Re-fracking wells and why they want to do it.

Editor's note: Jim Rike is a well-known Louisiana-based petroleum engineer and a consultant to some of the world's largest energy companies.

The hydraulic fracturing (“frack job”) of a shale gas well is a process that uses hydraulic energy to create a split and expose extra surface producing area in the productive shale, thus making it economically profitable to drill. This extra surface area is directly related to more oil or gas being produced per day.

Think of it this way: If valuable fluid was dripping from the ceiling of your cellar, you would be a lot richer if you had acres of ceiling surface producing that fluid. If your ceiling had lots of cracks and ridges, its surface area would be increased dramatically. Similarly, frack jobs increase that productive surface of shale available to the well.

We know we drain the oil and gas from only a short distance away from the fracture surface. We don't know whether that is a few feet or a few hundred feet, and it probably varies a great deal from one shale area to another, or possibly from one well to another.

Drillers found economic success when we started drilling horizontal wells into the shale producing zone and created additional producing surface area with multiple fracks, spaced along the horizontal length of the well bore. After the bore of a well reaches the shale, thousands of feet beneath the surface, it turns and runs through the shale itself, often great distances. It is in this horizontal section within the shale that fracturing points are placed at intervals in order to produce cracks in the shale to release its hydrocarbons. Each fracturing point creates an oval of fissures through which gas and/or oil flows into the well bore.

Drillers started with one or two or three of these fracturing points, but have found that more and closer-spaced fracks made for more productive and more profitable wells. Today, some companies are considering up to 40 fracturing points in a single well. Trial and error results will provide the only definitive answer as to the correct number that maximizes profit in a given region or well.

If we find that more profit is available as the spacing between “frack ovals” decreases to, say, 100 feet or less, then it likely will become attractive in the future to add fractures to existing wells that presently have more widely spaced fracks. Each of those subsequent frack jobs is likely to require a similar surface pad and large assembly of equipment as well as lots of water. However, most won't require the high derrick and massive drilling rig used when the well was originally drilled.

Some of those previously completed wells may be made more profitable by re-assembling a drilling rig and drilling a new lateral hole from the existing well. With good expertise and planning, this can be more economical than drilling an entirely new well, yet generate as much new income as a result.

The oil/gas industry will develop new technology as opportunities arise.

Some experts are suggesting fracking with compressed gas. Carbon dioxide has been successfully used to frack wells, where carbon dioxide is available at high pressure and low cost. Some “dreamers” visualize taking nitrogen from the air and compressing it on site to accomplish a frack job. At present, fracking with liquid-based materials is far less expensive and safer than these gas frack alternatives.

There is little doubt that the wells we are drilling today will be revisited in the future to increase their productivity. But there is little evidence that indicates we will re-frack the same frack ovals that have been produced and depleted. The existing source rock does not get replenished with enough oil/gas within a lifetime to make that re-stimulation economically viable.

There will be cases where the first frack was poorly designed or executed due to lack of knowledge or experience at the time. When these instances are found with reasonable surety, a re-stimulation job on that well can be quite successful. We know a lot about fracturing; we know a lot about shale; we know a lot about Marcellus Shale, but the industry continues to learn more with each frack job completed. The Utica Shale adds a complete new mystery; it almost certainly won't behave the same way as the Marcellus Shale.

But one thing is about as certain as things get in the oil and gas industry: the wells we're drilling today will not give up all of their resources from their initial frack jobs — and will probably produce for years to come as we continue to learn how best to support their ongoing productivity.