水湿环境下硫化氢对固井水泥石的腐蚀机理

<正>确认识硫化氢对固井水泥石腐蚀的基本规律.对于保障高含硫气藏的安全高效开发具有重要的作用。为此,根据硫化氢在井下的存在形式,在室内建立起气相腐蚀和液相腐蚀两种水湿环境,分别考察了硫化氢对固井水泥石外貌、腐蚀深度、微观形貌、物相组成、抗压强度、孔隙度和渗透率等性能的影响。结果表明:①水泥石在气相腐蚀条件下的腐蚀程度要低于液相腐蚀水泥石的腐蚀程度,说明外部水湿环境对硫化氢与固井水泥石之间的腐蚀有较大影响;②在气相腐蚀水泥石表面会形成一层致密石膏层,能够有效阻止后续腐蚀介质侵入水泥石基体;③在液相腐蚀水泥石表面会形成多孔的无定形硅胶层,致使腐蚀介质进一步侵入水泥石内部。结论指出,不同的水湿环境造成水化产物分解形成的离子在水泥石表面存在状态不同,是造成气相腐蚀和液相腐蚀环境下水泥石性能差异的主要原因。

Corrosion mechanism of hydrogen sulfide on well cement under water wet environments

To ensure the safe and efficient development of high-sulfur gas reservoirs, it is critical to correctly understand how hydrogen sulfide brings corrosion impacts to well cement. Based on the occurrence of hydrogen sulfide in wells, gaseous corrosion and liquid corrosion water wet environments were established in lab to examine the effect of hydrogen sulfide on well cement performances such as appearance, corrosion depth, microscopic morphology, phase composition, compressive strength and porosity and permeability. The study results show that the corrosion degree of hardened cement is lower under gaseous corrosion circumstance than that under liquid corrosion circumstance, indicating that the external water wet environment has a great influence on the corrosion of hydrogen sulfide on well cement. Moreover, a dense gypsum layer can be formed on the surface of gaseous corrosion hardened cement, which can effectively prevent the subsequent corrosive medium from intruding into the hardened cement matrix. A section of porous amorphous silica gel would be formed on the surface of liquid corrosion hardened cement, resulting in further intrusion of corrosive medium into the inside of hardened cement. It is concluded that different water wet environments result in different existences of ions formed from the decomposition of hydrated product on the surface of hardened cement, which is the leading cause for different performances of hardened cement under gaseous corrosion and liquid corrosion environments.