Post Carbon Fellow David Hughes Drilling Deeper report was cited in this article on mapping the fracking boom.

From the article:

From afar, it’s just a forest of lines. But if you zoom in, you’ll see that some areas have wells tightly packed in, whereas other areas have a solo wells. From what I’ve read—such as in assessments like those from geologist David Hughes in his recent report “Drilling Deeper”—the densely drilled areas are those where wells yield the most oil. These are the “sweet spots,” as the industry calls them.