Swelling Packer Technology Eliminates Problems in Difficult Zonal Isolation in Tight-Gas Reservoir Completion

Abstract

Abstract This paper discusses a difficult completion in which an operator required a completion that would provide zonal isolation for four different tight-gas reservoirs. Challenges included zonal isolation concerns but also drilling and cementing problems experienced in earlier wells. Previous research had determined that:Minimum fluid contact with the rock would provide the least drilling damage and wells should be drilled with a mud with very low leak-off.Cementing could compromise completion success since formation damage could occur from cement filtrate.Since most of the wells require fracturing, good zonal isolation was essential to preventing mechanical problems and casing collapse above the fracturing packer. Previous problems led to the investigation and adoption of a new type of packer isolation system that would achieve zonal isolation without the need for cementing, isolate the four zones, and eliminate the need for cement in the fracturing areas. The new packer design uses expanding rubber around the packer that is formulated depending on the type of mud used to expand to seal the annulus. The expansion provides the isolation required. Since this eliminates the need for cement at the fracturing zones, fracturing operations are simplified, and costs are reduced as a result of reduced rig time and materials. In addition, the expanding material will develop high differential pressure resistance that continues to increase with time. The design procedures will be described along with how swelling packer technology was capable of providing superior sealing for the isolated zones. The operational procedures will discuss how isolation before fracture operations is accomplished, and how each zone is individually fractured successfully. Principal Concerns Drilling Most gas reservoirs contain only gas and residual water. Those reservoirs should be drilled with water-based mud (WBM) because oil-based mud (OBM) will introduce a third fluid into the reservoir, modifying relative permeability and reducing gas permeability through out the life of the well. This is critical in a tight-gas reservoir. Even drilling with a water-based mud will modify the near-bore concentrations and consequently the relative permeability. This is a temporary problem cleaned up with the production. To overcome this problem a very low leak-off mud with a low spurt loss should be designed. Drilling fluids with sized carbonate can solve this problem and has the benefit of removal with acid pumped through coiled tubing with the well flowing. Another solution is underbalanced drilling. The low productivity of a non-fractured tight-gas well does not help cuttings removal but makes the drilling phase easier due to low surface separation requirements. This will prevent fluid invasion and changes in original permeability. Cementing Since most tight-gas wells must be fractured to become commercial, it is a good completion practice to cement the casing. Zonal isolation should be complete and effective. To achieve this requirement, a good washer should be spotted removing all the filter cake. After removing the filter cake, a spacer will be spotted and the formation will be susceptible to damage by fluid invasion. The cement slurry includes chemicals to prevent gas migration. During setting, the cement will lose additional water to the formation. Up to this point, all the concerns are due to fluid invasion, and no chemical compatibility between filtrates and formation has been considered. Cementing a tight-gas formation is not the best option even though a fracture is planned. Alternatives were developed for casing and cementing to create a secure environment to fracture multi-zone tight-gas formations.