Damage mechanism of cement slurry to CBM reservoirs with developed fractures and cleats: A case study from eastern Yunnan and western Guizhou in China
The coalbed methane (CBM) reservoirs in the areas of eastern Yunnan and western Guizhou are characterized by developed cleats and fractures and low fracturing pressures, so cementing slurry (“slurry” for short) can invade into CBM reservoir easily, resulting in reservoir damage and abnormal increase...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
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KeAi Communications Co., Ltd.
2019-04-01
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| Series: | Natural Gas Industry B |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S2352854019300282 |
| _version_ | 1797288297632890880 |
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| author | Hansen Sun Chengwen Wang |
| author_facet | Hansen Sun Chengwen Wang |
| author_sort | Hansen Sun |
| collection | DOAJ |
| description | The coalbed methane (CBM) reservoirs in the areas of eastern Yunnan and western Guizhou are characterized by developed cleats and fractures and low fracturing pressures, so cementing slurry (“slurry” for short) can invade into CBM reservoir easily, resulting in reservoir damage and abnormal increase of reservoir transformation fracturing pressure. In order to reveal the damage mechanisms of slurry to this type of coal reservoirs, we analyzed the physical and chemical properties and potential damage modes of coal rocks. Then, the development situations of fractures and pores before and after the coal core samples were internally contaminated and the invasion and plugging situations of slurry in fractures and pores were analyzed intuitively by means of CT scanning and scanning electron microscope (SEM), and the percentage of slurry and fractures in coal core volume was calculated. In this way, a method to quantitatively evaluate the damage of slurry to coal reservoirs was established. And the following research results were obtained. First, under the effect of differential pressure, slurry and its filtrate invade into coal reservoirs along the fractures. The invasion degree varies with the development degree of fractures and pores. The more developed the fractures and pores, the higher the invasion degree. Second, the cement products formed after the slurry in the reservoirs gets cemented and solidified fill the fractures and pores tightly and cover the surface of coal core samples densely, so CBM flowing channels are blocked severely. Consequently, the permeability of coal core samples decreases and the compressive strength of coal rocks increase, leading to the abnormal increase of subsequent fracturing pressure and impacting the fracturing stimulation effects. Third, the effect of slurry filtrate on the alkali sensitivity and velocity sensitivity of coal rocks is much less than the damage degree of slurry invasion to coal rocks. In conclusion, this newly developed quantitative evaluation method for the damage of slurry to coal reservoirs is of guiding significance to improving the cement job quality of coal reservoirs and ensuring the efficient CBM development. Keywords: Eastern Yunnan and western Guizhou, Coalbed methane, Reservoir, Developed cleat and fracture, Cementing slurry, Damage mechanism, Damage evaluation, Coal core, Permeability |
| first_indexed | 2024-03-07T18:47:15Z |
| format | Article |
| id | doaj.art-51ed9cdff70e48ebb7971151d0e5b22b |
| institution | Directory Open Access Journal |
| issn | 2352-8540 |
| language | English |
| last_indexed | 2024-03-07T18:47:15Z |
| publishDate | 2019-04-01 |
| publisher | KeAi Communications Co., Ltd. |
| record_format | Article |
| series | Natural Gas Industry B |
| spelling | doaj.art-51ed9cdff70e48ebb7971151d0e5b22b2024-03-02T02:20:33ZengKeAi Communications Co., Ltd.Natural Gas Industry B2352-85402019-04-0162145150Damage mechanism of cement slurry to CBM reservoirs with developed fractures and cleats: A case study from eastern Yunnan and western Guizhou in ChinaHansen Sun0Chengwen Wang1China United Coalbed Methane Co., Ltd., Beijing 100016, China; Corresponding author.College of Petroleum Engineering, China University of Petroleum (East China), Qingdao, Shandong 266580, ChinaThe coalbed methane (CBM) reservoirs in the areas of eastern Yunnan and western Guizhou are characterized by developed cleats and fractures and low fracturing pressures, so cementing slurry (“slurry” for short) can invade into CBM reservoir easily, resulting in reservoir damage and abnormal increase of reservoir transformation fracturing pressure. In order to reveal the damage mechanisms of slurry to this type of coal reservoirs, we analyzed the physical and chemical properties and potential damage modes of coal rocks. Then, the development situations of fractures and pores before and after the coal core samples were internally contaminated and the invasion and plugging situations of slurry in fractures and pores were analyzed intuitively by means of CT scanning and scanning electron microscope (SEM), and the percentage of slurry and fractures in coal core volume was calculated. In this way, a method to quantitatively evaluate the damage of slurry to coal reservoirs was established. And the following research results were obtained. First, under the effect of differential pressure, slurry and its filtrate invade into coal reservoirs along the fractures. The invasion degree varies with the development degree of fractures and pores. The more developed the fractures and pores, the higher the invasion degree. Second, the cement products formed after the slurry in the reservoirs gets cemented and solidified fill the fractures and pores tightly and cover the surface of coal core samples densely, so CBM flowing channels are blocked severely. Consequently, the permeability of coal core samples decreases and the compressive strength of coal rocks increase, leading to the abnormal increase of subsequent fracturing pressure and impacting the fracturing stimulation effects. Third, the effect of slurry filtrate on the alkali sensitivity and velocity sensitivity of coal rocks is much less than the damage degree of slurry invasion to coal rocks. In conclusion, this newly developed quantitative evaluation method for the damage of slurry to coal reservoirs is of guiding significance to improving the cement job quality of coal reservoirs and ensuring the efficient CBM development. Keywords: Eastern Yunnan and western Guizhou, Coalbed methane, Reservoir, Developed cleat and fracture, Cementing slurry, Damage mechanism, Damage evaluation, Coal core, Permeabilityhttp://www.sciencedirect.com/science/article/pii/S2352854019300282 |
| spellingShingle | Hansen Sun Chengwen Wang Damage mechanism of cement slurry to CBM reservoirs with developed fractures and cleats: A case study from eastern Yunnan and western Guizhou in China Natural Gas Industry B |
| title | Damage mechanism of cement slurry to CBM reservoirs with developed fractures and cleats: A case study from eastern Yunnan and western Guizhou in China |
| title_full | Damage mechanism of cement slurry to CBM reservoirs with developed fractures and cleats: A case study from eastern Yunnan and western Guizhou in China |
| title_fullStr | Damage mechanism of cement slurry to CBM reservoirs with developed fractures and cleats: A case study from eastern Yunnan and western Guizhou in China |
| title_full_unstemmed | Damage mechanism of cement slurry to CBM reservoirs with developed fractures and cleats: A case study from eastern Yunnan and western Guizhou in China |
| title_short | Damage mechanism of cement slurry to CBM reservoirs with developed fractures and cleats: A case study from eastern Yunnan and western Guizhou in China |
| title_sort | damage mechanism of cement slurry to cbm reservoirs with developed fractures and cleats a case study from eastern yunnan and western guizhou in china |
| url | http://www.sciencedirect.com/science/article/pii/S2352854019300282 |
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