La Calera is an unconventional wet gas field located close to Añelo city in Neuquén province. There are currently 30 horizontal wells in production from Vaca Muerta formation, drilled at three different landings in 3-wells pads. As in every unconventional asset development, well spacing stands as one of the main optimization objectives in order to maximize project net present value. This paper aims to show that performing interference tests at different times of the life of a well can help to get a better understanding of the optimum well spacing.

This study is focused on the analysis of several interference tests performed on a specific pad with three horizontal wells. So far, four interference tests were conducted with downhole pressure measurement. The first test had the objective of analyzing the interference between the wells after being fractured and first opened. After two years of production, all three wells were closed to minimize frac hits effects from child wells being stimulated 350 m (1150 ft) apart. A second interference test was performed before the stimulation of the child wells and a third one was done after it. Finally, when the child wells were first opened, a fourth test was performed between parent and child wells.

The information analyzed consists of pressure registers from well head sensors and downhole gauges located in the parent wells and gas and liquid production information measured in both pads. In order to complete the analysis, water tracers were injected in the child wells and then sampled in all the six wells.

During the first test, moderate interference was observed among the three wells even though there is a vertical offset of 120 m (400 ft) between the lower and upper landing. The second test helped to quantify how interferences varied after two years of production. Important frac hits were observed during stimulation of the child wells using well head pressures gauges. Once the parent wells were back on production, changes in water and condensate production were observed. Water tracers sampled in both pads incorporated valuable information as they showed that some fractures from the child wells affected parent wells although there was no increment in pressure detected.

All the information gathered will help to gain insight of the optimum well spacing, understand if a 350 m-spacing (1150 ft) is appropriate, and determine if a new interference test between pads should be performed after achieving a whole year of production from the child wells. Finally, it is important to establish if the risk of a possible loss of productivity should be considered for the parent wells when forecasting a full field development.

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