Efficiency in Cement Jobs for Fresh Water Formations Isolation During Plug and Abandonment in Canadon Seco Field, South Argentina

Abstract

In the San Jorge Basin, located in South Argentina, Well Plug and Abandonment (P&A) regulations include the guarantee of fresh water formations isolation from once productive formations. Cement Bond and Variable Density Logging (CBL/VDL) are recorded after a squeeze job to confirm cement integrity in the annulus, allowing protecting the most important fresh water formation in the basin: Patagoniano. Historically, to isolate the Patagoniano multiples of costly squeeze jobs were done to achieve an appropriate result in the CBL/VDL. The main problem from this shallow formation is its high degree of fluid losses, most slurry is lost in these unconsolidated and high-permeability shallow sands (while pumping and during cure). Under this condition costs in the Canadon Seco Field for P&A were exceeded. To overcome this problem, a review of previous results was done and many flaws were identified in the slurry physical characteristics and the used placement techniques. A new slurry and procedure was selected (after being laboratory tested) to be applied in the field; then a campaign of 14 wells was done using the selected slurry and following a general technique; cost/time reduction was drastic in comparison with previous P&A operations. This paper presents the whole procedure for achieving these results and also includes details in each phase of testing/design and execution. Geological and mechanical features of the wells are shown, as well as a description of the new technique / slurry (including concepts) and the obtained field results.