ABSTRACT
Cement solubility in acid has proven to be a problem in the field and has recently been confirmed by laboratory testing. Traditional views have held that acid will react with cement for only a short period of time until it forms a protective skin which inhibits the acid attack. However, field experience has shown that a large percent (≈ 75%) of secondary squeeze cement jobs were breaking down after a HCI-HF acid stimulation. Further, 17% of primary cement jobs developed zonal isolation problems after a HCI-HF acid treatment of the producing perforations.
This paper will document the field evidence from the Eastern Operating Area, (EOA), of the Prudhoe Bay Field, Alaska indicating that HCI-HF acid is damaging to squeezed cement. It will also show from a series of lab tests that cement is quite soluble in several of the various acids used at Prudhoe Bay. HCI-HF acid, the most destructive acid tested, showed a 96% dissolution of a 2×2×2 in. (5.1×5.1×5.1 cm) cement cube when immersed in a stirred solution of 12-3% HCI-HF acid at 190° F. Finally, the data indicates that the major factors that effect the reaction rate are HF acid volume to cement surface area and acid shear rate at the cement/acid interface.
