When, Where, and How to Drill and Complete Pads of Multiple Wells? Four-Dimensional Considerations for Field Development in the Vaca Muerta Shale
Authors: Pichon Stephane , Cafardi Orihuela Federico Gaston , Lagarrigue Emilio , Cavazzoli Gustavo 
Published: October 2018

Development of organic shale reservoirs with large hydraulic fracture treatments has unveiled challenges related not only to the completion of a single well but also to interference with its surrounding neighbors. Interference can be caused by fracture hits while completing the well, competition for drainage area during production, or fracture geometry deterioration due to stress field variation when infill-drilling a child well near a produced parent well. A direct consequence of interference is production loss. Therefore, the drilling and completion schedule for field development becomes four-dimensional in time and space to account for interaction in between wells. The objective of this work is to set up a physics-based model of interference and perform a sensitivity study to propose guidelines for well spacing and a drilling timeline for multiple horizontal wells in the Vaca Muerta shale.

Production of organic shale responds to the reservoir deliverability and contact surface between the formation and the wellbore through hydraulic fractures. A reservoir-centric workflow applied to the Vaca Muerta shale is proposed by integrating all the steps from well construction to production including reservoir petrophysics and geomechanics, nonplanar hydraulic fracture geometry, and production simulation with fit-for-purpose simulators. With respect to space, a multiple-well model enables investigating possible hydraulic fracture overlap between laterals and competition for drainage as a function of the well spacing. With respect to time, reservoir depletion can be tracked, and the corresponding stress field variations are estimated using a three-dimensional geomechanical finite-element simulator. The hydraulic fracture geometry and production of a child infill well is simulated based on this updated stress field where a modified stress contrast has been created by the depletion of the parent well.

By running different scenarios, competition for drainage between wells is quantitatively evaluated to balance individual well performance and field recovery. Factors affecting well spacing such as lateral landing, stress profile, hydraulic fracture geometry, and number of pay intervals developed jointly are investigated. With regards to completion, well spacing acts as an additional geometrical constraint, and its impact on the completion optimization process, when compared to a standalone lateral, is discussed. Regarding the drilling sequence, a time-dependent relation between infill-drilling of a child well and the production loss due to the effect of stress alteration near a producing parent well is derived. Recommendations for well spacing and completion modifications are provided to minimize the production loss of the child well at different stages of the production of the parent well.

The proposed approach places the completion of each well in the field development context by considering a four-dimensional reservoir depletion, geomechanics, and hydraulic simulation coupling. The methodology provides a quantitative impact on production along with practical drilling timeline and completion recommendations when planning for multiple wells in a field development.