High Temperature Solid Free Water Base Drill-in Fluid

The reservoir formations in the Block Barua, west Venezuela, are characteristic of multiple interbedded mudstones and sandstones, unconsolidated sandstones because of poor cementation, borehole wall collapse and frequent mud losses, high temperatures and poor reservoir physical properties. A drilling fluid named BH-ELASTICO-HTHP has been developed based on the "fluid casing concept" to try to maintain borehole stability during drilling and to minimize skin contamination of the reservoir formations. The BHELASTICO- HTHP drilling fluid has high viscosity and low gel strengths, and can be used to stabilize borehole wall and reduce skin factors when treated with dolomitic CaCO₃ as a temporary plugging agent. The low-shear-rate viscosity of the BH-ELASTICO-HTHP drilling fluid helps clean the borehole. As a high temperature drilling fluid formulation, with its main additives easy to degrade, this drilling fluid is suitable for use in drilling formations with low pore pressure, low permeability, and unconsolidated formations. The application of this drilling fluid in the well MGB-0066 demonstrates that the BH-ELASTICO-HTHP drilling fluid has strong mud loss controlling capacity and shale inhibitive capacity; it helps protect reservoir formations from being damaged and is environmentally friendly. The well MGB-0066 has actual oil production rate 30%more than that of the offset well. The use of the BH-ELASTICOHTHP drilling fluid realized safe drilling and enhanced production. The "fluid casing concept" will help in designing drilling fluid formulations for use in old oilfield or in reservoirs with poor physical properties.