Considering Time and Space in Drilling and Completion Can Reduce Well Interference
Authors: Feder Judy 
Published: September 2019

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 191836, “When, Where, and How To Drill and Complete Pads of Multiple Wells? Four-Dimensional Considerations for Field Development in the Vaca Muerta Shale,”by Stephane Pichon, SPE, Federico Gaston Cafardi Orihuela, Emilio Lagarrigue, and Gustavo Cavazzoli, SPE, Schlumberger, prepared for presentation at the 2018 SPE Argentina Exploration and Production of Unconventional Resources Symposium, held in Neuquén, Argentina, 14–16 August. The paper has not been peer reviewed.
Development of organic shale reservoirs with large hydraulic-fracture treatments not only poses challenges to the completion of a single well, but also to interference with surrounding wells. A direct consequence of interference is production loss. Therefore, the drilling and completion schedule for field development must be 4D in time and space to account for interaction in between wells. The complete paper describes a physics-based model of interference and a sensitivity study to propose guidelines for well spacing and a drilling timeline for multiple horizontal wells in the Vaca Muerta shale.
Introduction
Effective field development relies on the tradeoff between the capital expenditure (CAPEX) and the production profile generating cash flow. Both CAPEX and the production profile are directly controlled by the number of wells and the pace at which these wells are tied in to the production facilities. With respect to tight rocks, the need for horizontal drilling and hydraulic fracturing adds a layer of geometrical complexity to unlock such resources.
In very-low-permeability reservoirs, the drainage area is controlled by the hydraulic-fracture geometry. However, the relatively large size of the fracturing treatments performed in a multistage manner across several different perforation clusters within a same stage makes hydraulic fractures difficult to control. In practice, fracture dimensions are not constant along a lateral. Additionally, because limited contribution of the matrix is expected in a nano-Darcy environment, the spacing between laterals tends to be smaller than the reach of the hydraulic fractures. This has been evidenced by the increasing concern over fracture hits in the industry, and already has been experienced in the Vaca Muerta.
Interference can be caused by fracture hits while completing the well, competition for drainage area during production, or fracture-geometry deterioration caused by stress field variation when infill-drilling a child well near a produced parent well. Even if some overlap between the hydraulic fractures of two neighboring wells is advisable to avoid leaving reserves behind, the tradeoff between well spacing, completion intensity, and production interference remains a delicate exercise. Hydraulic fracturing should be considered at the field level, rather than independently for each well, giving completion a multiple-well spatial dimension.
As an additional complexity, child wells completed later in the development of a lease tend to perform more poorly than the parent wells. This performance impairment might have several different sources, but one of the most-accepted hypotheses is that the heterogeneous contrast in the stress field generated by the depletion around the parent negatively affects the contact area provided by the hydraulic fractures of the child well.