Technical Difficulties and Countermeasures for Cementing in Plateau Gas Storage under Complex Working Conditions

As a typical depleted oil and gas reservoir-type gas storage, Mabei Gas Storage is a key project for the Qinghai Oilfield in China to build an energy highland in Qinghai-Tibet and achieve high quality green and low carbon development. It is not only the world’s highest altitude gas storage but also China’s first plateau gas storage, possessing significant strategic and engineering value. During the cementing operation of this gas storage, there are numerous technical challenges, such as a high risk of leakage, great difficulty in effectively isolating oil-water layers, a large well deviation, low surface temperatures, and irregular wellbores. These issues make it difficult to guarantee the quality of cementing. Moreover, as the gas storage well operates for an extended period, the wellbore is subject to periodic changes in temperature and pressure, which impose extremely high requirements on the primary cementing quality and the long-term sealing integrity of the cement sheath. The failure of cementing in any single well could put the entire gas storage at risk of abandonment. In response to the cementing technical challenges of the Mabei Gas Storage, a series of key countermeasures have been developed: Firstly, conduct in-depth engineering geological condition analysis to accurately determine the cementing leakage pressure, rationally design the slurry column structure and construction displacement. This can reduce the leakage risk while ensuring the displacement efficiency. Secondly, based on the measured well diameter and deviation data, scientifically design the type, quantity, and installation position of centralizers to ensure that the casing centralization degree reaches over 80%, providing favorable conditions for the good displacement of cement slurry and improving the bonding quality. Finally, adopt a dual-thickening, natural gas self-healing, tough, and early strength cement slurry system. This system can ensure the rapid development of compressive strength at low temperatures. Its excellent toughness can meet the strict requirements for the integrity of the cement sheath during subsequent injection and production operations. Additionally, its good self-healing ability can further reduce the risk of annular pressure build-up in the later stage. This technical system has been applied 9 times at the Mabei Gas Storage site and achieved remarkable results. The cementing quality results show that the average qualification rate for the entire well section is 100%, the average excellent rate is 98.23%, and the excellent rate for the caprock and reservoir sections is 100%. This fully demonstrates the effectiveness and reliability of this technical system, marking a significant breakthrough in plateau gas storage cementing technology. It provides solid technical support for improving China’s energy strategic layout and ensuring energy security.