Completion Efficiency Evaluation in Horizontal Wells and its Importance in Vaca Muerta Formation

Abstract

In Argentina, unconventional reservoir development learning processes have been continuously advancing, specially lowering project costs in Vaca Muerta's different zones, light oil, gas-condensate and dry gas. However, the actual international oil and gas prices are forcing companies to search for additional improvements to keep on developing these fields. Vaca Muerta Oil and gas potential with big pay thickness requires the review of completion efficiency and its incidence on initial hydrocarbons production in order to improve the project cash flow. The analysis should be focused on horizontal wells-orthogonal fractures interface which, in Argentina, has not been properly evaluated, leading us to underestimate the production loss by using the status quo of approved technologies for our projects. Big thicknesses increase the pressure loss effects due to flow convergence from the fracture into the well, to which we have to add the near wellbore bottleneck causing a conductivity reduction due to inappropriate final concentration design, over flush and proppant grain size and quality that are not capable of holding the confining pressure, in special in some of the completion technologies. In dry gas and gas-condensate reservoirs, non-Darcy effects and condensate accumulation in the SRV when pressure drops below the dew point, are also influenced by an inappropriate completion. Vaca Muerta over pressure forces us to pay attention to plays whit high production due better reservoir characteristics and SRV quality induced by fracturing. Interfaces must be designed to support such high pressures and maintain a good fracture conductivity. Technology review and selection is strongly recommended, in special in those where treatment is divided into multiple fracturing in different clusters with over flush to clean the well and/or displace guns/plugs and ball fractures between stages. Benefits from obtaining bigger and more stable SRV through new microproppant technologies and longer horizontal wells, will not be appreciated if fractures-wellbore interfaces are not improved allowing a better fluids evacuation into the wellbore by reducing restrictions to flow. At the same time, available literature shows dissimilar results when looking to improve cash flow through refracturing depleted wells. The purpose of this article is to show the importance of including the evaluation of production loss magnitude and its incidence on the project cash flow. This will allow considering different completion strategies on each project, some of them already available. Changes in fracture design and proppant quality will lead to a better and more stable fracture-wellbore interface.