科研之友
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摘要
Restoration of carbonate reservoir core material for special core analysis has been debated in the literature for some time. An important goal of core restoration is to reproduce initial reservoir wetting properties because wettability dictates important reservoir parameters, such as capillary pressure and relative permeability of oil and water. It has previously been found that acidic polar components in crude oil dictate the wetting properties in carbonate core material. In this paper, the effects on chalk wettability from crude oil flooding, core aging, and mild core cleaning were investigated experimentally. The experimental results confirmed that adsorption of acidic polar components is an instantaneous process and that a dynamic equilibrium was achieved with a specific adsorption capacity of the initially very water-wet chalk surface. The crude oil flooding reduced the water wet surface area. Core aging for 2 weeks at the test temperature reduced the water-wet surface area even further, which appeared to be closer to a thermodynamic equilibrium. Spontaneous imbibition tests confirmed mixed-wet conditions, regardless of aging or not. A second oil flooding was performed on a mildly cleaned, initially mixed-wet chalk core. The dynamic adsorption equilibrium of polar organic components was now drastically reduced. On the basis of the results from this experimental study, the wetting in outcrop chalk is dependent upon the amount of crude oil allowed to contact the rock surface and the time period of contact, i.e., the aging period. A core restoration procedure involving mild core cleaning and a controlled small volume of crude oil injection could be a more optimal core restoration procedure for reservoir chalk and limestone cores.
- 出版日期2016-9
