Acid injection and fracturing method for porous subterranean geological formation

An acid injection and fracturing method with downhole corrosion inhibition of an oil and gas well in a porous subterranean geological formation, comprising:

• injecting an acidic treatment fluid into the oil and gas well at a first pressure through metal tubing into pores of the porous subterranean geological formation to react with and/or dissolve rock of the porous subterranean geological formation and thereby increase a permeability of the porous subterranean geological formation;
• then
• fracturing the rock at a second pressure that is greater than the first pressure;
• wherein the acidic treatment fluid is an aqueous solution comprising (i) a corrosion inhibitor composition comprising gelatin and an intensifier selected from the group consisting of CuI, KI, and formic acid, and (ii) 14 to 16 wt. % of HCl, based on a total weight of the acidic treatment fluid,
• wherein the gelatin is present in the acidic treatment fluid in a concentration of 0.5 to 2.5 wt. % per total volume of the acidic treatment fluid,
• wherein the intensifier is present in the acidic treatment fluid in a concentration in a range of from 0.01 to 0.05 wt. % per total volume of the acidic treatment fluid,
• wherein the gelatin has a Bloom number in a range of from 50 to less than 220, and
• wherein the gelatin has free carboxyl groups in a range of from 78 to 115 mmol per 100 g of protein.