Quantitative Comparison of T2 Spectra from 1D and 2D Nuclear Magnetic Resonance Methods in Monitoring Imbibition Behavior of Tight Reservoirs

Self Cite

After flowback, the residual fracturing fluid will reduce the gas seepage space and influence natural gas production, which attracts widespread attention. In this study, the irreducible water saturation was investigated, and its controlling factors were clarified. We target the Upper Paleozoic Taiyuan and Shihezi Formations, which belong to a tight gas reservoir in the eastern Ordos Basin. The main experiments include porosity, permeability, mineral composition, nitrogen adsorption, mercury intrusion porosimetry, nuclear magnetic resonance, and high-speed centrifugation. The specific surface area is very low and varies from 0.95 to 4.03 m 2 /g, and the median pore-throat diameter ranges from 28.6 to 698.6 nm. Through the T 2 cutoff value, the water saturation can be divided into movable water saturation (S mov ) and irreducible water saturation (S irr ). Furthermore, the S irr can be divided into water saturation in large pores controlled by the small throat (S irrl ) and water saturation controlled by the capillary force (S irrc ). In both formations, the S irr has a negative relationship with porosity, permeability, and average pore diameter and exhibits a positive relationship with the specific surface area. The S irrl has a positive relationship with the median pore-throat diameter in Taiyuan Formation, but the S irrl has a weak relationship with the median pore-throat diameter in Shihezi Formation. The S irrc has a negative relationship with porosity, permeability, and average pore diameter and displays a positive relationship with the specific surface area in Taiyuan Formation, but the S irrc has a weak relationship with these parameters in Shihezi Formation. The relationship difference between Taiyuan and Shihezi Formations was mainly caused by the pore structure, demonstrated by the amplitude ratio in three peaks. Based on the above analysis, this study is conducive to understanding the mechanism of water occurrence and its controlling factors.

Section: Resultsmentioning

confidence: 99%

Rock Fabric of Tight Sandstone and Its Influence on Irreducible Water Saturation in Eastern Ordos Basin

Meng

Shen

et al. 2023

Self Cite

“…First, the coal samples used in this study contained a small amount of weakly paramagnetic minerals, which did not significantly affect the surface relaxivity. Second, the surface relaxivity was found to be similar for different coal types 15 despite the broad distribution of the T 2 spectrum. Third, the reduced water after centrifugation increases over the relaxation time (Figure 4), showing a direct link between the pore capillary pressure and NMR relaxation time.…”

Section: ■ Appendix a Nmr Relaxation Mechanismsmentioning

confidence: 94%

“…In contrast, MIP is inaccurate for micropores; therefore, the two methods must be combined to obtain a more accurate full-scale PFS . In addition, SEM, TEM, and CT have a common problem, i.e., high accuracy leads to a small field of view, and only partial PFS information is obtained. − Fortunately, nuclear magnetic resonance (NMR) has the advantages of being rapid, nondestructive, and large-scale, and it can statistically characterize PFS in coals. − …”

Section: Introductionmentioning

confidence: 99%

Integrated NMR Analysis for Evaluating Pore-Fracture Structures and Permeability in Deep Coals: A One-Stop Approach

Liu,

Zhou,

Chen

et al. 2024

Accurate evaluation and quantitative characterization of deep coal porefracture structure (PFS) is crucial for enhancing coalbed methane recovery efficiency. A novel approach combining transverse relaxation time and nuclear magnetic resonance (NMR) cryoporometry was employed to obtain a comprehensive pore size distribution by using NMR equipment alone. The relationship between the PFS and reservoir quality index was formulated. Two NMR permeability prediction models are further proposed for deep coals, providing a "one-stop" PFS permeability evaluation. The results show that it is practical to determine the surface relaxivity and obtain the pore size distribution by combining NMR cryoporometry tests with the surface relaxivity for coals from the mine of Pingdingshan, China, estimated to be approximately 4.63 μm/s. Seepage pore porosity, fractal dimension, and connectivity can be used to quantitatively characterize the differences in the PFS among coal samples and predict their influence on permeability. Coal samples with superior reservoir quality tended to display seepage pores characterized by high porosity, low heterogeneity, and enhanced connectivity. The proposed NMR permeability prediction models can accurately predict deep coal permeability, providing a rapid, nondestructive, and effective reservoir quality evaluation method.

“…Marine shale gas has been widely developed in the United States and the Fuling gas field of southern China. , Hydraulic fracturing is a central technique to exploit natural gas from shale reservoirs. − From the field experience, a shale well with high production usually has a higher fracturing fluid retention, which could not be displaced out of formation under conventional flowback measures. − Therefore, understanding the water occurrence is beneficial to understanding the retention mechanism. At present, nuclear magnetic resonance (NMR) was widely used to appraise water occurrence, and the T 1 – T 2 map can qualitatively differentiate fluid states, including movable fluid, adsorbed fluid, crystal fluid, and so on. − At the same time, the T 2 spectrum associated with centrifugation can quantitatively distinguish movable water and irreducible water, which has been widely used to appraise water movability. , Pore structure characterization is a basic aspect of understanding reservoir property. Abundant methods are used to investigate the pore structure, such as helium porosity, nano/micro computed tomography (CT), small/ultrasmall angle neutron scattering (SANS and USANS), nitrogen adsorption (NA), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and so on.…”

Section: Introductionmentioning

confidence: 99%

Insight into Water Occurrence and Pore Size Distribution by Nuclear Magnetic Resonance in Marine Shale Reservoirs, Southern China

Meng

Shen

et al. 2022

Self Cite

The exploitation of shale gas has been a hot topic, and the understanding of water occurrence and pore size distribution in shale reservoirs plays a crucial role in efficiently developing this type of resource. In this study, we target moderate-shallow marine shales from the Lower Cambrian Niutitang Formation and deep marine shales from the Lower Silurian Longmaxi Formation. Low-field nuclear magnetic resonance is applied to investigate the water occurrence and pore size distribution together with complementary experiments including mineral component analysis, scanning electron microscopy (SEM), contact angle measurement, and high-speed centrifugation. The SEM analysis shows that the moderate-shallow shales have some inorganic nanopores and cracks but almost no organic pores, while the deep shales have abundant organic nanopores. The average movable water saturation of moderate-shallow and deep shales is only 15.5% and 15.2%, respectively. It implies that the high irreducible water saturation is a typical characteristic for both marine shales, which is ascribed to the strong capillary force of the nanopore inhibiting water flowing out of the pore space. By means of high-speed centrifugation and contact angle measurement, the converting factor of the T 2 value into pore size was obtained. The average pore size in moderate-shallow shales is 19.4, 21.8, and 26.8 nm, respectively, while the average pore size in deep shales is 109, 57, and 68.4 nm, respectively, for the tested samples. This indicates that organic pores in deep shales contribute to the development of abundant nanopores. This study brings insight into characterizing the water occurrence and pore size distribution of moderate-shallow and deep marine shales.