Abstract

Acid fracturing, as a conventional and effective stimulation method, has been widely used in carbonate formation. But because of serious acid leak-off and rapid acid/rock reaction speed, the length of effective acid etched fracture is always restricted, even the high viscosity acid and emulsified acid were applied; besides, the effective duration of etched fracture was short, especially in deep well. The propped fracturing can supply longer fracture and long-term effective duration, but its ability of connecting natural fracture or fissure is poor because the fracturing fluid is unreactive with the formation. So the propped fracturing with a novel surface cross-linked acid (SXA) is proposed, because it can not only realize long fracture length/deep penetration, but also connect more natural fracture/fissure to maximize the permeable area as possible.

In order to realize the technique, a novel temperature-stability and shearing resistance delayed cross-linked acid (SXA) was developed to qualify for the fracturing treatment. Meanwhile the effect of HCl on one high strength ceramic proppant was also studied, and the results showed the crush resistance and conductivity of proppant is unaffected. So the SXA and the acid- resisting proppant provide the basis for acid propped fracturing, and a comprehensive fracturing technique was developed.

Acid propped fracturing with SXA was processed in the carbonate formation with depth > 5000m and temperature >140℃. A volume of 36.2m3 proppant was successfully pumped into the formation with the maximal proppant concentration exceeding 450kg/m3. The net pressure matching indicated that the propped fracturing created long conductive fracture and realized deep penetration. The new technique provided a new and broader option of carbonate stimulation.

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