This study focuses on the multiphase flow in horizontal wells based on distributed acoustic sensing (DAS) monitoring. Through laboratory experiments and field data analysis, it was found that the micro-seismic differences in flow patterns can be clearly observed in the fiber optic micro-seismic waterfall chart. In the case of slug flow, the DAS acoustic energy decreases when the inclination angle increases. The performance of annular flow is similar to that of bubble flow, with the DAS energy increasing as the inclination angle increases. Overall, the order of DAS acoustic energy from the strongest to weakest is slug flow, followed by annular flow, and then bubble flow. The research shows that fiber optic DAS monitoring signals can effectively identify differences in gas volume, well inclination, and flow pattern, which provides an important technical basis and research foundation for the monitoring and analysis of multiphase flow in horizontal wells.

In the production process of horizontal wells, wellbore temperature data play a critical role in predicting shale gas production. This study proposes a coupled thermo-hydro-mechanical (THM) mathematical model that accounts for the influence of the stress field when determining the distribution of wellbore temperature. The model integrates the effects of heat transfer in the temperature field, gas transport in the seepage field, and the mechanical deformation of shale induced by the stress field. The coupled model is solved using the finite difference method. The model was validated against field data from shale gas production, and sensitivity analyses were conducted on seven key parameters related to the stress field. The findings indicate that the stress field exerts an influence on both the wellbore temperature distribution and the total gas production. Neglecting the stress field effects may lead to an overestimation of shale gas production by up to 12.9%. Further analysis reveals that reservoir porosity and Langmuir volume are positively correlated with wellbore temperature, while permeability, Young’s modulus, Langmuir pressure, the coefficient of thermal expansion, and adsorption strain are negatively correlated with wellbore temperature.

This study presents a systematic investigation of high-temperature effects on optical fiber telemetry and distributed sensing in oil and gas applications, integrating theoretical analysis with numerical simulations. Within the framework of the thermo-optic effect, this study investigated the signal attenuation mechanisms in multimode fibers (MMFs) and single-mode fibers (SMFs) under downhole temperatures ranging from 303.15 K to 473.15 K. First, numerical simulations indicate that at 473.15 K, MMFs exhibit significantly lower attenuation than SMFs. Second, quantitative analysis at the 1.55 μm communication wavelength shows that the thermo-optic effect substantially reduces signal bandwidth. MMFs demonstrate pronounced temperature-dependent dispersion, whereas SMFs display linear phase evolution at frequencies above 0.013 Hz. Finally, the attenuation characteristics of both fiber types were further evaluated across various operating wavelengths under high-temperature conditions. MMFs exhibit an attenuation peak at 1.55 μm, beyond which attenuation increases exponentially with wavelength. For SMFs, the mode field diameter (MFD) increases with wavelength but decreases linearly with rising temperature. These findings offer crucial insights for selecting optical fibers in high-temperature sensing applications. The SMFs exhibit significantly enhanced performance compared to MMFs in downhole optical telemetry applications under high-temperature conditions at the 1.55 μm communication wavelength. The characterized MFD variations in SMFs under different wavelengths and temperatures enable effective evaluation and compensation of thermal-induced MFD variations. This work establishes a theoretical foundation for developing temperature-compensated signal processing algorithms and advanced downhole optoelectronic telemetry systems.

To address the critical challenges of severe fragmentation in cuttings, persistent cuttings bed accumulation, and abrupt friction torque increases during horizontal well drilling of Jurassic continental shale oil formations in J Block, Sichuan Basin—rooted in the unique high clay content that induces colloidal stability of fine cuttings and resistance to conventional cleaning—this study innovatively proposes a coupled prevention–removal hole-cleaning technology. The core methodology integrates three synergistic components: (1) orthogonal numerical simulations to optimize drilling parameters, reducing the cuttings input rate by 43.48% through “hydraulic carrying + mechanical agitation” synergy; (2) a modified Moore model with horizontal section correction factors to quantify slip velocity of cuttings, lowering the prediction error from ±20% to ±5%; and (3) a helical groove cutting removal sub with 60 m optimal spacing, enhancing local turbulence intensity by 42% to disrupt residual cuttings bed. Field validation in Well J110-8-1H demonstrated remarkable improvements: a 50% reduction in sliding friction, a 25% decrease in rotational torque, and 40% shortening of the drilling cycle. This integrated technology fills the gap in addressing the “fragmentation–colloidal stability” dilemma in shale with high clay contents, providing a quantifiable solution for safe and efficient drilling in similar continental formations.

This study presents a systematic investigation of high-temperature effects on optical fiber telemetry and distributed sensing in oil and gas applications, integrating theoretical analysis with numerical simulations. Within the framework of the thermo-optic effect, this study investigated the signal attenuation mechanisms in multimode fibers (MMFs) and single-mode fibers (SMFs) under downhole temperatures ranging from 303.15 K to 473.15 K. First, numerical simulations indicate that at 473.15 K, MMFs exhibit significantly lower attenuation than SMFs. Second, quantitative analysis at the 1.55 μm communication wavelength shows that the thermo-optic effect substantially reduces signal bandwidth. MMFs demonstrate pronounced temperature-dependent dispersion, whereas SMFs display linear phase evolution at frequencies above 0.013 Hz. Finally, the attenuation characteristics of both fiber types were further evaluated across various operating wavelengths under high-temperature conditions. MMFs exhibit an attenuation peak at 1.55 μm, beyond which attenuation increases exponentially with wavelength. For SMFs, the mode field diameter (MFD) increases with wavelength but decreases linearly with rising temperature. These findings offer crucial insights for selecting optical fibers in high-temperature sensing applications. The SMFs exhibit significantly enhanced performance compared to MMFs in downhole optical telemetry applications under high-temperature conditions at the 1.55 μm communication wavelength. The characterized MFD variations in SMFs under different wavelengths and temperatures enable effective evaluation and compensation of thermal-induced MFD variations. This work establishes a theoretical foundation for developing temperature-compensated signal processing algorithms and advanced downhole optoelectronic telemetry systems.