Well placement and design under geological uncertainties represents a major risk for field development processes. Recent enhancements in geological modeling tools allow reservoir geologists to generate large numbers of alternative 3D models which honor available log and seismic data. For subsurface engineers such models behave quite differently which will impact well design and field development scenarios. Including alternative geological realizations in a manually optimized development plan has proven to be cumbersome and very time consuming. In practical cases, a single reference model is often used as a basis for the dynamic model which creates a major risk of underestimating static uncertainties.
This paper presents a workflow for well path design and optimization under geological uncertainties. Well path screening methods are developed for fast evaluation of alternative well designs in a heterogeneous reservoir model. The method is applied to horizontal well designs including multiple design points for a trajectory honoring geological and technical constraints.
The introduced workflow is capable of handling a large number of design options. Efficient parameterizations of well design parameters in target regions are chosen to limit the introduction of constraint handling methods. Static and dynamic simulations generate performance indicators. A performance overview is supported by the application of experimental design techniques and optimization processes for this study are supported by evolutionary algorithms. Alternative geological models are included in an integrated approach to generate risk profiles representing geological uncertainties.
The workflow is applied to a North Sea condensate field which has two main formations of interest. Information from an exploration well indicates that the uncertainties are related to sand connectivity and net sand content. The specific objective of the case study is to find optimum well positions and designs for horizontal wells by maximizing cumulative gas production. All well candidates are evaluated on the basis of three risked geological realizations which represent a base-, conservative- and optimistic case.
A well screening and well production optimization workflow is developed and successfully applied to complex well designs. Practical experience in a real field application underline benefits for generating risked cumulative production profiles in an extended risk assessment.