Pore geometry is an effective parameter in controlling the fluid flow in porous media especially in presence of wettability alteration. However, Heavy oil displacement behavior by hydrocarbon solvents at different wettability conditions under the influence of pore geometry and connate water in five-spot models remains a topic of debate in the literature.
In this work several one-quarter five-spot network patterns along with those obtained from thin sections/SEM pictures of sandstone and carbonate rocks were etches on glass surfaces. The models were initially saturated with the heavy crude oil, and used to perform a series of solvent injection experiments. Wettability of the micromodels was altered towards strongly water-wet and oil-wet conditions by applying chemical procedures. Macroscopic displacement efficiency of solvent floods at various strongly wetted media by considering the effect of connate water has been studied. Influence of effective pore geometry parameters on oil recovery and microscopic displacements was investigated during miscible floods. Precise analyses of the high quality pictures, provided continuously during injection process, were used to explore the solvents' displacement behavior.
The results of the experiments performed on the network patterns demonstrated that higher coordination number along with lower ratio of pore-throat size of the flow paths could improve the displacement efficiency. The trend of oil recovery in real heterogeneous patterns was among those observed in network patterns with coordination number of three and four. Heterogeneity of the media reduced the miscible displacement efficiency because of more oil-bypassing and less direct contact. The microscopic observations confirmed that the presence of connate water in strongly water-wet medium could improve the final recovery, while its extent greatly depends on the coordination number of the media. Although wettability was an effective parameter in oil displacement, but its effect in absence of connate water was at a lower level.
Many difficult problems are understandably associated with the enhanced recovery of crude oil. These enhanced oil recovery problems are due to such factors as the complex nature of fluid flow in underground reservoirs and the inability of producers to exercise control over the distribution and flow of fluids in the reservoirs. In this respect, underground reservoirs of crude oil typically consist of vast numbers of often small, interconnected pores and cracks in sandstone and carbonate rocks. Not only are single reservoirs typically composed of several or many different layers of rock having significantly different permeabilities, but the flow of fluid through the reservoir rocks is along a great many small, extremely tortuous and non-uniform channels and fissures. Thus a major problem is that when attempts are made to displace such oil by another fluid, the oil tends to be bypassed as the displacing fluid follows paths of lesser flow resistance.
Pore geometry is an effective parameter in controlling the fluid flow in porous medium. The sizes and shapes of the pores are largely governed by the sizes and shapes of the grains, although subsequent solution enlargement can result in larger than normal rounded pores.