深水气井井筒碳酸钙垢生成预测与防治方法

Prediction and prevention methods of calcium carbonate scale formation in deepwater gas wellbore

深水气藏储层地层水矿化度高,气井井筒温度变化剧烈,环境压力降低会造成CO_(2)逸出,导致气井井筒通常面临着较高的结垢风险,如何准确预测井筒结垢、量化井筒结垢风险并为井筒结垢风险防治提供理论支持是深水气井生产过程中重要挑战。本文基于深水气井井筒垢物生成类型和结垢机理,分别建立了析晶垢和颗粒垢的沉积速度模型,考虑温压场和井筒产出液对垢层冲蚀,建立了垢层剥离速率模型,考虑井筒结垢过程由沉积和剥离共同作用,得到了气井井筒结垢预测模型,实现了井筒内结垢沉积和剥离过程的定量预测,模拟结果表明:随着产气量减少和产水量的增加,井筒日沉积量和井筒年结垢厚度也随之增加,针对南海某实例井NH-1,当产气量为30万m3/d、产水量为132 m3/d时,深水气井井筒垢日沉积量为685.08 g/d,该气井生产25年井筒总垢层厚度会达到28.29 mm。此外,本文还利用高温结垢实验装置评价了适用于南海某实例井NH-1的防垢剂,实验结果显示:在130℃、防垢剂浓度为60 mg/L时,防垢剂PESA可以达到90%的防垢率,能达到现场防垢标准,给出了防垢剂注入时机和注入速度。本文研究结果可为深水气井井筒结垢预测和防治提供理论支持。

The formation water of deepwater gas reservoirs has high salinity,and gas well bore temperature changes drastically.The reduction of environmental pressure will cause CO_(2) to escape,resulting in a higher risk of scaling in the gas wellbores.It is an important challenge in the production process of deepwater gas wells to accurately predict well bore scaling and quantify well bores scaling risk and providing theoretical support for wellbore scaling risk prevention.Based on the type of scale formation and scaling mechanism in deepwater gas wells,the deposition rate models of crystallization scale and granular scale are established herein respectively.Considering the erosion of the scale layer by the temperature and pressure field and the wellbore produced fluids,a scale layer stripping rate model is established.Considering the combined effects of deposition and stripping of the wellbore scaling process,a gas well wellbore scaling prediction model is obtained,which realizes the quantitative prediction of the scaling deposition and stripping process in the wellbore.The simulation results show that as the gas production decreases and the water production increases,the wellbore daily sedimentation volume and the wellbore annual scaling thickness also increase.For an example,Well NH-1 in the South China Sea,when gas production is 300000 m3/d and water production is 132 m3/d,the daily amount of scale deposit in the deepwater gas wellbore is 685.08 g/d.The total scale thickness of the gas well would reach 28.29 mm in 25 years of production.In addition,the high-temperature fouling experiment device is also used herein to evaluate the anti-scaling agent suitable for NH-1 in an example well in the South China Sea.The experimental results show that the anti-scaling agent PESA can reach 90%anti-scaling rate and meet the on-site anti-scaling standard at 130°C and the anti-scaling concentration of 60 mg/L.The timing and injection rate of anti-scaling agent injection are given herein.The research results in this paper can provide theoretical support for the prediction and prevention of scaling in deep-water gas wells on site.