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.

Oil discovery and development in Comodoro Rivadavia City (South Argentina) has over 100 years of history and more than 2000 wells have been drilled within the city border. The urban development requires take into account considerations related on Plug & Abandonment (P&A) well status, safety radius and additional special safety conditions. It is important to notice that many of the wells in the city have been pluged and abandoned before the current P&A governmental regulation that was approved in 1996. A particular case is the Well Ch-1943, which was drilled in 1970, P&A in 1984, and later in 1986 a school was built on top of the well underestimating the associated risks in ignoring the assigned safety radius. Sed School remines active and functioning to this day. The operator, assuming civic responsibility planned to bring the well to current P&A regulations. The Plug & Re-Abandonment of the well was scheduled to happen during the school summer break between December, 2009 and January, 2010. At that time the challenge was assigned to the P&A Team. The intervention involved many risks and the job needed to be finished in a very limited period of time. Chalenges included well planning, contracts approval, well location restrictions, site preparation to connect the well to the ground level, school roof removal, coiled tubing unit preparation for the well intervention with additional job deck and final surface job and had to be completed without affecting the school building structure. This document describes the main tasks required to complete the particular challenging intervention complying with the highest safety and quality standards. The Well Intervention was completed successfully in 12 days with a 2″ Coiled Tubing Unit. The total length of the planning/preparation and execution of this project was 46 days. The Case Story includes: –Well Planning–Well Location–Safety Risk Analysis–Site Preparation–Well Intervention ○Coiled Tubing Rig Up.○Well Calibration – Milling old cement plugs and scrap○Casing Corrosion & Bond Logs Annulus isolation guarantee○Squeeze & Balanced Cement Plugs–Final surface reconstruction Joint efforts between service companies and the operator was a key factor in achieving the planned P&A results.