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Abstract

A continuous process of hydraulic fracturing of a well with in situ nitrogen foam generation, comprising the steps of: (a) preparing an aqueous solution of NH.sub.4 Cl having a concentration of from 2.0-6.0M; (b) preparing an aqueous solution of NaNO.sub.2 having a concentration of from 6.0-9.0 M; (c) preparing an aqueous solution of acetic acid having a concentration of about 40% v/v; (d) adding hydroxyethylcellulose (HEC) to said NH.sub.4 Cl solution at a concentration of from 0.3-1.2% w/v to form a viscosified NH.sub.4 Cl solution; (e) simultaneously pumping said viscosified NH.sub.4 Cl solution and said NaNO.sub.2 solution to form a mixture having a equimolar amounts of NH.sub.4 Cl and NaNO.sub.2 thereby initiating an equimolar reaction between the components of said mixture; (f) pumping the acetic acid solution into the equimolar mixture of NH.sub.4 Cl solution and NaNO.sub.2 solution, so as to initiate foam generation, while keeping the pH of the mixture between 4.75 and 5.50; (g) injecting a cushion of the generated foam into the well (pre-flash); (h) initiating the fracturing of the formation by injecting foam to which is added sand as a propping agent, said agent being added to the viscosified NH.sub.4 Cl solution, in amounts varying from zero to 0.92 kg/l of the foaming mixture; and (i) after the fracturing, injecting in the well a cushion of sand-free foam (over-flash) of the same composition as the fracturing foam.

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