A Novel Plasma Technique to Stimulate Tight Carbonate Rocks

Abstract

Tight formations are normally fractured using different fluids under high pressure to improve well permeability and consequently improve productivity. In this paper, a new sophisticated technique is proposed to treat tight formations, especially those containing large deposits of heavy oil. The technique consists of exposing the wellbore to an argon plasma jet to insure instantaneous and efficient heat transfer to the surrounding wellbore rocks. The high temperature associated with the plasma jet changes the basic properties of the rock, resulting in a significant increase in its porosity and permeability. In this study the effect of high temperature on the carbonate rock porosity and permeability is investigated. Limestone rocks were subjected to high temperatures ranging from 800 to 1200°C. At temperatures beyond 600°C, the carbonate rock decomposes to form calcium oxide and carbon dioxide. Thermogravimetric analysis (TGA) of carbonate samples indicated that the rate of decomposition at atmospheric pressure depended mainly on reaction temperature. At low temperatures, the rate of reaction was so slow that only 5% of the carbonate converted to calcium oxide in a period of 1 h, while at 1000°C complete conversion was achieved in 5 min. The changes of the pore structure under different temperatures were also observed using scanning electron microscope (SEM). Porosity and permeability analysis of heated carbonate samples indicated that the porosity and permeability increased by 100% and 4500%, respectively, at 1000°C.