Study Details Evolution of Operator’s Completions in Vaca Muerta
Authors: Carpenter Chris 
Published: April 2024

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 212574, “From Exploration to Development: The Completion Evolution in Vaca Muerta,” by Juan C. Bonapace, SPE, Luis A. Riolfo, and Rodrigo Zrain, Total, et al. The paper has not been peer reviewed.

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Operators in the Neuquén Basin have developed Vaca Muerta with different results. In the case of the operator whose work is featured in the complete paper, vertical exploratory wells almost 10 years ago have given way to a current development phase with multihorizontal well pads targeting different landings. The authors discuss how the operator has become more efficient and cost-effective by increasing production and reducing well-delivery-cycle time, while fostering the long-term sustainability of the project by reducing the environmental impact of operations.

Evolution of Field Completions
The authors focus on the operator’s Field A, where the most progress has been made over the years. The exploratory and appraisal phases of the development are detailed in the complete paper.
Pilot Phase.
The primary goal for this phase was to validate the productivity of two previously identified landing zones, namely Zones B and D. The wells were located near the vertical wells.
Completion. The campaign program accounted for 12 drilled horizontal wells, only 10 of which were completed (two wells were lost because of drilling and casing-integrity issues). Well lateral length ranged between 1000 and 1500 m. The final well architecture was composed of three strings: a 13⅜-in. surface casing, a 9⅝-in. intermediate casing, and a 5½-in. production casing.
The completion technique applied was plug-and-perf (PnP) and considered an average stage length of 100 m. Two base designs were defined for each landing zone according to the results obtained in the vertical exploratory wells.
An initial sensitivity trial was completed in Zone B, with two different treatment sizes, base and alternative, designed to evaluate the effect on cost and production performance. The results showed a lower production for the wells with the alternative treatment.
Operational Issues. Operational problems included casing restriction, detected only once in a well in Zone D during plug drillout operations; and well interference, in that one well presented a change in production during the flowback period on a new neighboring well. This was the result of reduced spacing because of drilling conditions between the new well and the pre-existing one.
This phase showed wells in Zone B performing beyond expected production, while those in Zone D underperformed.
Development Phase I.
It was decided to locate all wells of this phase on the east side of the pilot in the dry-gas window. The main driver for this decision was expected lower CO2 production in this region, based on observations from appraisal wells.
Completion. Initial development considered 20 horizontal wells, mainly targeting Zone B. Two additional target zones were added for testing, Zones A and C. In pursuing cost optimization for this development phase, a change to a slimmer architecture was made. Finally, 19 wells were completed. The final well architecture was composed of three strings: a 10¾-in. surface casing, a 7⅝-in. intermediate casing, and a final 4½-in. production casing.