Abstract
Results of polymer gel treatments in injection wells, suggest worldwide that there is a positive correlation between larger gel volumes and resulting incremental oil production in offset producing wells1–5 . However, gel placement procedures, particularly in matrix (unfractured) reservoirs, remain a source of controversy. Many operators heavily rely on the permeability contrast in heterogeneous matrix reservoirs to assure the correct placement of the gel treatment, claiming that polymer gels will not penetrate and damage lower permeability zones to any significant degree. However, other studies indicate that in a matrix environment, the gel will enter any layer(s) that is not mechanically isolated during the gel injection, risking damage to "unprotected" zones. This paper presents PDVSA's experience in Venezuela with a polymer gel treatment that was placed without mechanical isolation into an injector in the Lagomar Field with positive results. This layered reservoir, characterized as highly heterogeneous, has been under waterflood for over 4 decades and currently, high water cuts are affecting its production and forcing the closedown of production wells in the area. In this work we include new evidence that might explain why this placement technique has been successful in this originally "unfractured" reservoir. In this new analysis, geological and geomechanical features are revised as part of the diagnosis, in order to determine the low sweep efficiency problem, and this information is used to aid in the injection strategy planned for the well.
Results from the treatment were evaluated with Production logging tools (PLT) run before and after the treatment, showing the blockage of the thief zones and redirection of injection water to lower permeability zones. A total of 3700 bbls of gel were injected and response in two associated producers was observed 5 months after the treatment with an average reduction of 30% in the water cut and 26,850 bbls of incremental oil.
