Xiangzhen Yan

Elastoplastic Analysis of Mechanical Response of Buried Pipelines under Strike-Slip Faults

AbstractA two-dimensional elastoplastic analytical model of stress–strain analysis of the pipeline under strike-slip faults was established based on the plastic flow theory and elastoplastic-beam theory, considering the effects of service loads and the nonlinearities of the pipeline and the pipe–soil interaction. According to the plastic flow theory, the axial, radial, and hoop plastic strains were derived, and the stress–strain relation was established under the plane stress state. The axial stress and strain of the pipeline induced by fault displacements were analyzed based on the elastoplastic beam theory. Additionally, the axial stresses, hoop stresses, and strains induced by the service loads (i.e., the internal pressure and the temperature variation) were also considered. The proposed model was verified by comparing the analytical results and the finite-element results. The results show that the proposed model can predict accurately the mechanical response of the pipeline subjected to strike-slip fa...

Analysis of Casing Failure Associated with Bedded Salt Cavern Gas Storage

The mechanical properties and creep characteristic parameters of bedded rock salt were obtained by uniaxial and triaxial tests stimulating underground conditions. The bedded rock salt samples used in the experiments were obtained from H-10 well of a salt cavern gas storage in China. The “casing-cement-rock salt” numerical model was established to calculate the external pressure subjected to completion casing in bedded rock salt formation. Basing on the model, the influences of formation dip, interlayer friction coefficient, and creep time on the casing stresses and deformations were studied. The calculated results show that the external pressures are related to the angle between principal stress, location, and creep time. The maximum external pressure produced by creep is larger by about 10% than in-situ stress. When the formation dip is smaller than about 50°, the stresses and deformations of casing increase with the formation dips, and which achieve the maximum at about 50°, and then decrease. The stresses and deformations decrease as the increase of interlayer friction coefficient.

Improved Gauss-Newton-Marquardt algorithms for displacement back analysis of casing external loads in salt stratum

An improved Gauss-Newton-Marquardt (GNM) algorithm is proposed in the paper for displacement back analysis of casing external loads in salt stratum to optimize the solution based on traditional GNM algorithm. In the improved GNM algorithm, the direct solution method of partial derivative used in stochastic finite element method is adopted to substitute the difference method employed in traditional GNM algorithm. The calculation results show that the improved GNM algorithm is more efficient and precise in solving the displacement back analysis of casing external loads in salt stratum than traditional GNM algorithm. And the improved GNM algorithm is worthy to be applied greatly in the engineering practice. The calculating results of displacement back analysis are agreeable with the measured values indicating its suitable and valuable in practice. The improved GNM algorithm is versatile and suitable to solve the displacement back analysis problems in other engineering fields.

Strain Design and Experimental Study of Casing in Thermal Recovery Well Based on the Elastic-Plastic Constitutive Model

When using thermal recovery for the exploitation of heavy oil, the casing is the only channel of steam injection and crude oil extraction. Keeping the casing safe is critical to the operation. The authors conducted low-cycle experiments using strain-controlled material and the MTS809 material testing system. Mechanical property parameters of thermal recovery casing in high-temperature conditions were obtained. The experimental data and stress-strain constitutive relation led to numerical models of formation-cement sheath-casing based on actual geological structure and rock parameters of the recovery wells. Mechanical responses of casings in the thermal recovery wells were simulated for different high-temperature constitutive models and creep constitutive models of casing materials. Under Results indicate that the stress and strain caused by bending loads on casings change greatly at the dogleg part. Moreover, creep has a remarkable effect on casing strain in a thermal recovery well, which cannot be neglected in design. This research provided the basic parameters and technical references for strain design of casing in a thermal recovery well.

The Quality Safety Evaluation and Life Prediction of Casing String in Underground Gas Storage

Underground natural gas storage can carry out seasonal peak regulation and provide emergency gas supply to industry; however, its completion casing string is subjected to many undesirable influences by high-pressure gas injection and corrosion environment. Therefore, the bearing capacity and service life of casing string will be reduced. By establishing the reliability life prediction model of casing string, the expected life of casing can be computed quantificationally. The collapsing strengths are calculated based on the API 5C3 standard and the ISO10400-2007 standard, respectively. The results are compared with that of a casing collapse experiment; the application ranges of the two standards are obtained under different casing thicknesses. In this paper, the authors calculated the casing collapsing strength and the collapsing safety factor of the Su-11 well according to the casing collapsing strength theory. The results indicate that collapsing strength satisfies the strength requirement of casing in the whole range of well depth. According to the Norsok corrosion model, casing corrosion rates are predicted in an acid environment considering the impact of corrosion protection film. The actual casing corrosion rates and the life span of the Su-11well’s casing string are calculated by the casing string residual life comprehensive evaluation theory, which gives the well a remaining casing life of more than 30 years for underground gas storage.

Failure Analysis on Pipe Body Fracture of S135 Drill Pipe in West-East Gas Pipeline for Direction Crossing

The S135 drill pipe occurred failure accident for direction crossing rive during West-East natural gas transmission In order to analyze the failure reason, this paper carries on the overall analysis to the drill pipe sample based on the magnetic particle testing, fractography, and metallography, et.al. The analysis discovers that: the fracture has many cycle cracks and the sulfur content in the lateral fracture is higher than that in the other area of the drill pipe. The cracks show the typical characteristic of hydrogen sulfide stress corrosion cracking. It concludes that the fractures are hydrogen sulfide stress corrosion cracking. The drill pipe with anti-hydrogen sulfide property should be used and the drill pipe should be stored for a period before using in this oil field.

Nonlinear Dynamic Response Analysis of Oil/Gas Pipeline under Seismic Loads

For the vast territory of China, numerous oil and gas pipelines have to pass the high incidence area of earthquake, which has great menace to the safety of oil and gas pipelines in these areas. In the paper, the finite element model (FEM) is established to obtain the nonlinear dynamic response model of pipeline under seismic loads. The numerical methods are used to solve the model. At the same time, a field pipeline is calculated as an example. Moreover, the effects of seismic intensity, spring stiffness, resistance ratio, and site type, etc, on the response law, stress, deformation, and acceleration of pipeline are studied. The results show that the seismic response of pipelines increases as the increase of earthquake intensity. When the damping ratio keeps stationary, the seismic response of pipeline increases with increasing stiffness coefficient, whereas the displacement decreases gradually and basically has an inverse proportion with stiffness coefficient. The seismic response of the pipeline increases with increasing damping ratio, and the displacement and the stress gradually decrease under the same stiffness coefficient. The seismic response of pipeline has a relation with field. When the site soil gradually transits from the hard soil or rock to soft soil, the maximum displacement of the pipeline does not become larger, indicating the soft soil could reduce the damage of pipeline in earthquake.

Study on Plastic Limit Load of X80 Steel Pipe Elbow with Non-Uniform Wall Thickness

The analytical formulas of plastic limit load of X80 steel pipe elbow with non-uniform wall thickness leading by production error have been established on the basis of the force balance method. The influences of external diameter (D0), rate of internal and external diameter (K), and curvature radius (R) on plastic limit load of pressurized elbow are studied. The analysis results indicate that the plastic limit load is equidirectional with the increase of the rate of internal and external diameter, and curvature radius. However, the curvature radius and external diameter have little effect on the limit load. In order to validate the accuracy of the analytical formulas, 3-D finite element model of pipe elbow has been built up. The comprehensive results show that the analytic solutions are in good accordance with the numerical solutions, which can be serviced as the foundation and reference of the calculation of pipe elbow plastic limit load in field engineering.

Study on the Deformation of Completion Casing for Salt Cavern Gas Storage

In order to improve the injection and production rate of salt cavern gas storages, the diameter of completion casing is generally larger than that of oil well. Moreover, the loads capacity of rock salt surrounding completion casing decreases for the creep of salt, inducing the increase of external pressure subjected to the completion casing. It may lead the collapse of casing. In this paper, indoor experiments were carried out to obtain the characteristic parameters of rock salt, such as damage index, Young’s modulus, etc. The numerical simulation models of completion casings were established according to the parameters. The effects of damage index, Young’s modulus, creep time, and non-uniform of in-situ stress on the deformations and stresses of completion casing were studied. The studied results show the time of external pressure reaching the maximum value decreases as the increase of depth, and the deformation rate increases with depth. The maximum horizontal in-situ stress increases with time and gradually becomes stable, whereas the minimum horizontal in-situ stress decreases with time when it reaches the maximum value. The creep of rock salt increases the non-uniform of in-situ stress, which is bad for the safety of completion casing. High grade steel and large thickness casing are recommended in the completion of salt cavern gas storages.

Study on Residual Collapse Pressure of Casing in Bend Part of Medium/Short Radius Horizontal Wells

In order to get the quantitative relationship between the residual collapse pressure of casing and the build-up rate of bend part in horizontal wells, by theoretical analysis and finite element simulation method, we analyze residual collapse pressure of casing of three different diameters under the bending load and the outer pressure. The results show that casing cross-section roundness caused by bending has little effect on residual collapse pressure. The relationship between residual collapse pressure and build-up rate of bend part is the second inverse relationship. When the build-up rate of wellbore is the same, the relationship between residual collapse pressure of casing and the rate of diameter to thickness is inverse exponential relationship. The research provides a design reference for the collapse pressure of bend part casing in medium/short radius horizontal wells.