Page 333 - Enhanced Oil Recovery in Shale and Tight Reservoirs

306 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 10.16 (continued).

Table 10.5 Relationship among T 2 , pore size, IUPAC pore classification.
T 2 Relaxation time, ms Pore radius (r), nm Pore type
0.01 T 2 0.1 r p < 2 Micropores
0.1 < T 2 2.5 2 < r p 50 Mesopore
T 2 > 2.5 r p > 50 Macropore

by an anionic surfactant and an amphoteric surfactant, but increased oil recov-
ery by the cationic surfactant tallow amine. They suspected that increased
alkali may change the optimum salinities of the anionic and amphoteric sur-
factants. However, they presented another experimental data showing adding
alkali decreased oil recovery from a cationic surfactant solution. They
explained that the soap and the cationic surfactant had opposite charges result-
ing in a much more hydrophobic mixture and altering the wettability and/or
IFT in an unfavorable way. Alkaline precipitation was observed as the imbi-
bition progressed for the cationic surfactant with alkali added in the 30% TDS
brine (total dissolved salt). Their experimental data showed the nonionic