With the recent increases in price of a barrel of oil and the growing scarcity of easily exploited oil, efforts to improve productivity of older wells have intensified. Some options for accomplishing this include re-stimulating the well and/or adding laterals that extend past the original wellbore. In open-hole limestone formations, one innovative technique can achieve both of these goals simultaneously, creating pre-stimulated "tunnels" that bypass existing near-wellbore damage to make contact with new reservoir rock.

The new technology relies on limestone's acid solubility and a coiled tubing-conveyed bottomhole assembly comprised of components that tilt the tool toward the formation. A high-pressure nozzle then jets acid to extend new tunnels from the wellbore. The technique is applicable in all open-hole wells drilled in carbonate formations and can be used to remediate old wells or complete multiple drainage tunnels in new wells.

This acid tunneling technique and tool have been utilized around the world. They were first used in the United States to create three additional tunnels in an Oklahoma well that has been producing since 1924. This paper will describe the acid tunneling tool and design along with: an operational timeline, summary of lessons learned during the United States operation, comparison of pre and post-job production information for the treatment.

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