An Approach to Calculating Casing Bearing Capacity with Parabolic Deformation Characteristics Under Local Radial Loading

Abstract

In the process of waterflooding technology in the Jilin oilfield, local radial compressive stress caused by rock deformation results in local casing collapse. According to statistics regarding casing-deformation characteristics, a certain number of these characteristics are approximately parabola-shaped at the radial-deformation bottom, and the boundary of the whole deformation area is approximately symmetrical and double-parabola-shaped. The main work of this article focused on occurrences of such casing deformation. Assuming that, in the process of casing deformation, external work is totally converted into energy consumption due to the deformation, the variation regularity of bearing capacity under local radial load was obtained. In the Qing-1 stratum of the Jilin oilfield, by selecting casing with radial collapse deformation parameters of 41/2"J 55 , 51/2"J 55 , 41/2"N 80 , and 51/2"N 80 , radial bearing capacity was calculated. Study results showed that the casing bearing-capacity value was reduced by 39.69% compared with the current API 5C3 standard when under the action of a local radial load. The casing collapsed due to the impact of local radial loads produced by mudstone creep. A series of relationships between radial bearing strength and casing parameters were also obtained. The research results are of significant academic value for the compilation of casing design codes or standards under local radial loading.Energies 2020, 13, 1769 2 of 16 deformation. Therefore, casing strength design is an opportunity for researchers to prevent casing failure. In the 1940s, scholars of the Soviet Union ГИНИ(Булгaкoв, 1930) and Г.М.Caркисo developed a casing strength design; then, in the early 1980s, ищенкo established the mechanical model of the casing wall under heterogeneous load. By means of stress superposition, the theoretical formula of stress change in casing was obtained [8]. Since then, the strength-design standard represented by the American Petroleum Association (API) has been widely used in many countries. At present, the API 5C3 and ISO 10400 standards [9,10] are used as the design standards of casing strength in the petroleum industry, but most of those standards are based on calculated results under uniform and non-uniform loads [11][12][13][14][15][16]. By using the lead-mold method to determine the casing-deformation characteristics of the Jilin oilfield, it was found that the casing deformation was due to local radial deformation, as shown in Figure 1 [17]. Previous studies [18,19] have found that casing deformation is mainly manifested as axial extrusion deformation and shear deformation. Axial compression failure occurs at the production stage, while axial shear failure occurs at the edge of the collapse area. Many scholars [20][21][22][23][24][25][26][27] have found that the main reason for local radial casing deformation is the lateral extrusion formed by water-absorption mudstone expansion. The finite element analysis is applied to establish the shape of casing deformation characteristics. Re...

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