前置酸压裂提高煤层气单井产量机理与适用性研究

范耀

doi:10.3969/j.issn.1001-1986.2021.04.018

前置酸压裂提高煤层气单井产量机理与适用性研究

doi: 10.3969/j.issn.1001-1986.2021.04.018

范耀^{1, 2,}

基金项目:

陕西省创新能力支撑计划项目 2018TD-039

详细信息

第一作者:
范耀，1983年生，男，陕西咸阳人，博士研究生，副研究员，从事煤层气地质与勘探开发工作. E-mail：fanyao@cctegxian.com

中图分类号: P634
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- 文章访问数: 154
- HTML全文浏览量: 18
- PDF下载量: 22
- 被引次数: 0
出版历程
- 收稿日期: 2020-07-29
- 修回日期: 2021-03-31
- 发布日期: 2021-08-25
- 网络出版日期: 2021-09-10

Mechanism and applicability of increasing coalbed methane well production by pre-positioned acid fracturing

FAN Yao^{1, 2
,}

摘要

摘要: 针对目前我国煤层气地面开发单井产量低、开发效益差的现状，为探索研究适用于煤层气井的经济高效增产改造技术，借鉴常规油气藏前置酸压裂技术的成功经验，采集焦坪矿区4-2煤层煤样，进行前置酸改善压裂效果评价实验，结合宏观观察、X射线衍射分析及扫描电镜–能谱手段对比分析实验前后矿物质成分与含量变化，研究前置酸压裂技术煤层增产机理和适用条件。结果表明：前置酸可改善煤储层孔裂隙之间连通性，大大降低压裂液本身对煤层的伤害，改造效果显著；酸化溶解(堵塞和填隙物质)为主要增产机理，形成不规则酸岩溶蚀面、酸盐反应生成CO₂促进CH₄解吸等作用是辅助增产机理；前置酸压裂技术适用于含矿物质较高、渗透性较差煤层增产改造和近井地带解堵，首选富含方解石、白云石、菱铁矿和赤铁矿等酸溶性充填物为主的煤层，对于含有较高黏土矿物的煤层或以解除近井地带污染为目的，重点考虑减少二次沉淀带来的负效应问题。建议采用二次沉淀物预防措施、综合防滤失技术、低密度支撑剂、低伤害/高黏度压裂液等对策来解决前置酸酸化后二次伤害和煤层压裂液滤失大的问题。
- 前置酸压裂 /
- 煤层气 /
- 增产机理 /
- 适用条件 /
- 连通性
Abstract: At present, the production shortfall and benefits decline of the coalbed methane reservoirs in China are the leading problems. In order to explore and study the economic and efficient stimulation technology suitable for the coalbed methane wells, this paper studies mechanism and applicable conditions on increasing coalbed methane well production by the pre-positioned acid fracturing technology, by drawing on the successful experiences of conventional oil and gas reservoir with this technology. The coal samples of No.4-2 coal seam in Jiaoping Mining Area were collected to evaluate the effect of improving fracturing with acid preposition. The changes of mineral composition and content before and after the experiment were analyzed by macroscopic observation, X-ray diffraction and scanning electron microscope energy dispersive spectrometry. The results indicate that the pre-positioned acid achieved remarkable effect in improving the connectivity between pores and fractures of coal reservoir and reducing the damage of fracturing fluid to coal seam. The main stimulation mechanisms is acid dissolving plugging and interstitial materials, and the auxiliary stimulation mechanisms include forming irregular acid dissolution surface and promoting CH₄ desorption by CO₂ generated from acid salt reaction. Pre-acid fracturing technology is suitable for increasing production and reforming of coal seams with high mineral content and poor permeability, and near the well zone plug removal. The coal seams with rich acid-soluble fillings such as calcite, dolomite, siderite and hematite are the first choice. While for coal seams containing high clay minerals or for the purpose of eliminating pollution near well, the negative effect caused by secondary sedimentation should be mainly considered. It is suggested to adopt secondary sediment prevention measures, combined with anti-filtration technology, low density proppant, low damage/high viscosity fracturing fluid and other countermeasures to solve the problems of secondary damage after pre-acid acidification and large filtration loss of fracturing fluid in coal seam.
- pre-positioned acid fracturing /
- coalbed methane /
- stimulation mechanism /
- applicable conditions /
- connectivity

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图 1 煤心样

Fig. 1 Core samples

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图 2 方解石扫描电镜–能谱分析

Fig. 2 SEM-EDS analysis of calcite

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图 3 白云石扫描电镜–能谱分析

Fig. 3 SEM-EDS analysis of dolomite

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图 4 高岭石扫描电镜–能谱分析

Fig. 4 SEM-EDS analysis of kaolinite

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图 5 石英扫描电镜–能谱分析

Fig. 5 SEM-EDS analysis of quartz

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图 6 实验样品

Fig. 6 Experimental samples

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图 7 酸化前后煤样

Fig. 7 Coal samples before and after acidification

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图 8 酸化前后扫描电镜照片

Fig. 8 SEM photos before and after acidification

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表 1 煤心X衍射定量分析结果

Table 1 Quantitative analysis results of X-ray diffraction of coal core samples

煤样号	矿物质量分数/%
煤样号	高岭石	方解石	白云石	石英	锐钛矿	菱铁矿	赤铁矿	磷灰石	有机碳	未检出
1	5	19	10	8	0	0	0	2	55	1
2	6	20	8	8	0	0	0	2	55	1
3	5	19	9	7	0	0	0	3	56	1
4	10	10	5	3	1	2	1	1	67	0
平均	6.50	17.00	8.00	6.50	0.25	0.50	0.25	2.00	58.25	0.75

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表 2 前置酸压裂液对煤样影响评价结果

Table 2 Evaluation results of influence of pre-positioned acid fracturing on coal core samples

压裂液类型	克氏渗透率/10^–3 μm²	孔隙率/%	渗透率变化率/%
活性水	0.499 8	3.52	10.87
	0.256 0	3.31	8.98
	0.929 9	3.63	14.96
15%盐酸体系+活性水	0.256 1	2.46	–154.44
15%盐酸体系+活性水	0.175 1	3.40	–276.01

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表 3 溶蚀后煤心X衍射定量分析结果

Table 3 Quantitative analysis results of X-ray diffraction of acidification coal core samples

煤样	矿物质量分数/%
煤样	高岭石	方解石	白云石	石英	锐钛矿	菱铁矿	赤铁矿	磷灰石	有机碳
1	8	0	0	3	1	0	0	1	87
2	6	0	0	5	0	0	0	2	87
平均	7	0	0	4	0.5	0	0	1.5	87

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