Research And Application On Hthp Sour Gas Well Integrity

Proved reserves of high sulfurous natural gas with H2S over30g/m3is nearly1trillion m3in China, generally with deep burial, high temperature, high pressure, complex geological conditions, mostly located in densely populated areas. Its resource utilization is faced with difficulties such as strong corrosion, high cost, big toxicity, serious accidents. Since2009, Lg gas field and Pg gas field have been put into production, and part of the gas wells have appeared under pressure phenomena in annulus between tubing and production casing or intermediate casing, posing severe challenges on gas well integrity and safe production.Aiming at this kind of high temperature, high pressure, high sulfur gas wells, the paper states theoretical research, laboratory test and field application research from abnormal under pressure diagnosis, well completion string strength integrity, well completion string tightness, cement ring tightness and wellhead integrity. Gas well integrity evaluation method, prevention and control measures for abnormal under pressure gas well have been developed for high temperature, high pressure, high sulfur gas well, providing technical support to prevent abnormal annulus under pressure in new wells and ensure safe production in existing abnormal under pressure well.1. Completion tubing string strength research has been carried out combining with the actual condition, forming a set of packer completion string triaxial stress intensity integrity evaluation methods and processes under different working condition based on the fourth strength theory. Quantitative control evaluation analysis of completion string under alternating loads is innovatively presented by applying Goodman curve. The example analysis shows that this method is practical and reliable.2. Pressure relief/recovery characteristic curve of gas well with abnormal annulus pressure is proposed. Wellbore temperature, annulus pressure prediction, annulus pressure calculation model for quantitative analysis of diagnostic tests in production process is established for packer completion string. Calculation model of annulus blowout rate and impact load for packer completion string is innovatively presented.3. Completion tubing string sealing reliability calculation model and parameter selection have been determined through completion string sealing reliability research, composite loads laboratory test and finite element simulation, revealing that high sulfur gas well tubing string sealing reliability has biggest drop (50%lower in10years) as production time goes on, clearing about mechanics mechanism of good sealing performance of special thread such as the VAM TOP. Tests prove that less times of pressure change on thread is better for sealing integrity.4. Cement ring end face corrosion evaluation method and cement end face corrosion rate formula under different acidic condition are innovatively put forward, clearing about corrosion mechanism of cement ring under H2S and CO2condition, making a new understanding of special corrosion transition layer.5. Multiphase flow numerical simulation analysis on wellhead erosion, internal leakage and bearing capacity shows:mechanical bearing capacity of wellhead body is safe comparing to pressure depletion in gas reservoir development and wellhead sealing performance should be more considered; upper tubing hanging, main sizes and side size, lower part of flange connection is the most prone to erosion damage parts and phased array detector test, stress concentration detection and ultrasonic detection analysis are recommended for wellhead integrity online evaluation.Application practice shows:the high temperature, high pressure, high sulfur gas well integrity evaluation method, prevention and control measures for abnormal under pressure gas well in this paper provide significant technical support to prevent abnormal annulus under pressure in new wells and ensure safe production in existing abnormal under pressure gas wells in Lg gas field and can be promoted and applied in similar high temperature, high pressure, high sulfur gas fields.