Abstract

Calcium carbonate scale is a common oil field occurrence in many areas in Indonesia including certain wells operated by Maxus Southeast Sumatra, Inc., (formerly IIAPCO). Wells in the Farida and Zelda fields have shown severe production decline rates and frequent submersible pump failures, which are both attributed to calcium carbonate scale.

High levels of calcium ions dissolved in formation water are normally held in solution at reservoir conditions. Under certain conditions, calcium may precipitate as calcium carbonate and crystallize in areas of pressure change and turbulence, such as perforation tunnels and downhole pumps. Additionally, well conditions may, in some cases, accelerate the deposition of calcium carbonate scale.

When scale is present, production is reduced due to blockage of perforations and reduction of the internal diameters of tubulars.

A chemical treatment using a solution of EDTA (Ethylene Diamine Tetraacetic Acid) has been used successfully to remove calcium carbonate scale without subsequent reprecipitation, inherent in the use of HCL. EDTA treatments have substantially extended submersible pump run times in wells which are prone to calcium carbonate scaling.