Study of hydrochemical characteristics of CBM co-produced water of the Shizhuangnan Block in the southern Qinshui Basin, China, on its implication of CBM development

et al. 2020

Sci Rep

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The development of coalbed methane (CBM) is not only affected by geological factors, but also by engineering factors, such as artificial fracturing and drainage strategies. In order to optimize drainage strategies for wells in unique geological conditions, the characteristics of different stages of CBM production are accurately described based on the dynamic behavior of the pressure drop funnel and coal reservoir permeability. Effective depressurization is achieved by extending the pressure propagation radius and gas desorption radius to the well-controlled boundary, in the single-phase water flow stage and the gas–water flow stage, respectively, with inter-well pressure interference accomplished in the single-phase gas flow stage. A mathematic model was developed to quantitatively optimize drainage strategies for each stage, with the maximum bottom hole flow pressure (BHFP) drop rate and the maximum daily gas production calculated to guide the optimization of CBM production. Finally, six wells from the Shizhuangnan Block in the southern Qinshui Basin of China were used as a case study to verify the practical applicability of the model. Calculation results clearly indicate the differences in production characteristics as a result of different drainage strategies. Overall, if the applied drainage strategies do not achieve optimal drainage results, the coal reservoir could be irreversibly damaged, which is not conducive to expansion of the pressure drop funnel. Therefore, this optimization model provides valuable guidance for rational CBM drainage strategy development and efficient CBM production.

Section: Resultsmentioning

confidence: 99%

Quantitative optimization of drainage strategy of coalbed methane well based on the dynamic behavior of coal reservoir permeability

Yan

et al. 2020

Sci Rep

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“…Thereafter, the containers were filled to the brim, carefully closed, and then sealed using paraffin wax. After the collection was completed, the samples were sent to the First Exploration Bureau Testing Center of China National Coal Geology Administration within 48 h for full analysis according to the standard “General Provisions of Coal Mine Water Quality Analysis (MT/T 894-2000)” (Zhang et al., 2016). Finally, the cations K + + Na + , Mg 2+ , Ca 2+ and the anions HCO 3− + CO 3 2− , SO 4 2− , Cl − were tested.…”

Section: Methodsmentioning

confidence: 99%

Analysis of productivity differences in vertical coalbed methane wells in the Shizhuangnan Block, Southern Qinshui Basin, and their influencing factors

Yan

Energy Exploration & Exploitation

et al. 2020

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Coalbed methane wells in the Shizhuangnan Block exhibit significant productivity differences. The reasons were determined based on the impact analysis of geological factors and drainage strategies on production capacity at 82 wells. Grey relational analysis was further utilized to quantitatively analyze the correlation degree of geological parameters to production characteristics. It is found that the main reason for wells with high water production is the ingress of external water, i.e. connecting adjacent aquifer by natural faults or artificial fractures. And aquifer characteristics, especially thickness of aquifer has the greatest influence on the water production, followed by pore connectivity, porosity, and shale content. For the wells that have not been affected by external water, the gas productivity differences are mainly affected by reservoir conditions and drainage strategies. Finally, an analytical process was proposed to provide theoretical support for rational production of coalbed methane wells.

“…Surface discharge in the study area occurs through bedrock channels of varying sizes, with low flow or dry streams in the dry season and rainfall supplied in the rainy season. The groundwater of strata is supplied from injection of meteoric water in the southern outcrop area of the SZN block (Zhang et al, 2015(Zhang et al, , 2016.…”

Section: Hydrogeologymentioning

confidence: 99%

“…Stable and long drainage period was adopted to weaken the contamination influence of fracturing fluid. Zhang et al (2016) reported that 10 meq/L Clconcentrations could be considered a cut-off point for evaluation of the degree of fracturing fluid contamination, with Clconcentrations below 10 meq/L indicating no influence of fracturing fluid on hydrochemical signatures. In the present study, Clconcentration of all water samples was less than 10 meq/L, suggesting that the effect of fracturing fluid could be ignored.…”

Section: Samples Collectionmentioning

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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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.