scholarly journals Investigation into the Pore Structure and Multifractal Characteristics of Shale Reservoirs through N2 Adsorption: An Application in the Triassic Yanchang Formation, Ordos Basin, China

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Zhikai Liang ◽  
Zhenxue Jiang ◽  
Zhuo Li ◽  
Fenglin Gao ◽  
Xiaoqing Liu
Keyword(s):  
Organic Matter ◽  
Pore Structure ◽  
Mineral Content ◽  
Gas Adsorption ◽  
Ordos Basin ◽  
Total Pore Volume ◽  
Silty Mudstone ◽  
Nitrogen Gas ◽  
Rock Composition ◽  
Yanchang Formation

To understand the pore structure and heterogeneity of pore size distribution (PSD) is essential for revealing fluid mechanics and evaluating the utilization of unconventional resources. In this study, there are multiple shale examples collected from the Chang 7 section in the Ordos Basin for the investigation was conducted on the basis of various experiments on total organic carbon (TOC), X-ray diffraction (XRD), and nitrogen gas adsorption, through scanning electron microscopy (SEM) and multifractal method. The multifractal characteristic parameters, including the width of singularity spectra ( Δ α ), Hurst exponent ( H ), D 1 / D 0 , and nitrogen gas adsorption, were used to find out about the characteristics of pore development and to quantify the complexity and heterogeneity of pore structure. Depending on the exact mineral composition, the Yanchang Formation of Chang 7 shales is classified into either silty mudstone (SM) or muddy siltstone lithofacies (MS). According to the investigative results, the Chang 7 lacustrine shale features a complex pore system with the pores ranging from 1.5 to 10 nm in diameter. Besides, mesopores contribute significantly to the total pore volume (TPV) and total surface area (TSA). As for TPV and TSA of the SM lithofacies in the samples under investigation, they are nearly 1.09–1.78 and 0.80–1.72 times greater as compared to the MS lithofacies samples. The dominant types of reservoir spaces include organic matter (OM) pore and interparticle pore which are related to inorganic minerals. The value of Δ α is higher for MS lithofacies than for SM lithofacies, indicating a greater heterogeneity of PSD in the MS lithofacies. The pore structure of MS lithofacies is determined mainly by TOC and siliceous mineral content, whereas the influencing factors for SM lithofacies are TOC and clay mineral content. There is a significant relationship between multifractal parameters and pore structure parameters for both SM and MS lithofacies. The TOC of SM and MS lithofacies exhibits a close correlation with Δ α , suggesting that the pores in organic matter are dominated by those nanopores with a complex and heterogeneous pore structure. The rock composition of the lithofacies can affect Δ α to a varying extent, which means that the minerals have an evident impact on the heterogeneity of MS and SM lithofacies.

Fractures in continental shale reservoirs: a case study of the Upper Triassic strata in the SE Ordos Basin, Central China

2015 ◽  
Vol 153 (4) ◽  
pp. 663-680 ◽  
Author(s):  
WENLONG DING ◽  
PENG DAI ◽  
DINGWEI ZHU ◽  
YEQIAN ZHANG ◽  
JIANHUA HE ◽  
...  
Keyword(s):  
Organic Matter ◽  
Shale Gas ◽  
Mineral Content ◽  
Ordos Basin ◽  
Total Content ◽  
Upper Triassic ◽  
Thin Sections ◽  
Yanchang Formation ◽  
Fracture Development ◽  
Shale Reservoirs

AbstractFractures are important for shale-gas reservoirs with low matrix porosity because they increase the effective reservoir space and migration pathways for shale gas, thus favouring an increased volume of free gas and the adsorption of gases in shale reservoirs, and they increase the specific surface area of gas-bearing shales which improves the adsorption capacity. We discuss the characteristics and dominant factors of fracture development in a continental organic matter-rich shale reservoir bed in the Yanchang Formation based on observations and descriptions of fracture systems in outcrops, drilling cores, cast-thin sections and polished sections of black shale from the Upper Triassic Yanchang Formation in the SE Ordos Basin; detailed characteristics and parameters of fractures; analyses and tests of corresponding fracture segment samples; and the identification of fracture segments with normal logging. The results indicate that the mineral composition of the continental organic-matter-rich shale in the Yanchang Formation is clearly characterized by a low brittle mineral content and high clay mineral content relative to marine shale in the United States and China and Mesozoic continental shale in other basins. The total content of brittle minerals, such as quartz and feldspar, is c. 41%, with quartz and feldspar accounting for 22% and 19% respectively, and mainly occurring as plagioclase with small amounts of carbonate rocks. The total content of clay minerals is high at up to 52%, and mainly occurs as a mixed layer of illite-smectite (I/S) which accounts for more than 58% of the total clay mineral content. The Upper Triassic Yanchang Formation developed two groups of fracture (joint) systems: a NW–SE-trending system and near-E–W-trending system. Multiple types of fractures are observed, and they are mainly horizontal bedding seams and low-dip-angle structural fractures. Micro-fractures are primarily observed in or along organic matter bands. Shale fractures were mainly formed during Late Jurassic – late Early Cretaceous time under superimposed stress caused by regional WNW–ESE-trending horizontal compressive stress and deep burial effects. The extent of fracture development was mainly influenced by multiple factors (tectonic factors and non-tectonic factors) such as the lithology, rock mechanical properties, organic matter abundance and brittle mineral composition and content. Specifically, higher sand content has been observed to correspond to more rapid lithological changes and more extensive fracture development. In addition, higher organic matter content has been observed to correspond to greater fracture development, and higher quartz, feldspar and mixed-layer I/S contents have been observed to correspond to more extensive micro-fracture development. These results are consistent with the measured mechanical properties of the shale and silty shale, the observations of fractures in cores and thin-sections from more than 20 shale-gas drilling wells, and the registered anomalies from gas logging.

Characteristics of Chang 7 shale gas in the Triassic Yanchang Formation, Ordos Basin, China

2017 ◽  
Vol 5 (2) ◽  
pp. SF31-SF39 ◽  
Author(s):  
Xiangzeng Wang
Keyword(s):  
Organic Matter ◽  
Clay Mineral ◽  
Shale Gas ◽  
Mineral Content ◽  
Ordos Basin ◽  
Central China ◽  
Late Triassic ◽  
Yanchang Formation ◽  
Geochemical Parameters ◽  
Porosity And Permeability

The Yanchang Formation in the Ordos Basin in North Central China represents a large, long-lived lacustrine system of the late Triassic Period. The extensive shales within this system provide hydrocarbons (HCs) for conventional and unconventional oil and gas reservoirs. In the formation, the Chang 7 shale is the thickest shale with the best geochemical parameters, and it is the main source rock in this area. In recent years, the discovery of shale gas in the Chang 7 shale has promoted the exploration and development of lacustrine shale gas in China. We have estimated the shale gas resource potential based on the analysis of the geologic conditions of the Chang 7 shale. The average thickness of the Chang 7 shale reaches 42.6 m, and the main organic matter types are types [Formula: see text] and [Formula: see text]. The average content of organic carbon is more than 3%, and the average HC potential is [Formula: see text]. However, the thermal maturity of the Chang 7 shale is low with a vitrinite reflectance [Formula: see text] ranging from 0.83% to 1.10%. The Chang 7 shale lithology consists of shale and sandy laminations or thin sandstones. The shale is characterized by high clay mineral content and poor porosity and permeability, with an average porosity of 1.8% and an average permeability of [Formula: see text]. The sandy laminations or thin sandstones are characterized by relatively higher brittle mineral content, relatively lower clay mineral content, and higher porosity and permeability. The pores of the Chang 7 shale include primary intergranular and intragranular pores, secondary intragranular and intragranular dissolved pores, fracture pores, and organic-matter-hosted pores. The proportion of adsorbed gas, free gas, and dissolved gas is approximately 52%, 37%, and 11%, respectively, and the shale gas resources of the Chang 7 shale are [Formula: see text].

Whole-aperture characteristics and controlling factors of pore structure in the Chang 7th continental shale of the Upper Triassic Yanchang Formation in the southeastern Ordos Basin, China

2018 ◽  
Vol 6 (1) ◽  
pp. T175-T190 ◽  
Author(s):  
Wei Yang ◽  
Yan Song ◽  
Zhenxue Jiang ◽  
Qun Luo ◽  
Qianyou Wang ◽  
...  
Keyword(s):  
Pore Structure ◽  
Surface Area ◽  
Gas Adsorption ◽  
Ordos Basin ◽  
Total Pore Volume ◽  
Controlling Factors ◽  
Organic Carbon Content ◽  
Positive Variation ◽  
Shale Reservoirs ◽  
20 Nm

Quantitative assessment is still lacking on the pore-sizes distribution of micropores and mesopores, and the major controlling factors remain enigmatic for the continental Chang 7th shale reservoirs in southeastern Ordos Basin. In this study, scanning electron microscopy, organic geochemical analysis, low-temperature gas adsorption, high-pressure mercury injection, and X-ray diffraction analysis were conducted on 29 core samples from representative eight wells in the Xiasiwan-Yanchang area, yielding a particular investigation on characteristics and controlling factors of the structure in the Chang 7th shale. The Chang 7th shale is mainly characterized by organic and secondary micropore and mesopore, respectively, ranging the peaks of pore size from 0.35 to 0.65 nm, 0.75 to 1.00 nm, 1.10 to 1.35 nm, and from 4 to 13 nm. Whole-aperture characterization of the pore structure shows that meso- and macropores demonstrate a major contribution to total pore volume (PV), and the surface area is mainly provided by micro- and mesopores with pore radii less than 20 nm. A weak positive variation was identified between the PV of micromesopores and total organic carbon content, implying that micropores are currently in the process of developing. The micromesopore specific surface area and volume, respectively, yield a significant positive and weak variation with the quartz and clay mineral content, suggesting that siliceous minerals are favorable for micromesopore development. The infusion of siliceous biogenic debris and silica-replaced carbonate biogenic debris from the northeastern and southwestern source areas, respectively, is likely responsible for development of biogenic siliceous minerals in the Chang 7th shale. Furthermore, the hollow cavities in siliceous organisms have considerably contributed to the preservation of primary pores owing to their characteristic skeleton-supported framework.

scholarly journals Nanometer Pore Structure Characterization of Taiyuan Formation Shale in the Lin-Xing Area Based on Nitrogen Adsorption Experiments

Minerals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 298
Author(s):  
Chenlong Ding ◽  
Jinxian He ◽  
Hongchen Wu ◽  
Xiaoli Zhang
Keyword(s):  
Specific Surface ◽  
Pore Structure ◽  
Surface Area ◽  
Specific Surface Area ◽  
Shale Gas ◽  
Pore Volume ◽  
Ordos Basin ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Taiyuan Formation

Ordos Basin is an important continental shale gas exploration site in China. The micropore structure of the shale reservoir is of great importance for shale gas evaluation. The Taiyuan Formation of the lower Permian is the main exploration interval for this area. To examine the nanometer pore structures in the Taiyuan Formation shale reservoirs in the Lin-Xing area, Northern Shaanxi, the microscopic pore structure characteristics were analyzed via nitrogen adsorption experiments. The pore structure parameters, such as specific surface area, pore volume, and aperture distribution, of shale were calculated; the significance of the pore structure for shale gas storage was analyzed; and the main controlling factors of pore development were assessed. The results indicated the surface area and hole volume of the shale sample to be 0.141–2.188 m2/g and 0.001398–0.008718 cm3/g, respectively. According to the IUPAC (International Union of Pure and Applied Chemistry) classification, mesopores and macropores were dominant in the pore structure, with the presence of a certain number of micropores. The adsorption curves were similar to the standard IV (a)-type isotherm line, and the hysteresis loop type was mainly similar to H3 and H4 types, indicating that most pores are dominated by open type pores, such as parallel plate-shaped pores and wedge-shaped slit pores. The micropores and mesopores provide the vast majority of the specific surface area, functioning as the main area for the adsorption of gas in the shale. The mesopores and macropores provide the vast majority of the pore volume, functioning as the main storage areas for the gas in the shale. Total organic carbon had no notable linear correlation with the total pore volume and the specific surface area. Vitrinite reflectance (Ro) had no notable correlation with the specific surface area, but did have a low “U” curve correlation with the total pore volume. There was no relationship between the quartz content and specific surface area and total pore volume. In addition, there was no notable correlation between the clay mineral content and total specific surface area and total pore volume.

scholarly journals Multifractal Characteristics and Classification of Tight Sandstone Reservoirs: A Case Study from the Triassic Yanchang Formation, Ordos Basin, China

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2242 ◽  
Author(s):  
Zhihao Jiang ◽  
Zhiqiang Mao ◽  
Yujiang Shi ◽  
Daxing Wang
Keyword(s):  
Pore Structure ◽  
Ordos Basin ◽  
Type I ◽  
Tight Sandstone ◽  
Throat Radius ◽  
Yanchang Formation ◽  
Porosity And Permeability ◽  
Sandstone Reservoir ◽  
And Migration ◽  
Mercury Injection Capillary Pressure

Pore structure determines the ability of fluid storage and migration in rocks, expressed as porosity and permeability in the macroscopic aspects, and the pore throat radius in the microcosmic aspects. However, complex pore structure and strong heterogeneity make the accurate description of the tight sandstone reservoir of the Triassic Yanchang Formation, Ordos Basin, China still a problem. In this paper, mercury injection capillary pressure (MICP) parameters were applied to characterize the heterogeneity of pore structure, and three types of pore structure were divided, from high to low quality and defined as Type I, Type II and Type III, separately. Then, the multifractal analysis based on the MICP data was conducted to investigate the heterogeneity of the tight sandstone reservoir. The relationships among physical properties, MICP parameters and a series of multifractal parameters have been detailed analyzed. The results showed that four multifractal parameters, singularity exponent parameter (αmin), generalized dimension parameter (Dmax), information dimension (D1), and correlation dimension (D2) were in good correlations with the porosity and permeability, which can well characterize the pore structure and reservoir heterogeneity of the study area, while the others didn’t respond well. Meanwhile, there also were good relationships between these multifractal and MICP parameters.

Study on the distribution of extractable organic matter in pores of lacustrine shale: An example of Zhangjiatan Shale from the Upper Triassic Yanchang Formation, Ordos Basin, China

2017 ◽  
Vol 5 (2) ◽  
pp. SF109-SF126 ◽  
Author(s):  
Yuxi Yu ◽  
Xiaorong Luo ◽  
Ming Cheng ◽  
Yuhong Lei ◽  
Xiangzeng Wang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Oil And Gas ◽  
Storage Capacity ◽  
Ordos Basin ◽  
Organic Content ◽  
Capacity Control ◽  
Yanchang Formation ◽  
Geochemical Characterization ◽  
Extractable Organic Matter

Shale oil and gas have been discovered in the lacustrine Zhangjiatan Shale in the southern Ordos Basin, China. To study the distribution of extractable organic matter (EOM) in the Zhangjiatan Shale ([Formula: see text] ranges from 1.25% to 1.28%), geochemical characterization of core samples of different lithologies, scanning electron microscope observations, low-pressure [Formula: see text] and [Formula: see text] adsorption, and helium pycnometry were conducted. The content and saturation of the EOM in the pores were quantitatively characterized. The results show that the distribution of the EOM in the shale interval is heterogeneous. In general, the shale layers have a higher EOM content and saturation than siltstone layers. The total organic content and the original storage capacity control the EOM content in the shale layers. For the siltstone layers, the EOM content is mainly determined by the original storage capacity. On average, 75% of the EOM occurs in the mesopores, followed by 14% in the macropores, and 11% in the micropores. The EOM saturation in the pores decreases with the increase in pore diameter. The distribution of EOM in the shale pores is closely related to the pore type. Micropores and mesopores developed in the kerogens and pyrobitumens and the clay-mineral pores coated with organic matter are most favorable for EOM retention and charging.

The effects of shale composition and pore structure on gas adsorption potential in highly mature marine shales, Lower Paleozoic, central Yangtze, China

2017 ◽  
Vol 54 (10) ◽  
pp. 1033-1048 ◽  
Author(s):  
Yuguang Hou ◽  
Sheng He ◽  
Nicholas B. Harris ◽  
Jizheng Yi ◽  
Yi Wang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Pore Structure ◽  
Surface Area ◽  
Sorption Capacity ◽  
Gas Adsorption ◽  
Bet Surface Area ◽  
Lower Paleozoic ◽  
Longmaxi Formation ◽  
Methane Sorption ◽  
Shale Composition

The Ordovician Wufeng Formation and Silurian Longmaxi Formation are two of the most organic-rich and gas-prospective shale formations in the central Yangtze area, China. In this study, we investigate the controls exerted by shale composition and pore structure on methane sorption of these highly matured marine shales (Ro ranges from 2.0% to 4.0%). Samples were analyzed by SEM pore imaging of Ar-ion milled samples, high pressure methane adsorption, and low temperature nitrogen adsorption. In the high TOC Wufeng and lower Longmaxi formations, numerous organic matter pores are present. A positive correlation exists between TOC, BET surface area, and CH4 sorption capacity, indicating that porosity associated with organic matter is the key factor controlling methane sorption capacity of shale samples. In the organic-lean upper Longmaxi Formation, pores within clay particles and carbonate minerals are the major pore types. Organic-lean shale samples from the upper Longmaxi Formation have higher clay content, lower BET surface area, and lower adsorption capacity than organic-rich shales. Within several low TOC samples, a relatively strong correlation exists between illite content and methane sorption capacity, which is interpreted to result from clay mineral-hosted porosity.

Liquid hydrocarbon characterization of the lacustrine Yanchang Formation, Ordos Basin, China: Organic-matter source variation and thermal maturity

2017 ◽  
Vol 5 (2) ◽  
pp. SF225-SF242 ◽  
Author(s):  
Xun Sun ◽  
Quansheng Liang ◽  
Chengfu Jiang ◽  
Daniel Enriquez ◽  
Tongwei Zhang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Source Rock ◽  
Ordos Basin ◽  
Depositional Environments ◽  
Source Rocks ◽  
Type I ◽  
Hydrocarbon Generation ◽  
Type Ii ◽  
Thermal Maturity ◽  
Yanchang Formation

Source-rock samples from the Upper Triassic Yanchang Formation in the Ordos Basin of China were geochemically characterized to determine variations in depositional environments, organic-matter (OM) source, and thermal maturity. Total organic carbon (TOC) content varies from 4 wt% to 10 wt% in the Chang 7, Chang 8, and Chang 9 members — the three OM-rich shale intervals. The Chang 7 has the highest TOC and hydrogen index values, and it is considered the best source rock in the formation. Geochemical evidence indicates that the main sources of OM in the Yanchang Formation are freshwater lacustrine phytoplanktons, aquatic macrophytes, aquatic organisms, and land plants deposited under a weakly reducing to suboxic depositional environment. The elevated [Formula: see text] sterane concentration and depleted [Formula: see text] values of OM in the middle of the Chang 7 may indicate the presence of freshwater cyanobacteria blooms that corresponds to a period of maximum lake expansion. The OM deposited in deeper parts of the lake is dominated by oil-prone type I or type II kerogen or a mixture of both. The OM deposited in shallower settings is characterized by increased terrestrial input with a mixture of types II and III kerogen. These source rocks are in the oil window, with maturity increasing with burial depth. The measured solid-bitumen reflectance and calculated vitrinite reflectance from the temperature at maximum release of hydrocarbons occurs during Rock-Eval pyrolysis ([Formula: see text]) and the methylphenanthrene index (MPI-1) chemical maturity parameters range from 0.8 to [Formula: see text]. Because the thermal labilities of OM are associated with the kerogen type, the required thermal stress for oil generation from types I and II mixed kerogen has a higher and narrower range of temperature for hydrocarbon generation than that of OM dominated by type II kerogen or types II and III mixed kerogen deposited in the prodelta and delta front.

Pore types, pore-network analysis, and pore quantification of the lacustrine shale-hydrocarbon system in the Late Triassic Yanchang Formation in the southeastern Ordos Basin, China

2017 ◽  
Vol 5 (2) ◽  
pp. SF63-SF79 ◽  
Author(s):  
Robert G. Loucks ◽  
Stephen C. Ruppel ◽  
Xiangzeng Wang ◽  
Lucy Ko ◽  
Sheng Peng ◽  
...  
Keyword(s):  
Organic Matter ◽  
Clay Mineral ◽  
Mineral Content ◽  
Ordos Basin ◽  
Pore Network ◽  
Black Shales ◽  
Late Triassic ◽  
Ductile Material ◽  
Crushed Rock ◽  
Porosity And Permeability

Continental Upper Triassic Yanchang “black shales” in the southeastern Ordos Basin have been proven to be unconventional gas reservoirs. Organic-matter-lean and organic-matter-rich argillaceous mudstones form reservoirs that were deposited in a deeper water lacustrine setting during lake highstands. In the stratified lake, the bottom waters were dysaerobic to anoxic. This low-energy and low-oxygen lake-bottom setting allowed types II and III organic matter to accumulate. Interbedded with the argillaceous mudstones are argillaceous arkosic siltstones deposited by gravity-flow processes. Rock samples from the Yanchang Chang 7–9 members are very immature mineralogically. Mineral grains are predominantly composed of relatively equal portions of quartz and feldspar. The high clay-mineral content, generally greater than 40%, has promoted extensive compaction of the sediments, permitting the ductile material to deform and occlude interparticle pores. Furthermore, this high clay-mineral content does not favor hydraulic fracturing of the mudstone reservoir. The pore network within the mudstones is dominated by intraparticle pores and a lesser abundance of organic-matter pores. Interparticle pores are rare. The mean Gas Research Institute (GRI) crushed-rock porosity is 4.2%. Because the pore network is dominated by poorly connected intraparticle pores, permeability is very low (the GRI-calculated geometric mean permeability = 9.9 nd). The dominance of intraparticle pores creates a very poor correlation between GRI porosity and GRI permeability. Several methods of porosity analysis (GRI crushed rock, nitrogen adsorption, and point count) were conducted on each samples, and the results were compared. There is no significant correlation between the three methods, implying that each method measures different pore sizes or types. There is also no relationship between the porosity and permeability and total organic carbon. Much of the mature (peak oil window) organic matter is nonporous, suggesting that it is of type III. Most of the organic-matter pores are in migrated solid bitumen. Overall, the samples analyzed have low porosity and permeability for mudrocks.

Sign in / Sign up

Export Citation Format

Share Document