The expected worldwide average recovery factor is around 35% with current development strategies and practices in place. Recoveries in the offshore fields are much lower compared to onshore fields predominantly due to larger well spacing, inadequate reservoir characterisation and shorter life cycles. Efforts are in place to maximise recovery by applying Enhanced Oil Recovery (EOR) techniques. Reservoir rocks saturated with hydrocarbons are complex in both a macroscopic and microscopic scale and this complexity controls the initial quantity and distribution of hydrocarbons and flow behaviour of fluids within the reservoir. Therefore, reservoir characterisation is of utmost importance for the evaluation process in EOR. Core and log analysis along with pressure-production data greatly assist in defining the reservoir and reducing the uncertainties associated with it.
This paper discusses the importance and criticality of core analysis starting from core acquisition, preservation, laboratory studies, analysis to the application of data. Discussions are conducted for the selection of the most appropriate coring technique while lab studies were carried out on cores for reservoir description, estimation of EOR incremental oil and formation damage during injection and production processes. Critical analysis is made to highlight the quality and quantity of core analysis data needed for petrophysical interpretation, understanding the storage and flow behavior during primary, secondary and tertiary recovery stages. Important guidelines are also provided for the selection of number of plug samples for studies, laboratory methodologies, their strengths and weaknesses, and Quality Control (QC)/Quality Assurance (QA) techniques.
The paper further elaborates the recent advances in EOR processes particularly on core analysis, in-situ saturation monitoring, and the interaction between injectants and rock-fluid along with mitigation experiments. Digital core/Pore network modeling is one such emerging technique utilised for the visualisation, characterisation and special core analysis (SCAL) measurements of reservoir rocks. It can provide routine and special core analysis measurements and petrographic analysis which can be used in the quick evaluation of static and dynamic petrophysical properties and flow behavior.