Acid Environment Oil Casing Design And Applicability Evaluation

The oil and gas industry is heading toward development of high pressure, high temperature severe sour service containing H2S,CO2, and water wells in China, which can expose low alloy,carbon steel production casing,some of casing and tubing under acidic conditions in Jidong Oilfield.it must to be done,based on current evaluation technology specifications how to present reliable evaluation technology specifications for sulfur casing performance evaluation and material selection according to characteristics of acidic gas. Aiming at the harsh environment in Jidong Oilfield,the main content and research ideas of this paper is based on Plenty of literatures at home and abroad,based on spot and data collecting.This paper carries out the mechanism study of Corrosion of tubing,casing in acidic conditions on Jidong Oilfield,research for wells to choose proper casing material,acid gases partial pressure calculation and tubing testing,Solutions presented in this thesis can be summarized as follows:1.This paper have carried out the analysis and research obout environmental factors leading Corrosion failure of casing,including primarily:temperature CO2 pressure,solute chemical properties,flow velocity,pH value of solutions;Through the research and analysis of electrochemistry erosion in wet H2S circumstances environmental stress cracking,corrosion cracking mechanisms on acidic conditions,finds that tubing failure in Jidong Oilfield is stress corrosion cracking or hydrogen embrittlement,or both.2.On the basis of ISO11960:2009, ISO15156:2009 and Sumitomo Metal etc.standards, this paper present the casing and tubing selection recommended practices according to various temperature, pH value, H2S and CO2 partial pressure and Cl- contents. These recommended practices provide an important reference for casing and tubing design and material selection in sour service containing H2S, CO2, and water.3.Through experimental research and contrast,this paper have evaluated new orthodoxy which applicated on strength calculation for oil well pipe of all OCTG size. Due to non-closed oval curve of SY-T5322-2008 design equation for triaxial yield of pipe body, so it suggests using the design equation for triaxial yield of pipe body in ISO/TR 10400:2007, because of more influence factors included such as the radial coordinate, component of axial stress not due to bending, component of axial stress due to bending, the torsional (shear) stress etc.4.stress concentrations around the etching pits are anlysized and evaluated in this paper for Casing corrosion on acidic conditions;and the rule about change of casing nondimensional internal pressure strength impacted by pitting. The study shows that:As corrosion depth lower than 10% of wall thickness,the resisting inner pressure declined sharply;As corrosion depth is 10%?70% of wall thickness,the resisting inner pressure decreased hardly.As Pitting depth is half of casing-wall thickness,all of the dimensionless surplus the internal pressure strength are less than 50%.5.Through the applicability testing of casing and tubing in Jidong Oilfield,the study have got the influence rule of temperature,moisture content,pressures on Casing corrosion (N80,P110,3Cr,5Cr),and The students have put forward materials selection recommendations for Liubei,Gaoqian,Miaoqian in Jidong Oilfield,to support EOR- CO2 corrosion prevention management and economic oilfield exploitation.