1. Field of the Invention
Embodiments disclosed herein generally relate to wellbore fluids for forming and subsequently removing filtercake residue from subterranean formations.
2. Background Art
During the drilling or completion of an oil and gas well, the walls of oil and gas formations are often exposed to wellbore fluids which may damage producing formations. To prevent such damage, a wellbore often requires the deposit of a low-permeability filtercake on the walls of the wellbore to seal the permeable formation exposed by the drilling operation. The filtercake functions to limit drilling fluid losses from the wellbore as well as protect the formation from possible damage by the fluids filtering into the walls of the wellbore. Solids, such as particulate fines, suspended in the drilling fluid may also contribute to damaging hydrocarbon producing formations.
To protect formations from damaging fluids and solids, a filtercake is formed and/or deposited on the surface of the subterranean formation. Filtercakes are formed when particles suspended in a wellbore fluid coat and plug the pores in the subterranean formation such that the filtercake prevents or reduce both the loss of fluids into the formation and the influx of fluids present in the formation. A number of ways of forming filtercakes are known in the art, including the use of bridging particles, cuttings created by the drilling process, polymeric additives, and precipitates. Fluid loss pills may also be used where a viscous pill comprising a polymer may be used to reduce the rate of loss of a wellbore fluid to the formation through its viscosity
After drilling or completion operations have been completed, removal of filtercake (formed during drilling and/or completion) remaining on the sidewalls of the wellbore may be necessary. Although filtercake formation and use of fluid loss pills are essential to drilling and completion operations, the barriers can be a significant impediment to the production of hydrocarbon or other fluids from the well if, for example, the rock formation is still plugged by the barrier. Because filtercake is compact, it often adheres strongly to the formation and may not be readily or completely flushed out of the formation by fluid action alone.
Typically filtercake residue is removed by filling the open hole section with a clean up fluid (often referred to as a breaker fluid) that attacks the filtercake. In some situations, such as wells with gravel packed completions or other types of screen/slotted liners, ensuring that the treatment effectively contacts the filtercake on the wellbore face can present challenges. For example, in the case of unconsolidated formations, where it is often desirable to gravel pack the wellbore after drilling an interval but before the filtercake is completely removed, the act of gravel packing the wellbore may further limit the fluid's contact with the filtercake, as it both reduces the physical volume of fluid that can be present in the zone and restricts direct flow to the filtercake. As a consequence, the effectiveness of the breaking of the filtercake is dramatically reduced.
One of the most problematic issues that exist with many of the methods used by the prior art references in removing the filtercake downhole, includes the problem of controlling the breaking of the filtercake so that production fluids may not enter the wellbore before the entire, or at least most, of the filtercake is degraded. When degrading a filtercake with a breaker fluid, the breaker fluid may not have completely covered the entire interval of exposed formation, causing premature flowing of production fluids or the loss of breaker fluids into the formation from one portion of the interval before another portion has even been exposed to breaker fluid.
Accordingly, there exists a continuing need for wellbore fluids that effectively remove filtercake residue and debris in subterranean formations after drilling or completing a well.