Perforation of oil and gas wells by a high-velocity jet of polymer solution

Abstract

ABSTRACT: The work is devoted to the development of a technological process for perforating oil and gas well casing strings by a high-velocity jet of a polymer solution. The proposed method of well perforation refers to methods for the secondary opening of productive deposits in the well by hydrojet perforation of the casing strings, annulus cement ring (stone) and rock. The new knowledge about the dynamics of polymer solutions under the conditions of flow through the jet-forming nozzles of a hydroperfora-tor, which create a high-velocity jet, became the main scientific basis for this method of hydroperforation of oil and gas well casings. The study of the reaction of polymer solutions to the hydrodynamic effect with stretching led to the formulation of a structural con-cept, the “common denominator” of which is a strong deformation effect of the hydrodynamic field on macromolecular coils, which in terms of nonequilibrium thermodynamics generates a kind of rubber-like high elasticity. The peculiarities of the hydrodynamic behaviour of aqueous solutions of polyethylene oxide (PEO) during flow under the conditions of various nozzle jets were modelled, and the regularities of the influence of the resulting dynamic structures on the efficiency of hydrojet water–polymer perforation were established. The mechanism of hydrojet water–polymer perforation of casing columns in oil and gas wells was clarified. The mecha-nism of the large destructive capacity of a high-velocity polymer solution jet is not due to the reduction of turbulent friction by small polymer additives (the Toms effect), but consists in the destructive action of the dynamic pressure of the water–polymer jet “rein-forced” by highly developed macromolecular coils and the dynamic structures formed under the action of extended flow in the inlet section of the hydroperforator nozzles. The method of perforating oil and gas well casings comprises the exact determination of the perforation zone in lowering on production tubing a hydroperforator with 2–4 jet flow-forming nozzles for directing hydrojet to the zone of perforation, sealing the inside cavity of tubing pipes and the jet operators, actuating a ball valve at the bottom of the jet operators, sealing the annulus with a self-sealing gland and supplying the working cutting fluid to the tubing – which differs in that the aqueous solution of PEO used as a working cutting fluid has a molecular weight of 6 · 106 and a concentration 0.003–0.007% by weight and a working pressure of 100–300 MPa. The PEO additives are very environmentally friendly because this polymer is not harmful to humans or the environment. Experimental and industrial testing of this method of well perforation, which was carried out during the secondary opening of a reservoir at a well in the Carpathian oil- and gas-bearing region, confirmed the practical and eco-nomic feasibility of its use.