Lingshui 25-1 gas field is the first deepwater high-pressure gas field development project. Complex deep water pressure conditions bring potential threats to cementing quality, and the integrity of cement sheaths seal is a key prerequisite for the smooth development and production of gas fields.
In order to overcome the limitations of conventional deep-water cement slurry system and evaluation methods, based on the geological characteristics and well structure of Lingshui 25-1 gas field, a cement slurry system suitable for target gas field was constructed, a series of HTHP seal integrity evaluation devices and methods were developed and established, and the influencing factors of cement sheath integrity were explored combined with the micro-morphology characteristics.
The cement additive is optimized through research, and the high temperature difference and gas invasion proof cement slurry system suitable for Lingshui 25-1 high-pressure gas well is constructed. A systematic experiment was carried out according to the integrity evaluation device developed and established. The results showed that when the pressure inside the casing increased by 30MPa, the stress distribution on the section of the cement sheath showed non-uniformity, and the comprehensive stress on cementing interface I was the largest, showing radial cracks caused by tensile failure and circumferential cracks caused by shear failure, which resulted in the failure of the sealing integrity of the cement sheath.
For purpose of guarantee that the cement sheath in Lingshui 25-1 gas field has a safe and reliable sealing ability in the special deep-water high-pressure environment. At the same time, this analysis method can provide reference for the development of deepwater high-pressure gas fields around the world.
With the breakthrough of key theories and core technologies of offshore drilling and completion, offshore oil gas exploration and development has gradually advanced to deep water. The discovery of Lingshui 25-1 gas field not only provides an excellent opportunity for deep water development, but also puts forward a more stringent ordeal for deep water drilling and completion capability. Compared with conventional deep water Wells, Lingshui 25-1 deepwater high-pressure gas well faces more complex environmental conditions, such as shallow low temperature, HTHP of reservoir and narrow safety density window, which make it difficult to effectively guarantee the cementing quality. Cement sheath is very easy to form micro-annulus, resulting in packer failure, wellhead channeling, annulus pressure and other phenomena, and even the risk of abandonment of oil gas Wells (Liu et al.,2021).
