Advancement of Hydraulic Fracturing Optimization Shows Promising Economics in Tight Bakken Formation

Abstract

Bakken is a leading unconventional reservoir which has lead to the resurgence of North Dakota oil boom. Although multi-stage hydraulic fracturing technologies have been used successfully to tap unconventional reservoirs like Bakken, challenges still remain in terms of optimal fracture design, e.g. fracture spacing along a horizontal wellbore, and further improving capital efficiency. In this paper, we present a new workflow that integrates the properly coupled flow simulation and fracture models to optimize hydraulic fracture design for Bakken wells. Our new workflow starts with geomechanical modeling, for example, Young's modulus and Poisson's ratio, to identify possible fracturing zones from logs. Fracture properties are calibrated in those individual zones, before migrate to a novel in-house 3D reservoir simulator. We then capture capillarity with the consideration of imperative pore size distribution (PSD) characteristics. Owing to the distinct production driving mechanism caused by nano-pores in unconventional reservoirs, using commercial software without addressing those flow and phase behavior differences may lead to an inaccurate, and often underestimated, oil production. Using the new model, we consistently evaluate capillary force using PSD directly from core measurements to characterize flow mechanisms in shale formations. We further quantify the uncertainties arising from fracture modeling and simulation studies. Sensitivity simulations were performed using the coupled model to investigate the effect of geomechanical parameters on fracture design. Different hydraulic fracture geometry, and especially, fracturing spacing, are optimized to demonstrate the consideration of flow behavior in unconventional reservoirs. Results show that different and uneven hydraulic fracturing spacing should have been proposed, if capillarity is to be considered in the reservoir simulation. An over 30% improvement in ultimate recovery is observed using this novel workflow which parallels hydraulic fracturing design with production mechanism differentiators in unconventional reservoirs, such as capillarity. This paper provides an advanced and practical hydraulic fracture optimization approach using a novel tool that models the impact of capillarity for shale oil reservoirs. The new method may shed light to better mitigate uncertainties in unconventional reservoir management and improve economic benefit of hydraulic fracturing.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016