基于固体钙含量的CO腐蚀水泥石规律预测

Prediction of CO Corrosion of Cement Paste Based on Solid Calcium Content

袁彬 袁坤峰 徐璧华 颜爽

YUANBin YUANKunfeng XUBihua YANShuang

油气藏地质及开发工程国家重点实验室·西南石油大学, 四川 成都 610500 中国石油西南油气田公司川东北气矿, 四川 达州 635000

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China Northeast Sichuan Gas Field, Southwest Oil & Gas Field Company, PetroChina, Dazhou, Sichuan 635000, China

CO会腐蚀油井水泥环，导致其强度衰退，使其失去保护套管和封隔油、气、水层的作用，从而缩短油气井寿命，造成巨大经济损失。如果能够预测CO在井下的腐蚀深度和腐蚀规律，那么就可以预测油井寿命，进而对水泥环耐腐蚀性能进行改进。然而，目前的CO腐蚀深度模型，大多是基于实验数据拟合建立的半经验模型，不具普遍适用性。针对这一问题，根据质量守恒定律结合扩散对流方程及钙离子沉淀速度，建立了CO腐蚀深度预测模型。该模型考虑了CO的扩散作用以及钙离子的沉淀，具有较强的适用性。通过CO腐蚀实验验证了该模型的可靠性，并利用该模型分析了水泥石基质被腐蚀后的变化规律，结果表明，随着腐蚀时间增加，水泥环孔隙度、渗透率增加，孔道迂曲度减小从而导致物质对流扩散加快、腐蚀速率加快；距离腐蚀端面越近孔隙度、渗透率越大，孔道迂曲度越小。

CO will corrode the cement sheath of oil well, leading to its strength decline, make it lose the function of protecting casing and sealing off oil, gas and water. Thus shorten the life of oil and gas well and cause huge economic loss. If the corrosion depth and corrosion laws of CO downhole can be predicted, the life of the oil well can be predicted, and the corrosion resistance of the cement ring can be improved. However, most of the current CO corrosion depth models are semi empirical models based on experimental data fitting, which are not universally applicable. To solve this problem, a prediction model of CO corrosion depth was established based on the law of mass conservation, diffusion convection equation and calcium precipitation rate. The model takes into account many factors, especially the diffusion of CO and the precipitation of calcium ions, so it has strong applicability. The reliability of the model is verified by CO corrosion test, and the change law of cement matrix change after corrosion is analyzed by using the model. The results show that with the increase of corrosion time, the porosity and permeability of cement sheath increase, and the tortuosity decreases, which leads to the acceleration of material convection diffusion and corrosion rate; the closer to the corrosion end, the greater the porosity and permeability, and the smaller the tortuosity.

10.11885/j.issn.16745086.2021.04.29.03