To compliment the laboratory testing, and to further explain the formation damage mechanisms happening with in the core plugs, it is vital that a full suite of geological analysis in undertaken to fully comprehend the various formation damage mechanism(s) that are taking place and influencing permeability results.We recommend the following analysis -
XRD analysis, in conjunction with dry SEM analysis, on untested core material would give an indication of the bulk rock mineralogy and also the clay minerals present.
For the following methods of analysis an untreated sample should be analysed in order for a direct comparison to be draw between what is in situ and what has been altered by the testing processes. An untreated Dry SEM prior to testing also allows confirmation that the material is in a suitable condition to represent the reservoir.
Dry SEM investigates solid damaging mechanisms, i.e. drilling mud solids invasion, fines migration and/or scale precipitates.
Cryogenic SEM investigates fluid damaging mechanisms, i.e. retained drilling mud filtrate/chemical fluids and retained brine (in excess of formation brine that may be present as a thin layer associated with all grain surfaces).
For oil leg samples two types of cryogenic analysis are undertaken, a pore-filling and a pore-lining type. This second method enables the viewing of damaging mechanisms that previously would have been masked by the oil.
Thin section analysis will also aid in the identification of solid damaging mechanisms and will give an indication as to the depth of invasion of drilling mud solids, the significance of fines migration.
Corex papers referring to this subject can also be obtained.
Below are related papers published by Corex that may be of further interest.