Accumulation and Distribution of Natural Gas Reservoir in Volcanic Active Area: A Case Study of the Cretaceous Yingcheng Formation in the Dehui Fault Depression, Songliao Basin, NE China

Tight gas sandstone and volcanic gas reservoirs have received global attention in the energy arena for further exploration and exploitation attempts. Considering the Yingcheng Formation of Dehui fault depression in the Songliao Basin as an example, this study focused on the accumulation and distribution of natural gas reservoirs in volcanic area in a fault depression basin. Volcanic activities occurred in the Yingcheng Formation, which is distributed centrally in the northwest of the study area. During the sedimentation of the Yingcheng Formation, fan-delta, lacustrine, and nearshore subaqueous fan facies were deposited. The source rocks of the Yingcheng Formation have high abundance of organic matter mainly in type III at high-overmature stages, indicating favorable conditions for gas production. The porosity of volcanic reservoir is 3.0%-14.8%, the permeability is 0.0004 mD-2.52 mD, and the pore types are mainly secondary dissolved pores and fractures. Besides, the porosity of the tight sandstone reservoir is 0.5%-11.2%, and the permeability is 0.0008 mD-3.17 mD. The pore types are mainly interparticle pores, with a small proportion of intraparticle pores and microfractures. The intrusion of late volcanic magma provided sufficient heat for the thermal maturity progression of organic matter in Yingcheng Formation and promoted the generation of natural gas in large quantities. Volcanic rocks formed at the early and middle stages of volcanic activities occupied the sedimentary space and hindered the development of sedimentary sand bodies to a certain extent. However, volcanic rocks can become the seal to promote the formation of tight sandstone gas traps. Comparing tight sandstone reservoirs with volcanic ones, the latter are less affected by compaction; thus, their petrophysical properties do not vary much with depth, showing more homogeneous characteristics. The pyroclastic rocks influenced by volcanic activity and the secondary pores formed by dissolution in the later stages also provide reservoir space for gas accumulation. Ultimately, the tight sandstone and volcanic rocks in the study area form a complex gas reservoir system, which can become a reference for exploration and exploitation of natural gas in other petroliferous fault depressions that are affected by volcanisms.

Eruption Cycle of Volcanic Rocks Based on Virtual Reality Technology

The eruption cycle of volcanic rocks based on virtual reality technology is studied to reveal the spatial distribution of volcanic rocks and the genetic relationship between different lithologic assemblages, and effectively guide volcanic exploration. Taking Xujiaweizi fault depression and Yingshan depression in Songliao Basin as the research area, the monocular vision method of virtual reality technology is used to collect data from the study area. Then, the three-dimensional dynamic scene of the study area was constructed. Based on this, combined with the research steps and division basis of the volcanic eruption cycle, the eruption cycle of the volcanic region in the study area is studied. According to the characteristics of volcanic activity, volcanic facies sequence, and rock rhythm combination in Xujiaweizi fault depression, the first and three sections of Yingcheng formation are divided into three eruption periods according to the contact relationship between sedimentary strata and volcanic rocks in the eruptive intermittent period. Y1C1, Y1C2, Y1C3, Y3C1, Y3C2, and Y3C3 are respectively from bottom to top. Yingshan volcanic rocks in Yingshan depression are divided into three cycles and six periods. Each stage has significant stages and differences, and the eruption intensity is different. The overall performance is gradually enhanced, and the internal cycle is characterized by the first strong and then weak.

Study on volcanic reservoir characteristics of Yingcheng Formation in Xudong area of Xujiaweizi fault depression

Types of deep reservoir rich in Yingcheng formation of Xudong area in Xujiaweizi fault depression, the study of volcanic rocks of Yingcheng formation in the main, using the date of core, logging, oil test, from lithology, lithofacies and physical properties to study volcanic reservoir characteristics. The main lithology of volcanic reservoir in Yingcheng formation of Xudong area include rhyolite, rhyolitic tuff, rhyolitic tuff fused, rhyolitic breccia and rhyolitic tuff breccia. In accordance with lithology combination of features, volcanic facies can be divided into volcanic explosive facies, volcanic effusive facies and volcanic sedimentary facies. The main types of porosity have air vent of primary pore, remnants pores of air vent filled after, cracks, micro-cracks and feldspar corrosion hole of secondary porosity, volcanic ash corrosion hole, micro-pore produced by rhyolitic glass from glass off in spherules rhyolite, quartz crystal chip corrosion hole, and so on. Through studying the ratio of reservoir and formation for a single well, the frequency distribution of reservoir thickness, production capacity situation and pool-forming regularity, Xudong area can be divided into three reservoir development zone, so we will find out the most favorable reservoir development zone, then it can play a guiding role for the next step of the exploration deployment.

Evaluation of volcanic gas reservoir in Yingcheng formation of Block Shengshen2-1 of Northern Part of Songliao Basin

According to the thin sections of volcanic rocks, chemical composition analysis and log interpretation, and well data, it is determined that the volcanic rocks of Yingcheng Formation in Shengshen 2-1 block are mainly intermediate-acid volcanic lava and pyroclastic rocks. Through physical analysis of core samples, it is considered that Shengshen 2-1 block belongs to low-porosity and low-permeability reservoir. Microfracture-fracture is relatively developed in the compact section, and fracture is not developed in the porous section. Microfracture and reticular fracture can be seen in the thin section. Statistical analysis of porosity and density of volcanic reservoir shows that volcanic rock density below 2.53 can be used as reservoir. According to the relationship between reservoir space and gas content, the characteristics of volcanic lithology, lithofacies and reservoir space, the reservoir in this block can be divided into four types.