Recent Experience in Squeeze Treating Huff and Puff Wells for Control of Steamflood Generated Calcium Carbonate Scale

Abstract

Steamflooding technology introduction into hydrocarbon recovery operations often brings with it unwanted unavoidable mineral scaling challenges. In this example, steamflood generated calcium carbonate scale caused downhole equipment failure during cyclical steamflood stimulation (CSS) operations. The precipitated scale was effectively removed via mineral acid tubing wash, however mineral acid use for ad-hoc scale dissolving duty added significantly to the corrosion burden of well production tubing strings already regularly exposed to aggressive high concentration mineral acid during near wellbore matrix stimulation treatments. Scale inhibitor squeezing was proposed as a proactive alternative to mineral acid for downhole scale mitigation, and is the subject of this case history. The Middle Eastern heavy oil (HO) field has experience in employing scale inhibitors for topside scale control, but has limited experience in scale squeezing, and no experience of scale squeezing cyclical steam flooded wells. The initiative therefore presented some interesting challenges with respect to the Scale inhibitor selection (thermal stability concerns, compatibility and calcium carbonate efficacy concerns), where to place the scale squeeze in the CSS treatment programme, the squeeze design and its placement within the CSS well, and introduction and execution of routine well scaling health monitors for assessing the performance of the scale squeeze across the full CSS life-cycle. Detailed bullheaded scale squeeze designs were prepared for two pilot HO field CSS wells that had experienced CaCO3 scaling. Once prepared, the squeeze treatments were quickly scheduled and executed without significant issue - either during treatment application or post-squeeze/steamflood return. The well brine monitors (brine ion composition, residual scale inhibitor and suspended solids) revealed interesting trends during the surveillance phase, but most importantly showed that the scale squeezes performed according to design and successfully maintained the wells free of CaCO3 scale, up to and including the 266 days post-steamflood, at which point routine well produced water sampling was discontinued. After 360 days (at the final review meeting) the field operators advised that both squeezed wells were still in operation and had experienced no scaling downtime.