Acid fracturing is a good stimulation process. Typically an acid (usually HCl), or a viscous nonreactive fluid (the pad fluid) is injected into a carbonate formation at a pressure sufficient to fracture the formation. As the acid flows along the fracture, it causes a chemical reaction and portions of the fracture face are dissolved.
Acid fracturing can only be applied when the reaction rate between acid and the rock is intense, fast and complete. For example in carbonate reservoirs using HCl, combined with organic acids. This type of treatment is dependent on the fracture length and on the conductivity of the fracture.
We have been employing acid fracturing since the early 1970’s. However, this was restricted to our vertical wells. It wasn’t until the early 2000’s that a number of carbonate rock-based horizontal wells were acid fracced using coil tubing. Fast forward to 2014 and we began multi-stage acid fraccing on four horizontal drains in different fields. The campaign started with the drilling of DPE-14B well, this became the first offshore multi-stage acid fractured horizontal well for Dubai and the United Arab Emirates.
|Reservoir Condition||Treatment Style|
|High Perm, High Natural fractures||Viscous acid, fiber-based diverting agents|
High Perm, High Natural fractures
Emulsified Acid, viscous diverter, no fibers
|High Perm, High Natural fractures||Emulsified acid|
|Moderate Perm, minimal Natural Fractures||Viscous acid, fiber-based diverting agents|
|Moderate Perm, minimal Natural Fractures||Emulsified Acid, viscous diverter, no fibers|
|Moderate Perm, minimal Natural Fractures||Emulsified acid|
|Low perm||Emulsified acid + soaking|
Table: DPE Matrix for Acid Selection for Fracturing