Stable isotope characteristics of CBM co-produced water and implications for CBM development: The example of the Shizhuangnan block in the southern Qinshui Basin, China

Energy Exploration & Exploitation

et al. 2020

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To meet the global energy demands, the exploitation of coalbed methane has received increasing attention. Biogeochemical parameters of co-produced water from coalbed methane wells were performed in the No. 3 coal seam in the Shizhuangnan block of the southern Qinshui Basin (China). These biogeochemical parameters were firstly utilized to assess coal reservoir environments and corresponding coalbed methane production. A high level of Na+ and HCO3– and deuterium drift were found to be accompanied by high gas production rates, but these parameters are unreliable to some extent. Dissolved inorganic carbon (DIC) isotopes δ13CDIC from water can be used to distinguish the environmental redox conditions. Positive δ13CDIC values within a reasonable range suggest reductive conditions suitable for methanogen metabolism and were accompanied by high gas production rates. SO42–, NO3– and related isotopes affected by various bacteria corresponding to various redox conditions are considered effective parameters to identify redox states and gas production rates. Importantly, the combination of δ13CDIC and SO42– can be used to evaluate gas production rates and predict potentially beneficial areas. The wells with moderate δ13CDIC and negligible SO42– represent appropriate reductive conditions, as observed in most high and intermediate production wells. Furthermore, the wells with highest δ13CDIC and negligible SO42– exhibit low production rates, as the most reductive environments were too strict to extend pressure drop funnels.

Section: Hydrogeologymentioning

confidence: 99%

Section: Major Ion Composition and Cbm Productionmentioning

confidence: 99%

Biogeochemistry and the associated redox signature of co-produced water from coalbed methane wells in the Shizhuangnan block in the southern Qinshui Basin, China

Energy Exploration & Exploitation

et al. 2020

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“…The strata in the study area include Cambrian, Ordovician, the Carboniferous Benxi (C 2 b) and Taiyuan (C 3 t) Formations, the Permian Shanxi Formation (P 1 s), the Xiashihezi Formation (P 1 x), the Shangshihezi Formation (P 2 s), the Shiqianfeng Formation (P 2 sh), the Triassic Liujiagou Formation (T 1 l), and Quaternary deposits. The C 2 b unconformably overlies on the Ordovician Formation (Zhang et al, 2015). The main coal-bearing strata are the upper Carboniferous Taiyuan Formation (C 3 t) and the lower Permian Shanxi Formation (P 1 s), which contain the coal seams No.…”

Section: Geological Characteristics In the Shizhuangnan Blockmentioning

confidence: 99%

Prediction Model of Coal Reservoir Pressure and its Implication for the Law of Coal Reservoir Depressurization

Yan

Acta Geologica Sinica (Eng)

et al. 2019

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The main methods of coalbed methane (CBM) development are drainage and depressurization, and a precise prediction of coal reservoir pressure is thus crucial for the evaluation of reservoir potentials and the formulation of reasonable development plans. This work established a new reservoir pressure prediction model based on the material balance equation (MBE) of coal reservoir, which considers the self‐regulating effects of coal reservoirs and the dynamic change of equivalent drainage area (EDA). According to the proposed model, the reservoir pressure can be predicted based on reservoir condition data and the actual production data of a single well. Compared with traditional reservoir pressure prediction models which regard EDA as a fixed value, the proposed model can better predict the average pressure of reservoirs. Moreover, orthogonal experiments were designed to evaluate the sensitivity of reservoir parameters on the reservoir pressure prediction results of this proposed model. The results show that the saturation of irreducible water is the most sensitive parameter, followed by Langmuir volume and reservoir porosity, and Langmuir pressure is the least sensitive parameter. In addition, the pressure drop of reservoirs is negatively correlated with the saturation of irreducible water and the Langmuir volume, while it is positively correlated with porosity. This work analyzed the reservoir pressure drop characteristics of the CBM wells in the Shizhuangnan Block of the Qinshui Basin, and the results show that the CBM reservoir depressurization can be divided into three types, i.e., rapidly drop type, medium‐term stability type, and slowly drop type. The drainage features of wells were reasonably interpreted based on the comprehensive analysis of the reservoir depressurization type; the latter was coupled to the corresponding permeability dynamic change characteristics, eventually proving the applicability of the proposed model.

“…The hydrogen and oxygen isotope values near the Chinese meteoric water line (CMWL) and the local meteoric water line (LMWL) illustrate that the CBM co-produced water came from meteoric water ( Figure 7) [36]. Hydrogen and oxygen isotopes in groundwater are usually distributed on the right side of the LMWL or CMWL when formed by evaporation, water-rock interaction at high temperature, and mixture with seawater.…”

Section: Methanogenesis and Isotopic Compositionmentioning

confidence: 99%

“…In the study area, methanogenesis and low temperature water-rock interaction were the main reasons for hydrogen and oxygen isotopes in the water samples falling on the left side of the LMWL or CMWL [38]. Low temperature water-rock interaction, especially precipitation of carbonate in the coal reservoirs, caused the residual water to be depleted in 18 O and enriched in D. The hydrogen and oxygen isotope values near the Chinese meteoric water line (CMWL) and the local meteoric water line (LMWL) illustrate that the CBM co-produced water came from meteoric water ( Figure 7) [36]. Hydrogen and oxygen isotopes in groundwater are usually distributed on the right side of the LMWL or CMWL when formed by evaporation, water-rock interaction at high temperature, and mixture with seawater.…”

Section: Microbial Communities Associated With the Methanogenesis Andmentioning

confidence: 99%

Biogeochemistry and Water–Rock Interactions of Coalbed Methane Co-Produced Water in the Shizhuangnan Block of the Southern Qinshui Basin, China

et al. 2019

Water

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Coalbed methane is a major unconventional resource that has been exploited commercially for decades in the southern Qinshui Basin of China. The hydrogeochemical characteristics of coal reservoir water play a key role in the exploration and development of coalbed methane resources. In view of this, a detailed study was performed on coalbed methane co-produced water collected from the Shizhuangnan block to assess water–rock interactions and biogeochemical processes. Water samples were analyzed to establish major ions, isotopic compositions and perform 16S rRNA sequencing. Results suggest that the hydrochemistry was controlled by water–rock processes and that methane was consumed by sulfate reduction through calculation. Meanwhile, the isotopic compositions of water samples indicated that they had a predominantly meteoric origin and were influenced by microbial activity. The 16S rRNA sequencing results of bacteria and archaea provide an important foundation for understanding the activity of sulfate-reducing bacteria and methanogens at different hydraulic heads, which was consistent with isotopic analysis. Carbonates containing calcite and dolomite were found to be distributed at different hydraulic head due to the biogeochemical characteristics and associated water–rock interactions.