In the process of constructing deep natural gas wells in Sichuan and Chongqing, gas wells encounter various technical challenges such as high temperature, high pressure, and a corrosive environment containing H₂S and CO₂. The corrosion of rubber materials in these acidic environments can easily lead to seal failure in downhole tools. To better investigate the corrosion resistance of rubber materials in acidic environments, we utilized a dynamic cyclic corrosion experimental device capable of simulating the service conditions experienced by downhole tools under high-temperature, high-pressure multiphase flow. Corrosion-resistance tests were conducted on fluororubbers (FKM) 1, 2, 3, and HNBR (hydrogenated nitrile-butadiene rubber) under acidic conditions (80 °C and 160 °C), along with sealing corrosion tests on O-rings. These tests aimed to analyze the mechanical properties, hardness, and corrosion resistance before and after exposure to acid media as well as the sealing performance of O-rings. Ultimately, our goal was to identify suitable rubber materials for acidic pressure environments. Experimental results revealed that all four types of rubber exhibited decreased elongation at break after undergoing corrosion testing; however, fluororubber 3 demonstrated significant susceptibility to temperature effects while the other three types showed minimal impact from temperature variations. Fluororubber 1 and fluororubber 3 displayed substantial deformation levels whereas mechanical properties greatly deteriorated for fluororubber 2. Overall, HNBR showcased superior comprehensive performance.

Rock brittleness index is an important parameter that affects the volume fracturing effect of an unconventional reservoir. The higher the brittleness index, the larger the communication area of fracture network formed under volume fracturing. However, rock brittleness has strong heterogeneity, which seriously affects the propagation of volume fracture network. Most existing rock brittleness characterization methods start from macro brittleness and cannot analyze the influence of heterogeneity on reservoir brittleness. The mineral composition analysis method can characterize the heterogeneity of a reservoir by analyzing the influence of mineral composition on brittleness, but this is limited to qualitative analysis on different minerals, resulting in large errors. In this study, the relationship between macro mechanical properties and micro mineral composition of rocks was analyzed using multiple linear regression analysis and a large number of experimental core parameters on the Shahejie Formation to understand the quantitative characterization of rock brittleness distribution in a heterogeneous reservoir. The results showed that quartz, plagioclase, analcite, siderite, and pyrite were high brittle minerals while clay minerals were low brittle minerals. This method provides a new focus for the analysis of brittle distribution of heterogeneous reservoirs and an additional method to study rock fracture law.

The aim of this study was to solve the problems associated with the sealing and tearing failure of rubber packer cylinders during CO₂ downhole injection. Using Comsol Multiphysics 6.0 software, a rubber cylinder model in a supercritical CO₂ (SC–CO₂) environment was established. The thermal analogy method was used to simulate the CO₂ diffusion and rubber cylinder swelling process. We analyzed the deformation and stress of the rubber cylinder that was caused by temperature and pressure, with CO₂ as the swelling agent. The results show that in the SC–CO₂ environment, under the influence of CO₂ diffusion and the consequent swelling, the rubber cylinder body is prone to large deformations, and the maximum shear stress is significantly increased, leading to the shear failure of the rubber cylinder. Reducing the initial seating pressure can alleviate the impact of deformation, whereas reducing the maximum contact pressure can cause the rubber cylinder to lose its seal. We also analyzed the influence of various factors on the maximum contact stress of the rubber cylinder, providing a theoretical basis and technical support for improving the sealing performance of rubber packer cylinders in an SC–CO₂ environment.

Vortex drainage gas recovery has been used to carry liquid from gas wells. However, the traditional vortex tools in gas wells cannot produce long effective distance spiral flow at a low gas flow rate, and their operating mechanism has not been thoroughly analyzed. In this paper, the venturi acceleration vortex tool for a horizontal gas well is designed to improve drainage performance. The tube drainage, the vortex tool, and the venturi accelerated vortex tool were applied in a horizontal tube to investigate their drainage capacities by a horizontal well multiphase flow experimental device. The influence of different gas flow rates and liquid flow rates on the length of the spiral flow and pressure drop produced by the three tools was analyzed. The results show that the vortex tool can convert the gas–liquid mixing flow into the gas–liquid separation flow, that is, the liquid flows spirally along the wall and the gas flows in the center of the horizontal tube. Compared with the vortex tool, the venturi accelerated vortex tool can form a longer and more stable spiral flow. The laminar spiral flow reduces the total pressure drop in the tube. The length of the spiral flow increases with the increase in the gas flow rate. With the increase in the liquid flow rate, the spiral flow is not clear because of the turbulent flow. The length of the spiral flow and the pressure drop for the venturi accelerated vortex tool with different gas and liquid flow rates are analyzed to guide the application of the tool. This study provides a new means for the drainage of a horizontal gas well and further clarifies the working mechanism of the vortex drainage tool.

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.