A few years ago, Occidental Petroleum managers were puzzled by why their recent Permian Basin wells were producing more water per barrel of oil, so they asked some engineers to figure out what was wrong.
Their concern was understandable. While the company’s well evaluation system was supposed to screen out prospects likely to become big water producers, the amount of water flowing out of wells in the Delaware Basin drilled after 2018 far exceeded volumes from previous years.
“We found that newer wells had a steeper increase in water cut over time than older wells,” the coauthors of an Occidental paper wrote about the work done to answer the question. They added, that “pre-2018 wells had an average water cut increase of 4% in the first 300 days (after cleanup) and then stayed relatively flat after 300 days, whereas post-2018 wells’ water cut increased at an average of 12% in the first 300 days and 16% in the first 600 days before reaching a plateau” (URTeC 3720245).
Those trends, plus wells ultimately reaching an 80% water cut, suggested that a string of wells may have been drilled into water aquifers. While that is a risk in the Permian, the evidence suggests that the geology in the wells they compared was similar before and after 2018, even though the water cut levels were not.
A big difference was how the wells were fractured.
