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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.
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.
Drilling various depleted formations to enter the reservoir at the right location to extract the maximum gain is becoming more frequent and regular. In most cases, the overbalance reaches 1000 psi across various zones and is sometimes observed exceeding 5600 psi. Wellbore instability, deep fluid invasion, differential sticking, and mud losses are a few of the problems that need to be addressed when designing the fluid, irrespective of type of mud system (water-based or non-aqueous fluids). Also, casing isolation might not always be possible and can be very expensive. Therefore, it is necessary to identify a solution from the fluid's perspective that designs a suitable fluid mitigating the above concerns and makes the drilling easier, safer, and more efficient. With appropriate bridging, a good seal across the formation help maintain the wellbore stability and stop the fracture propagation. The seal that forms should be thin, effective, and have low permeability that can minimize the pore pressure transmission (PPT) into the formation which causes the formation to destabilize. Initially these fractures in the formation are in nano-size levels and typical products available in the market cannot bridge these properly which can lead to bigger fractures and ultimately end up in causing heavy mud loses, well control situations, and formation damage leading to lost production. Bridging software helps to predict the right combination of products required and also determines the requirement for any other, bigger particles. The latest developments in nanotechnology help in resolving the above concerns and can be used in the drilling fluids without having any adverse effect on the mud and environment. The technology features of the subject nano-sized solid particles allow them to be mixed in aqueous or non-aqueous drilling fluids and in any type of salt phase. Specific fluid design will depend on the application: whether it is to address shale stability, or overbalance or bridging requirements at the target well application with minimal material usage compared to conventional products that are presently used in the industry. The nano-sized particles are free flowing polymer particles (D50 between 100 - 200 nm) and are deformable. They can seal and mechanically plug the micro-fractures and pore throats, thus forming a semi-permeable membrane. This prevents fluid penetration and provides support to enhance hole stability. Nanotechnology helps in minimizing the overall product consumption and waste generation which can be a huge cost savings to the operator and significantly reduce the costs related to transportation movement and number of mixing hours which is indirect savings to the operator. This paper presents a detailed laboratory analysis of the product over a broad range of conditions at high overbalance pressures. Return permeability data shows the product is not damaging to reservoir, with minimal lift-off pressure and is beneficial to use for better production and improved return on investment. Due to its unique nature, it may be possible to forego breaker fluids, thus decreasing both the cost of operation and the rig time spent on each well. The product has seen great success in fields across the world and several applications were produced successfully.
In a case study of four wells located in offshore Sabah Malaysia, a field application using microemulsion technology to develop a customized in-situ breaker solution enhanced production rate by removing oil-based mud (OBM) and synthetic based mud (SBM) filter cake and remediating near-wellbore damage. All wells were completed as open–hole horizontal wells. Key challenges of the field are the multiple sand layers interbedded with intra-reservoir shale intervals necessitating a complex well trajectory and an operational preference for drilling with SBM drill-in fluid (SBM DIF). Lower than expected production rates were associated a water-impermeable SBM DIF filter cake and solids residue resulting from a conventional breaker system being unable to fully remove emulsion damage and effectively disrupt the filtercake. A series of laboratory tests for return permeability using formation cores from the offset wells and ceramic discs were completed as part of a feasibility study prior to field trials of the new microemulsion breaker system - a customized formulation consisting of a proprietary surfactant blend, organic acid, corrosion inhibitor and brine designed to remove the damage caused by the SBM DIF and restore open-hole flow conditions. The new breaker system has ultra-low interfacial tension which, when pumped into the open-hole section and allowed to soak for a sufficient period of time, diffuses into the rock matrix and forms an in-situ microemulsion completely and uniformly cleaning the near wellbore environment of SBM DIF residue, dispersing solids and leaving all surfaces water-wet. Laboratory results described in this paper show that the customized microemulsion breaker has the capability to remove SBM DIF filter cake, remediate emulsion damage caused by SBM-DIF, and restores the rock matrix back to its original permeability and predrilled state. All four wells in this field application have exceeded their expected production rate. The customized microemulsion breaker is the major contributing factor.
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