Casing Damage Mechanism In Daqing Oilfield

Because of high pressure water injection in Daqing oilfield,casings of 8000 oil and water wells were damaged cumulatively,8000000000 Yuan(RMB) were lost directly. Casing damage at home and abroad is very universal. It is a difficult problem in oilfield development at home and abroad. Therefore it is a urgent matter for us to carry out the study of casing damage mechanism and decrease casing damage ratio. For the study of casing damage mechanism,the technical limit and auti-corrosion measure were put forward during study. The following major works were did.The regularity,property and major influence factors of casing damage at home and abroad were analyzed in the study. We also dissected Daqing typical regions. Three major works were developed for the study of casing damage mechanism. One is to put forward 4 factors to lead to Daqing casing damage,or geologic factor,engineering factor,high pressure water injection and chemical factors,we developed that the ground stress lead to casing to be pulled,pressured,squeezed and sheared. The casing damage propertied were analyzed. Mechanical models were set up,we developed a lot of tests about lab sandstone and mudstone mechanical parameters and mudstone immersed regularity and the field test of casing damage mechanism was carried out.The mathematical model of reservoir fluid mechanics,reservoir solid mechanics and fluid-solid coupling was set up.For the test technique,three test methods were introduced and developed,mainly including the general test method of ground stress,on-line test of casing damage,test before(or after) damage,formation fracture principle and test technique of high pressure water injection,we give a new knowledge for theformation fracture pressure of high pressure water injection.On the basis of the casing conventional design,the bearing intensity model of casing with cement sheath was set up,we also considered the optimal design of completion casing under production circumstances.On the basis of the casing damage mechanism study,the fluid pressure field numerical modeling and finite element numerical modeling under solid mechanical propertied and fluid-solid coupling conditions were introduced. The software compilation was finished. We also developed the technical limit of typical regions.On the basis of the numerical modeling study,we put forward the controlled technical limit and local method of increasing casing strength in order to protect casing. The load supporting capability of bond cement was improved,the investment and expense cut down.Main and new technical ideas of the special topic are as follows:1. The models of fluid-solid coupling and solid-solid coupling,fluid mechanics and solid mechanics were set up,and the system was formed.2. The numerical modeling software compilation of casing damage was considered under formation dip,mudstone invasion water and drilling fault conditions. Determining the technical limit of casing damage was controlled.3. Stress test and technical diagnosis before (or after) on-line casing damage was developed and finished.4. The special technique of improving casing local strength was developed. The well cementing strength can be increased above 10-20 lined.5. The knowledge of formation fracture pressure was unproved. Conclusion1. The model of fluid-solid coupling was set up. The test result shows that the evaluation and solution of the model was conformable.2. The technical limit to protect casing damage can be determined through sensitivity analysis of fluid-solid coupling finite element software.3.The study of test technology was finished. The test technology is advanced. The test efficiency is high,cost low and covering range wide.4.The test method of fracturing pressure for high pressure water injection reservoir is easy to do. The new knowledge of high pressure water injection formation fracture pressure can guide to protect casing damage of oilfields.5. The new knowledge of formation fracture pressure was got.In a word,the theory of...