scholarly journals Influence of pressure, coal structure and permeability on CBM well productivity at various burial depths in South Yanchuan Block, China

2016 ◽  
Vol 20 (3) ◽  
pp. 1 ◽  
Author(s):  
Teng Li ◽  
Caifang Wu

With a burial depth of 1000 m as the demarcation, the coal reservoir in South Yanchuan Block, China is divided into deep reservoir and shallow reservoir regions. A combination of coalbed methane well production data, well logging interpretation, coalbed methane numerical simulations and reservoir properties were used to research various production characteristics at different depths. The results indicate that coal thickness and gas content are not key factors that influence methane production. The shallow reservoir is located in a tension zone, while the deep reservoir is located in both a transformation zone and a compression zone. Although the reservoir and closure pressures increase with the burial depth, the pressures fluctuate in the deep reservoir, especially in the transformation zone. This fluctuation influences the opened degree of the fractures in the reservoir. The effective stress is lower in the deep reservoir than in the shallow reservoir, leading to higher permeability in the deep reservoir. This difference in effective stress is the key factor that influences the methane production. The combination of coal thickness and gas content also significantly influenced the methane production. Influenced by the reservoir and closure pressures, the Type III coal in the shallow reservoir is more developed, while the deep reservoir contained more developed Type I and Type II coal. The permeability increases exponentially with increasing thickness of Type I and Type II coal, which determines the high reservoir permeability in the deep reservoir. The development of Type III coal leads to the poor reservoir hydraulic fracturing effect. However, a reservoir with thick Type I and Type II coal can have a positive effect. Influencia de la presión, la estructura del carbón y su permeabilidad sobre la productividad de gas metano de carbón en profundidades de enterramiento del bloque Yanchuan Sur, ChinaResumenCon una profundidad de enterramiento de 1000 metros, el yacimiento de carbón del bloque Yanchuan Sur, en China, se divide en dos: el depósito profundo y el depósito superficial. Este trabajo combina los datos de la información de producción de gas metano asociado carbón, la interpretación de registros de pozo, las simulaciones numéricas de metano asociado a carbón y las propiedades del reservorio para encontrar las características de producción a diferentes profundidades. Los resultados indican que el espesor del carbón y el contenido de gas no son factores que alcancen a influir en la producción de metano. El depósito superficial se encuentra en una zona de tensión, mientras el depósito profundo está ubicado en una región tanto de transformación como de compresión. Aunque el reservorio y la presión de cierre se incrementan con la profundidad de enterramiento, las presiones fluctúan en el depósito profundo, especialmente en la zona de transformación. Esta fluctuación influye en el grado de apertura de las fracturas en el depósito. La tensión efectiva es más baja en el depósito profundo, lo que significa una mayor permeabilidad. La diferencia en la tensión efectiva es el factor clave que incide en la producción de metano. Afectado por las presiones de cierre y del yacimiento, el carbón tipo III en el depósito superficial está más desarrollado, mientras que el depósito profundo contiene carbón tipo I y tipo II más desarrollado. La permeabilidad se incrementa exponencialmente con el incremento del espesor en el carbón tipo I y tipo II, lo que determina la alta porosidad en el depósito profundo. El desarrollo de carbón tipo III lleva a un pobre efecto de la fractura hidráulica en el depósito. Sin embargo, un depósito con carbón tipo I y tipo II espeso podría tener un efecto positivo.

2020 ◽  
Vol 38 (1-2) ◽  
pp. 3-23 ◽  
Author(s):  
Yang Zhao ◽  
Xiaodong Zhang ◽  
Shuo Zhang ◽  
Jiaosheng Yang ◽  
Xianzhong Li ◽  
...  

Adsorption and desorption of coalbed methane are generally at a dynamic equilibrium state under the undisturbed coal reservoir. However, as the reservoir pressure drops to a certain value during the extraction of coalbed methane, the equilibrium state is destroyed and thus more coalbed methane desorbs and escapes from coal to wellbore. Here the corresponding bottom-hole fluid pressure is called initial gas production pressure (IGPP) in the development practice of coalbed methane wells. This paper, which has taken Changzhi-Anze block in the central-southern part of Qinshui basin as the study object, addresses the distribution characteristic and control factors of IGPP of coalbed methane wells and then explores the key factors affecting IGPP using grey correlation analysis theory. The results indicate that IGPP varies from 1.09 MPa to 6.57 MPa, showing a distribution law with high in the middle and low in the west and east of the study area, which presents a similar distribution characteristic with burial depth, thickness, coal rank, gas content, original reservoir pressure, and in-situ stress. Further, through grey correlation analysis, it concludes that the correlation degrees of control factors affecting IGPP of coalbed methane wells in the descending order are decline rate of working fluid level, water yield before gas production, reservoir pressure, coal thickness, coal rank, minimum horizontal principal stress, burial depth, and gas content. Among these factors, engineering factors, including decline rate of working fluid level and water yield before gas production, present a key controlling effect, because they can determine the smooth migration pathway directly during initial water production. And another key factor, original reservoir pressure also builds strong and positive correlation with IGPP under the interaction of other geology and reservoir factors, revealing the capability of gas desorption and the transmission of pressure drops.


Author(s):  
Sudipa Mitra-Kirtley ◽  
Oliver C. Mullins ◽  
Andrew E. Pomerantz

This chapter gives an overview of sulfur x-ray absorption near edge spectroscopy (XANES) studies performed on some carbonaceous materials, viz. crude oil and related materials (asphaltenes, kerogens, bitumens, and resins), and coals. Thiophene, sulfide, sulfoxide, sulfone, pyrite, and sulfate are found in varying amounts in these materials. In source rock bitumens, sulfoxide is more abundant than in the kerogens, while within the kerogens, the less aromatic Type I samples show a smaller ratio of thiophenic/sulfidic sulfur than in Type II samples. Petroleum asphaltenes have a similar sulfur chemistry, regardless of the source or the burial depth. Resins and oil fractions retain the polar sulfoxide species of the parent oil similar to the more polar asphaltenes fractions. More aromatic sulfur species also dominate in the more matured coals than in the younger coals. Studies of nitrogen XANES also reveal that aromatic forms of nitrogen prevail in samples with increased aromatic carbon.


2015 ◽  
Vol 733 ◽  
pp. 96-99 ◽  
Author(s):  
Yu Shuang Hu ◽  
Yu Gang Hao ◽  
Hui Ting Hu

Based on coalbed methane geology theory, make use of coal and oil drilling data, from both of the coal reservoir characteristics and conservation conditions, Through comparative analysis of a number of geological factors of coalbed thickness, burial depth, metamorphic grade, gas content, roof and floor lithology, dip angle, etc, and found that there are many similarities between Jixi Basin and Black Warrior Basin in the United States of coalbed methane reservoir conditions. Compared to Black Warrior Basin, the advantages of Jixi Basin are that the coal metamorphism degree is high, the tired and single coalbed are thick, the closeness of roof and floor are good, the fault development and coalbed gas content are similar to it; the disadvantages of Jixi Basin are that the formation dip angle is large, the pressure gradient and permeability are small.


2013 ◽  
Vol 295-298 ◽  
pp. 3209-3212
Author(s):  
Li Ren Xing ◽  
Yan Bin Yao ◽  
Da Meng Liu ◽  
Jun Gang Liu ◽  
Lu Lu Zhou ◽  
...  

Southern Shizhuang Block has simple structure characteristics, relatively thick coal seams (3.1-10.5 m, 6 m in average), and favorable burial depth (450-900 m). The gas content of the No.3 coal seam in the Shanxi formation ranges from 6-20 m3/t, and it increases from the southeast to northwest area in the southern Shizhuang Block. Gas content is high in the structural low in the area, which means the gas accumulation is controlled by the geological characteristics of local structure and hydrogeologic conditions.


Energies ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1867 ◽  
Author(s):  
Xu Ge ◽  
Dameng Liu ◽  
Yidong Cai ◽  
Yingjin Wang

To study the gas potential of coalbed methane (CBM) in the Fukang area, southern Junggar Basin (SJB) of North China, different methods including multiple geophysical logging, the Kim method with proximate analysis data, and Langmuir adsorption were used to evaluate the gas content. Furthermore, the geological controls on gas content were evaluated. One hundred sixteen CBM wells with geophysical logging and 20 with field-measured gas content were adopted to assess the gas content in the Fukang area of SJB, NW China. The results show that the two geophysical logging variables (DEN and CNL) were favorable for evaluating the gas content due to the perfect correlation with the measured gas content. The gas content varies from 4.22 m3/t to 16.26 m3/t, and generally increases with increasing burial depth. The gas content in coal seams along the synclinal axis is significantly higher than that along the synclinal wing in the west zone. In the east zone, the gas content of the westward is higher than that of the eastward because of the fault coating effect by reverse fault. Generally, the gas content of the SJB is in the order of syncline > surrounding reverse fault > slope of syncline > slope of anticline > central of reverse fault, if only geological structure features are considered. The favorable areas for CBM concentration appear to be a composite gas controlling result of multiple geological factors. Two typical geological scenarios with low gas content and high gas content were revealed. In the Fukang area of SJB, the low gas content is mainly due to the normal fault and roof lithology of sandstone. The most favorable area of high gas content for CBM exploration and development is in the northeast, where reversed fault, synclinal axis, mudstone roof lithology, and burial depth coincide with high gas content.


2013 ◽  
Vol 734-737 ◽  
pp. 331-334
Author(s):  
Tao Tao Yan ◽  
Zhi Qiang Liu ◽  
Li Ren Xing ◽  
Yong Luo ◽  
Ya Dong Bai ◽  
...  

Gas content is one of the most important factors in the process of exploration and development of coalbed methane (CBM). The relationships between gas content and characteristics of geophysical logs have been evaluated for the No. 5 coal seam in Weibei CBM field. It is found that the main well loggings that have good responses for gas contents are the compensating density, natural gamma-ray, compensating neutron, natural spontaneous potential and acoustic. A theoretical model was proposed to calculate the gas content by using these well logging data and as well as the burial depth. The calculated gas contents fits well with the measured data with a small relative-error of 0.38-5.05%. In the model, both tectonic movement intensity and the gas accumulation were taken into consideration. Key words: Coalbed methane, Weibei coalfield, Ordos Basin, Gas content, Geophysical logging


2009 ◽  
Vol 27 (5) ◽  
pp. 307-332 ◽  
Author(s):  
Xiaodong Zhang ◽  
Yanhao Liu ◽  
Geoff Wang ◽  
Hao Liu

Jiaozuo coalfield is located in the northwest of Henan province, China, and close to the Southern Qinshui coal basin, the most successfully commercial CBM resource developed area in China. The No. II1 coal seam is the main economic coal seam in Jiaozuo coalfield and its average thickness exceeds 5.36m. The maximum reflectance of vitrinite (RO,max) of the No. II1 coal across the Jiaozuo is between 3.16% and 4.78%. The coalbody structure of the No. II1 coal seam changes greatly in different part and can be generally divided into 1∼3 sub-layers. The micropores in the No.II1 coal seam is the major pores, secondly are transitional pores, and then less macropores and mesopores. The No. II1 coal seam has stronger adsorption, and the reservoir natural permeability has an evident heterogeneity vary from 0.0001 to 83.71mD. High permeability region is often near fault structure or the boundary of fault block. The CBM genetic type is homologous thermal cracking gas of humic coal with high matunity. Gas content with the burial depth of 163∼1070m varies very greatly from 4.65 to 45.75m3/t, with an average value of 18.3m3/t, and gradually increases from northeast to southwest. According to the latest evaluation for CBM resource in Jiaozuo coalfield, the existing total in-place CBM resources in the No. II1 coal seam with the depth of shallower than 2000 m are close to 1.2 × 1012m3, most of them mainly distribute in the depth of 1000 ∼ 1500 m. The existing total in-place CBM resources is dominated by the inferred CBM resource reserves (more than 70%), which distribute the undrilled places with few coal geological knowledge and deeper than 1000m. The resource concentration of the No. II1 coal seam in Jiaozuo coalfield is in the range of (0.513–3.478)x108 m3/km2, with an average value of 1.805×108 m3/km2. Based on the CBM resource investigation and reservoir evaluation, the most prospective target zones for CBM production in Jiaozuo coalfield include Guhanshan coal mine, Jiulishan coal mine and the west part of Qiangnan coal district.


2014 ◽  
Vol 962-965 ◽  
pp. 21-28
Author(s):  
Bei Liu ◽  
Wei Hua Ao ◽  
Wen Hui Huang ◽  
Qi Lu Xu ◽  
Juan Teng

Coalbed methane (CBM) productivity is influenced by various factors. Based on field production data and test data of southern Qinshui Basin, factors including geological factors, engineering factors and drainage factors that affect CBM productivity are analyzed. Analytic hierarchy process (AHP) is introduced to calculate the contribution of each parameter to CBM productivity. A three-level model for evaluating CBM productivity based on AHP is established. The results show that average daily gas production of single well in southern Qinshui Basin increases with gas content, coal seam thickness, permeability, porosity, gas saturation, critical desorption pressure. Filling minerals in pores and fractures of coal can decrease gas content, porosity and permeability of coal reservoir. When burial depth is deeper than 500m or reservoir pressure is greater than 2MPa and burial depth is shallower than 1000m or reservoir pressure is less than 10MPa, CBM productivity is relatively high. According to the calculation, the weight of geological factors, engineering factors and drainage factors are 50%, 25% and 25%, respectively. Reservoir physical properties, geological conditions, fracturing technology and drainage process have the most impact, the weight of which are 33.33%, 16.67%, 11.79%, and 15.00%, respectively.


2015 ◽  
Vol 733 ◽  
pp. 100-103
Author(s):  
Liu Wang ◽  
Xue Rui Ma ◽  
Jing Han Wang ◽  
Yu Ting Zhou ◽  
Xun Liu

Based on coalbed methane geology theory, make use of coal and oil drilling data, from both of the coal reservoir characteristics and conservation conditions, Through comparative analysis of a number of geological factors of coalbed thickness, burial depth, metamorphic grade, gas content, roof and floor lithology, dip angle, etc, and found that there are many similarities between Jixi Basin and Black Warrior Basin in the United States of coalbed methane reservoir conditions. Furthermore, referred the domestic and abroad coalbed methane mining experience, a number of geological factors of Jixi Basin were made grading evaluation, optimized favorable blocks, and we found that the favorable coalbed methane target area are the F and H in the south of the basin, and the F block can be used as the preferred favorable coal exploration area.


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