Research and application of a high-temperature high-density drilling fluid system in Well Shunbei-4XH

Well Shunbei-4XH is a key preliminary prospecting well for the No. IV fault zone of the Shunbei oilfield. The Ordovician Yijianfang formation and Yingshan formation of the production casing section of this well are well-developed with micro fractures and karst vugs and represent fracture-type carbonate gas reservoir with the formation temperature exceeding 170 ℃. To enhance the gel thermal stability, plugging and anti-collapse performance, and high-temperature settlement stability of the drilling fluid system and also avoid reservoir damage, the water-based drilling fluid system with thermal resistance to 200 ℃ and density of 2.00–2.25 g/cm³ was developed via development and optimization of key additives. The filter loss at 180 ℃ is 9.2 mL and the 7-day settlement stability coefficient at 200 ℃ is 0.513. The test results of the oscillatory rheometer and dynamic light scattering as well as the field application demonstrate that the presented system has premium flow and lubricating performance, favorable high-temperature settlement stability, and low filter loss at high temperature and high pressure (≤10 mL). It can immediately plug micro fractures of the reservoir to deliver desired temporary plugging.