The Under-Utilised Formation Tester – The Reservoir Characterisation Instrument (RCI) Case
The RCI is a modular formation testing and sampling tool designed to provide a more complete description of reservoir fluid and behavior. The RCI2s modularity provides the flexibility to record formation pressures and sample fluids in a wide range of geological environments and borehole conditions.
It includes a controllable packer section for variable-volume and variable-rate drawdown, small and large displacement pumps, sample tanks, multi-tank carrier system for sample recovery, and SampleView, an infrared analyzer module for downhole fluid characterization.
The RCI tool is generally applied in formation pressure tests and in fluid sampling for PVT analysis. For pressures, the packer is controlled to make contact with the formation, a drawdown applied and pressure of the formation is recorded. For the samples, the displacement pumps are utilised to rid the formation of mud cakes formed by drilling muds before the formation fluid sample is taken
RCI DATA ANALYSIS AND CASE FOR PROPER UTILISATION.
Most times the RCI tool is applied in formation pressure tests and fluid sampling for PVT analysis. The pressures so obtained are usually used to estimate reservoir pressures and also to estimate the extent of depletion of producing reservoirs and these information can be utilised to optimise future development or production strategy. The PVT analysis performed on the obtained fluid samples are analysed to yield properties such as viscosity, compressibility and mostly fluid composition.
Worthy of note here is that there are lots more outputs from an RCI logging job, other than pressure and fluid samples, which are hitherto ignored or under-utilised as the case may be. Such outputs include the mobility in mD/cP and temperature data in F.
Note here that formation permeability can be more accurately estimated from the mobility information, represented in mD/cP if the fluid viscosity (in cP) is known and the fluid viscosity is obtainable from PVT analysis of the fluid samples.
Furthermore, formation temperature gradient could be established on a reservoir basis and used to estimate temperature at any point in reservoir temperature estimation. This could be done based on the temperature obtained at the various pressure test points.
Finally, on a personal opinion note, fluid contacts and free water level (FWL) in a reservoir could be established more accurately with the transition zones properly obtained if enough pressure test are performed using the RCI, say every foot, in addition to the usually obtained fluid type (based on pressure gradients) and FWL.