南海高温高压气藏机械防砂筛管动态腐蚀评价实验研究

Experimental Evaluation of Dynamic Mechanical Sand Screen Corrosion for the High Temperature Pressure Gas Reservoir in South China Sea

机械防砂筛管腐蚀寿命评价及筛管评价优选对于高温高压气藏尤为重要,目前以静态金属挂片腐蚀实验为主要手段的筛管腐蚀评价难以适应气藏的动态生产条件。针对该问题,利用防砂筛管动态腐蚀评价系统,基于南海某高温高压气藏温度、压力和流体条件,对典型的机械防砂筛管的基管、挡砂介质(多层滤网、烧结纤维、绕丝筛板、泡沫金属镍)和外保护罩组件进行了动态腐蚀评价实验。结果表明:典型高温高压气藏条件下,N80钢基管为中度腐蚀,深度腐蚀速率为0. 073 8 mm/a,316L钢多层滤网挡砂介质为轻度腐蚀,深度腐蚀速率为0. 017 4mm/a,304钢外保护罩腐蚀程度介于两者之间,深度腐蚀速率为0. 029 3 mm/a;筛管各组件的质量腐蚀速率随CO2分压增大而加快,三者的质量腐蚀速率在CO2分压超过7. 0 MPa后差异更明显;各组件质量腐蚀速率随温度升高先上升后下降,在温度为120~140℃时达到最高质量腐蚀速率;水气比增加会加快腐蚀。多层滤网、绕丝筛板、烧结纤维和泡沫金属镍4种典型的挡砂介质的深度腐蚀速率分别为0. 017 4、0. 030 6、0. 010 5、0. 005 8 mm/a,差异明显。延长筛管腐蚀寿命的主要途径为选择合适的筛管类型和介质类型、优化筛管结构参数、改变外保护罩和基管的材料等。动态腐蚀寿命评价方法为不同油气储层的机械防砂筛管及井下工具的腐蚀评价和寿命预测提供了更加可靠的手段。

The corrosion life evaluation and optimization of mechanical sand screen are considered as key issues for the high temperature and high pressure gas reservoir.The available corrosion evaluation based on static metal hanging sheet test is difficult to meet the dynamic production condition of gas reservoir.A dynamic corrosion evaluation system of sand screen was used based on the temperature,pressure and fluid conditions of a high temperature-pressure gas reservoir in the South China Sea.A dynamic corrosion evaluation was completed for the typical mechanical sand screen,including the base pipe,sand retaining medium(multi-layer filter screen,sintered fiber,wire-wrapped sieve plate,foam metal nickel)and the outer protective cover.Research indicates that under the typical high temperature-pressure gas reservoir conditions,the N80 steel base pipe is moderately corroded with a corrosion rate of 0.0738 mm/a,316L steel multi-layer filter sand retaining medium is mildly corroded with a corrosion rate of 0.0174 mm/a.The corrosion level of 304 steel outer protective cover is between the former two types and the corresponding corrosion rate is 0.0293 mm/a.With the increase of temperature,the corrosion rate of each component increases firstly and then decreases,and the maximum corrosion rate is reached when the temperature is 120~140℃.The increase of water-air ratio will accelerate the corrosion.The corrosion rates of multi-layer filter screen,sintered fiber,wire-wrapped sieve plate and foam metal nickel are 0.0174,0.0306,0.0105,0.0058 mm/a respectively,which indicate significant differences.The major means to prolong the corrosion life of sand screen include optimizations of sand screen and medium types,structure parameter design,adjustment of the outer protective cover material and base tube material,etc.This dynamic corrosion life evaluation method provides a more reliable means to the corrosion evaluation and life prediction of mechanical sand screen and downhole tools in different hydrocarbon reservoirs.