In the complex fracturing process of shale gas wells, casing is subjected to serious deformation, which can easily to the failure of wellbore integrity and the reduction of well construction productivity. It is particularly important to clarify the casing deformation mechanism and carry out effective control. Based on the logging data of casing deformation from well and full-scale indoor tests, the casing deformation mechanism is mainly considered to be shear and non-uniform extrusion deformation caused by formation slip and displacement control, i.e., the ultimate working conditions. The slip displacement boundary (<40 mm) under complex fracturing conditions is quantified to provide the design and optimization basis. Then, the influence laws of steel grade and wall thickness on the shear and non-uniform extrusion bearing characteristics are studied, using unconventional oil and gas well casing simulation test systems for 110 ksi (φ139.7 × 10.54 mm) and 125 ksi (φ139.7 × 12.7 mm) casings. Furthermore, combined with the full-scale simulation tests and finite-element simulation, the effects of elastic and modified cement slurry with hollow glass beads on casing deformation are compared and studied. The results show that the deformation capacity mitigation of casing is limited by reducing the cement elastic modulus and increasing the elastic cement thickness. By reasonably adding hollow glass beads of modified cement slurry, the maximum geological movement absorption of cement slurry is up to 27 mm. This new method can obviously decrease casing deformation and have an excellent control effect. Combined with the cementing technology of Luzhou blocks, the formula of modified cement slurry is optimized, and the optimization window of the casing deformation control process is formed, which can ensure the smooth progress of engineering fracturing.

During the production of deep oil and gas, scaling, waxing, hydrate ice plugging and other problems easily occur. To solve these problems, reducing the temperature loss of oil pipelines is a feasible method. In order to protect the outer wall coating from being damaged and losing its thermal insulation performance, this paper proposes a developed technology for a novel inner wall coating-insulated oil pipeline. A new temperature-resistant and heat-insulating material aerogel was optimized and developed, and it has an extremely low thermal conductivity of less than 0.055 W/m·K. The influence of different coating processes on the thermal insulation coefficient was analyzed, and a novel inner wall coating-insulated oil pipeline was developed. A testing and evaluation platform for its thermal insulation effect was built, and a finite element model was established to analyze the temperature field distribution. When the thickness of the inner coating was 0.5 mm, the thermal insulation effect of the new oil pipeline improved by about 29%. This technology could be widely used in the production of deep oil and gas, high salinity oil and water reservoirs, thin oil reservoirs, etc., to alleviate scaling and waxing phenomena.

A large amount of casing deformation has occurred in shale gas wells during the complex fracturing process, which affects the fracturing construction and single well production. Based on the statistical analysis of casing deformation wells and caliper logging interpretation, the main mechanism of casing deformation of shale gas wells is revealed as formation slip. By comprehensively considering the rotating speed under casing running condition, the cement solidification heat release under cementing condition, and the fracturing fluid temperature drop under fracturing condition, the safe service margin of the casing is large. Moreover, simply increasing the casing steel grade and wall thickness has no obvious effect on casing deformation prevention, so full wellbore casing deformation prevention measures should be considered. By using the method of unconventional oil and gas well casing string simulation test and numerical simulation, the mechanical response of wellbore and the mechanism of bridge plug resistance are analyzed. By analyzing the influence of elastic modulus and wall thickness of cement on the casing minimum drift diameter after shear deformation, an analytical model of the minimum drift diameter of shale gas casing under the effect of fracture slip is established and verified, which provides technical support for parameter selection of cement and measures to prevent casing deformation.

CO₂ injection composite fracturing is an effective method for shale oil and gas well development. The downhole casing is prone to uniform corrosion, pitting, perforation, and even corrosion fracture in the CO₂ environment. Therefore, it is particularly important to reveal the physical characteristics of CO₂ under actual geological conditions and the impact of CO₂ corrosion on the performance of casing. A mathematical model for the temperature and pressure field of CO₂ in the wellbore under fracturing conditions is established in this paper, and the temperature and pressure distribution along the depth of the well is calculated. By optimizing the CO₂ state equation and using the S-W equation, Lee model, and RK model to calculate the CO₂ density, viscosity and compression factor, respectively, the phase distribution pattern of CO₂ along the actual wellbore is obtained. Through CO₂ corrosion tests on the casing, the influence of temperature and CO₂ concentration on the corrosion rate of the casing is clarified. The peak corrosion rate of Q125 steel corresponds to 80 °C, and the corrosion rate increases with the increase in CO₂ concentration. Finally, a prediction model for the uniform corrosion rate of casing under different temperatures and CO₂ concentration conditions is obtained, which can provide technical support for the design of CO₂-enhanced fracturing technology.

In order to reveal the physical properties of CO₂ under actual formation conditions, this paper establishes a mathematical model of the temperature field and pressure field in the wellbore under CO₂ injection conditions, optimizes the state equation of CO₂ physical-property parameters, calculates the change trend of CO₂ density, viscosity, and compression factor along the wellbore, and obtains the influence law of CO₂ corrosion on the casing and interface. The viscosity showed a downward trend along the well depth; the compression factor showed an upward trend. The surfaces of the three casings were smooth and flat without obvious defects, the cement structure was dense, and there was no obvious pore structure. After corrosion, with the increase of Cr content, the change of interfacial corrosion decreases. The morphology of the Q125 and 3Cr interface is loose after corrosion, while there is no obvious change in the 13Cr interface. With the prolongation of corrosion time, low wellbore internal pressure easily causes casing yield, and high wellbore internal pressure easily causes cement-sheath compression failure. The circumferential stress of the casing increases with the corrosion time extension, and the radial stress of the casing and cement sheath decreases first and then increases with the corrosion time. The compressive strength of the cement sheath does not exceed the compressive strength.

Under shear and non-uniform loads, the deformation of the section shape of a casing results in an irregular section, and the spatial continuity is poor. The change in the distance between the wall of the casing before and after stress is recorded to analyze the deformation of the casing, and the distance value is taken as the key characteristic of the casing. A large number of the key characteristic values of shale gas casing deformation can be obtained by using the circular traversal detection method. At the same time, this article focuses on the center deviation between the laser sensor axis and the pipe string axis, as well as on the disturbance problem during measurement. An eccentricity error correction algorithm is derived to correct the eccentricity error that occurs during the detection process, and then we use interpolation algorithms to draw cubic spline curves to improve detection accuracy. The test results show that the algorithm can effectively eliminate eccentricity errors in measurement and achieve the accurate measurement of deformation casing characteristic values, which can provide basic data for the study of a shale gas casing deformation mechanism.