Abstract The use of hydrochloric acid (HCl) in gas well stimulation of high temperature reservoirs is currently facing different challenges. These challenges include rapid corrosion of the well tubulars, face dissolution, very high and uncontrolled reaction rate, and formation damage in high clay content and iron-rich reservoirs. In this study, water-soluble diethylene triamine penta acetic acid (DTPA) chelating agent is introduced as alternative to eliminate the risk associated with HCl at high temperatures. In addition, the potential of using seawater to replace fresh water in the stimulation process is explored to save the cost of fresh water transportation to deep offshore oil and gas wells. The effect of seawater on the reaction kinetics of DTPA with carbonate rocks under high pressure and high temperature conditions is investigated using the rotating disk apparatus. The reactions of DTPA solution diluted with fresh water (DTPA/DI) and seawater (DTPA/SW) with carbonate rocks were carried out at the same conditions. In the case of fresh water, the reaction is controlled by the surface reaction regime. Adding HCl to adjust DTPA pH did not turn the reaction into a mass transfer controlled reaction like the case of using HCl alone. The heavy matrix of seawater increased the resistance of ions diffusion, which resulted in a low reaction rate and transformed the reaction into a mass transfer limited regime. Corrosion tests were carried out on production and coiled tubing coupons obtained from the gas wells and the results of the new DTPA/SW formulation is compared to the standard HCl formulation. DTPA showed very low corrosion rate of 0.0034 g/cm2 without adding corrosion inhibitors compared to 0.205 g/cm2 of 15 wt% HCl with 3% corrosion inhibitors while the industry limit is 0.0244 g/cm2 in 6 h. The reaction regime of DTPA chelating agent with calcite is identified to be mass transfer limited in seawater and surface reaction limited in fresh water. The rate expression for the dissolution of Ca2+ in DTPA/SW solution is obtained. Coreflooding experiments were performed to determine the optimum injection rate using low permeability Indiana limestone core samples. The optimum injection rate required to stimulate a very deep carbonate gas well was found to be 1.4 bbl/min after scaling up the coreflooding results to field scale. The application of the new DTPA/SW formulation in treating deep gas wells is expected to save the cost of fresh water and eliminate the cost of corrosion inhibitors.

中文翻译：

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使用海水和螯合剂增产高温碳酸盐岩气藏：反应动力学

摘要 盐酸(HCl)在高温储层气井增产中的应用目前面临着不同的挑战。这些挑战包括井管的快速腐蚀、工作面溶解、非常高且不受控制的反应速率以及高粘土含量和富含铁的储层中的地层损坏。在这项研究中，水溶性二亚乙基三胺五乙酸 (DTPA) 螯合剂被引入作为替代品，以消除高温下与 HCl 相关的风险。此外，探索在增产过程中利用海水替代淡水的潜力，以节省淡水输送至深海油气井的成本。使用转盘装置研究了在高压和高温条件下海水对DTPA与碳酸盐岩反应动力学的影响。用淡水稀释的 DTPA 溶液 (DTPA/DI) 和海水 (DTPA/SW) 与碳酸盐岩的反应在相同条件下进行。在淡水的情况下，反应由表面反应机制控制。添加 HCl 以调节 DTPA pH 值并没有像单独使用 HCl 的情况那样将反应转变为传质控制反应。海水的重基体增加了离子扩散的阻力，导致反应速率低，并将反应转变为传质受限状态。对从气井获得的生产和连续油管试样进行腐蚀测试，并将新 DTPA/SW 配方的结果与标准 HCl 配方进行比较。与含 3% 腐蚀抑制剂的 15 wt% HCl 的 0.205 g/cm2 相比，DTPA 显示出非常低的腐蚀速率，为 0.0034 g/cm2，而工业限值为 6 小时内 0.0244 g/cm2。DTPA螯合剂与方解石的反应机制被确定为在海水中受传质限制，在淡水中受表面反应限制。得到了Ca2+在DTPA/SW溶液中溶解的速率表达式。使用低渗透性印第安纳石灰岩岩心样品进行岩心驱油实验以确定最佳注入速率。在将岩心驱油结果放大到油田规模后，发现刺激非常深的碳酸盐岩气井所需的最佳注入速率为 1.4 bbl/min。新的DTPA/SW配方在深部气井处理中的应用有望节省淡水成本并消除缓蚀剂的成本。