A Study on the Electrical Characteristics of Fractured Gas Hydrate Reservoirs Based on Digital Rock Technology

Abstract

The electrical characteristics of fractured gas hydrate reservoirs were investigated through the diffusion-limited aggregation model, digital rock technology, and the finite element method. The results show that the fracture and gas hydrate have a significant effect on the electrical characteristics of rock partially saturated with gas hydrate, where the matrix pore and fracture mixed gas hydrate form a dual-porosity system. Due to the fracture and gas hydrate effect, the electrical characteristics of fractured gas hydrate reservoirs cannot be described well by traditional Archie equations. The resistivity index vs. water saturation curve of fractured gas hydrate reservoirs shows a nonlinear relationship for different gas hydrate pore habits (pore-filling, cementing, and grain-coating types), and this curve consists of two parts with different gas hydrate saturation exponents for pore-filling and cementing gas hydrate and presents a curve without a fixed water saturation exponent for grain-coating gas hydrate. Fractured gas hydrate reservoirs with different fracture apertures, different gas hydrate pore habits, and saturation features will lead to macroscopic electrical anisotropy. The results of theoretical analysis and numerical simulation show that the electrical anisotropy coefficient of fractured gas hydrate reservoirs is a function of gas hydrate saturation. The function curve consists of three segments with the turning point for pore-filling and cementing gas hydrate, and this curve can be divided into two parts through the turning point. The findings of this study can help for a better understanding of the electrical characteristics of fractured gas hydrate reservoirs, which have great significance for the exploration and development of gas hydrate resources.

Review and Outlook on Fracturing Technology and Mechanism of Hydrate-Bearing Sediments

“…The results show that the initial presence reduces the strength and stiffness of HBS and improves the effectiveness of hydrate hydraulic fracturing. The effect change is mainly caused by three aspects: (1) Microfractures provide the starting location and relative expansion path for prefracturing, and the existing open pathways make it easier for fracturing fluid to enter the hydrate layer, increase the permeability and release effect of hydrate, and reduce the injection energy consumption. − (2) Natural fractures can be used as the dominant permeability path to guide fracturing fluid diffusion to adjacent areas, where particles are continuously slipping and shearing., generating more stress concentration points, and branch fractures formed further trigger fracture expansion through connecting paths, enhancing fracture network connectivity. (3) Stress changes during fracturing can cause deformation and rearrangement of sediments, changing the pore structure of sediments, and further expansion can increase the connectivity of existing pores, increasing the permeability of hydrates. , In addition, natural fractures can be used as flow channels for hydrocarbons, increasing the permeability and flow capacity of hydrocarbons, which can flow more easily through natural fractures to the extraction wellheads, increasing production and extraction efficiency …”

Numerical Simulation of Electrical Properties for Pore-Scale Hydrate-Bearing Sediments with Different Occurrence Patterns and Distribution Morphologies

“…In addition, it has been shown in the literature that the electrical conduction patterns of sediments differ under different hydrate occurrence conditions. This is mainly attributable to the change in pore structure caused by the growth of hydrate, which in turn affects electrical properties [24][25][26]. However, most of the aforementioned studies are qualitative analyses, which basically analyze the general trend of the influence of these factors on resistivity, and further work can be completed on the quantitative analysis of resistivity changes.…”