Papers by Keyword: Casing

Abstract: In recent years, with the rapid development of modern petroleum industry, some conventional oil country tubular goods (OCTGs) have been unable to meet the requirements of ultra-deep oil and gas drilling and production. Titanium alloy OCTGs showed broad application prospects due to its high specific strength, Low elastic modulus and strong CO₂+H₂S+Cl^- corrosion resistance. However, large-scale applications of titanium alloy OCTGs were seldom reported, which is mainly attributed to the lack of anti-corrosive resistance and mechanical performance of titanium alloy OCTGs in the working conditions. In the present work, the research progress on properties and application of titanium alloy OCTGs were reviewed. The resistance to uniform corrosion, stress corrosion cracking, pit and crevice corrosion, mechanical properties of the titanium alloy OCTGs in air and downhole corrosion media were comprehensively discussed. Application status and prospect of titanium alloy OCTGs in oil and gas exploration were also summarized.

Abstract: With the increasingly harsh conditions of complex oil and gas wells such as high-temperature and high-pressure deep wells and long-distance horizontal well, the integrity of casing string puts forward higher requirements for compression performance of premium thread connections. The requirements of high compression resistance of connection is complicated, including ensuring the integrity of structure and sealability for thread at the same time under high compression load being equal to the bearing capacity of casing body, and considering the structural fatigue, environmental fracture and seal failure caused by the weakening of thread bearing performance under cyclic load. Based on the failure cases of some casing connections, laboratory tests and finite element analysis results, this paper discusses the key technical points in the above mentioned problems, and provides the suggestions for the performance optimization of high-performance casing premium connections based on failure prevention.

Abstract: In recent years, the oil and gas well casing is confronted with more complex service environment, and the casing is subjected to higher service load and temperature. In this study, the strength and plasticity of Cr - Mo low alloy casing steel of 80, 90 and 110 steel grades commonly used under high temperature service conditions was studied. The results show that with the increase of temperature, the yield strength and tensile strength of casing steel decreased. The sensitivity of high steel grade to temperature change was higher than that of lower steel grade; with the increase of steel grade, the fracture mechanism of casing steel changed from microporous polymerization fracture induced by large size second phase particles to shear propagation fracture induced by sub grain boundary microporous polymerization. This study has important guiding significance for the service safety and strain design of high grade steel under high temperature conditions.

Abstract: Corrosion leakage became serious due to cyclic sewage injection and continuous increase in water injection pressure. Corrosion behavior for N80 casing was studied during long-term service, using corrosion reaction kettle and weight loss method. The morphology and composition were characterized with laser confocal microscopy (LCM), scan electron microscopy (SEM) and energy disperse spectroscopy (EDS). These results showed that corrosion rate remained constantly at initial stage, and increased gradually, then sharply reached to 0.327mm/a at later stage, accompanying with inflection point under oxygen condition. Meanwhile, corrosion rate decreased significantly from 0.028mm/a to 0.020mm/a under oxygen-free condition. The corrosion of N80 steel was dominated by dissolved oxygen, and accelerated by chloridion. The micro-mechanism was suggested to be the transition of defect structure from crack with micron range to etch pit with millimeter range.

Abstract: In view of the external thread fracture during casing running in a well in Xinjiang Oilfield, the failure reasons of thread fracture were analyzed by combining the theory with experiment, and the casing safe service window with harsh working conditions was given. The operation of the failed casing and determined the actual working conditions of the casing threaded joints during the running process were investigated in this paper. According to the theoretical method, the boundary conditions and load conditions of the fracture casing joint in service were determined. With the aid of full-scale physical simulation test device, as well as the above boundary conditions and load conditions, the same batch casing tensile bearing characteristics were determined. Through nondestructive testing, the metallographic observation, scanning electron microscopy, spectral analysis and up-and-down test, the main controlling factors of casing thread fracture were determined. By the finite element analysis, the casing threads service state under axial tension and bending loads was established, the safety performance of threads under ideal working conditions was studied, and the fatigue mechanism of threads was revealed. Combined with the analysis results, the corresponding relationship between the casing tensile bearing characteristics and safety factor was given, which provides technical support for the safe service selection of casing body and thread under harsh conditions, saving cost and shortening the well construction period.

Abstract: The tubing and casing in the thermal recovery well are subjected to corrosion damage of multiple thermal fluid flow during the service period, which may cause safety accidents such as thinning, perforation and even fracture of the pipe wall. In this paper, the corrosion behavior of J55 casing steel and N80 tubing steel in flowing media were studied by using high temperature and high pressure reactor. The test results reflected the effects of single gas concentration and temperature of O₂ and CO₂ on tubing and casing corrosion. Comparing and analyzing the corrosion law of tubing in distilled water and produced water, the results of column corrosion rate under hot steam injection and production conditions were obtained, which indicated the difference of corrosion and the influencing factors of tubing in two working conditions.

Abstract: At present, most of the studies of the stability of the formation-cement sheath-casing combination have been mainly based on the plane, and the three-dimensional model established is only one example. There is no systematic study of the influence of physical parameters and process parameters on the stability of the combined body under the three-dimensional model and the action of triaxial crustal stress. Through the establishment of three-dimensional formation-cement sheath-casing linear elastic combination model, we can study the influence of operational parameters (cement sheath pressure, casing cross section pressure, inner casing pressure, ellipticity of borehole, centrality of casing, thickness of cement sheath) by the two interfaces’ Von Mises stress and the total displacement of the combination body. It is pointed out that the pressure of cement sheath, and casing cross section pressure have no effect on the stability of formation, cement sheath and casing; The higher the ellipticity of the borehole, the eccentricity of the casing (position 1, 2) and the thickness of the cement sheath, the higher the stability of the second interface of the cementing; The higher the inner casing pressure and the eccentricity of the casing(position 3), the lower the stability of the second interface of the cementing; The higher the eccentricity of the casing (position 2,3) and the thickness of the cement sheath, the higher the stability of the first interface of the cementing; The higher the inner casing pressure, the eccentricity of the casing (position 1) and the ellipticity of the borehole, the lower the stability of the first interface of the cementing; The higher the eccentricity of the casing (position 2,3) and thickness of the cement sheath, the higher the stability of the casing; The higher the inner casing pressure, the ellipticity of the borehole and the eccentricity of the casing(position 1), the lower the stability of the casing. Through this study, according to the formation stress, the formation physical parameters (elastic modulus, Poisson's ratio, density), optimize the operational parameters, ensure the long-term integrity of the combination.

Abstract: For unconventional oil and gas well perforating technology, field complex fracturing process to carry out the casing perforation physical simulation test, determine the different perforating process corresponding to the aperture size morphology, based on this, according to the physical simulation test results, perforating casing finite element model is established, the analysis of stress concentration around the perforation under different construction conditions, determine the outer extrusion safety factor, for complex oil and gas field casing string design and provide technical support. Keywords: complex fracturing;perforation; casing; mechanical properties

Abstract: With the exploitation of deep well, ultra-deep well, thermal recovery Well and Geothermal Well, the temperature of tubing and casing is increasing constantly. The influence degree of temperature on tubing and casing material performance has attracted much attention in the design of tubular strings. The experimental study on the yield strength and tensile strength of tubular materials with temperature change is carried out, which includes C110, 140ksi, P110 and S13Cr110. In this paper, the yield strength correction coefficient of tubular material is defined, and the material performance model of different steel grade tubular material with temperature change is established. The paper describes the influence of underground high temperature on the design of tubular strings and shows that the yield strength of tubular material will decrease under high temperature. This directly affects the safety parameter of tubing and casing design, and greatly impact on the safety reliability and service life of the tubular strings. This paper points out the defects which exist in the current API formulas, when calculating the force of the tubular string. It is suggested that the yield strength at high temperature should be used as the design basis for deep well and ultra-deep well when the underground temperature is high. The results can be used to guide the design and check of tubular strings under high temperature and high-pressure gas well.Keywords:deep and ultra-deep well; special performance tubing and casing; high temperature; yield strength; tubular strings integrity;OCTG

Abstract: The aim of this work was to develop an alternative way to obtain casings used with irradiation targets containing uranium, for the production of the radionuclide Mo-99-Tc99m. The targets used for the production of Mo-99 are materials containing U-235 designed to be irradiated in a nuclear reactor. Usually these targets are encapsulated in aluminum or stainless steel. The idea here is to obtain casings by encapsulating a uranium button or a metallic cylinder with compacted and sintered nickel powder, this serving as a sealing for the fissile products occurring during U-235 irradiation. The sintered high purity nickel powder samples were compacted in uniaxial hydraulic press at 195 MPa. The sintering of the samples was carried out in an open-air furnace in an atmosphere with a certain control using titanium-machining chips at 600 °C. The samples bulk density was evaluated by the Archimedes' principle. The porosity of 20.08% was measured by mercury porosimetry. The microstructure was investigated by scanning microscopy revealing interconnected porosity and nickel oxide at the particles boundary surface. The results obtained by sintering of nickel powder according to the experimental undertaken, indicate the feasibility of achieving a casing for uranium targets.