Abstract

The selection of the objective target in unconventional shale formations is a determinant factor on the productivity of wells. In thick unconventional formations, as is Vaca Muerta, the operators are looking for new ways of quantifying the production of each stage of hydraulic fracturing executed in the well.

It is of vital importance for the operators to be certain that every section of the well that has been stimulated is effectively contributing to the well production, and that the clean-out of all stages has been correctly carried out.

Other challenges, such as optimal spacing between clusters, stages and wells, which in turn allow to optimize drilling & completion costs, maximizing ultimate recovery (EUR), appear amongst the main preoccupations.

One of the techniques that the industry has developed to answer those questions has been the use of chemical tracers during the stimulation process. Since 2013, the use of chemical tracer technologies to simultaneously tag water, oil and gas has gained great acceptance in unconventional players in USA, with more than 30,000 stages tagged using this technology. In Argentina, Shale operators are quickly gaining experience too.

This paper describes the technique used on site to apply chemical tracers in a multi-stage horizontal well with 15 stages, in Vaca Muerta formation, Argentina. The paper also comments on the data interpretation and necessary steps to obtain the oil and flowback water production profile during the first 60 days following well startup.

Chemical tracer results showed evidence of zones with higher oil production, and higher stimulation water flowback, as well as confirming the complete cleaning of the well.

A production monitoring tool with long term reach, as are chemical tracers, offers the operator the possibility to correlate operational changes (e.g. choke changes) with the individual response of every stage. It is possible to identify which stages are contributing to the incremental oil production, after each operative change.

Finally, it was observed that the information generated with chemical tracers, geological interpretation, and microseismic results collected during the stimulation along the horizontal section of the well, showed a high level of correlation. This helped the Reservoir Engineering team to explain the differences in productivity of each of the fractured stages of the horizontal interval of the well.

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