Abstract
Horizontal wellbores can present unique problems during water and gas shutoff operations. The primary challenges include the extended length of many horizontal wells, which could be outside the reach of coiled tubing (CT), and the fact that many are completed with open holes, gravel packs, or slotted liners. With gravel pack and slotted liner completions, it can be extremely difficult, if not impossible, to obtain complete zonal isolation. Even when the offending water or gas producing zones are clearly demarcated from the producing zones, chemical remediation remains arduous. Mechanical plugs can be set inside gravel pack screens or slotted liners and a chemical sealant can be pumped into this isolated internal section. However, it is difficult to limit fluid flow in the outer annular space. Because most chemical sealants are designed to have relatively low viscosity, they tend to slump to the low side of the wellbore, either inside or outside of this isolated section. Consequently, the water and/or gas zones are not uniformly exposed to the treatment, which could result in an incomplete seal. Because more horizontal wells are being drilled, water/gas shutoff systems are necessary for these types of completions. An ideal sealant system would exhibit flow properties facilitating pumping and placement while, immediately upon placement in the desired location, resist slumping by behaving as a thick paste.
This paper presents three systems designed to address the challenges associated with treatment of zones within horizontal wellbores. The objective was to develop sealant systems that would not slump upon placement and subsequently undergo polymerization, crosslinking, or setting and provide lasting seals to prevent water/gas flow. The fluids discussed include polymeric and monomeric gels and a Sorel cement based system, which additionally contains additives to provide slump resistant properties. The chemistries that impart the slump resistant properties are discussed. In addition, laboratory data is presented to include slump measurements, gelation times, and flow resistance measurements.
