Heavy-oil carbonate reservoirs are complicated to produce. Heavy-oil saturated fractured limestone formations present tremendous completion, stimulation and production challenges because they commonly contain thick completion intervals with extreme permeability ranges. In Mexico, completion and stimulation engineers must consider these complexities during the design stage and when selecting appropriate stimulation technologies to optimize production and hydrocarbon recovery.

A valid option to treat these complex reservoirs is the viscous fingering stimulation technique. The situation is further complicated when the reservoir is saturated with heavy-oil. Carbonate reservoirs are stimulated using acid-predominantly hydrochloric acid (HCl) strengthened with organic acetic acid to create conductive pathways from the reservoir to the wellbore, and to bypass the wellbore region that has been damaged during drilling and cementing.

Acid-fracturing techniques are also used in areas where the natural permeability of carbonate reservoirs is insufficient to promote effective matrix acid stimulations. The goal in carbonate reservoir stimulation is to effectively treat all latent productive zones, reducing formation skin and improving productivity, improving heavy-oil mobility.

Viscous fingering stimulation technique involves the displacement of a more viscous fluid by a less viscous fluid in porous media, the less viscous fluid tends to form fingers into the flow channel, hence the term viscous fingering. The viscous fingering acid injection technique maximizes acid contact time with reservoir faces and is essential to create long and highly conductive etched pathways to facilitate the viscous and heavy-oil flow from the reservoir to the wellbore.

Also, solvent/surfactant special additives are mixed then with acid system designed to stimulate heavy-oils wells for increased productivity. This article examines the viscous fingering stimulation procedures and designs performed in Mexico on heavy-oil carbonate reservoirs, onshore and offshore, reviewing historic cases, production results and the development and trends in the short and medium term.

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