scholarly journals Factors Controlling Shale Reservoirs and Development Potential Evaluation: A Case Study

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Chao Luo ◽  
Hun Lin ◽  
Yujiao Peng ◽  
Hai Qu ◽  
Xiaojie Huang ◽  
...  
Keyword(s):  
Shale Gas ◽  
Mineral Content ◽  
Gas Content ◽  
Longmaxi Formation ◽  
Development Potential ◽  
Reservoir Characteristics ◽  
Lower Silurian ◽  
Single Well ◽  
Shale Reservoir ◽  
Shale Reservoirs

The shale of the Lower Silurian Longmaxi Formation is an important gas-producing layer for shale gas development in southern China. This set of shale reservoir characteristics and shale gas development potential provide an important foundation for shale gas development. This study takes wellblock XN111 in the Sichuan Basin, China, as an example and uses X-ray diffraction (XRD), scanning electron microscopy (SEM), isothermal adsorption, and other techniques to analyze the shale reservoir characteristics of the Lower Silurian Longmaxi Formation. The results show that the Lower Silurian Longmaxi Formation was deposited in a deep-water shelf environment. During this period, carbonaceous shale and siliceous shale characterized by a high brittle mineral content ( quartz > 40   wt . % , carbonate   mineral > 10   wt . % ) and a low clay mineral content (<30 wt.%, mainly illite) were widely deposited throughout the region. The total organic carbon (TOC) content reaches up to 6.07 wt.%, with an average of 2.66 wt.%. The vitrinite reflectance is 1.6–2.28%, with an average of 2.05%. The methane adsorption capacity is 0.84–4.69 m3/t, with an average of 2.92 m3/t. Pores and fractures are developed in the shale reservoirs. The main reservoir space is composed of connected mesopores with an average porosity of 4.78%. The characteristics and development potential of the shale reservoirs in the Lower Silurian Longmaxi Formation are controlled by the following factors: (1) the widespread deep-water shelf deposition in wellblock XN111 was a favorable environment for the development of high-quality shale reservoirs with a cumulative thickness of up to 50 m; (2) the high TOC content enabled the shale reservoir to have a high free gas content and a high adsorptive gas storage capacity; and (3) the shale’s high maturity or over maturity is conducive to the development of pores and fractures in the organic matter, which effectively improves the storage capacity of the shale reservoirs. The reservoir characteristic index was constructed using the high-quality shale’s thickness, gas content, TOC, fracture density, and clay content. Using production data from shale gas wells in adjacent blocks, a mathematical relationship was established between the Estimated Ultimate Recovery (EUR) of a single well and the Reservoir Characteristics Index (Rci). The EUR of a single well in wellblock XN111 was estimated.

Effect of Slick Water on Permeability of Shale Gas Reservoirs

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Bin Yuan ◽  
Yongqing Wang ◽  
Zeng Shunpeng
Keyword(s):  
Shale Gas ◽  
Immersion Time ◽  
Permeability Change ◽  
Capillary Effect ◽  
Gas Reservoirs ◽  
Longmaxi Formation ◽  
Lower Silurian ◽  
Shale Reservoirs ◽  
Induced Fractures ◽  
Vdw Force

In this study, we analyzed the flow-back resistance of slick water fracturing fluid in shale reservoirs. The flow-back resistance mainly includes capillary force, Van der Waals (VDW) force, hydrogen bond force, and hydration stress. Shale of Lower Silurian Longmaxi Formation (LSLF) was used to study its wettability, hydration stress, and permeability change with time of slick water treatment. The results reveal that wettability of LSLF shale was more oil-wet before immersion, while it becomes more water-wet after immersion. The hydration stress of the shale increased with increasing immersion time. The permeability decreased first, then recovered with increasing immersion time. The major reason for permeability recovery is that the capillary effect (wettability) and the shale hydration make macrocracks extension and expansion and hydration-induced fractures formation.

scholarly journals Differences of Main Enrichment Factors of S1l11-1 Sublayer Shale Gas in Southern Sichuan Basin

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5472
Author(s):  
Xuewen Shi ◽  
Chao Luo ◽  
Gaohui Cao ◽  
Yifan He ◽  
Yi Li ◽  
...  
Keyword(s):  
Shale Gas ◽  
Sichuan Basin ◽  
Mineral Content ◽  
Enrichment Factors ◽  
Gas Content ◽  
Longmaxi Formation ◽  
The Difference ◽  
Organic Porosity ◽  
Gas Bearing ◽  
Organic Pores

In this study, shale cores from 20 wells in the S1l11-1 sublayer of Longmaxi Formation buried in shallow shale (<3500 m) and deep shale (>3500 m) in the southern Sichuan Basin, China were collected to compare their pore structures and gas-bearing properties using multiple experiments. Results showed that the deep layer has relatively lower brittle mineral content, which is disadvantageous in terms of the higher requirements it imposes on hydraulic fracturing. Results also showed that the most important factor controlling the differential enrichment of S1l11-1 shale gas in southern Sichuan Basin is porosity. Moreover, the porosity composition of shallow shale and deep shale has significant differences: the porosity of shallow shale is dominated by organic pores, while for deep shale, both organic and inorganic pores are important. The inorganic pores provide significant storage space for free gas in deep shale; their contribution warrants more attention. We also found that the difference in organic porosity of the shallow and deep shale samples resulted from large differences in pore development ability, while the highest inorganic porosity was concentrated near the optimal mineral composition when the content of quartz plus feldspar plus pyrite was about 70%. This study revealed the primary factor controlling the difference in gas content between shallow and deep shale and detailed the characteristics of microscopic pore structure, providing a basis for the exploration and development of deep shale gas in the Wufeng-Longmaxi Formation in the southern Sichuan Basin.

Clay minerals in shales of the Lower Silurian Longmaxi Formation in the Eastern Sichuan Basin, China

Clay Minerals ◽  
2017 ◽  
Vol 52 (2) ◽  
pp. 217-233
Author(s):  
Geng Yi-Kai ◽  
Jin Zhen-Kui ◽  
Zhao Jian-Hua ◽  
Wen Xin ◽  
Zhang Zhen-Peng ◽  
...  
Keyword(s):  
Clay Minerals ◽  
Clay Mineral ◽  
Mixed Layer ◽  
Shale Gas ◽  
Mineral Content ◽  
High Pressures ◽  
Gas Reservoirs ◽  
Longmaxi Formation ◽  
Lower Silurian ◽  
Layer I

AbstractThe present study examines the characteristics of clay minerals in shale gas reservoirs and their influence on reservoir properties based on X-ray diffraction and scanning electron microscopy. These analyses were combined with optical microscopy observations and core and well-log data to investigate the genesis, distribution characteristics, main controlling factors and pore features of clay minerals of the Lower Silurian Longmaxi Formation in the East Sichuan area, China. The clay mineral assemblage consists of illite + mixed-layer illite-smectite (I-S) + chlorite. This assemblage includes three sources of clay minerals: detrital, authigenic and diagenetic minerals. The lower section of the Longmaxi Formation in the Jiaoshiba area has sealing ability which resulted in abnormal high pressures during hydrocarbon generation which inhibited illitization. Therefore, an anomalous transformation sequence is present in which the mixed-layer I-S content increases with depth. This anomalous transformation sequence can be used to infer the existence of abnormal high pressures. The detrital components of the formation also affect the clay-minerals content indirectly, especially the abundance of K-feldspar. The transformation of mixed-layer I-S to illite is limited due to the limited availability of K+, which determines the extent of transformation. Three types of pores were observed in the shale reservoir rocks of the Longmaxi Formation: interparticle (interP) pores, intraparticle (intraP) pores and organic-matter pores. The clay-mineral content controls the development of intraP pores, which are dominated by pores within clay particles. For a given clay mineral content, smectite and mixed-layer I-S were more conducive to the development of shale-gas reservoirs than other clay minerals.

New Calculation Method and Application of Gas Loss From Coring Shale Gas Well

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Wuguang Li ◽  
Zhang Jian ◽  
Xiaokai Chen ◽  
Hao Chen
Keyword(s):  
Shale Gas ◽  
New Method ◽  
Gas Content ◽  
Gas Well ◽  
Measuring Device ◽  
Gas Dispersion ◽  
Well Production ◽  
Single Well ◽  
Shale Reservoir ◽  
Gas Loss

Abstract Gas content is one of the most important parameters of shale reservoir evaluation and productivity evaluation. In order to obtain gas content accurately, based on the first law of Fick and material balance equation, mathematical model of gas dispersion flow in shale reservoir is established, analytical solution is obtained, and evaluation method of gas dispersion in shale reservoir is formed. On the basis of this study, the onsite desorption gas measuring device and testing process for coring shale gas wells are designed, the time-varying shale desorption gas is obtained, and the residual gas of shale is measured by the crushing method. The calculation formula of shale gas content is obtained by fitting the test data, the shale gas loss, and total gas content are calculated, and then analyzed the influences of the shale gas-bearing properties and gas content on single well production and geological reserves by combining the data of shale absorbed gas. The results show that the gas content calculated by the new method is about 6.54% more than that of log interpretation, and about 7.57% on average more than that obtained by traditional empirical method. The gas content proportion of long Yi1 subsegmental small layers 1 and 2 is smaller than that of long Yi1 subsegmental small layers 3 and 4 and long Yi2 subsegmental. It is considered that the amount of shale gas lost is large, because of the pressure release during the coring, and the comparative error of gas content obtained by several methods is within the acceptable range. So the new method can be used as an important mean to obtain shale gas content. The most direct factors affecting gas content are complex: Buried depth, porosity, total organic carbon content, water saturation, and formation temperature. Shale gas content is the material basis of single well production and geological reserves of shale gas, and it is also the decisive factor. Therefore, the accurate evaluation of shale gas content is one of the key techniques to evaluate shale gas well productivity and shale gas resources, which is of great significance.

Experimental Study on Shut-in-Time Optimization for Multi-Fractured Horizontal Wells in Shale Reservoirs

2022 ◽  
Author(s):  
Liang Tao ◽  
Jianchun Guo ◽  
Zhongbo Wang ◽  
Yi Liu ◽  
Yuhang Zhao ◽  
...  
Keyword(s):  
Clay Mineral ◽  
Shale Gas ◽  
Mineral Content ◽  
Type I ◽  
Diffusion Experiment ◽  
Ion Diffusion ◽  
Water Imbibition ◽  
Study Results ◽  
Shale Reservoir ◽  
Shale Reservoirs

Abstract The optimization of shut-in-time in shale gas well is an important factor affecting the production of single well after volume fracturing. In this study, a new method for determining the optimal shut-in-time considering clay mineral content and ion diffusion concentration was proposed. First, a novel water spontaneous imbibition apparatus under the conditions of formation temperature and confining pressure was designed. Then, the water imbibition satuation of 15 shale samples from the Longmaxi Formation (LF) of the Sichuan Basin were measured to quantitatively evaluate the water imbibition ability and classify reservoir types. Finally, the salt ion concentration diffusion experiment was carried out to optimize the shut-in-time of different types of shale reservoirs. The experimental results shown that the clay mineral content was the key factor affecting water wettability of shale, the shale reservoirs can be divided into two types and the critical value of clay mineral content was about 40%. Based on the law of salt ion diffusion in shale, the initiation time of micro-fractures induced by shale hydration was about 10-15 days. Under the experimental conditions, the optimal shut-in time of type I shale reservoir and type II shale reservoir were about 20 days and 15 days respectively. The average daily gas production has increased from 15.6×104 m3/day to 25.1×104 m3/day. The study results can provide scientific basis for the optimization of flowback regime of shale gas resrvoirs.

scholarly journals Reservoir Characteristics of the Lower Silurian Longmaxi Shale in Zhaotong Region, Southern China

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Chao Luo ◽  
Nanxin Yin ◽  
Hun Lin ◽  
Xuanbo Gao ◽  
Junlei Wang ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Total Organic Carbon ◽  
Shale Gas ◽  
Southern China ◽  
Gas Content ◽  
High Quality ◽  
Longmaxi Formation ◽  
Lower Silurian ◽  
Longmaxi Shale ◽  
Scanning Electron

The lower Silurian Longmaxi Formation hosts a highly productive shale gas play in the Zhaotong region of southern China. According to core observation, X-ray diffraction analyses, and scanning electron microscopy (SEM) observations, the shale comprises primarily quartz, carbonate minerals, and clay minerals, with minor amounts of plagioclase, K-feldspar, and pyrite. The clay mineral content ranges from 15.0% to 46.1%, with an average of 29.3% in the Zhaotong region. Organic geochemical analyses show that the Longmaxi Formation has good potential for shale gas resources by calculating total organic carbon, vitrinite reflectance, and gas content. Scanning electron microscope images demonstrate that reservoir pore types in the Longmaxi shale include organic pores, interparticle pores, intercrystalline pores, intraparticle pores, and fractures. Reservoir distribution is controlled by lithofacies, mineral composition, and geochemical factors. In addition, we investigated the relationships between reservoir parameters and production from 15 individual wells in the Zhaotong region by correlation coefficients. As a result, the brittleness index, total organic carbon (TOC), porosity, and gas content were used to define high-quality reservoirs in the Longmaxi shale. Based on these criteria, we mapped the thickness and distribution of high-quality reservoirs in the Longmaxi Formation and selected highlighted several key sites for future exploration and development.

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

Energies ◽  
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.

scholarly journals Prediction of Shale Gas Reservoirs Using Fluid Mobility Attribute Driven by Post-Stack Seismic Data: A Case Study from Southern China

2020 ◽  
Vol 11 (1) ◽  
pp. 219
Author(s):  
Jing Zeng ◽  
Alexey Stovas ◽  
Handong Huang ◽  
Lixia Ren ◽  
Tianlei Tang
Keyword(s):  
Shale Gas ◽  
Seismic Data ◽  
Spectral Decomposition ◽  
Southern China ◽  
Gas Reservoirs ◽  
Seismic Attribute ◽  
Longmaxi Formation ◽  
Shale Gas Reservoirs ◽  
The Sichuan Basin ◽  
Shale Reservoirs

Paleozoic marine shale gas resources in Southern China present broad prospects for exploration and development. However, previous research has mostly focused on the shale in the Sichuan Basin. The research target of this study is expanded to the Lower Silurian Longmaxi shale outside the Sichuan Basin. A prediction scheme of shale gas reservoirs through the frequency-dependent seismic attribute technology is developed to reduce drilling risks of shale gas related to complex geological structure and low exploration level. Extracting frequency-dependent seismic attribute is inseparable from spectral decomposition technology, whereby the matching pursuit algorithm is commonly used. However, frequency interference in MP results in an erroneous time-frequency (TF) spectrum and affects the accuracy of seismic attribute. Firstly, a novel spectral decomposition technology is proposed to minimize the effect of frequency interference by integrating the MP and the ensemble empirical mode decomposition (EEMD). Synthetic and real data tests indicate that the proposed spectral decomposition technology provides a TF spectrum with higher accuracy and resolution than traditional MP. Then, a seismic fluid mobility attribute, extracted from the post-stack seismic data through the proposed spectral decomposition technology, is applied to characterize the shale reservoirs. The application result indicates that the seismic fluid mobility attribute can describe the spatial distribution of shale gas reservoirs well without well control. Based on the seismic fluid mobility attribute section, we have learned that the shale gas enrich areas are located near the bottom of the Longmaxi Formation. The inverted velocity data are also introduced to further verify the reliability of seismic fluid mobility. Finally, the thickness map of gas-bearing shale reservoirs in the Longmaxi Formation is obtained by combining the seismic fluid mobility attribute with the inverted velocity data, and two favorable exploration areas are suggested by analyzing the thickness, structure, and burial depth. The present work can not only be used to evaluate shale gas resources in the early stage of exploration, but also help to design the landing point and trajectory of directional drilling in the development stage.

scholarly journals Difference Analysis of Organic Matter Enrichment Mechanisms in Upper Ordovician-Lower Silurian Shale from the Yangtze Region of Southern China and Its Geological Significance in Shale Gas Exploration

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Ming Wen ◽  
Zhenxue Jiang ◽  
Kun Zhang ◽  
Yan Song ◽  
Shu Jiang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Shale Gas ◽  
Southern China ◽  
Sedimentary Organic Matter ◽  
Gas Content ◽  
Silicon Isotope ◽  
Upper Ordovician ◽  
Lower Silurian ◽  
Excess Silicon ◽  
Lower Yangtze

The upper Ordovician-lower Silurian shale has always been the main target of marine shale gas exploration in southern China. However, the shale gas content varies greatly across different regions. The organic matter content is one of the most important factors in determining gas content; therefore, determining the enrichment mechanisms of organic matter is an important problem that needs to be solved urgently. In this paper, upper Ordovician-lower Silurian shale samples from the X-1 and Y-1 wells that are located in the southern Sichuan area of the upper Yangtze region and the northwestern Jiangxi area of the lower Yangtze region, respectively, are selected for analysis. Based on the core sample description, well logging data analysis, mineral and elemental composition analysis, silicon isotope analysis, and TOC (total organic carbon) content analysis, the upper Ordovician-lower Silurian shale is studied to quantitatively calculate its content of excess silicon. Subsequently, the results of elemental analysis and silicon isotope analysis are used to determine the origin of excess silicon. Finally, we used U/Th to determine the characteristics of the redox environment and the relationship between excess barium and TOC content to judge paleoproductivity and further studied the mechanism underlying sedimentary organic matter enrichment in the study area. The results show that the excess silicon from the upper Ordovician-lower Silurian shale in the upper Yangtze area is derived from biogenesis. The sedimentary water body is divided into an oxygen-rich upper water layer that has higher paleoproductivity and a strongly reducing lower water that is conducive to the preservation of sedimentary organic matter. Thus, for the upper Ordovician-lower Silurian shale in the upper Yangtze region, exploration should be conducted in the center of the blocks with high TOC contents and strongly reducing water body. However, the excess silicon in the upper Ordovician-lower Silurian shale of the lower Yangtze area originates from hydrothermal activity that can enhance the reducibility of the bottom water and carry nutrients from the crust to improve paleoproductivity and enrich sedimentary organic matter. Therefore, for the upper Ordovician-lower Silurian shale in the lower Yangtze region, exploration should be conducted in the blocks near the junction of the two plates where hydrothermal activity was active.

Sign in / Sign up

Export Citation Format

Share Document