Experimental simulation of dissolution to dolomite in formation water of Jixianian Wumishan Formation in the Xiong'an New Area
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摘要: 为了研究雄安新区雾迷山组地层水对白云岩的溶蚀作用,文章以雾迷山组白云岩为研究对象,以井下雾迷山组地层水为实验流体,开展高温高压条件下溶蚀模拟实验。实验结果表明:(1)样品在地层水中的溶蚀速率随温度增加总体呈下降趋势,具有快速下降—缓慢增加—快速下降的特征,在100~140 ℃范围内明显增加。样品在地层水中的溶蚀速率随压力增加明显增大。反应溶液的Ca2+、Mg2+浓度增加量随温度、压力变化特征与样品溶蚀速率随温度、压力变化特征一致;(2)孔隙、微裂隙欠发育的样品仅在样品表面发生溶蚀,使得样品表面变模糊。孔隙、微裂隙发育的样品,沿粒间、晶间孔隙及各类裂隙溶蚀、扩展,最终呈一定程度连通;(3)埋藏成岩环境下,在100~140 ℃范围存在一个保持较高溶蚀能力的温度窗口,这可能是研究区雾迷山组白云岩岩溶储层形成的有利温度区间。Abstract:
With the richest geothermal resources and the best development and utilization conditions in the central and eastern China, the Xiong'an New Area is the home of three large and medium-sized geothermal fields—Xiongxian, Rongcheng and Gaoyang. The Jixianian Wumishan Formation in the Xiong'an New Area has good reservoir endowment, large water yield and easy reinjection, which is the focus of geothermal resource exploration. At present, acid solutions, high-salinity water solutions or sea water which are prepared by researchers themselves are mainly used in simulation experiments, but less formation water is used as the experimental fluid. In this study, the dolomite of Wumishan Formation in the Xiong'an New Area is taken as the research object, and the formation water of Wumishan Formation in the underground is taken as the experimental fluid. The dissolution simulation experiment under high temperature and high pressure has been carried out to analyze the influence of temperature, pressure, lithology, structure and other factors on the dissolution of dolomite. This experiment adopts the simulation experimental device of dissolution kinetics under the conditions of high-temperature and high-pressure independently designed by Karst Geology Research Institute of the Chinese Academy of Geological Sciences. The formation water from the whole section of Wumishan Formation in the geothermal well of the Xiong'an New Area is taken as the reaction fluid. At the same time, considering the two factors of temperature and pressure, a total of 12 groups of experiments in the range of 40 ℃, 10 MPa to 150 ℃, 20 MPa have been carried out to simulate the dissolution of formation water of Wumishan Formation in the Xiong'an New Area on dolomite from the shallow burial to the deep burial. The experimental results show that dissolution rates of samples in the formation water decreased with the increase of temperature in general. The rates experienced a rapid decrease before a slow increase and then a rapid decrease again, with an obvious increase from 100 ℃ to 140 ℃. Dissolution rates of samples in formation water increased obviously with the increase of pressure. The variation of Ca2+ and Mg2+ concentrations with temperature and pressure was consistent with that of dissolution rates with temperature and pressure. All samples showed a certain degree of corrosion under the experimental conditions, mainly the corrosion of the sample surface. The samples with less developed pores and microcracks only corroded on the surface, which blurred the sample surface. The samples with developed pores and microcracks were eroded and expanded along intergranular pores, intercrystalline pores and various fractures, and finally connected to a certain extent. Therefore, the results of this study show that the buried dissolution of carbonate rocks will decrease in the burial diagenetic environment, with the increase of depth and temperature. But there is a window with higher dissolution capacity in the range of 100 ℃-140 ℃, which may be a favorable temperature range for the formation of dolomite karst reservoirs in the Wumishan Formation in the study area. For the samples with undeveloped pores and microcracks, it is difficult for soluble fluid to enter the sample for large-scale corrosion, but only to stay on and blur the sample surface during the experiment. The samples with pores and microcracks developed are corroded and expanded along intergranular and intercrystalline pores and various fractures and fissures, and are finally connected to a certain extent. -
图 2 实验样品的溶蚀速率随温度、压力变化曲线
(a) A1,粉晶白云岩 (b) A2,纹层状白云岩 (c) A3,中晶白云岩 (d) A4,中晶白云岩 (e) A5,泥晶灰岩 (f) A6,亮晶砂屑灰岩
Figure 2. Dissolution rate curve of experimental samples with the variation of temperature and pressure
(a) A1, Powder crystal dolomite (b) A2, Laminated dolomite (c) A3, Mesocrystalline dolomite (d) A4, Mesocrystalline dolomite (e) A5, Micrite limestone (f) A6, Sparite arenaceous limestone
图 4 实验样品实验前后照片对比
(a) 粉晶白云岩,实验前 (b) 粉晶白云岩,实验后 (c) 纹层状白云岩,实验前 (d) 纹层状白云岩,实验后 (e) 中晶白云岩,实验前 (f) 中晶白云岩,实验后 (g) 中晶白云岩,实验前 (h) 中晶白云岩,实验后 (i) 泥晶灰岩,实验前 (j) 泥晶灰岩,实验后 (k) 亮晶砂屑灰岩,实验前 (l) 亮晶砂屑灰岩,实验后
Figure 4. Comparison of photos of experimental samples before and after the experiment
(a) Powder crystal dolomite, before experiment (b) Powder crystal dolomite, after experiment (c) Laminated dolomite, before experiment (d) Laminated dolomite, after experiment (e) Mesocrystalline dolomite, before experiment (f) Mesocrystalline dolomite, after experiment (g) Mesocrystalline dolomite, before experiment (h) Mesocrystalline dolomite, after experiment (i) Micrite limestone, before experiment (j) Micrite limestone, after experiment (k) Sparitearenaceous limestone, before experiment (l) Sparite arenaceous limestone, after experiment
图 5 实验样品实验前后显微镜下照片对比
(a) 中晶白云岩,实验前 (b) 纹层状白云岩,实验前 (c) 粉晶白云岩,实验前 (d) 中晶白云岩,实验后 (e) 纹层状白云岩,实验后 (f) 粉晶白云岩,实验后
Figure 5. Comparison of photos of experimental samples under microscope before and after the experiment
(a) Mesocrystalline dolomite, before experiment (b) Laminated dolomite, before experiment (c) Powder crystal dolomite, before experiment (d) Mesocrystallinedolomite, after experiment (e) Laminated dolomite, after experiment (f) Powder crystal dolomite, after experiment
表 1 实验样品主量元素测试结果
Table 1. Test results of major elements of experimental samples
样品编号 采样位置 层位 岩性 组份/% SiO2 Al2O3 TFe2O3 CaO MgO K2O Na2O TiO2 P2O5 MnO LOI A1 D03井 雾迷山组 粉晶白云岩 26.86 1.56 0.35 20.88 15.27 0.32 0.02 0.08 0.03 0.01 33.92 A2 D03井 雾迷山组 纹层状白云岩 23.85 0.02 0.10 22.98 16.47 0.01 0.02 0.01 0.00 0.01 35.99 A3 D03井 雾迷山组 中晶白云岩 2.17 0.01 0.14 29.99 21.46 0.00 0.02 0.00 0.00 0.00 45.48 A4 D16井 雾迷山组 中晶白云岩 1.28 0.04 0.17 30.06 21.55 0.07 0.02 0.00 0.00 0.01 46.02 A5 蓟县野外剖面 高于庄组 泥晶灰岩 9.36 0.28 0.14 45.62 4.20 0.14 0.03 0.00 0.01 0.01 40.06 A6 桂林七星岩 / 亮晶砂屑灰岩 0.55 0.21 0.08 54.26 1.00 0.06 0.03 0.01 0.00 0.00 43.55 表 2 溶蚀实验反应液水化学特征
Table 2. Hydrochemical characteristics of reaction solutions in the dissolution experiment
成分/ mg·L−1 K+ Na+ Ca2+ Mg2+ Cl− 含量 30.07 579.57 37.40 19.28 790.63 成分/mg·L−1 ${\rm{SO}}_4^{2-}$ ${\rm{HCO}}_3^{-}$ ${\rm{CO}}_3^{2-}$ ${\rm{NO}}_3^{-}$ pH 含量 2.79 341.37 32.64 <0.05 8.49 表 3 本次溶蚀模拟实验选取的温度和压力
Table 3. Temperature and pressure selected for the dissolution experiment
实验编号 温度/ ℃ CO2分压/MPa 压力/MPa 实验编号 温度/ ℃ CO2分压/MPa 压力/MPa 1 40 3 10 7 40 6 20 2 60 3 10 8 60 6 20 3 80 3 10 9 80 6 20 4 100 3 10 10 100 6 20 5 120 3 10 11 120 6 20 6 150 3 10 12 150 6 20 表 4 实验样品的溶蚀速率计算结果
Table 4. Calculation results of dissolution rates of experimental samples
温度、压力 溶蚀速率/10−5g·cm−2·h−1 A1粉晶白云岩 A2纹层状白云岩 A3中晶白云岩 A4中晶白云岩 A5泥晶灰岩 A6亮晶砂屑灰岩 40 ℃ 10 MPa 3.70 3.82 4.14 4.60 / 130.90 60 ℃ 10 MPa 2.24 3.49 1.66 2.03 28.99 43.16 80 ℃ 10 MPa 2.75 3.02 0.99 1.01 29.79 44.30 100 ℃ 10 MPa 2.87 1.88 1.70 1.89 26.95 35.53 120 ℃ 10 MPa 3.80 2.60 2.16 1.81 29.60 50.75 150 ℃ 10 MPa 0.93 1.83 1.10 1.33 17.48 28.15 40 ℃ 20 MPa 5.18 5.02 5.82 4.58 53.34 168.47 60 ℃ 20 MPa 3.47 5.04 5.54 4.50 56.86 160.61 80 ℃ 20 MPa 4.64 4.14 4.64 4.06 55.37 128.20 100 ℃ 20 MPa 4.69 3.57 3.10 2.83 50.84 108.19 120 ℃ 20 MPa 5.98 5.38 3.42 3.49 38.80 113.99 150 ℃ 20 MPa 3.92 4.66 2.02 2.03 37.08 88.38 表 5 实验前后反应液的Ca2+、Mg2+浓度
Table 5. Concentrations of Ca2+ and Mg2+ in reaction solutions before and after the experiment
温度
/℃压力
/MPa实验前离子浓度/mg·L−1 实验后离子浓度/mg·L−1 离子浓度增加量/mg·L−1 Ca2+ Mg2+ Ca2++Mg2+ Ca2+ Mg2+ Ca2++Mg2+ Ca2+ Mg2+ Ca2++Mg2+ 40 10 37.40 19.28 56.68 346.98 69.44 416.42 309.58 50.16 359.74 60 10 37.40 19.28 56.68 151.00 36.68 187.68 113.60 17.40 131.00 80 10 37.40 19.28 56.68 143.50 34.35 177.85 106.10 15.07 121.17 100 10 37.40 19.28 56.68 141.07 35.08 176.15 103.67 15.80 119.47 120 10 37.40 19.28 56.68 147.30 35.12 182.42 109.90 15.84 125.74 150 10 37.40 19.28 56.68 44.89 31.52 76.41 7.49 12.24 19.73 40 20 37.40 19.28 56.68 422.04 84.65 506.69 384.64 65.37 450.01 60 20 37.40 19.28 56.68 359.91 80.98 440.89 322.51 61.70 384.21 80 20 37.40 19.28 56.68 273.30 62.40 335.70 235.90 43.12 279.02 100 20 37.40 19.28 56.68 299.05 74.40 373.45 261.65 55.12 316.77 120 20 37.40 19.28 56.68 319.70 69.70 389.40 282.30 50.42 332.72 150 20 37.40 19.28 56.68 303.34 62.99 366.33 265.94 43.71 309.65 -
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