Based on the massive static and dynamic data of 137 fractured wells in WY shale gas block in Sichuan, China, this paper carried out the analysis of shale gas fracturing production influencing factors, production prediction model, and fracturing parameter optimization model research. Taking geological, engineering, fracturing operation, and production data of fractured wells in WY block as data set, the main control analysis method is used to construct the shale gas fracturing production influencing factors as the sample set. A production prediction model based on six machine learning (ML) algorithms including random forest (RF), back propagation (BP) neural network, support vector regression (SVR), extreme gradient boosting (XGBoost), light gradient boosting machine (LightGBM), and multivariable linear regression (LR) has been established; the evaluation results show that the XGBoost model has the best performance on this sample set. The selection method of shale gas well fracturing operation scheme set is studied; the production rate and the ratio of cost and profit (ROCP) are comprehensively considered to select the final fracturing operation scheme. Research result shows that the data-driven production prediction model and fracturing parameter optimization model can not only be used to predict the production of shale gas fracturing and optimize operation parameters but also realize the sensitivity analysis of fracturing parameters and the effect comparison of fracturing operation schemes, which has good field application value.

Fracability is the ability of the reservoir to form a complex fracture network under hydraulic fracturing. In order to effectively evaluate the fracability of the deep tight sandstone gas reservoir in Changling Block, Songliao Basin of China, the velocities change with stresses, the stress–strain characteristics under uniaxial compression, combined with acoustic emission (AE) measurement experiments of the reservoir samples were conducted. Then, the experimental results of elastic parameters and the stress were used to calibrate the well logging data, and the in situ stress profiles and natural fractures development of the reservoir were systematically obtained. The research results indicate that the main controlling factors affecting the fracability of the deep tight sandstone gas reservoirs include matrix brittleness, natural fractures, compressive strength, the horizontal stress difference, and the minimum principal stress. The b-value of AE is derived from the Gutenberg formula, which can characterize the complexity of fractures. The larger the b-value, the higher the complexity of fractures. Then, a quantitative method for fracability evaluation of deep tight sandstone gas reservoirs was obtained based on the main controlling factors. The weights of each influencing factor were acquired by the correlation analysis of each influencing factor with the AE b-value. The quantitative method for fracability evaluation was then used for a vertical well and verified by the fracture-controlled production data indicating the reliability of the method. Finally, the suggestion for fracturing is put forward. It is recommended that during hydraulic fracturing, make the main fracture fully extend and communicate with as many natural fractures as possible. The natural fractures could be treated as the branching fracture of the hydraulic fracture. Then, a complex fracture network will be formed by increasing the net pressure inside the fracture.

The production of shale oil and gas is increasingly recognized as being influenced by temperature fields. Hydraulic fracturing involves the injection of substantial amounts of fracturing fluid into the reservoir, which alters the temperature field distribution and, in turn, affects shale gas production. In this work, we study the shale formations of Longmaxi, analyzing the factors that affect the thermophysical properties of shale under normal pressures. Using Hot Disk equipment, thermophysical properties were measured and a thermal conductivity model for shale was formulated from such data. The results reveal that mineral composition, temperature, and bedding characteristics are the primary determinants of shale thermophysical properties, while no significant correlation was found for porosity, permeability, or water saturation. We also identified variations for two distinct temperature ranges, below and above 60°C, as each exhibited different rates of change in thermophysical properties. Notably, pronounced bedding leads to less uniform heat transfer within the reservoir. This study offers theoretical insights into predicting temperature changes during hydraulic fracturing, which may aid oil and gas production.

During horizontal drilling in coal-rock gas reservoirs, the particle size distribution (PSD) of drilled cuttings directly affects drilling efficiency, hole cleaning, and wellbore stability. However, the evolution of cuttings PSD and its controlling mechanisms during coal-rock fragmentation remain insufficiently understood. In this study, a drill bit–coal-rock interaction model was established using the discrete element method (DEM) and calibrated against uniaxial compression experiments. The effects of weight on bit (WOB), rotational speed, and depth of cut (DOC) on cuttings PSD were quantitatively investigated. The results show that the relative influence on the maximum cutting size followed the order of DOC > WOB > rotational speed, whereas the influence on the average cutting size followed the order of rotational speed > WOB > DOC. Increasing DOC from 0.5 mm to 1.5 mm increased the maximum cutting size from 11.6 mm to 29.4 mm. Increasing WOB promoted the generation of medium- and large-sized cuttings, thereby increasing hole-cleaning requirements. Meanwhile, increasing rotational speed from 40 rpm to 90 rpm reduced the average cutting size and shifted the dominant cutting fraction from 4–6 mm to 1–4 mm. DEM observations reveal that cutting PSD evolution is jointly controlled by primary brittle fracture and secondary particle breakage through a five-stage fragmentation process involving stress concentration, microcrack initiation, crack propagation and coalescence, fragment detachment, and secondary fragmentation. Field validation using 146 cutting samples demonstrated the applicability of the proposed optimization strategy. Under the investigated drilling conditions, a DOC of approximately 0.5 mm and a rotational speed of 70–90 rpm were found to effectively limit oversized cutting generation. These findings improve the mechanistic understanding of cutting PSD evolution and provide practical guidance for drilling parameter optimization and hole-cleaning management in coal-rock gas horizontal wells.

CO2 pre-fracturing offers the dual advantages of enhancing oil recovery and generating complex fractures, demonstrating positive application effects in the field. However, there is a scarcity of research on the characteristics of fracture propagation associated with CO2 pre-fracturing. This paper presents a comparative experimental study between CO2 pre-fracturing and hydraulic fracturing, utilizing a true triaxial fracturing simulation system. The study examines the fracture propagation patterns of CO2 pre-fracturing through the integration of acoustic emission (AE) monitoring and CT scanning techniques. The findings indicate that CO2 pre-injection significantly reduces the breakdown pressure in the subsequent hydraulic fracturing phase. After the pre-injection of CO2, the pressure curve during the hydraulic fracturing process exhibited a distinct zigzag pattern, with higher pressure fluctuation frequency, AE rate, and cumulative AE counts, indicating that the CO2 pre-fracturing had generated a large number of micro-fractures. CT scan results before and after the fracturing process demonstrate that the fractures formed following CO2 pre-fracturing have a larger fractal dimension, indicating a more complex fracture network. Additionally, the pre-injection of CO2 activates the beddings within the formation, which subsequently influences the direction of fracture propagation during the following hydraulic fracturing. This study confirms that CO2 pre-fracturing provides superior stimulation effects compared to conventional hydraulic fracturing methods. Consequently, the application of CO2 pre-fracturing technology is recommended for the development of shale oil. 1. INTRODUCTION: Shale oil is one of the most important unconventional oil and gas resources in China, and due to its tight reservoir and poor crude oil mobility, it needs to be stimulated by large-scale fracturing to realize the effective mobilization of crude oil. Shale oil wells are developed through large-scale fracturing, but problems such as rapid depletion of formation energy and rapid decline in production often occur during the production process. Some oilfields have conducted CO2 pre-fracturing tests, effectively alleviating the above problems. The results of production data analysis show that after the implementation of CO2 pre-fracturing, the oil well pressure maintenance level was greatly improved, the production decline rate was significantly reduced, and the oil recovery rate was effectively improved.