Accelerating the time to first hydrocarbon has become a strategic imperative for oil and gas companies. Special core analysis (SCAL) is part of the process as it provides key input for log interpretation and reservoir models. Because SCAL measurements may take a long time, speeding them up may contribute significantly to reducing the overall time-to-market. In order to face this challenge, ENI labs have implemented several fast SCAL methods. They are used on a regular basis to obtain the m&n parameters needed for electric log interpretation, the capillary pressure curves and the water-gas relative permeability end-points in a considerably shorter time compared to the standard approaches. The paper discusses the physical principles behind the methods and presents operative examples to demonstrate them.
Special core analysis represents a bottleneck for reservoir characterization. While log acquisition and interpretation is a matter of days, SCAL measurements may take months. Log interpretation is probably the area where the issue is particularly problematic. Log registration takes one day; log data are sent to petrophysicists in real time and petrophysicists are able to deliver a preliminary interpretation in a couple of days. At this point they must wait for the lab results. Only when the lab results become available, the final log interpretation is released. Several months may elapse between the preliminary and the final log interpretation. The m&n parameters coming from Ultrafast method reduce this gap to a couple of weeks. Conforming lab times to log times does not improve log interpretation only in terms of time-to-market but it also increases the level of integration among the involved disciplines resulting in a higher overall technical quality.
Capillary pressure (Pc) curves are measured in conjunction with m and n. The new method is not only faster than the conventional porous plate but also faster than a conventional centrifuge test. Typically, conventional centrifugations require 5 to 10 rotational steps for the definition of the Pc curve. One single rotational speed is sufficient with the fast method, meaning that test duration is reduced by a factor of 5 to 10. Compared to the standard centrifuge experiment, the fast method is also less rock-damaging. This feature turned out to be extremely beneficial in cases of weak lithologies that did not resist elevated centrifugal stresses.
