Carbonate acidizing in horizontal wells

There is no entirely reliable placement method for carbonate acidizing in horizontal wells. However, with reasonable and carefully selected attempts at placing the treatment, successful matrix acidizing and add fracturing treatments of horizontal wells are possible. This is true even in very long horizontal open-hole wellbores. 

For successful acidizing of horizontal wells producing from carbonate formations, the keys are treatment placement and efficient use of acid fluids. It is necessary to utilize one or more methods of acid placement or diversion, to impart treatment coverage over as much of the target interval as possible. This is especially challenging in open-hole completions or those utilizing slotted or predrilled uncemented liners. Such completions preclude use of ball sealers and most solid-particulate diverters. 

Figure 23. The gel electrofocusing apparatus used by Leaback and Rutter (78). It comprises a perspex lid bearing terminals connected to horizontal carbon or platinum electrodes (E), and a glass base to carry the gel (G) and the electrode wells (A and B). The base consists of a glass plate to which 4 strips of ass are bonded (with Araldite epoxy-resin) to form a watertight well 18 X 8 X 0.2 cm, a perspex strip 8 X 2 X 0.2 cm displaced at (A) and another at (B) before the well is filled with polymerization mixture. Electrode wells (A) and (B) are filled with aqueous solution of phosphoric acid and diaminoethane respectively. The samples are added to slots (S) and with the lid in position, a potential difference is applied to the electrodes with the current kept at or below 2 mA. A moist pad (C) prevents excessive evaporation from the gel surface. (Leaback and Rutter, 37.)...

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