Abstract
Multistage acid fracture treatments are utilized in low-permeability carbonate reservoirs (permeability <10 md) to stimulate the formation by creating highly conductive fractures in the formation and bypassing near wellbore damage. The fracture is generated at high pressures that are required to break the rock open while using a viscous pad. The fracture is then kept open by adding gelled or emulsified acid to create uneven etches on the surface of the fracture.
Pre-job acid fracturing treatment fluids’ reaction and compatibility analysis in the laboratory are crucial as the operational success is highly dependent on its chemicals’ reactions. The key problem with acid fracturing treatments is the difficulty in appraising the actual downhole reactions and performance of the treatment chemicals within the heterogeneous rock. This problem can be resolved when flow back fluids and the chemical ions are analyzed to understand the reactions that occurred down hole. Also, since acid fracture treatments require pumping large volume of fluids, flowing back the entire fluids becomes a challenge due to the low reservoir permeability and the associated reservoir rock capillary pressure effects.
This paper will discuss the pre-fracture treatment evaluation based on laboratory experiments - core flood, rock dissolving capacity, and fluid compatibility in addition to comparing the expected chemical ion returns with the actual ions observed in the flow-back fluids.
The results of this flow-back fluid analysis showed a recovery of 17% of the chemicals pumped during the treatment with a stabilized production rate of 3 MBOPD. Further water analysis indicated the presence of 25-30% formation water while the critical ions analyzed showed the effectiveness of the corrosion inhibitor package, acid system dissolving capacity, and crosslinker fluid recovery. It is expected that this paper will provide a learning process for optimizing future multistage acid fracture treatment in Saudi Arabia.
