SPE Member

Abstract

Many carbonate formations cannot be successfully fracture acidized at pressures above the formation fracture pressures above the formation fracture pressire using standard fracture acidizing pressire using standard fracture acidizing techniques. This situation exists because standard techniques rely on acid etched, uneven removal of the fracture face to produce fracture flow channels or fracture produce fracture flow channels or fracture Many times the etched fracture face is either too smooth, softens with acid, or the formation strength itself is insufficient to prevent closure due to overburden pressure, as in chalk formations.

The "closed" fracture acidizing technique is designed to allow acid to flow through existing "closed" fractures below fracturing pressure in a channelling manner. Wide grooves or channels in the fracture face are then formed as acid is pumped at low rates and allowed to pumped at low rates and allowed to dissolve large flow channels. These grooves tend to remain open with good flow capacities under severe closure conditions and also allow fines or emulsions to be more easily produced. The initial fractured system can be natural fractures, previously created fractures, or fractures created previously created fractures, or fractures created and etched just prior to the "closed" treatment.

Laboratory test results on formation cores and field results verify this technique.

Discussion
Standard Fracture Acidizing

Standard fracture acidizing treatments on carbonate formations generally give excellent results. These are normally performed with the bottomhole treating pressure (BHTP) above formation fracturing pressure (BHTP) above formation fracturing pressure, and rely on fluid pressure to pressure, and rely on fluid pressure to keep the created fracture open. Acid flows through the open fracture, dissolving or etching the fracture face in such an uneven manner that flow channels are developed. These flow channels then remain open after the treating pressure has been reduced and the fracture closes.

Various acid systems, fluid loss control systems, and injection systems have been developed to aid in creating and etching these flow channels. Under most conditions, excellent fracture flow capacities can be developed.

There are formation conditions however, where these necessary flow channels are not developed in a satisfactory manner in standard fracture acidizing treatments.

P. 43

This content is only available via PDF.
You can access this article if you purchase or spend a download.