Pores, fractures, caves, and other storage spaces are commonly distributed in fractured-vuggy carbonate reservoirs. During the drilling process, more than half of all drill-in fluid loss issues are caused by developed caves. Cave scales range from centimeters to meters, making leak prevention increasingly difficult through the use of traditional technologies. Currently, there is still high demand for the understanding of feasible loss control techniques, especially in fractured-vuggy carbonate reservoirs. Multistage Bridge Plugging (MBP) technology has facilitated pioneering experiments in many oilfields, but the success rate of plugging is less than 50%, and the effects of plugging are uncontrollable and difficult to predict. This is due to a lack of clarity regarding the plugging mechanism and the key controlling factors. In this study, we used the Discrete Element Method (DEM) simulation method to investigate the controlling factors of MBP technology, and analyzed its applicable conditions. We found that the prerequisite for the success of MBP is the presence of a constricted throat near the wellbore when drilling the well hole; the first-stage bridging ball is the key to the success of MBP. Larger ball radius, cave inclination and initial flow rate, and lower ball velocity are beneficial to the first-stage bridging. All discussion in this research is based on the ideal situation. However, the cave pattern is difficult to describe using several models, let alone by one ideal model. With the progress of seismic fine description technology and mud logging, more accurate characterization of caves in carbonate reservoirs will help to accurately formulate the plugging scheme and greatly improve the success rate of plugging technology. Additionally, the engineering risks of this technology, such as plugging the coiled tubing, need to be further studied.

The research on the developmental characteristics and evolution process of pores in dolomite reservoirs is a hot spot in petroleum geology. In this paper, taking the dolomite reservoirs of the Longwangmiao Formation in the Gaoshiti area as an example, the differential distribution and evolution of pore parameters have been systematically studied combined with downhole cores, logging, cast thin sections, and scanning electron microscope data. We used statistical methods and image analysis techniques to quantitatively characterize the pore distribution of the Longwangmiao Formation in the study area. Moreover, the factors controlling the distribution of pores in the dolomite of the Longwangmiao Formation were identified, namely, lithology, sedimentary facies and diagenesis. Finally, the evolution mode of pores of the Longwangmiao Formation was constructed. The results show that the main types of pores developed in the Longwangmiao Formation in the study area include intergranular and intragranular dissolved pores, intercrystalline dissolved pores and mold pores. Among them, the intergranular dissolved pores are the main pore type. The pores with surface porosity higher than 0.5% in the Long 2 Member in the study area account for 46% of the total pores, while those in the Long 1 Member account for 25.5%. Therefore, the degree of development of pores in the Long 2 Member is better than the Long 1 Member. In addition, the granular dolomite in the grain shoal facies is favorable for the formation of large-scale pores, and the oolitic dolomite is the most favorable reservoir type. The most favorable factors for the development of pores are the atmospheric freshwater dissolution and dolomitization in the quasi-contemporaneous period; the former caused the formation of a large number of intergranular dissolved pores, while the dolomitized particles and their ring-edge cements in the latter promoted the retention of residual intergranular dissolved pores. The dissolution, dolomite cementation and hydrothermal action in the burial stage promoted the reformation of pores.

The Permian Qixia dolostone in the Central Sichuan Basin is a significant hydrocarbon reservoir of hydrothermal origin, linked to the Emeishan Large Igneous Province and structurally controlled by E–W strike–slip faults. However, how this process controls reservoir quality remains poorly understood. To address this, we integrate core observation, thin-section petrography, XRD analysis, thickness mapping, MICP, and μ-CT to characterize the lithofacies and pore structures of the Qixia Formation in the study area. Six lithofacies are recognized, including mudstone (F1), wackestone (F2), packstone (F3), grainstone (F4), rudstone (F5), and dolostone (F6), and F6 is further divided into three subtypes (F6-1, F6-2, F6-3). Dolostones exhibit superior reservoir quality relative to limestones, and among the dolostone, reservoir quality improves progressively from F6-1 to F6-3 with increasing crystal size and dolomite content. Dolostone distribution is spatially tied to E–W strike–slip faults, and its formation age coincides with documented fault activity, implicating these faults as the primary fluid conduits. Quantitative pore structure analyses further indicates that dolomitization enhanced permeability by enlarging pore–throat radii and improving macropore connectivity, with associated dissolution contributing additional secondary porosity.

In this paper, taking the first Member of the Canglangpu Formation of the Cambrian Series 2 in the northern central Sichuan Basin as an example, the diagenesis and its influence on porosity are systemically studied based on the observations and identifications of cores, casts and cathodoluminescence thin sections. The results show that the rock types of the first member of Canglangpu Formation are various, including mixed rocks, carbonate rocks and clastic rocks. The specific lithology is dominated by sand-bearing oolitic dolomite, sandy oolitic dolomite, sparry oolotic dolomite and fine-grained detrital sandstone. At the same time, the Cang 1 Member has experienced five types of diagenetic environments, including seawater, meteoric water, evaporative seawater, shallow burial, and medium-deep burial diagenetic environments. Moreover, the main diagenetic processes under different diagenetic environments include cementation, dissolution, compaction, chemical compaction, dolomitization and structural fractures. According to the analysis, fabric-selective dissolution in meteoric water diagenetic environment, dolomitization in evaporative seawater environment, and non-fabric-selective dissolution, dolomitization and structural fractures in buried diagenetic environment are beneficial to the development of pores. However, cementation, compaction and chemical compaction in medium and deep burial environments, are unfavorable for the development of pores.

Corrigendum: Diagenesis of the first member of Canglangpu formation of the Cambrian Series 2 in northern part of the central Sichuan Basin and its influence on porosity