In recent years, significant progress has been made in the determination of fracture geometry. However, most effort is geared toward massive hydraulic fracturing treatments with proppants. Little progress has been made in the determination of fracture geometry especially for acidizing treatments.

This paper presents a method of determining fracture geometry for fracture acidizing treatment. The fracturing fluids used in an acidizing treatment are classified into four stages: preflush, viscous preflush, acid and overflush, each with different rheological properties. If viscous preflush is not used, relative positions of all fluids together with the resulting geometry are determined simultaneously based on the assumption that fluid pumped at a later time is unable to overtake fluid pumped at earlier time. If viscous preflush is used, relative positions of all fluids, together with the resulting geometry, are determined simultaneously allowing the possibility that acid and overflush can tunnel through and even completly overtake the viscous preflush pumped ahead of acid. Before the acid over takes the viscous preflush, the advancement of acid inside the fracture is rapid, and the acid creates an effective etching pattern. Once the acid overtakes the viscous preflush, its advancement slows down resulting in less effective etching pattern. An optimum design would most likely be the one where live acid barely overtakes the viscous preflush.

Two examples will demonstrate the effective use of this method for better acidizing design.

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