Phase Behavior of Fluid Composition in Coalbed Methane Wells Pre- and Post-Workover: An Examination of the Panzhuang Block, Qinshui Basin, Shanxi, China
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1. Unfortunately, there is no information in the manuscript concerning reservoir pressure in studied wells before development. These wells seem to produce large volumes of water. They may take some time to reach peak gas production, typical for areas with normal hydrostatic reservoir pressure prior to operations.
2. Taking into account that the Panzhuang production block (in the Qinshui Basin) is densely faulted and coal seam No. 3 of lvb, sa and anthracite rank has high adsorption capacity it is difficult to believe that there is no hydrologic communication between deep reservoir coal beds and shallow aquifers, even if the seam rests and overlapped by low-permeability mudstone.
3. In the abstract is written (lines 19-22) “During the stable production stage, before and after the workover, the proportion of Na+, Cl-, Ca2+ and Total Dissolved Solids (TDS) in the water samples showed a downward trend as a whole, while the HCO3- increased, but after the workover, the Na+, Cl-, Ca2+ and TDS all increased suddenly, while the HCO3- decreased”. So, this may suggest that flow is not only effectively confined within the coal body but also may be fed by cross-formational water channelling.
Author Response
1.Unfortunately, there is no information in the manuscript concerning reservoir pressure in studied wells before development. These wells seem to produce large volumes of water. They may take some time to reach peak gas production, typical for areas with normal hydrostatic reservoir pressure prior to operations.
Response: I greatly thank the reviewers’ positive and constructive comments and suggestions. Information relating to reservoir pressure in studied wells before development is not included in our manuscript for the following reasons: 1) Qinshui CBM development block in Shanxi Province is the most commercially valuable block in China, which is very well explored. Many references have been published on the relationship between reservoir pressure and water yield. 2) The main focus of this paper is on the changes in the water medium before and after the workover of the coalbed methane well, and the selected well sites are all located in locations with simple hydrogeological conditions. Without the disruption of workover, there is little difference in the historical data for water yield from adjacent coalbed methane wells. For the above reasons, we do not provide information on the reservoir pressure before workover.
- Taking into account that the Panzhuang production block (in the Qinshui Basin) is densely faulted and coal seam No. 3 of lvb, sa and anthracite rank has high adsorption capacity it is difficult to believe that there is no hydrologic communication between deep reservoir coal beds and shallow aquifers, even if the seam rests and overlapped by low-permeability mudstone.
R：Thanks for your constructive suggestions. Sampling wells in this paper are located in the synclinal wing with simple structural conditions (the detailed interpretation can be found in 3.1 Sampling method). Geological data show that there is no fault cutting through the coal seam cap and the overlying water-bearing rock series in this area.
- In the abstract is written (lines 19-22) “During the stable production stage, before and after the workover, the proportion of Na+, Cl-, Ca2+ and Total Dissolved Solids (TDS) in the water samples showed a downward trend as a whole, while the HCO3- increased, but after the workover, the Na+, Cl-, Ca2+ and TDS all increased suddenly, while the HCO3- decreased”. So, this may suggest that flow is not only effectively confined within the coal body but also may be fed by cross-formational water channelling.
R：Thanks for the guidance. The phenomena described in the abstract are objective. It has also been shown in the literature [1-2] that the change of HCO3- may be due to the desulphation of desulphate-reducing bacteria SO42- + C +H2O→ HCO3- +H2S, in addition to being related to the cross-formational water channelling. HCO3- +H2S. In response to the reviewer's statement, we will conduct a detailed study of the connection between the cap fissure and surface water at the We will conduct a detailed study of the connection between the cap fissure and surface water at the selected well sites.
[1] Che Y., Wu J. Quality Analysis of Water Produced From CBM Wells of Zhaozhuang District in Qinshui Basin[J]. Energy and energy conservation, 2015, 118(7): 5-6+85.
[2] Li, Z.C., Tang, S.H., Wang, X.F., et al.
Study on the relationship between chemical characteristics of produced water and production capacity of coalbed methane wells in Qinshui Basin[J]. Journal of China University of Mining and Technology, China. 2011, 40(3):6.DOI:CNKI:SUN:ZGKD.0.2011-03-017.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsManuscript titled Phase Behavior of Fluid Composition in Coalbed Methane 2 Wells Pre- and Post-Workover: An Examination from the Pan-3 Zhuang Block, Qinshui Basin, Shanxi, China present high quality of work, science and research. Coal Bed Methane production and associated wells workover are demanding problem to solve. Authors present high quality of background, work, method and results discussion. It is really important to maintain wells workover with the best background, technique and scientific support.
However, type of presented research requires discussion and results presentation in “reporting style”. Chapter 4 is very well written but hard to read and understood by someone outside the industry.
In the text the phrases like “We have analyzed […]” sometimes occur. It is adopted to use: Authors analyzed or in the Authors opinion.
Author Response
Manuscript titled Phase Behavior of Fluid Composition in Coalbed Methane 2 Wells Pre- and Post-Workover: An Examination from the Pan-3 Zhuang Block, Qinshui Basin, Shanxi, China present high quality of work, science and research. Coal Bed Methane production and associated wells workover are demanding problem to solve. Authors present high quality of background, work, method and results discussion. It is really important to maintain wells workover with the best background, technique and scientific support.
However, type of presented research requires discussion and results presentation in “reporting style”. Chapter 4 is very well written but hard to read and understood by someone outside the industry.
In the text the phrases like “We have analyzed […]” sometimes occur. It is adopted to use: Authors analyzed or in the Authors opinion.
R：Thanks for the guidance. We will improve the style of writing to make it easier to understand. “In the text the phrases like “We have analyzed […]” sometimes occur. It is adopted to use: Authors analyzed or in the Authors opinion.”，The words in the text have been checked and revised in its entirety. Changes have been highlighted in the text.
Author Response File: Author Response.pdf
