Process for secondary recovery

DETAILED DESCRIPTION OF THE INVENTION Prior to practicing the process of this invention it is sometimes desirable to open up a communication path through the formation by a hydraulic fracturing operation.
Hydraulic fracturing is a well-known technique for establishing a communication path between an injection well and a production well.
Fracturing is usually accomplished by forcing a liquid such as water, oil or any other suitable hydrocarbon fraction into the formation at pressures of from about 300 to about 3000 psig which are sufficient to rupture the formation and to open up channels therin.
By use of this method it is possible to position the fracture at any desired vertical location with respect to the bottom of the oil-filled zone.
It is not essential that the fracture planes be horizontally oriented, although it is, of course, preferable that they be.
After the fracture has been established, and without diminishing the fracture pressure, a propping agent may be injected into the fraction in order to prevent healing of the fracture which would destroy its usefulness for fluid flow communication purposes.
Gravel, metal shot, glass beads, sand, etc.
and mixtures thereof are generally employed as propping agents.
When sand is utilized as the propping agent particles having a Tyler mesh size of from about 8 to about 40 are preferred (i.
e.
, from about 0.
016 to about 0.
093 inches).
The copolymers of acrylamide and vinyl sulfonic acid employed in this invention comprise recurring A-type units of the formula: ##STR1## and recurring B-type units of the formula: ##STR2## wherein M is selected from the group consisting of hydrogen, sodium, potassium and ammonium and wherein in the said copolymer the weight percent of the A-type units ranges from about 65 to about 95 with the balance being B-type units.
Generally the number average molecular weights of the acrylamide-vinyl sulfonic acid copolymers will range from about 10,000 to about 2,000,000 or more.
The copolymers of acrylamide-vinyl sulfonic acid and salts thereof are known materials which can be prepared by the usual vinyl compound polymerization methods