Dynamic Laboratory Wettability Alteration

We present experimental wettability alteration results in originally strongly water-wet, outcrop chalk core plugs using a static and two dynamic aging methods. Dynamic aging with continuous crude oil injection during the entire aging process exhibited greater reduction in water-wetness of the strongly water-wet chalk plugs than static aging without flushing. Two dynamic aging procedures were tested to find an optimal flooding rate for the most efficient reduction in water-wetness: (1) a constant crude oil flooding at 3 cm(3)/h using variable aging times (48, 96, and 192 h) and (2) a constant aging time (96 h) with variable flooding rates (1, 3, and 5 cm(3)/h). The aging temperature was kept constant in all tests (90 degrees C), and the impacts from varying aging times, pore volumes injected, and crude oil injection rate on the wettability alteration process were investigated. Aging was performed on consolidated, porous chalk samples with initial water present in the pore space. It was shown that static aging, i.e., aging in a stagnant, limited amount of crude oil, and dynamic aging, i.e., with continuous flooding of crude oil, performed equally well in terms of average Amott-Harvey water indices (I-w similar to 0.6) for short aging times (72 h or less). For longer aging times, the static approach failed to established an Amott-Harvey water index under I-w = 0.25 and required 3 times as long of an aging time compared to dynamic aging (7 days for dynamic or 24 days for static required to establish I-w similar to 0.25). Amott-Harvey water indices lower than I-w = 0.25 were established with dynamic aging for shorter aging times (less than 12 days). At a given constant aging time (96 h), it was found that wetting was sensitive to the crude oil injection rate and that there exists an optimal crude oil injection rate with the greatest change in wettability.