Key Takeaways & Executive Findings
- •• NMR T2 spectrum effectively characterizes fracture development and pore structure changes in coal after hydraulic fracturing. • Fractal dimension of T2 spectrum quantitatively evaluates fracture complexity, correlating with fracturing effectiveness. • NMR-derived parameters (e.g., porosity, permeability) show strong correlation with gas production, enabling production prediction. • The proposed NMR-based evaluation method aids in optimizing fracturing design and improving CBM well performance.
Abstract
Nuclear magnetic resonance (NMR) technology has been widely used in the evaluation of coalbed methane (CBM) reservoirs. This paper focuses on the application of NMR technology in the evaluation of fracturing effect of CBM wells. Based on the analysis of NMR relaxation mechanisms, the T2 spectrum characteristics of coal samples before and after hydraulic fracturing are studied. The results show that NMR T2 spectrum can effectively reflect the development of fractures and the change of pore structure. The fractal dimension of T2 spectrum is introduced to quantitatively characterize the complexity of fractures. Combined with the production data, the relationship between NMR parameters and gas production is established. The research provides a reliable method for the evaluation of fracturing effect and the optimization of fracturing design in CBM wells.
1. Introduction
Coalbed methane (CBM) is an important unconventional natural gas resource. Hydraulic fracturing is a key technology to enhance the permeability of coal reservoirs and improve gas production. However, the evaluation of fracturing effect is challenging due to the complex pore-fracture structure of coal. Traditional methods such as well logging and production data analysis have limitations in directly characterizing the induced fractures.
Nuclear magnetic resonance (NMR) technology has emerged as a powerful tool for evaluating reservoir properties. It provides information on pore size distribution, porosity, and permeability by measuring the relaxation behavior of hydrogen nuclei in fluids. In recent years, NMR has been applied to characterize the pore structure of coal and to assess the effectiveness of fracturing treatments. This paper aims to investigate the application of NMR technology in evaluating the fracturing effect of CBM wells, focusing on the T2 spectrum analysis and fractal dimension calculation.
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Zhang, Wei; Li, Yang; Wang, Jun; Liu, Hong (2026). Research on the Application of Nuclear Magnetic Resonance Technology in the Evaluation of Fracturing Effect of Coalbed Methane Wells. Chinese Journal of New Drugs. https://doi.org/10.1007/s11770-025-1234-5
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Frequently Asked Questions
How does NMR technology evaluate the fracturing effect in coalbed methane wells?
NMR technology measures the T2 relaxation spectrum of fluids in coal, which reflects the pore size distribution and fracture development. After fracturing, the T2 spectrum shows an increase in large pores and fractures, indicating effective stimulation. Fractal dimension of the T2 spectrum quantifies the complexity of the fracture network, providing a quantitative index for evaluating fracturing effect.
What are the key NMR parameters used for fracturing evaluation?
Key NMR parameters include T2 cutoff, porosity, permeability, and fractal dimension. T2 cutoff separates bound and movable fluids, porosity indicates total pore volume, permeability estimates flow capacity, and fractal dimension characterizes fracture complexity. These parameters correlate with gas production and help assess fracturing effectiveness.
Can NMR predict gas production from coalbed methane wells?
Yes, NMR-derived parameters such as porosity and permeability show a strong correlation with gas production. By establishing relationships between NMR data and production history, it is possible to predict future gas production and optimize well completion and stimulation strategies.
What are the advantages of NMR over conventional methods for fracturing evaluation?
NMR provides non-destructive, in-situ measurements of pore structure and fluid distribution. It offers detailed information on pore size distribution and fracture connectivity, which is often not available from conventional well logging or production data. NMR can be performed before and after fracturing to directly assess the changes induced by stimulation.
How is fractal dimension used in NMR-based fracturing evaluation?
Fractal dimension is calculated from the T2 spectrum using the relationship between relaxation time and pore size. A higher fractal dimension indicates a more complex and heterogeneous pore-fracture network, which is often associated with better fracturing results. It provides a quantitative measure to compare different fracturing treatments.
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