounded by three monitoring wells, set at an appropriate distance away. Ideally there should be more than three observation wells to provide some redundancy of measurement and to help avoid inhomogeneity being confused with anisotropy. These should also not be located diametrically opposite each other.
The central well can be set up for production with a pump or injection. In the latter case the well would normally have a packer, or packer system, lowered into it on the end of tubing. The monitoring wells are fitted with pressure transducers either set between packers or cemented in place. It is important that the transducers are checked for connectivity to the formation before the test commences.
Injection into or production from the central well then takes place until a clear pressure response is seen in the observation wells. Recovery is permitted to follow. Analytical techniques permit the directional permeability and compressibility or storage behaviour of the reservoir to be determined.
Where gas caps exist production is the only sensible option.
Interference techniques may also be applied to production wells. In this case the testing is usually run over a longer period to yield the effects of permeability change due to dewatering and shrinkage of coals. Here, the process required to arrive at the reservoir behaviour is usually one of history matching.
Sigra can undertake interference tests, either in isolation or as part of a production monitoring programme. Sigra has all the requisite capabilities of reservoir monitoring and injection equipment hardware. It also has the analytical skills to interpret the results.