Determining Optimum Aging Time Using Novel Core Flooding Equipment

Abstract

New methods for enhanced oil recovery are typically developed using core flooding techniques. Establishing reservoir conditions is essential before the experimental campaign commences. The realistic oil-rock wettability can be obtained through optimum aging of the core. Aging time is affected by temperature, crude oil, formation brine, and coreplug lithology. Minimum time can significantly reduce the experimental cost while insufficient aging time can result in false conclusions. Real-time online resistivity measurements of coreplugs are presented and a novel method is introduced for determining the optimum aging time regardless of variations in crude oil, rock, and brine properties. State of the art core flooding equipment has been developed that can be used for consistently determining the resistivity of the coreplug during aging and waterflooding using advanced data acquisition software. In the proposed equipment, independent axial and sleeve pressure can be applied to mimic stresses at reservoir conditions. 10 coreplugs (four sandstones and six chalk samples) from the North Sea have been aged for more than 408 days in total and more than 29000 resistivity data points have been measured to consistently investigate the change of wettability during aging. At 60°C and 100 bars a homogeneous sandstone coreplug attained optimized wettability after 5 days, a heterogeneous coreplug required 30 days of aging. Chalk coreplugs needed 45 days of aging. This shows that coreplugs originating from the same field, when aged at equivalent conditions can have significantly different aging times because of minor variations in the coreplug properties. No fixed aging time can be recommended on the other hand a method is recommended which can determine the extent of aging. Coreplug aging patterns were studied for variation in pressure (20 to 130 bar) and temperature (60 to 130°C). Based on these experiments an algorithm has been developed which distinguishes the effect of wettability alteration, pressure, and temperature on coreplug resistivity. This study highlights the use of hydraulic oil to avoid release of fluids in the effluent pipes during the aging process. Furthermore, the described multiple monitoring devices are useful in detecting any experimental error that may have occurred during mounting of the coreplug in the core holder. Thus imperfect waterflooding which can otherwise produce misleading data can be avoided. The presented equipment can instantly and continuously calculate the mineral wettability throughout the aging process at any pressure, temperature condition and for any combination of rock and crude oil. Thus, using the stated core flooding equipment can not only decrease the cost and time of doing aging and waterflooding studies but can also significantly increase the accuracy in conducting core flooding experiments.

Wettability Indicator Parameter Based on the Thermodynamic Modeling of Chalk-Oil-Brine Systems

“…Figure shows the aging effect on the final oil recovery from spontaneous imbibition tests. Although variable optimum aging times are reported in the literature, the time required to achieve uniform initial wetting conditions upon contact with the crude oil is most likely unique to each core sample and experimental conditions …”

“…Although variable optimum aging times are reported in the literature, the time required to achieve uniform initial wetting conditions upon contact with the crude oil is most likely unique to each core sample and experimental conditions. 111 The purpose of the aging time is to ensure equilibrium between the rock-brine-crude oil. The fact that the recovery changes depending on the aging time (Figure 7b) indicates that the core had not reached the equilibrium with the oil and the water during the aging procedure and the cores most likely have different initial wetting conditions.…”

Experimental investigating of the effect of CO2 injection parameters on asphaltene precipitation and formation damage in live oil

“…At last, the core was devoured in dead oil and put in the oven at formation temperature for 40 days. 28 V water (after saturation) − V water (exited after oil injection) = V connate water (11) CO 2 core flooding To execute CO 2 flooding experiments and evaluate the effect of different parameters including pressure, injection rate, and gas composition on formation damage, a core flooding setup was prepared. Another purpose of core flooding is to investigate oil recovery during CO 2 injection in different conditions.…”

Low Salinity Water–Polymer Flooding in Carbonate Oil Reservoirs: A Critical Review

“…Then, the core is allowed to age for 5 to 40 days to restore the wettability of the reservoir. [64,73] During the aging period, the system's pressure and temperature are kept constant.…”