Basfar Salem, Mohamed Abdelmjeed, Elkatatny Salaheldin, Al-Majed Abdulaziz
College of Petroleum Engineering and Geosciences, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Saudi Arabia.
Materials (Basel). 2019 Jun 17;12(12):1945. doi: 10.3390/ma12121945.
Barite sag is a serious problem encountered while drilling high-pressure/high-temperature (HPHT) wells. It occurs when barite particles separate from the base fluid leading to variations in drilling fluid density that may cause a serious well control issue. However, it occurs in vertical and inclined wells under both static and dynamic conditions. This study introduces a combined barite-ilmenite weighting material to prevent the barite sag problem in water-based drilling fluid. Different drilling fluid samples were prepared by adding different percentages of ilmenite (25, 50, and 75 wt.% from the total weight of the weighting agent) to the base drilling fluid (barite-weighted). Sag tendency of the drilling fluid samples was evaluated under static and dynamic conditions to determine the optimum concentration of ilmenite which was required to prevent the sag issue. A static sag test was conducted under both vertical and inclined conditions. The effect of adding ilmenite to the drilling fluid was evaluated by measuring fluid density and pH at room temperature, and rheological properties at 120 °F and 250 °F. Moreover, a filtration test was performed at 250 °F to study the impact of adding ilmenite on the drilling fluid filtration performance and sealing properties of the formed filter cake. The results of this study showed that adding ilmenite to barite-weighted drilling fluid increased fluid density and slightly reduced the pH within the acceptable pH range (9-11). Ilmenite maintained the rheology of the drilling fluid with a minimal drop in rheological properties due to the HPHT conditions, while a significant drop was observed for the base fluid (without ilmenite). Adding ilmenite to the base drilling fluid significantly reduced sag factor and 50 wt.% ilmenite was adequate to prevent solids sag in both dynamic and static conditions with sag factors of 0.33 and 0.51, respectively. Moreover, HPHT filtration results showed that adding ilmenite had no impact on filtration performance of the drilling fluid. The findings of this study show that the combined barite-ilmenite weighting material can be a good solution to prevent solids sag issues in water-based fluids; thus, drilling HPHT wells with such fluids would be safe and effective.
重晶石沉降是在钻高压/高温（HPHT）井时遇到的一个严重问题。当重晶石颗粒与基液分离时就会发生这种情况，这会导致钻井液密度变化，可能引发严重的井控问题。然而，它在垂直井和斜井的静态和动态条件下都会出现。本研究引入了一种重晶石 - 钛铁矿复合加重材料，以防止水基钻井液中的重晶石沉降问题。通过向基础钻井液（重晶石加重）中添加不同百分比的钛铁矿（占加重剂总重量的25%、50%和75%）来制备不同的钻井液样品。在静态和动态条件下评估钻井液样品的沉降趋势，以确定防止沉降问题所需的钛铁矿最佳浓度。在垂直和倾斜条件下都进行了静态沉降试验。通过在室温下测量流体密度和pH值，以及在120°F和250°F下测量流变性能，来评估向钻井液中添加钛铁矿的效果。此外，在250°F下进行了过滤试验，以研究添加钛铁矿对钻井液过滤性能和形成的滤饼密封性能的影响。本研究结果表明，向重晶石加重的钻井液中添加钛铁矿会增加流体密度，并在可接受的pH范围（9 - 11）内略微降低pH值。钛铁矿在HPHT条件下使钻井液的流变性能保持在最小程度的下降，而基础流体（不含钛铁矿）则出现了显著下降。向基础钻井液中添加钛铁矿显著降低了沉降系数，50%重量的钛铁矿足以在动态和静态条件下防止固体沉降，动态和静态条件下的沉降系数分别为0.33和0.51。此外，HPHT过滤结果表明，添加钛铁矿对钻井液的过滤性能没有影响。本研究结果表明，重晶石 - 钛铁矿复合加重材料可以成为防止水基流体中固体沉降问题 的良好解决方案；因此，用这种流体钻HPHT井将是安全有效的。
