During the fracturing process of oil and gas wells, casing eccentricity directly affects the mechanical integrity of cement sheaths, but the law and degree of influence are not clear at present, and there are no measures to address the influence of casing eccentricity on the mechanical integrity of cement sheaths. This paper took the lead in developing a set of experimental devices for cement sheath integrity. A comparative experimental study on the mechanical integrity of cement sheaths was carried out for the first time under casing concentric and eccentric conditions, and the influence of casing eccentricity on the mechanical integrity of cement sheaths in fractured wells of the Wushi 17-2 oilfield was also investigated. The numerical simulation method was used to perform stress analysis on cement sheaths of fractured wells under casing concentric and eccentric conditions. The influences of casing wall thickness, cement sheath thickness, the elastic modulus of cement sheath, and formation on radial stress of the cement sheath were analyzed, and the mechanical integrity safeguard or remedy measures of the cement sheath under the casing eccentric condition were proposed for the first time. The results show that casing eccentricity can easily lead to stress concentration at the narrow edge of the cement sheath. Under the condition of the same strength of the cement sheath, the integrity of the cement sheath is more likely to fail under the casing eccentric condition. The tensile failure cracks are concentrated at the narrow edge of the cement sheath. With the increase in casing eccentricity, the stress at the narrow edge of the cement sheath increased, the critical failure pressure of the cement sheath decreased, and the failure pressure of cement sheath integrity decreased by 17.72% at a casing eccentricity of 33% compared within a casing eccentricity of 0%. Improving the casing center degree, increasing the casing wall thickness and cement sheath thickness, and reducing the elastic modulus of the cement sheath can minimize the stress of the cement sheath and prevent mechanical integrity failure. This study is helpful to evaluate the mechanical integrity of the cement sheath in fractured wells accurately and can provide a technical reference for optimizing the casing center degree.

In oil and gas production in deep-water high-pressure−hightemperature (HP−HT) wells, wellhead uplift may cause the seal failure of wellbore integrity. Aiming at the oil and gas production stage in deep-water HP−HT wells, we considered the influence of cement sheath cementation and developed a model for calculating the height of wellhead uplifts, and simulation experiments for wellhead uplifts were carried out under the condition of the double pipe string at different cement return heights and multilayer pipe string coupling cementing and noncementing based on a self-developed HP−HT wellhead uplift simulation device. The results show that the elongation of the double pipe string under the condition of a cement return height of 100% is reduced significantly compared with that under the condition of a cement return height of 50%. Also, the maximum elongation of the multilayer pipe string under the condition of coupling and cementing is significantly reduced compared with that under the condition of noncementing. These show that cement sealing has a binding effect on wellhead uplifts. The error between the calculated and the experimental results is less than 10%; thus, the model can be used to predict the wellhead uplift height under different working conditions and provide technical guidance for designing scientific measures to prevent wellhead uplifts.

In the process of coal bed methane (CBM) production, the output of CBM is mainly related to the relative permeability of gas and water in coal seams. However, during the drilling process, the invasion of drilling fluid into CBM reservoirs changes the wettability, which may cause the gas and water’s redistribution through the pores and cracks, further changing their two-phase seepage characteristics and influencing CBM production. Therefore, studying the effect of drilling fluid on coal’s gas-water two-phase seepage has practical implications. Using a steady-state method, the influence of changing wettability and reducing the solution’s interfacial tension on relative permeability is investigated by adding different surfactants. The increase in coal’s hydrophilicity exhibits an impact on its relative gas-water permeability. At the same water saturation level, the relative gas permeability decreases and the relative water permeability increases. The hydrophilicity of coal was enhanced after adding anionic surfactants, which reduced gas permeability. Cationic surfactants are difficult to adsorb to the surface of coal due to the fact that the interfacial tension of the water and coal surface is reduced when the coal seam water is added to the cationic surfactants. After adding cationic surfactants, the gas permeability increased in favor of CBM production. The findings of this study could help to better understand the influence of drilling fluid intrusion on coal’s gas-water two-phase seepage and provide technical guidance for selecting better surfactants during the preparation of drilling fluids and help to increase CBM production.

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ROP is an important index to evaluate the efficiency of oil and gas drilling. In order to accurately predict the ROP of an oilfield in Xinjiang working area, a ROP prediction model based on the historical drilling data of this working area was established based on stacking ensemble learning. This model integrates the K -nearest neighbor algorithm and support vector machine algorithm by stacking ensemble strategy and uses genetic algorithm to optimize model parameters, forming a new method of ROP prediction suitable for this oilfield. The prediction results show that the accuracy of ROP prediction by this method is up to 92.5%, and the performance is stable, which can provide reference for the optimization of drilling parameters in this oilfield and has specific guiding significance for improving the efficiency of drilling operations.