Study of barium sulfate dissolution by scale dissolver based on solutions of DTPA

Abstract In offshore oil wells it is very common to perform seawater injection through injection wells for hydrocarbon recovery. When seawater, rich in sulfate ion, mixes with formation water, whose composition can contain divalent cations such as barium and calcium, it often leads to sulfate salts formation due to their chemical incompatibility. These salts can cause serious damage in production wells. The barium sulfate (BaSO4) is the most problematic scale and may cause many complications. In order to solve this issue, polycarboxylic acids, such as diethylene triamine pentaacetic acid, are used. Thus, the primary focus of this work was to develop an experimental procedure to study the BaSO4 dissolution. Initially, through static tests to understand the relationship between dissolver concentration, temperature and dissolution time, and then through dynamic tests in sandstone reservoirs. Based on the results obtained, in the static tests the best condition for barite to dissolve was at high temperatures (80 ºC) and contact time of 48 hours, since from 50 °C there is an increase in dissolution rate, associated with a long contact time between dissolver and barite. In the dynamic tests, after scale formation, barite could be removed, but the high DTPA concentration should be avoided.

摘要 海上油气开采过程中，通过注入井注入海水以提升油气采收率是极为常见的工艺手段。富含硫酸根离子的海水与含有钡、钙等二价阳离子的地层水混合时，因二者化学不相容，往往会生成硫酸盐垢。此类垢物会对生产井造成严重损害，其中硫酸钡（barium sulfate, BaSO₄）是危害最为突出的垢种，可引发诸多工况并发症。为解决该结垢问题，工业界常采用聚羧酸类药剂，例如二乙三胺五乙酸（diethylene triamine pentaacetic acid, DTPA）。据此，本研究的核心目标为开发一套用于探究硫酸钡溶垢过程的实验方法：首先通过静态实验，明确溶垢剂浓度、温度与溶垢时长三者间的关联规律；随后针对砂岩油藏开展动态实验。基于实验结果，静态实验中重晶石（硫酸钡垢）溶垢的最优条件为高温（80℃）与48小时接触时长——当温度高于50℃时，溶垢速率随溶垢剂与重晶石的接触时间延长而显著提升。动态实验结果表明，虽可在垢层生成后完成重晶石垢的清除，但需避免使用过高浓度的二乙三胺五乙酸（DTPA）。