The goal of this project is to provide a better understanding of potential technical issues involving the use of proppants in the Bakken Formation, and thereby assist in maximizing the development of the formation. Toward this goal, researchers will evaluate the effect of fracturing fluids on proppant performance and formation integrity under reservoir conditions.

Energy & Environmental Research Center (EERC), Grand Forks, ND 58202-9018

The Bakken Formation in North Dakota comprises a significant portion of the largest contiguous oil reserve ever discovered in the lower 48 states. The U.S. Geological Survey’s (USGS) original study of the Bakken Formation found 4.3 billion barrels of recoverable oil in the Montana and North Dakota portion of the Williston Basin. According to federal testimony provided by the director of the North Dakota Department of Mineral Resources, “Hydraulic fracturing is a critical component of developing the Bakken Formation, indeed every shale play throughout the U.S. and Canada. Without hydraulic fracturing, under regulation of the states, this resource could not be produced.” Hydraulic fracturing is the process of improving the ability of oil to flow through a rock formation by creating fractures. The process includes pumping a mixture of water and additives that include various sizes of sand, resin-coated sand (RCS), or ceramic particles called proppants that are designed to “prop” the fractures open, creating greater conductivity of fluids to the wellbore. While ceramic and resin-coated sand proppants typically outperform sand in creating and maintaining reservoir conductivity, they are less widely available and also more expensive. In addition, selecting a proppant type and injection scenario is important because field evidence suggests that propped fractures in the Bakken lose hydraulic continuity over time. This research seeks to identify the parameters responsible for the collapse of these propped fractures and the resulting loss of conductivity, including:

• The evaluation of formation integrity relative to exposure to various fracturing fluids and acidic native fluids
• The evaluation of proppant performance under reservoir conditions and exposure to fracturing

The results of this project will provide industry with critical information to better understand the mechanisms of propped fracture failure and to evaluate alternative fracturing strategies or fluid systems to minimize conductivity loss. Initial results of this work suggest that various fluids can decrease proppant strength and formation hardness, thereby increasing the likelihood of propped fracture closure and associated proppant loss. The results also suggest that conductivity loss within the Bakken and Three Forks formations can be attributed to multiple mechanisms, including mechanical failure of the proppant and resulting fines generation, as well as loss of formation integrity and associated proppant embedment and formation spalling. The value to North Dakota is an improved understanding of conductivity in the Bakken and Three Forks Formations, which may directly influence fracturing practices and lead to improved oil recovery with substantial economic impact.

To better understand proppant performance in the Bakken Formation, laboratory experiments were conducted through this effort. Three different proppant types (Ottawa sand, RCS, and lightweight ceramic proppant) and three different rock types (Middle Bakken, Lower Bakken, and Three Forks) were evaluated for strength and hardness, respectively, following exposure to various fluids in a reactor for 30 days at 3000 psi and 250 degrees Fahrenheit. The fluids used for exposure included slickwater, gelled diesel, guar-based cross-linked gel, Bakken formation water (brine), and Bakken Formation crude oil. The rock hardness was tested using a Brinell Hardness index methodology. Proppant strength was tested using a Forney one-dimensional compression test apparatus to compare the amount of strain in each proppant type as a function of applied stress (up to 11,675 psi).

In addition to proppant strength and rock hardness testing, proppant conductivity testing is also being conducted using the three different proppants and rock types. Two different test methodologies are being used. One entails a standard method for long-term conductivity testing and the other is a modified method that allows for use of standard rock core shapes and sizes.

Previous accomplishments included:

• Measured the conductivity of Ottawa sand, resin-coated sand, and Econoprop lightweight ceramic proppants within fractures of the Middle Bakken, Lower Bakken, and Three Forks Formations at formation temperatures and pressures.
• Evaluated the hardness of the Bakken and Three Forks rock cores prior to and following fluid exposure using a Brinell hardness testing methodology.
• Determined the strength of the three proppant types prior to and following fluid exposure using a Forney universal compression apparatus.
• Exposed rock and proppant samples to various fracturing and formation fluids in a reactor for 30 days at 3000 psi and 250 °F.
• Successfully cut friable Bakken and Three Forks rock cores into various shapes and sizes for testing using a waterjet cutting technique.

This project is completed. The final eport is available below under "Additional Information".

$113,201

$0

NETL – John Terneus (john.terneus@netl.doe.gov or 304-285-4254)
Energy & Environmental Research Center – Bethany Kurz (bkurz@undeerc.org or 701-777-5050) 
If you are unable to reach the above personnel, please contact the content manager.

Final Project Report [PDF-10.5MB]