In high-temperature deep well operations, barite powder that has undergone surface modification treatment exhibits the best performance and is the most optimal choice for comprehensive performance under current technological conditions.

Despite the existence of various high-density weighting materials, the thermal stability, rheological properties, and settling stability of the materials become key limiting factors in deep well environments with temperatures exceeding 150 ℃. After upgrading technologies such as micronization, surface modification, and reasonable particle size distribution, the high-temperature adaptability of barite powder (barium sulfate, BaSO ₄) can be significantly improved, with a temperature resistance of up to 260 ℃ and a viscosity reduction efficiency of 45%. It also effectively improves the rheological properties and filtration and wall forming properties of high-density drilling fluids.

1. Surface modified barite: Strong high-temperature stability and mature application
Temperature resistance: After treatment with non/anionic composite surfactants, the collision between barite particles is reduced, the plastic viscosity is lowered, and stable performance can be maintained at 260 ℃.
Rheological optimization: micronization technology reduces the apparent viscosity, plastic viscosity and gel strength by 30%~50%, improves the dynamic suspension capacity and prevents high-temperature sedimentation.
Engineering verification: The ultra-high temperature and high-density oil-based drilling fluid (density 2.50-2.80g/cm ³) constructed by Qiu Zhengsong et al., using ultrafine barium sulfate and high-density barite composite weighting, successfully achieved engineering application with a temperature resistance of 220 ℃.
2. Manganese trioxide (Mn ∝ O ₄): a new acid soluble material suitable for reservoir protection
Density: about 4.7-4.9 g/cm ³, higher than barite
Advantages:
Micro sized particles have excellent static settling stability, with no settling after 15 days at 180 ℃ and a settling resistance of>1.95N
The acid solubility rate is as high as 95.31%, and the residual solid content is less than 0.5wt%, which is beneficial for later acidification and plug removal, and protects the permeability of the reservoir
The permeability recovery rate is greater than 90%, significantly better than the traditional barite system
Applicable scenarios: Especially suitable for high-temperature deep wells that require acidification to increase production, such as low-permeability gas reservoirs or carbonate reservoirs
3. Iron ore powder and hematite: high density but high wear and tear, limited use
Density can reach 5.0 g/cm ³ or above, suitable for ultra-high density requirements
But the Mohs hardness is as high as 5.5-6.5, which can easily cause severe wear and tear on the drilling tools, and is more prone to equipment failure at high temperatures
Under certain operating conditions, it is prohibited and needs to be replaced with activated barite
4. Solid free completion fluid: an alternative solution for extreme high temperatures
The solid free completion fluid developed by CNOOC Oilfield Services has a density of 1.85 kg/L, a temperature resistance of 170 ℃, and a corrosion rate of<0.076 mm/a. It is suitable for high-temperature and high-pressure gas fields in the South China Sea
Although not a traditional "weighting agent", it represents a new direction in high-temperature deep well fluid technology - by dissolving and densifying high concentration inorganic salts (such as zinc bromide and calcium chloride) to avoid solid phase settling problems

In summary, in high-temperature deep wells:
Preferred solution: Surface modification+micronized barite powder, mature technology, controllable cost, and reliable performance
Advanced choice: Manganese trioxide, suitable for well sections that require reservoir protection and acidification operations
Special scenario: Consider using a solid free saltwater system to avoid the risk of solid settling