Gas Desorption of Low-Maturity Lacustrine Shales, Trassic Yanchang Formation, Ordos Basin, China

AbstractRecent exploration activities on Triassic Yan-chang Formation has indicated significant potential for shale-gas resources. Even though some areas have been put into pilot production, challenge exists in effectively determining shale-gas content, whichmake it difficult to estimate reserve and forecast production. This is primarily due to the low maturity of the shale and complicated relationships between oil, water and gas. However, studies on the gas generation and accumulation of low-maturity shales are lacking in the literature and previous desorption experiments did not consider the effects of oil and water. In this study, eight core samples are used to run the gas-desorption experiment. Shale-gas composition and isotopic fractionation data are analyzed to provide insights on gas adsorption, expulsion and accumulation processes in the Yanchang Formation. The experiment results indicate that the overall methane content decreases (from 68.8% to 58.9%), heavy hydrocarbon-gas content (from 20.30% to 36.12%) and δ13C1 increase (from -51.43% to - 34.63%) during the desorption process. Gas yield reached up to 3.89 m3/t shale, and the content of lost gas can account for more than 20% of total desorbed gas during the coring process. The recoverable shale gas content is estimated to be 80% of the total gas-desorption volume. Desorbing the rest 20% requires extra heating under much higher temperature.

Download Full-text

Shale Gas Content Calculation of the Triassic Yanchang Formation in the Southeastern Ordos Basin, China

Energies ◽

10.3390/en10121949 ◽

2017 ◽

Vol 10 (12) ◽

pp. 1949 ◽

Cited By ~ 5

Author(s):

Jiao Su ◽

Yingchu Shen ◽

Jin Hao ◽

Bo Liu

Keyword(s):

Shale Gas ◽

Ordos Basin ◽

Gas Content ◽

Yanchang Formation

Download Full-text

Experimental Study of the Characteristic Changes of Coal Resistivity during the Gas Adsorption/Desorption Process

Advances in Materials Science and Engineering ◽

10.1155/2018/1450187 ◽

2018 ◽

Vol 2018 ◽

pp. 1-7 ◽

Cited By ~ 2

Author(s):

Zengchao Feng ◽

Chen Wang ◽

Dong Dong ◽

Dong Zhao ◽

Dong Zhou

Keyword(s):

Gas Adsorption ◽

Gas Content ◽

Resistivity Change ◽

Adsorption Experiment ◽

Desorption Process ◽

Continuous Adsorption ◽

Gas Desorption ◽

Original Figure ◽

Adsorption Desorption ◽

The Relationship

To study the influence of gas adsorption-desorption on the resistivity of coal, the resistivity changes in conditions of continuous adsorption/desorption and isovolumetric adsorption/desorption were tested by high-precision resistance measurement, and the relationship between coal resistivity and gas content was investigated. The results show that gas adsorption/desorption has obvious effects on the resistivity of coal. Similar behavior was observed both in continuous adsorption/desorption and in isovolumetric adsorption/desorption experiments. The coal resistivity decreased gradually at the very beginning and then tended to stabilize as the gas adsorption capacity increased; in the process of gas desorption, the resistivity demonstrated a linear relationship with gas content. When comparing resistivities for the different adsorption modes, it was found that, for the same gas content in each mode, the resistivity change in the isovolumetric adsorption experiment was more obvious than in the continuous adsorption experiment. Also, the coal resistivity in the isovolumetric experiment differed further from the original figure when the desorption ended. The results are significant for predicting gas content in the coal mining process.

Download Full-text

Shale Gas Content Calculation of the Triassic Yanchang Formation in the Southeastern Ordos Basin, China

10.20944/preprints201710.0052.v1 ◽

2017 ◽

Author(s):

Jiao Su ◽

Yingchu Shen ◽

Bo Liu ◽

Jin Hao

Keyword(s):

Shale Gas ◽

Calculation Method ◽

Indirect Method ◽

Ordos Basin ◽

Gas Content ◽

Dissolved Gas ◽

Yanchang Formation ◽

Free Gas ◽

Shale Reservoirs ◽

Method Show

Shale gas content is the key parameter for shale gas potential evaluation and favorable area prediction. Therefore, it is very important to determine shale gas content accurately. Generally, we use the USBM method for coal reservoirs to calculate gas content of shale reservoirs. However, shale reservoirs are different from coal reservoirs in depth, pressure, core collection, etc. This method would inevitably cause problems. In order to make the USBM method more suitable for shale reservoir, an improved USBM method is put forward on the basis of systematic analysis of core pressure history and temperature history during shale gas desorption. The improved USBM method modifies the calculation method of the lost time, and determines the temperature balance time of water heating. In addition, we give the calculation method of adsorption gas content and free gas content, especially the new method of calculating the oil dissolved gas content and water dissolved gas content which are easily neglected. We used the direct method (USBM and the improved USBM) and the indirect method (adsorption gas, free gas and dissolved gas) to calculate the shale gas content of 16 shale samples of the Triassic Yanchang Formation in the Southeastern Ordos Basin, China. The results of the improved USBM method show that the total shale gas content is high, with an average of 3.97 m3/t, and the lost shale gas content is the largest proportion with an average of 62%. The total shale gas content calculated by the improved USBM method is greater than that of the USBM method. The results of the indirect method show that the total shale gas content is large, with an average of 4.11 m3/t, and the adsorption shale gas content is the largest proportion with an average of 71%.  The oil dissolved shale gas content which should be taken attention accounts for about 7.8%. The relative error between the improved USBM method and indirect method is much smaller than that between USBM method and indirect method, which verifies the accuracy of the improved USBM method.

Download Full-text

Coupling between Source Rock and Reservoir of Shale Gas in Wufeng-Longmaxi Formation in Sichuan Basin, South China

Energies ◽

10.3390/en14092679 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2679

Author(s):

Yuying Zhang ◽

Shu Jiang ◽

Zhiliang He ◽

Yuchao Li ◽

Dianshi Xiao ◽

...

Keyword(s):

Source Rock ◽

Shale Gas ◽

Sichuan Basin ◽

Gas Content ◽

Potential Zone ◽

Hydrocarbon Generation ◽

Gas Generation ◽

Longmaxi Formation ◽

Siliceous Shale ◽

Organic Pores

In order to analyze the main factors controlling shale gas accumulation and to predict the potential zone for shale gas exploration, the heterogeneous characteristics of the source rock and reservoir of the Wufeng-Longmaxi Formation in Sichuan Basin were discussed in detail, based on the data of petrology, sedimentology, reservoir physical properties and gas content. On this basis, the effect of coupling between source rock and reservoir on shale gas generation and reservation has been analyzed. The Wufeng-Longmaxi Formation black shale in the Sichuan Basin has been divided into 5 types of lithofacies, i.e., carbonaceous siliceous shale, carbonaceous argillaceous shale, composite shale, silty shale, and argillaceous shale, and 4 types of sedimentary microfacies, i.e., carbonaceous siliceous deep shelf, carbonaceous argillaceous deep shelf, silty argillaceous shallow shelf, and argillaceous shallow shelf. The total organic carbon (TOC) content ranged from 0.5% to 6.0% (mean 2.54%), which gradually decreased vertically from the bottom to the top and was controlled by the oxygen content of the bottom water. Most of the organic matter was sapropel in a high-over thermal maturity. The shale reservoir of Wufeng-Longmaxi Formation was characterized by low porosity and low permeability. Pore types were mainly <10 nm organic pores, especially in the lower member of the Longmaxi Formation. The size of organic pores increased sharply in the upper member of the Longmaxi Formation. The volumes of methane adsorption were between 1.431 m3/t and 3.719 m3/t, and the total gas contents were between 0.44 m3/t and 5.19 m3/t, both of which gradually decreased from the bottom upwards. Shale with a high TOC content in the carbonaceous siliceous/argillaceous deep shelf is considered to have significant potential for hydrocarbon generation and storage capacity for gas preservation, providing favorable conditions of the source rock and reservoir for shale gas.

Download Full-text

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

Geological Magazine ◽

10.1017/s001675681500062x ◽

2015 ◽

Vol 153 (4) ◽

pp. 663-680 ◽

Cited By ~ 21

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.

Download Full-text

Modeling Gas Adsorption in Marcellus Shale With Langmuir and BET Isotherms

SPE Journal ◽

10.2118/170801-pa ◽

2016 ◽

Vol 21 (02) ◽

pp. 589-600 ◽

Cited By ~ 77

Author(s):

Wei Yu ◽

Kamy Sepehrnoori ◽

Tadeusz W. Patzek

Keyword(s):

Shale Gas ◽

Langmuir Isotherm ◽

History Matching ◽

Gas Adsorption ◽

Marcellus Shale ◽

Methane Adsorption ◽

Gas Reservoirs ◽

Gas Desorption ◽

Shale Gas Reservoirs ◽

Bet Isotherm

Summary Production from shale-gas reservoirs plays an important role in natural-gas supply in the United States. Horizontal drilling and multistage hydraulic fracturing are the two key enabling technologies for the economic development of these shale-gas reservoirs. It is believed that gas in shale reservoirs is mainly composed of free gas within fractures and pores and adsorbed gas in organic matter (kerogen). It is generally assumed in the literature that the monolayer Langmuir isotherm describes gas-adsorption behavior in shale-gas reservoirs. However, in this work, we analyzed four experimental measurements of methane adsorption from the Marcellus Shale core samples that deviate from the Langmuir isotherm, but obey the Brunauer-Emmett-Teller (BET) isotherm. To the best of our knowledge, it is the first time to find that methane adsorption in a shale-gas reservoir behaves similar to multilayer adsorption. Consequently, investigation of this specific gas-desorption effect is important for accurate evaluation of well performance and completion effectiveness in shale-gas reservoirs on the basis of the BET isotherm. The difference in calculating original gas in place (OGIP) on the basis of both isotherms is discussed. We also performed history matching with one production well from the Marcellus Shale and evaluated the contribution of gas desorption to the well's performance. History matching shows that gas adsorption obeying the BET isotherm contributes more to overall gas recovery than gas adsorption obeying the Langmuir isotherm, especially at early time in production. This work provides better understanding of gas desorption in shale-gas reservoirs and updates our current analytical and numerical models for simulation of shale-gas production.

Download Full-text

Geochemistry and shale gas potential of the lower Permian marine-continental transitional shales in the Eastern Ordos Basin

Energy Exploration & Exploitation ◽

10.1177/0144598720979242 ◽

2020 ◽

pp. 014459872097924

Author(s):

Jingyi Wei ◽

Yongli Wang ◽

Gen Wang ◽

Zhifu Wei ◽

Wei He

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Total Organic Carbon ◽

Shale Gas ◽

Higher Plants ◽

Ordos Basin ◽

Organic Matter Content ◽

Lower Permian ◽

Gas Desorption ◽

Geochemical Parameters

Marine–continental transitional strata were widely developed in the Ordos Basin in Upper Carboniferous - Lower Permian. The Taiyuan - Shanxi Formation possesses promising shale gas exploration layers. Shale samples from two drilling wells of Shanxi-Taiyuan Formation in Shilou and Xixian, Ordos Basin, were investigated to study their carbon–sulfur contents and distribution characteristics of organic components using carbon/sulfur analyzer and gas chromatography–mass spectroscopy. Using results of total organic carbon analyses, Rock-Eval pyrolysis, X-ray diffraction analysis, shale gas desorption experiments, and other relevant experimental data, the shale samples were comprehensively analyzed. The exploitability of the shale in the study area was evaluated. The Shanxi-Taiyuan Shale in the Shilou and Xixian areas was characterized by high total organic carbon contents of 7.1% and 2.1% and high Tmax values of 499 and 505 °C, respectively. The organic matter of the shale is types II2 and III. Moreover, biomarker parameters including n-alkanes, Paq, Pwax, average carbon chain length, and the ternary diagram of C27-C28-C29 steranes show the organic matter constituted terrestrial higher plants and aquatic low biological algae. Multiple n-alkane parameters show the organic matter input in the Shilou area is mainly derived from terrestrial higher plants. The Pr/Ph value and trace element indicators show the deposition environment is dominated by weak oxidation–reduction conditions. A shale gas desorption experiment shows the average desorbed gas contents of the shale samples in the Shilou and Xixian areas were 1.79 and 0.37 m3/t, respectively. The organic matter content determined the differences in shale gas properties between the two areas in Ordos Basin. The composition and content of inorganic minerals affect the reservoir physical properties. According to the analyses, the shale in the Shilou area has good shale gas reservoir characteristics in terms of desorbed gas content and the above-mentioned geochemical parameters. Furthermore, the Shanxi shale has good potential for shale gas industrial exploitation.

Download Full-text

Shale favorable area optimization in coal-bearing series: A case study from the Shanxi Formation in Northern Ordos Basin, China

Energy Exploration & Exploitation ◽

10.1177/0144598717748951 ◽

2017 ◽

Vol 36 (5) ◽

pp. 1295-1309 ◽

Cited By ~ 4

Author(s):

Wei Guo ◽

Weijun Shen ◽

Shangwen Zhou ◽

Huaqing Xue ◽

Dexun Liu ◽

...

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Total Organic Carbon ◽

Shale Gas ◽

Ordos Basin ◽

Sedimentary Facies ◽

Gas Content ◽

Burial Depth ◽

Organic Carbon Content ◽

River Channels

Shales in the Well district of Yu 106 of the Shanxi Formation in the Eastern Ordos Basin is deposited in the swamp between delta plains, distributary river channels, natural levee, the far end of crevasse splay, and depression environments. According to organic geochemistry, reservoir physical property, gas bearing capacity, lithology experimental analysis, combined with the data of drilling, logging, testing and sedimentary facies, the reservoir conditions of shale gas and the distribution of an advantageous area in Shanxi Formation have been conducted. The results show that the total organic carbon content of the Shanxi Formation is relatively high, with an average content value of 5.28% in the segment 2 and 3.02% in segment 1, and the organic matter is mainly kerogen type II2 and III. The maturity of organic matter is high with 1.89% as the average value of Ro which indicates the superior condition for gas generation of this reservoir. The porosity of shales is 1.7% on average, and the average permeability is 0.0415 × 10−3 µm2. The cumulative thickness is relatively large, with an average of 75 m. Brittle mineral and clay content in shales are 49.9% and 50.1%, respectively, but the burial depth of shale is less than 3000 m. The testing gas content is relatively high (0.64 × 104 m3/d), which shows a great potential in commercial development. The total organic carbon of the segment 2 is higher than that of the segment 1, and it is also better than segment 1 in terms of gas content. Based on the thickness of shale and the distribution of sedimentary facies, it is predicted that the advantageous area of shale gas in the segment 2 is distributed in a striped zone along the northeast and the northsouth direction, which is controlled by the swamp microfacies between distributary river channels.

Download Full-text