Research On Mechanism Of Casing Damage In Heavy Oil Thermal Recovery Wells Based On Fluid-Solid-Thermal Coupling

Casing damage has seriously restricted the normal production of heavy oil thermal recovery and brought huge economic losses to the country.Casing damage in heavy oil thermal recovery wells is mainly affected by thermal stress in the process of steam huff and puff.Therefore,the research on the mechanism of casing damage in heavy oil thermal recovery wells based on fluid-solid-thermal coupling has certain reference significance for ensuring safe production in the field.In this thesis,based on the fluid-solid-thermal coupling finite element analysis method of transient heat transfer,a combined casing-cement sheath-formation system model in the perforated well section is established,and numerical simulations of the wellbore temperature and stress fields are performed to study the action mechanism of production and perforation factors on the casing damage.Considering the effect of wellbore cement sheath failure problems on casing damage,the radial and circumferential loss of cement sheath models and the loss of gas intrusion channel models are established to analyze the influence of cement sheath failure on wellbore integrity.The study finds that the damage to the perforated casing during the production process is mainly affected by the high-temperature thermal stress.Properly increasing casing wall thickness can effectively prevent the casing deformation.The damage to the casing is minimal when the perforation diameter is 15 mm or the angle is 60°.Reasonably increasing the perforation density is conducive to protecting the casing and improving the safe service life of the casing.When the missing thickness ratio of cement sheath reaches 1/5～3/5 or the missing angle exceeds 30°,the casing is prone to yield failure.When the missing angle is 60° or 120°,the cement sheath is prone to secondary collapse.As the higher proportion of gas intrusion channel area and the more gas intrusion channels,the higher the maximum Mises stress of the casing and the worse the wellbore integrity.The research in this thesis is expected to provide a reference for the selection of reasonable steam injection parameters,perforation methods in the field,and the prevention of cement sheath failure to prevent casing damage.