Jerry Lobdill comments on a situation in Virginia:
While this well may be a vertical well, if their results are positive they will come back for horizontal well drilling permits. Secondly, you should consider that once an aquifer is polluted, remediation is not possible. So the idea of monitoring the work and the condition of the ground water will only deliver prompt information that the water is no longer clean if things don’t go well. The drinking water source will be lost forever, essentially. So how do you justify a proposed fine for that?
Regarding fracking the shale, thousands of feet below the surface, it may or may not directly cause pollution of drinking water sources close to the surface, but there is one aspect of the wells that most likely is responsible for some of the many, many reports from all over the US of tap water containing combustible gas. It is the problem of failed cementing in the well bore.
In Texas drillers are required to cement gas wells from the surface to a depth somewhat exceeding the depth of the water table. Here, drillers point to this fact and the fact that the Barnett Shale lies about 7000 feet below the surface to back up their claim that the contamination could not possibly come from their wells. Actually, these facts are essential to the explanation of the presence of gas in tap water.
Have you ever seen a flagstone sidewalk that didn’t have cracks in some places between the mortar and the stones? This common situation is caused by weather and small ground motion effects that put stress on the interface between the stones and the mortar. In a well bore if the walls of the bore are not completely clean when the cementing is done the bond will be poor. Additionally, the interface between the casing and the cement is a weak point as the well ages because of the difference in the mechanical properties of cement and steel. Over time both of these interfaces of the cement with the casing and well bore will deteriorate.
When the bond fails the gas pressure in the well will cause the raw gas with its entrained liquids to find its way up the bore to geologic formations that contain the water that is used for drinking in homes.
How often do drillers achieve a good cement job? Dale Henry says not often. Dale Henry ran for TX RRC and lost in the last election. Dale (now retired) is the Red Adair of the well cementing problem world. He had a company that repaired wells with leaky cement jobs. He also cemented new wells. He says that drillers do not generally pay close attention to preparing the well bore. It is apparently a big problem.
In my opinion, the best policy is “Just say NO.”
Just my $0.02.
Jerry Lobdill
Ch. E. and physicist (ret.)
Fort Worth, TX.
Tags: cement, cementing, contamination, well casing
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