Cesium formate brine is a high-density, low-viscosity clear fluid that provides the basis for a non-damaging, hydraulically efficient HPHT reservoir drilling fluid. Anti-oxidant and water-structuring properties protect common drilling polymers (e.g. xanthan, PAC and starches) from thermal degradation. No weighting solids are needed in these fluids because the formate brine alone has the density needed to exert the required hydrostatic pressure to maintain well control. Formate brines are equally effective in conventional Overbalanced operations and possess particular attributes that benefit Underbalanced drilling and the newer Managed Pressure operations.

Very clear reservoir image logs in cesium formate brine

• Improved well control — with no solids to sag, or oil to solubilise hydrocarbon gases, the risk of a well control incident happening with cesium formate brine in an HPHT well is much reduced (e.g. 0 in 14 wells drilled to date).
  
  
• Faster, safer drilling — the use of low-solids drilling fluids based on cesium formate brines reduces ECD by around 0.05 s.g./0.42 ppg in a typical deep HPHT well. This allows safer drilling in reservoirs with narrow margins between pore pressure and frac gradient, and promotes increased ROP.
  
  
• Reduced formation damage and elimination of screen plugging — most users report well productivity indices that exceed expectations after drilling and completing in cesium formate brine. This is true both for perforated liner and open-hole screen completions.
  
  
• Improved well integrity — the use of cesium formate brine reduces the risk of catastrophic localised corrosion and stress corrosion cracking in well tubulars exposed to HPHT acid gas influxes.
  
  
• Setting new higher HSE standards and reducing liability — no other high-density fluids come close to matching the high HSE standards set by cesium formate brine. Using this modern state of the art fluid greatly reduces the risk of creating long-term liability down the line.
  
  
• Enabling HPHT MPD in narrow drilling windows — when the gap between pore pressure and fracture pressure in HPHT wells becomes very narrow (e.g. following reservoir depletion), cesium formate brine is used to make Fracture Gradient Enhancement (FGE or ‘stress cage’) drilling fluids for Managed Pressure Drilling operations. The FGE fluids utilise sized particles introduced into the high-density formate brine to compress the adjacent rock matrix and increase the effective fracture gradient in depleted formations.
  
  
• Accurate reservoir definition and imaging — Very reliable and consistent net reservoir definition is provided by LWD bulk density and resistivity measurements made in HPHT wells drilled with cesium formate brine. The highly conductive fluid environment created by cesium formate brine facilitates the generation of high-quality resistivity image logs (FMI). These image logs provide detailed reservoir information including structural dip, depositional environment, sedimentary features, facies, and geological correlations.
  

Stuck pipe pill
Aside from its use as an HPHT drilling fluid, cesium formate brine also has an interesting niche application as a fast-acting liquid pill for releasing drill pipes differentially stuck in OBM filter cakes. The pill of formate brine rapidly destroys the OBM filter cake and allows the pipe to be jarred free.