Well Des gn and Well Spacing Optimisation in Unconventional Plays

Abstract

Abstract The risk profile for an unconventional resource play differs from a conventional opportunity in that the producibility, per well Estimated Ultimate Recovery (EUR) and Unit Technical Cost (UTC) are more important for identifying potential success than proving the presence of in-place volumes. Unconventional plays are often characterised by a large number of wells, lower density of subsurface data, large geographical extent and corresponding large range of uncertainty in subsurface parameters. The rapid economic screening of well design and spacing parameters for multiple subsurface realisations is integral in the planning stages of large unconventional plays. An additional complexity is the use of horizontal or complex geometry well designs which may limit or complicate the application of full field reservoir simulation methods. Recoverable volumes are strongly dependent on the proposed well design and spacing. These should be systematically evaluated and optimised by identifying the well density beyond which the incremental recovery and commerciality benefit begins to erode due to the extra well costs and/or interference between wells. A method for efficient analysis and comparison of complex well design and well spacing options has been designed to assist in unconventional play planning and evaluation. The method involves the automatic generation and analysis of a large number (thousands) of dynamic reservoir simulation models. The models are analysed systematically for major value drivers to: identify the most efficient well design and optimal spacing factors; select the most economic well designs; assess the impact of subsurface uncertainties; and assist in rig selection and surface planning.