Geochemical factors affecting oxidation dissolution and permeability enhancement of Yichang gas producing shale, Hubei province
-
摘要: 为探究宜昌地区产气页岩氧化溶蚀增渗的地球化学影响因素,本研究以宜昌地区陡山沱组页岩为研究对象,选取了15wt%H2O2和0.5mol/L Na2S2O8两种氧化剂开展氧化溶蚀实验,实验探究了不同pH、地下水水化学离子及浓度和温度对氧化溶蚀效果的影响,结果表明,氧化溶蚀效果Na2S2O8优于H2O2,H2O2(15 wt%)和Na2S2O8(0.5mol/L)在酸性条件下氧化溶蚀效果均优于碱性条件,碱性环境不利于两种氧化剂的氧化;升温会促进Na2S2O8和H2O2的热分解,分别产生H2SO4和O2,有利于促进页岩的氧化溶蚀。外源钠离子(氯化物)的添加能促进页岩在Na2S2O8和H2O2氧化过程下Ca2+和Mg2+的释放,增强氧化溶蚀效果;而外源Ca2+、SO42-的添加,容易与碳酸盐酸蚀产生的SO42-、Ca2+产生石膏沉淀,从而引起页岩孔隙堵塞,降低页岩渗透性;同时,外源Mg2+易在弱碱性环境下生成硅酸镁沉淀,对页岩的氧化溶蚀产生负面影响。因此,今后在页岩气氧化压裂开采过程中,需要预先调查开采地层的地球化学参数,围绕温度、pH和阴阳离子来选择氧化液和开采方式。Abstract: [Objective]It has become a mature method to exploit shale gas by chemical oxidation and infiltration technology,The purpose of this study is to explore the influence of geochemical factors in the exploitation process. [Methods] In this study, the Doushantuo Formation shale in Yichang, Hubei Province, which has a good shale gas exploitation prospect and rich organic matter content of pyrite, was selected as the research object. Two commonly used oxidants, 15wt% H2O2 and 0.5mol/L Na2S2O8, were selected to carry out the oxidation corrosion experiment at normal temperature and pressure. The results were measured by the determination of cation concentration, pH, Eh, mass loss and XRD analysis after the reaction. According to the relevant ground water data, Na+ and SO42- are selected because they are the main ions in the Doushantuo Formation Marine sedimentary water, and Ca2+ and Mg2+, which are easy to precipitate by SO42- in the overlying Dengying formation water, are selected. The four ions and their concentrations, as well as the influence of pH and temperature, which have strong influence on the oxidation and dissolution effect in related mining technologies, are also selected. [Results]The results show that Na2S2O8 is superior to H2O2, and the advanced oxidation process driven by pyrite and the erosion effect of carbonate under acid production make the acidic environment more suitable for the dissolution of carbonate-rich shale, and the stronger the acidity, the better the oxidation dissolution effect. For carbonate-rich shale, it is necessary to appropriately increase the acidity of the reaction system to increase the permeability of shale. Temperature rise can promote the thermal decomposition of Na2S2O8 and H2O2.The thermal decomposition of H2O2 produces O2, and Na2S2O8 produces H2SO4, O2 and SO4?- with strong oxidation, so that the promotion effect of temperature on Na2S2O8 is better than H2O2. Sodium ion (chloride) can promote the release of Ca2+ and Mg2+ in the oxidation process of Na2S2O8 and H2O2, so the groundwater environment with high concentration of NaCl plays a positive role in the oxidation and dissolution of shale. Magnesium silicate precipitation will be produced in the reaction system of weakly basic magnesium ion, which is more obvious to inhibit the oxidative corrosion of H2O2. Both calcium ions and sulfate ions can produce gypsum precipitation by influencing the interaction between the reactions, thus affecting the oxidative dissolution of shale. Low concentration of exogenous calcium ions inhibits the buffer effect of carbonate and produces a promotion effect, while high concentration of exogenous calcium ions will produce secondary mineral precipitation, block shale pores and hinder the oxidation and dissolution of shale. However, the effect of sulfate ions on the oxidative corrosion of shale is opposite to that of calcium ions. The low concentration of exogenous sulfate ions inhibits the oxidative corrosion of shale by generating secondary ore and inhibiting the oxidation reaction of pyrite. [Conclusion]Therefore, in the future, in the process of shale gas oxidative fracturing, it is necessary to investigate the water chemical parameters of the exploitation formation in advance, and select the oxidation liquid and mining mode according to temperature, pH and cation ions. In chemical oxidation infiltration technology, there are still some problems, such as O2 doping in natural gas caused by H2O2 decomposition, which needs further research.
-
Key words:
- Shale /
- H2O2 /
- Na2S2O8 /
- Oxidation dissolution
点击查看大图
计量
- 文章访问数: 43
- PDF下载量: 2
- 被引次数: 0