Enhancing Stimulation Efficiency in a Highly Fractured Open-Hole Carbonate Reservoir Section by Diversion Design Using Advanced Modelling Techniques

Abstract

Stimulation fluids injected into a reservoir take the path of least resistance, leaving behind under-stimulated areas. As a result, the stimulation efficiency and effectiveness are reduced, affecting the overall production potential. The placement efficiency of a stimulation treatment depends on maximizing fluids contact in the zone of interest (good penetration) and uniform distribution across the section. To achieve uniform distribution, existing higher permeability areas or natural fractures must be efficiently and temporarily blocked, diverting the treatment towards the section with low permeability and higher skin. This process is known as diversion.

In this paper, we utilize an analytical model based on computational fluid dynamics and discrete element modeling to simulate treatment placement efficiency and diversion effectiveness in high-pressure/high-temperature (HPHT) carbonate formations, from a long open hole highly fractured reservoir interval in a well in South America. The case study demonstrates that parameters playing a key role were flow rate, spacers between diverting pills, type of diversion fluid carrier, rheology of carrier fluid, number of diversion stages, and displacement rate. The modeling calibrated against an actual field case demonstrates the space for improvement that can be customized depending upon the type of application.

The results indicate that without using diversion, the lower part of the openhole section is left under-stimulated in comparison to the top section as the top section had the presence of natural fractures. When diversion was utilized to optimize the design, the stimulation efficiency in the lower section improved considerably and ultimately had a high impact on the production of the well. This paper uses an actual case study to demonstrate the value created and overall production enhancement despite the excellent results achieved. It also summarizes the engineering workflow to optimize diversion design in carbonates HPHT openhole formations.

We believe that an engineering approach is critical in the design of a successful stimulation in an open hole with considerable presence of natural fractures in some parts of the section of interest. The results demonstrate the effectiveness of advanced modeling in evenly distributing the stimulation fluid and thereby increasing its effectiveness enhancing the production across the target zone. A case study from a field job in South America will be presented based on job evaluation and actual well production performance. Actual well intervention and treatment design are discussed. The lessons learned from this case study can be applied for stimulation design and planning for future jobs in the area.