页岩气井固井技术难点分析

TECHNOLOGIC CHALLENGES IN CEMENTING SHALE-GAS WELLS

页岩气是我国一个新的天然气矿种,具有非常广阔的开采前景。页岩气藏属于低孔低渗气藏,其特殊的生产方式对固井质量要求非常高。但页岩气藏地质特征、钻完井方式及开发方式决定了页岩气井固井难度远远大于常规油气井。结合我国页岩气资源特点,从顶替效率、水泥环完整性和水泥浆体选择三方面分析页岩气井固井技术难点,以期对页岩气固井技术开发提供帮助。分析表明:不规则井眼条件下的水平井固井、保证水泥环长期完整性和水泥浆性能与成本的平衡问题是我国页岩气井固井作业的主要难点。建议从"水平井复杂井况下提高顶替效率技术、水泥环长期完整性评价技术、页岩气固井水泥浆体系"三方面加强技术攻关,以提高我国页岩气井勘探开发效益。

As a novel natural-gas mineral in China, shale gas has a broad prospect for exploitation. Shale-gas reservoirs are characterized by low porosity and permeability, further resulting in a demand to high cementing quality. However, their geological characteristics, drilling and completion methods, and development modes may decide that it's more difficult to implement a cementing in shale-gas wells than that in conventional gas wells. Based on a lot of features of shale-gas resources in China, many cementing difficulties were analyzed in terms of displacement efficiency, cement-sheath integrity, and cement slurry selection. Results show that the main challenges include horizontal-well cementing with irregular borehole, ensuring the cement-sheath integrity for a long time, and keeping a balance between cement-slurry property and cost. In addition, three suggestions are made to increase exploration and development benefits for shale-gas wells, containing(1)to increase displacement efficiency under complicating well conditions,(2)to carry out an evaluation on long-term cement-sheath integrity, and(3)to develop a cement-slurry system.