@article{VSGU_2011_8_a12,
     author = {V. I. Astaf'ev and P. V. Roters},
     title = {Modeling of doubly periodic system of producing wells. {2.~Productivity} index},
     journal = {Vestnik Samarskogo universiteta. Estestvennonau\v{c}na\^a seri\^a},
     pages = {118--127},
     year = {2011},
     number = {8},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VSGU_2011_8_a12/}
}