Air Drilling Drill Corrosion Protection And Its Mechanism

Fluids of well corrupt badly drilling tools because it belongs to gas (mainly air), liquid (salt formation water, liqud additivies), solid (drilling cuttings, sands) multiphase blending flow, with sands and drilling cuttings abrasion and erosion. In order to control drilling tools corrosion in Iran TBK gas field, stable foam which added inhibitor and oxygen scavenger was adopted to drill well.The main research content and innovation of paper was listed as follow: Affecting drilling tools corrosion factors were first systematically studied by hanging S135 drilling pipe steel and ordered through orthogonal test and gray association analysis in simulating high temperature and high pressure corrosive environment. The conclusion could be drawn from orthogonal experiment and gray association analysis, namely four major factors of impacting drilling tools corrosion of air drilling were bottom temperature, pH value of drilling fluid, air pressure and drilling cuttings abrasion and erosion.S135 drill pipe steel electrochemistry behavior in different corrosion environment were studied by means of stable polarization, anodic linear potential sweep and electrochemical impedance spectroscopy (EIS). At the same time some of basic kinetic parameters were obtained. Corrosion products in different corrosive environment were analyzed by surface analysis such as scanning electron microscope (SEM), energy spectrum analysis and X ray diffraction (XRD). It proved that drilling tools corrosion products in high temperature and high pressure environment are Fe3O4, Fe2O3, CaCO3, CaSi2O5 and Na(K)Cl.FeC03C10. The main corrosion reaction mechanism was (1)high temperature and high pressure oxidation reaction; (2)dissolved oxygen corrosion; (3) carbon dioxide corrosion; (4) CY oxidation and penetration; (5)drilling cuttings abrasion and erosion.The optimal formulation of new style anticorrosion stable foam was 2.0%F4+0.3%HPAM+0.2%XC+0.5%CT2-17+0.05%Na2SO3. In the condition of dynamic test (20,55,75 grid drilling cuttings adding 10%, rotating rate 150r/min, air perrurel.OMPa, temperature64 C, pH valuelO, corrosion time 48h), foam quality is 70.7%, half life time is 61.3 min, corrosion inhibition rate is 95.6%, and can met TBK gas field drilling well demands. A systematic statement was made on the foam decay mechanism and affecting factors of its stability in theory.Foam corrosion inhibition mechanism first was put forward through analyzing laboratory data, which mostly consisted in foaming agent F4 absorption on steel surface; adhesion agent HPAM and XC complex characteristic; oxygen isolation; foam fixing sands,reduce erosion. Adding inhibitor CT2-17 and oxygen scavenger Na2SO3, foam corrosion inhibition ability was improved. This inhibitor was a mixed type inhibitor mainly prohibiting anode corrosion process.Recommending foam drilling replace air drilling and adjust pH value, add inhibitor and chemical agent can control drilling tools corrosion through analyzing mechanism of drilling tools corrosion and foam corrosion inhibition, combining research situation of home and abroad and TBK drilling practice. This method resolved drilling tools corrosion in air drilling encountering formation water, which possessed important theoretic signification and practical application merits, so deserved spread and application.