砂岩孔隙型地热井提高热效工艺分析

Analysis on the thermal efficiency improvement process for geothermal well in porous sandstone

李晓益 何汉平 段友智 李一凡

LI Xiaoyi HE Hanping DUAN Youzhi LI Yifan

中国石化石油工程技术研究院 中国石油华北油田分公司

SINOPEC Research Institute of Petroleum Engineering, Beijing 100101, China CNPC Huabei Oil field Company, Renqiu 062552, Hebei, China

针对国内砂岩孔隙型地热井井口水温相对较低、缺乏提高热效工艺的先导试验，开展了提高热效工艺与井口水温之间的适应性研究。采用开口系统稳定流动热力学模型，分别从地热井成井施工参数和井筒隔热工艺两个方面计算了多条件下的井筒水温曲线，对比了不同工艺方法下的增温效果、成本和可操作性。研究表明：小排量抽水时，沿程热损失和上层低温高渗井段主出水，综合导致井口水温较低；大排量抽水时，井口水温随着日抽水量的增大而增大，但增温幅度减小，日抽水量大于3 500 m³/d时增温幅度非常小且趋势趋平；主出水井段越深，井口水温越高，合理设计地热井止水器和滤水管安装深度，使得底层高温热储层动用起来，可以增加井口水温8~18 ℃以上；单纯增加泵挂深度井口水温增加不大于0.2 ℃；采用氮气环空隔热、气凝胶隔热、降低水泥环导热系数和延长固井段长度，可以增加井口水温0.23~1.3 ℃，但是成本较大，实现相对困难；延长抽水钢管长度并外刷隔热涂层，井口水温增加0.6~1 ℃，预增成本相对较少，容易实现。拟合了井口水温与日抽水量之间的函数方程，该函数方程可以快速预测相似结构管柱砂岩孔隙型地热井不同排量下的井口水温。该研究结果可为砂岩孔隙型地热井井口水温预测、现场提高热效工艺方式的选择提供参考。

In China, the wellhead water temperature of geothermal well in porous sandstone is lower and pilot tests on thermal effciency improvement process are defcient. To solve these problems, the adaptability between the thermal effciency improvement process and the wellhead water temperature was investigated in this paper. The water temperature curves of wellbore under various conditions were calculated from two aspects (i.e., geothermal well completion parameters and wellbore heat insulation technology) respectively by using the steady-fow thermodynamic model of open system. Then, different processes were compared from the aspects of warming effect, cost and operability. It is indicated that when the water is pumped at low rate, the wellhead water temperature is lower due to the joint effect of on-way heat loss and water production of low-temperature permeable hole section in the upper part. When the water is pumped at high rate, the wellhead water temperature increases with the daily water pumping capacity, but its increasing speed slows down. When the daily water pumping capacity is higher than 3 500 m/d, the temperature increasing speed is quite low and tends to fatten. The deeper the main water producing hole section, the higher the wellhead water temperature. The wellhead water temperature can be increased by 8-18 ℃ if the high-temperature thermal reservoir at the bottom is produced by designing rationally the installation depthof water stopping device and perforated pipe in the geothermal well. If only the pump setting depth is increased, the increase of wellhead water temperature is less than 0.2 ℃. If annulus nitrogen heat insulation or aerogel heat insulation is adopted, the thermal conductivity of cement sheath is decreased or the cementing section is extended, the wellhead water temperature can be increased by 0.23-1.3 ℃, but its cost is high and its implementation is diffcult. If the steel pumping pipe is extended and the insulating coating is painted, the wellhead water temperature can be increased by 0.6-1 ℃, and this process can be implemented easily with lower cost. Finally, the functional equation between the wellhead water temperature and the daily water pumping capacity was ftted. It is shown that by virtue of this functional equation, the wellhead water temperature of geothermal wells with the similar string structure in porous sandstone at different fow rates can be predicted quickly. The research results provide the theoretical basis and guide for the prediction of wellhead water temperature of geothermal wells in porous sandstones and the selection of thermal effciency improvement process on site.

10.13639/j.odpt.2017.04.016