Research On In-Situ Stress Based On Optimum Technique And Bearing Law Of Casing Pipe

Reservoir stress has an important effect on hydrocarbon migration and accumulation, which is also the main factor of casing damage. The study of stress characteristic and casing damage mechanism perform a guiding significance in oil andgas engineering.Firstly, the mathematical model based on multi-objective optimization technique was established to analyze the distribution of reservoir stress. Employed the sonic logging, hydraulic fracturing data and fracture detection information to calculate the principal stresses in typical wells. And then set the typical wells' in-situ stresses of L112 block as the constraints, and utilze the optimization back-analysis technique to study the reservior stresses. The distribution of ground stresses and the curves of three-dimensional principal stresses with depth for L112 block and Chunliang oilfield were obtained.Secondly, a displacement back-analysis method based on deformation data was put forward to calculate the casing loads. Retrieved the casing loads, making use of casing inwall displacements, which provided the research basis for casing deformation under non-uniform loading and prevention measures for casing collapse.Thirdly, the mechanisms of casing failure and its influences of various typical loads were studied based on the obtained research achievement and data collection. And the effects of non-uniform loadings on casing strength was investigated by means of FEM numerical simulation, whose results showed that the distribution of effective stresses and displacements were seriously affected by the non-uniform stresses, and both the casing pipe and the cement sheath presented obvious anisotropic properties. What's more, with the increase of heterogeneous coefficient of in-situ stress, the effective stresses concentration factors have different growth.Forthly, established the optimization design model for perforating casing using numerical simulation, and studied the stress distribution of perforated casing under non-uniform external pressure, by the research of casing strength for N80 and P110 pipes. Finally, carried out the research on casing design method based on in-situ stresses, put forward the concept of equivalent collapse resistance, and established the casing mechanical models under non-uniform loads, which has modified the calculation formula of ideal pipe collapsing strength, and abtained the formula of the actual casing pipe.