Bailey Bubach

Nano-dynamic mechanical analysis (nano-DMA) of creep behavior of shales: Bakken case study

Understanding the time-dependent mechanical behavior of rocks is important from various aspects and different scales such as predicting reservoir subsidence due to depletion or proppant embedment. Instead of using the conventional creep tests, nano-dynamic mechanical analysis (nano-DMA) was applied in this study to quantify the displacement and mechanical changes in shale samples over its creep time at a very fine scale. The results showed that the minerals with various mechanical properties exhibit different creep behavior. It was found that under the same constant load and time conditions, the creep displacement of hard minerals would be smaller than those that are softer. On the contrary, the changes in mechanical properties (storage modulus, loss modulus, complex modulus and hardness) of hard minerals are larger than soft minerals. The results from curve fitting showed that the changes in creep displacement, storage modulus, complex modulus and hardness over creep time follow a logarithmic function. We further analyzed the mechanical changes in every single phase during the creep time based on the deconvolution method to realize each phase’s response independently. Two distinct mechanical phases can be derived from the deconvolution histograms. As the creep time increases, the volume percentage of the hard mechanical phase decreases, while this shows an increase for soft phases. The results suggest that nano-DMA can be a strong advocate to study the creep behavior of rocks with complex mineralogy.

A Multidisciplinary Study of Stimulation Designs in the Three Forks Formation, ND

The Three Forks Formation in the state of North Dakota is one of the main plays with the record of one million barrels a day of hydrocarbon production, recently, combined with the Bakken. Three Forks formation is highly heterogeneous due to the presence of interbedded shale layers. The reservoir properties vary significantly within the basin, which makes the stimulation designs challenging. It’s well understood that to maintain the production, well completion and stimulation designs should be applied in a given field in Williston Basin; in this paper we combined several data sources in a multidisciplinary manner and compared completion design parameters such as: amount of proppant injected and type, fracturing fluid type, using acid, etc. with the goal of improving well productivity. The main objective of this study is to investigate how different fracturing components can impact the production. The production history data was limited to the days after the stimulation. Our investigation is based on proprietary and public data of the Three Forks Formation. We also included the name of each operator active in a single field to make an assessment of how different companies are performing completion and fracturing design compared to production. Introduction In the last decade, the Bakken shale has emerged as a major oil play in North America. Lately, however, more effort has been spent on Three Forks Formation. From across the country, oil companies have been flocking to the Williston Basin to get their shares. These companies have brought along their unique knowledge and experiences. They are constantly testing and refining their methods in order to have the most production out of the Bakken and Three Forks formations. As a result, there is a variety in the way these companies stimulate their wells. Each different approach had produced different result. Some approaches will result in higher production comparing to others. In this study, the focus will be on the Three Forks since it is the “next” formation. The Three Forks Formation was deposited during the late Devonian, in a very shallow and extensive epeiric platform. It is a mud dominated system composed of dolomitic siltstone, claystone and mudstone (Gutierrez et al., 2013). Even though Three Forks is an unconventional play, there are many subsurface structures involved in it, such as dome and anticlines, which form conventional traps throughout the basin. As such, production from these structures should be higher since they benefit from the conventional trap. For a major part, this study devotes to answer two questions: • What are the correlations between different fracing parameters and its corresponding production result? • Does it require higher pressure to open fracture on top of an anticline vs. away from an anticline? URTeC 2015 Page 1941