Study and Field Application of Calcium Sulfate Scaling in Fractured High Temperature Bedrock Gas Wells
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摘要: 柴达木盆地尖北、东坪气田储层温度为170 ℃，且垢样沉积具有多样化，对硫酸钙的溶垢研究提出了很大的挑战，为了解决该区块连续出现井筒结垢，影响气井生产及各项测试作业开展的难题。通过分析垢样组份、明确结垢机理和调研溶垢方法，针对现场垢样开展溶垢研究，区分井筒垢样沉积、储层结垢分别形成了碳酸盐置换溶垢、酸性有机磷酸溶垢配方及工艺，开展了现场应用。结果表明，井筒垢样成份为高纯度硫酸钙及少量的碳酸盐、铁质；垢样来源为高矿化度地层水中成垢离子随着压力逐渐降低，水份蒸发在井筒，炮眼、近井地带沉积结垢；碳酸盐物相置换溶垢法适用于井筒沉积的硫酸钙溶垢，可利用储层高温达到所需反应温度且对井筒管柱无腐蚀；酸性有机磷酸螯合剂溶垢法适用于沉积在炮眼、储层近井地带的硫酸钙溶垢，可同时结合相应的酸化液体系开展复合酸化工艺，减缓二次沉淀造成的储层伤害。最终有针对性的形成了2套溶垢剂配方及相应的溶垢工艺，可有效溶解储层硫酸钙，解决了现场技术难题，为气田增产、稳产做出了巨大的贡献。Abstract: The reservoir temperature of Jianbei and Dongping gas fields in Qaidam Basin is 170 ℃, and the scale deposits are diverse, which poses a great challenge to the study of calcium sulfate scale dissolution, problems affecting gas well production and test operation. In this paper, through analyzing the composition of scale sample, defining the scaling mechanism, investigating the scale dissolving method, the scale dissolving research is carried out for the scale sample on the spot, the formula and technology of carbonate displacement scale dissolution and acid organic phosphoric acid scale dissolution were formed by distinguishing the deposit of Wellbore scale sample and reservoir scale formation respectively. The results show that the sample is composed of high-purity calcium sulfate and a small amount of carbonate and iron, and the source of the sample is the scaling ion in the formation water with high salinity The carbonate phase displacement scale dissolving method is suitable for calcium sulfate scale dissolving in wellbore. The high temperature of reservoir can reach the required reaction temperature and has no corrosion to wellbore string The acid organic phosphate chelating agent scale dissolving method is suitable for the calcium sulfate scale dissolving in the drill hole and near the well of the reservoir, and can be combined with the corresponding acidizing liquid system to develop the complex acidizing process at the same time, which can slow down the formation damage caused by the secondary precipitation. Finally, two sets of scale solubilizer formulation and corresponding scale dissolving process are formed, which can effectively dissolve reservoir calcium sulfate, solve the field technical problems, and make great contribution to increasing and stabilizing production of gas field.
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表 1 垢样XRD衍射分析结果
井号 组份名称 组份含量/% 尖北1-2井 硬石膏（CaSO4） 99.5 石盐(NaCl) 0.5 尖Ｈ1-5井 硬石膏（CaSO4） 100.0 东坪1井 硬石膏（CaSO4） 100.0 
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表 2 东坪、尖北基岩储层地层水离子分析统计
区块 K++ Na+/
mg·L−1Ca2+/
mg·L−1Mg2+/
mg·L−1Cl−/
mg·L−1SO42−/
mg·L−1HCO3−/
mg·L−1总矿化度/
mg·L−1水型 东坪1区块 18 198 13 835 601 52 241 2438 165 87 889 CaCl2 东坪3区块 40 271 43 104 1174 138 078 3576 92 224 876 CaCl2 尖北区块 14 052 8042 1884 40 089 1397 571 66 074 CaCl2
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表 3 溶垢体系对尖1-2井块状堵塞物溶蚀的情况
液体
配方30 h溶蚀率/% 液体
配方30 h溶蚀率/% 10%HCl+20%有机磷酸螯合剂 43.25 5%EDTA(pH=8) 15.90 20%有机磷酸螯合剂 28.29 5%EDTA(pH=14) 27.37 5%Na2CO3浸泡30 h+6%HCl清洗 32.46 5%NaHCO3浸泡30 h+6%HCl清洗 33.60
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表 4 碳酸氢钠浸泡不同时间段对垢样的溶蚀结果
垢样 不同浸泡时间溶蚀率/% 3 h 5 h 8 h 12 h 尖北1-2井 24.87 22.72 21.56 25.92 尖Ｈ1-5井 14.77 13.03 15.24 14.31
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表 5 多轮次碳酸氢钠浸泡对垢样溶蚀结果
垢样 配方 溶蚀率/% 第一轮次 第二轮次3 h 第三轮次3 h 尖北1-2井 5%NaHCO3
浸泡后3%HCl
酸洗垢样24.87 42.13 54.8 22.72 37.22 51.00 21.56 38.31 52.34 25.92 43.13 53.61 平均值 23.76 40.19 52.93
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表 6 不同溶垢剂溶液腐蚀速率的测定结果
溶蚀剂/% 浸泡时
间/h挂片溶蚀
质量/g腐蚀速率/
g/m2·hpH 备注 5%Na2CO3 10 −0.0004 0 14 挂片表面光洁，
无蚀斑，无细纹5%NaHCO3 10 −0.0005 0 8 挂片表面光洁，
无蚀斑，无细纹
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表 7 尖北1-2井垢样在6%盐酸+不同浓度的 有机磷酸螯合剂中浸泡后的溶蚀率
有机磷酸
螯合剂/%溶蚀率/% 第一轮次12 h 第二轮次3 h 第三轮次3 h 5 49.10 61.24 71.33 10 44.17 47.47 58.80 15 49.37 51.54 59.46 20 41.10 48.05 58.54
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