Case Studies, Modeling and What’s Next…..
Some phrases from the afternoon papers titles.
“Improving recovery efficiency using modeling”
“ASR Dynamics…..and Solutions”
“Modeling…... Plume Geometry”
“Geochemistry, Geophysical ….Data Gaps”
These point out the unknowns; that we are dealing with a mobile & changing system; and that we have a need for a better understanding of these subsurface systems.
We use models to predict system response to a set of variables (a few known, many unknown). But keep in mind, we are working in a physical subsurface environment we can’t directly see in its entirety and our working knowledge is based on interpreting between core holes using our knowledge of stratigraphy, lithology, sedimentation, petrology, and geologic structures; or utilizing geophysics and geochemistry to postulate in two dimension or three dimensions. We have much regional hydrogeologic information, but we must have local – site specific data. Now, we are very good – I know I am speaking to the choir here, but we don’t have X-ray eyes to see into the subsurface, we are not Superman! So, we must model, we have no choice, society demands it, they need predictions (and who better to take this on but Professional Geologists and Engineers – modelers, mathematicians, and programmers, trained in the appropriate fields that understand the physical processes involved?). ASR is a proven technology…….but…… Beware! These aquifer units are heterogeneous, and we know some elements and compounds can be mobilized by oxidation or other processes from injected waters. We also know mobilization varies between cycle tests, between wells (even within the same field and stratigraphic horizon). We know porosity & permeability is increased, we know cementation and other processes clog systems in other situations. We must collect pilot test data from cores to assess the range in lithologic & geochemical compositions, and the physical parameters of the hydrogeology of the rock units. Local, site specific data is mandatory, and as data is collected we must be adaptive in our models and designs.
I recently read an article in Science by Orrin Pilkey titled “Society and Sea Level Rise”. In it he made several points regarding our society's and many of our professional colleague’s tendencies to accept models, and lose site of the need to use their “expert eye” and to adequately communicate the uncertainty of predictions. I think many of his points are equally applicable to ASR work as well as shoreline erosion of which he wrote. He pointed out; too often a “one model fits all” approach is applied to a highly complex natural environment with large spatial variations. Why? Often because it’s an easy to use analytical model, or we don’t wish to collect new field data, or there is no better alternative model, or maybe some just don’t understand the weaknesses or the invalidity of some models. Our modern understanding of the complex depositional, sedimentologic, and post-depositional geologic and hydrogeologic processes, supports the rejection of the simple predictive model approach. We must advocate recognition, and acceptance as fact, that we cannot accurately predict some subsurface processes or geometries, and we must instead suggest that predictions are based on extrapolations and our “expert eye” based on local experience and knowledge gained. We must have a thorough understanding of the various geologic constraints and range of variations. Qualitative predictions will improve as we learn more of the local geology.
With that introduction, I would like to begin our afternoon session titled: “Case Studies, Modeling and What’s Next….. and introduce the first speaker………