Numerical Simulation Of Casing Damage In The Process Of Oilfield Development

For the old oil fields, the underground rock’s stress condition has changed with the production time and continuous adjust of development plan in the oilfield development process. Then horizontal and vertical displacement has produced, resulting in large amount of casing failure. Imperfect well pattern is a prominent contradictions caused by casing damage, which directly influences the high and steady production of oilfield. To research casing damage in the oilfield production can effectively improve the oil wells casing life and provides guarantee for steady production, which is of great important.For the fact that among the different oilfields there lies great differences in the reservior properties and ways of oil development, the styles and mechanism of the casing damage is various. Take Shengli Oilfield for example, the reasons and mechanism of the casing damage under different reservoir conditions and development styles were studied carefully, which indicates that the main reasons for the casing damage are the rock mechanic damage of complex coupled physical fields and the water corrosion during the process of water injection and production. As to the corrosion reservoir, the corrosion style was studied for the examole of Shengli Oilfield and the mechanism inversion of the casing corrosion was conducted by use of scanning electron microscope, energy spectrum analysis, XRD test and TGA. Results showed that the casing corrosion of Shengli Oilfield is mainly affected by CO2, oxygen, SRB and high mineralization water.A linear elastic deformation field equation of high permeability reservoir was developed based on the assumption of finite deformation. A moderate and high permeability reservoir casing damage fluid-solid coupling model was established by jointing three dimension and two phase seepage model. The three-dimensional two-phase oil-water seepage model and the linear elastic deformation field equation were discrete with finite element method. The affecting law of casing displacement and Mises equivalent stress with the nature of the fault, reservoir parameters and the rock mechanics parameters was studied. The results indicated that under same conditions, the cross fault has the most vital influence on casing damage, followed by the normal fault, while the reverse fault is the lattermost. The smaller of the fault’s elasticity modulus, the greater of the casing’s displacement was. Otherwise, the smaller of the displacement, the greater of the fault’s angle, the greater of the casing’s displacement, the casing displacement and Mises equivalent stress slightly reduce with the reservoir elastic modulus increasing, the casing displacement and Mises equivalent is linear growth relationship with injection-production pressure, the casing displacement and Mises equivalent decrease and then increase with the injection ratio increasing, to ensure casing safety, injection-production pressure and the injection ratio should be the reasonable control when the wells fall through fault.The fluid-solid coupling finite element program was developed based on geological model, and the two dimensional geological mechanical model of Ying8block was established. Dynamic deformation and pore pressure dynamic variation in the injection-production process was studied applied with fluid-solid coupling finite element program. The results indicated that the pressure wave is difficult to penetrate the fault because of low permeability in the injection-production process. A large amount of deformation will generate on both sides of the fault because of asymmetric differential pore pressure, which results in casing damage of oil and water wells.