The evaluation of rock mechanic characteristics of shale reservoir is the key for the success of fracturing. Several limitations such as complex lithology can affect the accuracy of the rock mechanic property computation. In this research, the mechanical rock properties of shale reservoirs were analyzed based on experimental tests including shale-reservoir mineral composition, uniaxial compressive strength, and triaxial compression tests. The results showed that (1) the difference in mineral composition leads to easier fracturing of sand shale reservoirs compared with pure shale reservoir. (2) Under uniaxial conditions, the rock mechanical parameters along the vertical bedding direction of sand shale reservoirs are better than pure shale reservoir parameters. The mechanical properties of shale reservoirs in parallel bedding direction are less affected by lithology. Under triaxial conditions, the confining pressure increases more than 4.0 times with the compressive strength of rocks, and the rock Young’s modulus in the parallel bedding direction is higher compared with the vertical bedding direction. (3) Rock failure mode is mainly subdivided into cutting and splitting modes, and the bedding features of rock mechanic properties highly influence the drilling and fracturing operations. This study offers guidelines for the optimization of the drilling and fracturing process based on accurate evaluation of the rock mechanical properties.

Drilling engineers continue to grapple with the persistent challenge of maintaining wellbore stability. Throughout the drilling process, the wellbore pressure experiences fluctuations induced by various factors such as swab and surge pressure, leading to potential instability. This study employs a numerical approach, utilizing Abaqus software, to investigate the impact of swab and surge pressure on the natural fracture growth within the wellbore and the evolving pore pressure. A computational tool developed with MATLAB is then utilized to ascertain a safe operational mud window by assessing the time-dependent collapse and fracture pressures. The findings illustrated a notable increase in fracture width as a function of time in response to swab and surge pressure, with the most significant percentage increase reaching 69.92%. Notably, a 69.16% augmentation in fracture width is observed in the immediate vicinity of the wellbore following the application of swab and surge pressure. However, parameters such as fracture length, loss circulation rate, and pore fluid pressure exhibited marginal changes post-integration of swab and surge effects. The examination of the time-dependent wellbore stability after integration of swab and surge pressure indicated a narrowing of the initial mud window as a function of time, with a 14.33% increase in collapse pressure and a 13.80% decrease in fracture pressure. The numerical model verification against analytical solutions demonstrated good agreement, highlighting its potential utility in optimizing particle size for wellbore reinforcement and mitigating lost circulation through natural fracture sealing.

To meet the escalating demand for oil and gas exploration in microporous reservoirs, it has become increasingly crucial to develop high-performance plugging materials. Through free radical grafting polymerization technology, a carboxymethyl chitosan grafted poly (oligoethylene glycol) methyl ether methyl methacrylate acrylic acid copolymer (CCMMA) was successfully synthesized. The resulting CCMMA exhibited thermoresponsive self-assembling behavior. When the temperature was above its lower critical solution temperature (LCST), the nanomicelles began to aggregate, forming mesoporous aggregated structures. Additionally, the electrostatic repulsion of AA chains increased the value of LCST. By precisely adjusting the content of AA, the LCST of CCMMA could be raised from 84.7 to 122.9 °C. The rheology and filtration experiments revealed that when the temperature surpassed the switching point, CCMMA exhibited a noteworthy plugging effect on low-permeability cores. Furthermore, it could be partially released as the temperature decreased, exhibiting temperature-switchable and self-adaptive plugging properties. Meanwhile, CCMMA aggregates retained their reversibility, along with thermal thickening behavior in the pores. However, more detailed experiments and analysis are needed to validate these claims, such as a comprehensive study of the CCMMA copolymer’s physical properties, its interaction with the reservoir environment, and its performance under various conditions. Additionally, further studies are required to optimize its synthesis process and improve its efficiency as a plugging material for oil and gas recovery in microporous reservoirs.

The Volume 10, published for JFFHMT Journal.