A Cost/Benefit Review of Completion Choices in the Williston Basin Using a Hybrid Physics-Based-Modeling/Multivariate-Analysis Approach

Summary

In the Williston Central Basin, a well-completion design has a significant effect on well productivity and ultimate recovery. More than 12,000 horizontal wells have been drilled and completed while completion practices continue to vary widely across the basin. Several companies have adopted slickwater-only designs, whereas others have dramatically increased proppant mass. Completion strategies have differed depending on the area in the basin. The objective of this paper is to discuss the effect of various completion changes in the Central Basin and determine which particular change delivers the most “bang for the buck” using a metric of dollars spent per barrel of oil (USD/BO).

The approach centered around multivariate analysis (MVA) from an extensive petrophysical/completion/production database to verify what completion and petrophysical parameters independently drive production in different areas. Although MVA has been used by the authors and many others before, statistical models are limited by their ability to provide predictive relationships (mostly simple linear regressions, and unreliable beyond the data range). This paper provides a novel hybrid approach that uses calibrated relationships from physics-based modeling (combination of fracture and numerical reservoir modeling) between completion parameters and production response in combination with statistical MVA results. Specifically, the physics-based model is calibrated or “history matched” to a measured production/completion-parameter response as provided by MVA, thus delivering a constrained and more physically realistic production response to suggested completion changes. This model is then coupled with a completion-cost model to determine which completion method is the most effective to lower USD/BO.

Many common completion-parameter changes, such as increasing stage intensity, moving to plug-and-perforate cemented-well designs, increasing injection rate, and increasing proppant mass per lateral foot and fluid volume per lateral foot, have a positive effect on production and are advantageous to lower USD/BO in all areas of the Middle Bakken and Three Forks. The new hybrid MVA approach indicates that pumping slickwater treatments with average proppant concentrations of 1 lbm/gal and treatment sizes from 545 to 750 lbm/ft at pump rates approaching 100 bbl/min through a stage length of 200 ft (50 stages for a 10,000-ft lateral) might be the economic optimum, provided there are no significant well-communication issues.