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To figure out gas enrichment laws in Permian volcanic rocks, Sichuan Basin, an association among reservoir-forming elements was explored to analyze forming modes and point out exploration prospects in accordance with reservoir characteristics, gas source conditions, and fault elongation in Zhougongshan and Jianyang areas. Results show that there mostly exist porous volcaniclastic rock and lava reservoirs of explosive facies. In Jianyang with Lower Cambrian Qiongzhusi Formation as the principal source rock, early faults offered pathways to assemble ample initial oil and gas. Following an increase of burial depth, oil started cracking vastly to create oil-cracked gas. These elements constitute one reservoir-forming mode of Cambrian hydrocarbon supply–fault transporting–in-situ cracking in Jianyang. While in Zhougongshan with Lower Permian Maokou 1 Member as the main source, active faults during hydrocarbon generation and expulsion acted on trap preservation. Late kerogen-cracked gas gathered at structural highs far from giant faults. Thus, the other mode exhibited in Zhougongshan is Permian hydrocarbon supply–fault adjustment–effective trap accumulation. Reservoir-forming conditions in volcanic rocks present certain disparity among all kinds of tectonic settings inside the basin, giving rise to various volcanic gas reservoirs developed. The Permian volcanic rocks are expected to be a major domain for reserve and production increase in Sichuan Basin.

The tubing used in a gas well rarely collapses and fails during applying annulus pressure. In this study, the failure causes of tubing collapse were analyzed by means of data verification, macroscopic observation, magnetic particle inspection, physical and chemical inspection, optical microscopy, and tubing collapse test. Mechanical analysis of the string and full-scale physical simulation test simulating downhole working conditions. Finally, the verification analysis of the collapse test is carried out by the finite element analysis (FEA). The results showed that (1) the physical dimension, physical and chemical properties, and collapse resistance of this batch of tubing met the requirements of the tubing ordering technical standard. (2) Assuming that the well packer slip was unsealed and could slide freely, the mechanical theoretical analysis of collapsed tubing string and collapse test under simulated working condition load was carried out, which reproduced the load when the tubing collapsed. It can be seen from this that the packer did fail. (3) The FEA calculation results showed that when the external pressure was greater than 30.75 MPa, it would inevitably lead to collapse failure in case of packer unsealed. In conclusion, the root cause for the collapse failure of the 105th underground tubing string was that the packer lost its sealing function, resulting in an abnormal axial load. While under the action of external pressure, the tubing was overloaded and collapsed. It is recommended to carry out verification tests on the material performance of packer slip, the dimensional changes of packer tool outer diameter and inner diameter under actual well conditions, the creep behavior of packer seal, and the performance of shear pin under actual working conditions, especially in the well containing H2S, so as to prevent the pressure leakage of gas well annulus caused by packer unsealing and the reoccurrence of such downhole string collapse accidents. The first collapse test under simulated working condition load is conducted in this paper. Analyzing the collapse failure work and putting forward suggestions to effectively prevent similar failures from happening again are of great significance to the oilfield. [ABSTRACT FROM AUTHOR]