--> Solving Geological Complexity of the Bakken Shale Using a Slim Micro Imaging Tool: Implications for Fracture and Facies Characterization

AAPG ACE 2018

Datapages, Inc.Print this page

Solving Geological Complexity of the Bakken Shale Using a Slim Micro Imaging Tool: Implications for Fracture and Facies Characterization

Abstract

The Bakken shale oil play in the Williston Basin of North Dakota is an unconventional hydrocarbon resource that continues to be prolific and profitable in a low-price market. The lithological assemblage of the three main formations in this play, presents challenges to properly acquire good quality data from water based mud imaging tools for several reasons, including: oil emulsions in the wellbore walls, differential rock strength, and cost associated to deploy wireline imaging tools. In this case study, we used an efficient full bore electrical slim micro-imaging tool that allowed acquisition of optimal borehole image data to enable geological interpretation of tight formations. Geological interpretation using image data acquired over 9600’ of lateral section in the Bakken shale allowed us to perform detailed fracture identification, classification, and description of lateral facies changes, as well as tracking of up-dip and downdip variations in the trajectory to and through the target horizon. Additional integration was performed with acoustic measurements from the slim dipole sonic to characterize the natural fractures identified on the image and estimate the stress gradient considering anisotropic mechanical properties along the lateral.

The combined integrated results of sonic and borehole images allowed to identify several zones of different reservoir quality and completion quality for an efective geoengineered fracture stages.

This case study outlines the importance of natural continuous and litho-bound fractures that were interpreted throughout the interval, and a wide variety of different sedimentary textures, rock facies revealed from image logs in the lithological unit of interest, fractures distribution and facies variability across the lateral allowed us to conclude that the formation is not intensely fractured.

Finally, a discrete fracture network model was added to strengthen our data visualization and formation evaluation along the lateral.

Quantification of fracture intensity, geometry, aperture and azimuth trend supported by borehole images in slim holes has direct implications for planning fracking stages and optimize well completion designs. In this well we could confidently define visible sedimentary features in borehole images, something that has proven to be challenging in the Bakken, this has implications in future logging campaigns in the area to reduce logging risk and improve reservoir characterization.