Improved Conductivity and Proppant Applications in the Bakken Formation
Authors: Wilson Adam 
Published: February 2015

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 163849, ’Investigation of Improved Conductivity and Proppant Applications in the Bakken Formation,’ by Bethany Kurz, SPE, Energy and Environmental Research Center, Darren Schmidt, SPE, and Phil Cortese, SPE, Weatherford, prepared for the 2013 SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, USA, 4-6 February. The paper has not been peer reviewed.

Production from the Bakken and Three Forks formations within the Williston basin is continuing to climb as a result of applied horizontal drilling and hydraulic fracturing. Key to increased oil production is the evolution of reservoir-stimulation techniques, such as fracturing-fluid systems and proppant types. This study evaluated the key factors that may result in conductivity loss within the Bakken and Three Forks reservoirs. The results of this work suggest that certain fluids may affect both rock and proppant strength and, therefore, require consideration.

Introduction

This work was conducted in an effort to answer questions regarding reservoir stimulation in the Bakken petroleum system, specifically with respect to conductivity loss in hydraulic fractures over time. The key questions that were evaluated include

Can conductivity loss be attributed to proppant degradation, rock strength, or both?

What role do fluids have in affecting propped-fracture conductivity?

To what extent does fluid exposure affect the degradation of rock strength and proppant performance?

How do various proppants perform relative to one another under stress using actual core samples from the Bakken petroleum system?

Laboratory tests were conducted to evaluate the sensitivity of Bakken and Three Forks formation cores to various fluids; to evaluate the strength of Ottawa sand, an unspecified premium precured resin-coated sand (RCS), and a lightweight ceramic proppant (Econoprop) with respect to various fluids; and to measure the relative laboratory conductivity performance of propped fractures using actual rock core. Fluids used in experiments to examine potential strength degradation for both rock and proppant included the following:

Slickwater—a mixture of polyacrylamide and fresh water

Crosslinked gel—guar-polymer thickening agent, borate crosslinker, and fresh water

Gelled diesel—diesel fuel and phosphate ester

Bakken-formation crude—crude oil

Bakken-formation brine—highly concentrated saltwater

The fluids were selected on the basis of the most common fluids expected to be encountered in the Bakken formation.

Embedment

Brinell-hardness-index testing is a measure of rock strength that is determined by embedding a metal ball into formation rock at a given applied load. This type of index testing was used to gauge the relative strength of Bakken and Three Forks samples before and after exposure to formation and hydraulic-fracturing fluids.

Core samples used to study rock strength originated from the North Dakota Industrial Commission (NDIC) #16771 well, located in the Manitou field of Mountrail County. Rock strength was measured with a Brinell-hardness-test apparatus. Publicly available hardness data were available from two wells in proximity, including

NDIC #15986, Robinson Lake field, Mountrail County, approximately 10 miles to the southeast

NDIC #16083, Capa field, Williams County, approximately 10 miles to the southwest