Dynamic Instability Characteristics of Sandstone-Mudstone Combinations During Gas Drilling in Tight Sandstone Gas Reservoirs
Year: 2026
Type: article
Abstract: Gas drilling is an attractive technology for developing the tight sandstone reservoirs. However, there could be some risk involved in applying to tight sandstone pay zones, with wellbore instability being a primary concern, particularly occurring in intervals of interbedded sandstone and mudstone or mudstone interlayers. In this study, the dynamic instability characteristics of sandstone-mudstone combinations during gas drilling was investigated. The dynamic strength of sandstone-mudstone composite specimens with varying layer thickness ratios and strain rates was tested using the split Hopkinson pressure bar (SHPB) experiment. The crack propagation behavior of specimens was elucidated through the strain field obtained from digital image correlation (DIC). Combined discrete element method (CDEM) simulations further studied the crack initiation and propagation behaviors. Results show that dynamic strength increases with strain rate and sandstone proportion, with higher sensitivity in specimens with more sandstone. Crack propagation complexity rises with strain rate. Crack initiation shifts from mudstone to the sandstone-mudstone interface with increasing the strain rate, and propagation paths become more intricate, which leads to failure mode transition from tensile to mixed tensile-shear. Increasing sandstone proportion enhances interface strength, preventing crack propagation into the sandstone and altering failure behavior. Energy analysis reveals changes in transmitted, reflected, and dissipated energy ratios with varying sandstone proportion, with a turning point when the thickness of sandstone and mudstone is equal. Numerical calculations also confirm the significant influence of layer thickness ratio and strain rate on rock failure characteristics. The results provide new insights into the dynamic instability in interbedded sandstone and mudstone formations or mudstone interlayers during gas drilling in tight sandstone gas reservoirs.
Source: SPE Journal
DOI: 10.2118/231834-pa
Language: English
Subfield: Ocean Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7118312954