Using the most advanced technologies combined with a passion for geology leads to an ever-increasing level of understanding of rock properties and reservoirs. Welcome to an interview with Kitty Milliken, who shares her experiences and insights.

What is your name and your background?

Kitty Milliken; I have degrees in geology from Vanderbilt University (BA) and the University of Texas at Austin (MA, PhD). I have worked in various areas of sedimentary petrology since the mid-1970s.

How did you become interested in geology?

I was one of those childhood rock collectors. From about the age of 7 I knew that I wanted to be an earth scientist, though my earliest focus on paleontology lasted through my undergraduate days. It was in grad school that I encountered Bob Folk and sedimentary petrology and quickly gave up any further thought of working on paleoecology. There are so many great questions to be answered with microscopy.

Where did you do your field work for your degrees? What were your main findings or take-aways?

For my master’s thesis I collected specimens of silicified carbonates and evaporites in the Mississippian limestone and dolomite units of southern Kentucky. For my PhD I had shifted into clastic rocks and “field work” consisted of visiting core warehouses in Dallas, Tulsa, Denver, and New Orleans. This was an experience that highlighted for me the importance of core and sample preservation. The samples I needed were from offshore fields in the Gulf of Mexico and had been obtained by the companies with great difficulty and expense. It was shocking to discover how some of these materials were being sent to the landfill before their scientific value could be realized.

Since my PhD my further “field work” mostly has been shipboard with the IODP---basically a giant floating core description facility. Even though I’m definitely a laboratory scientist, I love field work so much that my main hobby is backpacking.

All my research work, from the time I first arrived at the University of Texas, has focused on the use of petrography to document the magnitude of subsurface reactions in sedimentary rocks. The big takeaway is that the cumulative reaction volumes (all the precipitations and dissolutions), summed across a long burial history, tend to be astonishingly large. This means that the rock you have in your hand has a chemistry rather different from the long-ago sediment. And it also means that elemental mobility is greater than you might think.

Please describe your work on pore architecture? Why is it important?

Understanding the size, shape, and spatial distribution of pores is important for understanding the behavior of fluids in rocks. But beyond information on how fluids might behave right now, there is broader knowledge to be gained about pore history----answers about how and why pores came to be as they are and how fluids might have moved through rocks in the past. To get to these broader questions it’s necessary to understand pores from the point of view of the pore walls---what are the walls made of and when and how did those materials come to be? For this reason, when I work on pore systems I actually spend most of my time observing and thinking about the solid parts of the rock.

Please describe a few examples of where understanding the pores made a significant difference.

In conventional reservoirs assessment of reservoir quality has become a routine part of exploration and production work flows (see recent Distinguished Lecture by long-time practitioner Lee Esch). No one wants to commit to drilling in a place where quartz or carbonate cementation has filled up the porosity. In production situations people seek to understand formation damage issues that might arise from the presence of certain types of clay cementation, or, perhaps fines migration related to absence of cement.

In the world of unconventional reservoirs, application of petrologic characterization is still evolving and is being applied routinely by some companies, but not others. It is clear that diagenetic characteristics such as large mineral-hosted pores propped open by cement or microcrystalline cements that promote brittle mechanical behavior have positive impacts on the success of unconventional reservoirs. The sorts of well-established models that allow for easy application of these concepts are still being worked out and spread through the oil and gas community.

What have your recent projects involved? What kinds of technologies are you using?

I am currently on an extended visit with colleagues in the rock property group at CSIRO in Perth, Australia and also at the CSIRO electron microbeam facility in Clayton. We are working on organic-rich mudstones of Proterozoic age from the MacKenzie Basin in the Northern Territories. In younger rocks, the presence of reactive skeletal material is a big part of the pore evolution puzzle, so, for me, this study is a great opportunity to grow my experience by examining mudstones deposited before the “invention” of shelled organisms. As usual with mudrocks, high-magnification imaging and analysis are key to understanding the rock’s basic components, and we will be working with field-emission scanning electron microscopy of several types, most notably cathodoluminescence.

Where do you think breakthroughs will happen?

For understanding the origins of rocks and their basic components, the intersection of new technologies for seeing with previous experience in examining a wide range of rock types provides fertile ground. This combo has proven itself again and again in the developments that have happened over the past 40 years or so. Once we have a new way of seeing, then we have a new way of measuring and answering questions, but it’s necessary to have experience to know what to measure and which questions to ask.

What worries you most about the impact of COVID-19 on the science of geology?

Getting people out into the field (and to core storage facilities!) is so important. To have a break from that is painful to contemplate. Also, for me, personally, the impact I’m seeing on teaching microscopy is quite awful. Normally, petrography instruction is accomplished by regular hands-on lab experiences with an instructor who visits each student microscope in turn, answering questions and posing questions, about features under the microscope. My colleagues who teach this are really struggling to provide materials on line that duplicate this experience in even the most basic way. This is presenting a terrific challenge for grad students who are just beginning their research life and need to learn microscopy skills to apply in their projects.

Please recommend a few books.

Although I didn’t become a paleontologist, I have greatly enjoyed all the popular writings of Stephen J. Gould. “Wonderful Life” makes it clear that we’re all so lucky to be here---read this and it’s hard to ever be glum again! Steven Pinker’s “The Blank Slate” is a more recent favorite that I think contributes a dose of common sense and practicality relevant to any number of current public conversations.