”Oil and gas wells and their integrity: Implications for shale and unconventional resource exploitation” - a paper on oil/gas well integrity was published in the March issue of Marine and Petroleum Geology by British scientists of ReFINE (Research Fracking in Europe), an independent consortium that focuses onn fracturing issues.
Well integrity is a hot topic in the aspect of the ongoing debate on unconventional oil and gas production.
”Well integrity” is understood as operations that are intended to minimize the risk of uncontrolled penetration of substances to the well from near-well rocks. Uncontrolled flow of natural gas to the well may cause blowout, whilst groundwater penetration to the well (for example caused by cement failure) may result in groundwater contamination. In order to prevent these failures various technologies, such as casing cementing, are used.
The authors of the paper have reviewed well integrity failure reported from the United States, the Netherlands and the United Kingdom. Importantly, they considered both active and abandoned wells. According to them, integrity failures were found on average in as little as 10% of onshore wells.
How integrity of unconventional oil and gas wells compares to conventional ones according to the study? In fact, they are much safer that traditional wells. In the case of Marcellus Formation in Pennsylvania, integrity failures were found in approx. 4.5% of wells, much less that for example in the Norwegian Shale (about 25%). This is primarily due to the characteristics of bas-bearing shale which is impervious to groundwater, but also to the efforts of oil and gas companies which, compelled by a number of allegations and requirements of environmental agencies, have introduced restrictive procedures and latest technologies.
Concluding, the study has demonstrated that shale gas exploration and production is not a serious risk to the environment and human health, provided that adequate standards and technologies are applied at each stage of the operations.
author: Wojciech Labuda