Non-Damaging Nano Polymeric Product Enhances Bridging Agents Packing for Limestone Reservoirs in the Persian Gulf

Abstract

Abstract Water-based drill-in fluids (WB DIF) with high concentrations of lubricants and other materials that assist in reducing the fluid loss are commonly used to drill tight and high overbalance reservoirs in the south-west Persian Gulf. Exposure and damage of the formation by these products is highly possible due to the characteristic high fluid loss of WB DIF. This paper discusses the improvement of a WB DIF by adding a non-damaging polymeric product to enhance filtercake packing. The chemistry and the particle size of the polymeric product enhances the bridging properties of the calcium carbonate, thus improving the wellbore strengthening and reducing formation damage. Return permeability (RP) testing is widely used in the oil industry to evaluate fluid-rock interaction. RP testing indicates potential causes of production impediments generated after drilling by filtercake deposition and filtrate invasion. Limestone outcrops from Mississippian formation with a permeability between 9-16 md and 14-18% porosity were used for the RP tests. Damage minimization from the drill-in mud with no requirement for a breaker were the main goals for the fluid development to drill the tight limestone reservoir. Therefore, higher RP values to permeable oil was the desired outcome of the tests. The solid particles used in the drill-in fluid should generate optimal packing to achieve lower filtrate invasion. Software simulation and calculations for bridging optimization are highly recommended, but brittle particles such as calcium carbonate could deviate from the predictions after passing though the drilling nozzles and changing their size with no control. The use of non-damaging polymeric and deformable particles could help with the packing of the bridging agents and improve the wellbore strengthening by reducing filtrate invasion. This paper presents results for a fluid before and after the addition of bridging enhancer. In the study, the addition of the non-damaging polymeric material had no effect on the rheological properties of the fluid. Furthermore, the fluid loss decreased almost 40% at 160°F and 85% at 250°F using paper as a filtration media. The RP of the original WB DIF was 79.7% at 4 cm3/min using LVT-200 as a permeating oil and 89% after centrifugation, indicating connate water damage. The RP of the enhanced fluid was 92.7% at 4.0 cm3/min and 93.5% after centrifugation, indicating no damage by connate water and a significant decline in the formation damage by filtrate invasion due to the improved packing of the bridging agents. No breaker was required for the fluid due to the high RP thus decreasing cost of the operation by reducing rig time and chemical treatments. Return permeability evaluation between the drill-in fluid and reservoir rock is essential for oil producer wells to determine damage caused by the fluid, filter cake, and filtrate. Improving the packing of the bridging agents enhances fluid loss and decreases formation damage.