Induced Geometry in Chalk during Hydrochloric Acid Stimulation

摘要

The oil bearing high porous chalk formations in the North Sea are characterized by a high CaCO_3 content and are hence highly soluble in acids. This combined with low permeability results in a frequent use of acid treatments for stimulation. Previous investigations concerning the created geometry suggest the acid to create wormholes in the chalk. Casing deformations and production-log results combined with the stimulation rates and pressures used indicate that other geometries may develop in the reservoir. The objective has been to test existing theories by stimulating chalk samples using different core setups in a tri-axial cell. This study confirms the importance of rock properties and flooding regime for the resulting acid etched geometry. SEM-studies are also included. We suggest the acid is most likely forming a cavity around the liner for the typical field stimulation rates and pressures used in North Sea chalks.