World's Largest Yard Testing of a Thixotropic Polymer Sealant for Chemical Annular Plug Applications in Low-temperature Horizontal Wellbores

Abstract

Forming a retrofit annular plug on controlled acid jet (CAJ) liners in horizontal wells can be challenging. Several conformance technologies have been tested with mixed results; optimal chemical placement is problematic, and results show that conventional treatments either slump or float along horizontal sections, fail to withstand the desired differential pressure, or are not achievable at low temperatures. This paper describes laboratory improvements and a large-scale yard test of a thixotropic polymer sealant (TPS). The TPS system is composed of an organically crosslinked polymer combined with optimized rheological modifiers, which enable predictable and controllable crosslinking times. This allows precise TPS placement into the horizontal or deviated wellbores to help control unwanted water or gas. Extensive laboratory testing was conducted on the TPS system to formulate the optimal rheology at low temperatures. A specialized laboratory-scaled test cell was purposely built to verify the development of the thixotropic blend at low temperatures of 35 to 40°C. After successful laboratory testing, a 520-ft long yard test was conducted to mimic a field trial. It consisted of centralized 4 1/2-in. tubing run horizontally inside a 7-in. casing. Four predrilled holes of 4-mm diameter were located midway along the tubing to represent the perforations, providing communication to the annulus of the tubing and casing. A 2.25-in. outer diameter (OD) high-pressure hose, representing coiled tubing, was placed inside the 4 1/2-in. tubing and used to deliver the TPS fluid to the perforations. The entire setup was pressure-tested to 5,000 psi and heated to 40°C using an insulated heating blanket. A high-pressure pump was used to pump and displace 6 bbl of TPS, which was sufficient to form a 300-ft annular plug. The chemical was allowed to crosslink and set for 45 hours. Results of this yard test showed that a 300-ft TPS annular plug is capable of withstanding up to 4,620-psi differential pressure. The setup was then cut at various locations, both treated and untreated, to confirm, assess, and observe TPS placement in the cross-section of the tubulars. It was observed that the TPS can flow in the smaller spaces between the tubing and the centralizer, helping ensure optimal sealing. The TPS system described here can be used to help reduce unwanted water or gas production in long horizontal wells with CAJ liners. The open annulus between the preperforated liner and the formation makes selective isolation for the presence of thief zones, high-permeability zones, or fractures extremely challenging. Left untreated, this can eventually result in a large increase in water production and eventually a reduction in the economic life of the field.