Abstract
One way to stimulate oil production from chalk reservoirs is to inject acid into the formation which results in the formation of wormholes that act as flow channels. The aim of this study was to investigate the mechanical stability of wormholes in chalk and the impact of the acidizing process on the rock strength. To this end, we have performed compaction tests with oil and brine-saturated Mons outcrop chalk containing wormholes produced by core flooding with HCl acid. Acidizing was stopped after acid breakthrough, and the wormholes were imaged by CT scanning prior to the compaction tests. Hydrostatic compaction tests reveal wormhole collapse a few MPa below the onset of pore collapse, with the pore-collapse pressure being significantly larger for oil-saturated samples as compared to brine-saturated samples. Comparison with hydrostatic compaction measurements carried out with intact core plugs also indicates a reduction of pore-collapse pressure.
