They are not Drilling Shale Wells Like they Used To

Source: SPE 189875.
In the Eagle Ford, denser development means that in the future the number of child wells is likely to exceed the number of higher-producing parent wells.

Maintaining production in the shale business is getting increasingly costly because new wells in major US shale plays are falling short of output from the parent wells.

A study of 10 major US basins by Schlumberger (SPE 189875) found that while the parent and child wells looked comparable at first glance—about half of new wells outperform the older wells and vice a versa—the picture changes when the results are adjusted for the higher cost of drilling and fracturing new wells.

This is a pressing issue in the shale sector where constant drilling is required to replace short-lived older wells, which is leading to increasingly dense development.

When the results remove the benefit of the longer laterals and bigger loads of sand pumped now, the parent wells outperform the next generation about 70% of the time, according to the study discussed at the SPE Hydraulic Fracturing Technology Conference this week. It defined a child well as one drilled at least 1 year after the parent well.

The results fall far short of the expectations of a few years ago when the industry assumed that ever-improving fracturing technology would mean ever-rising output. Instead, operators are spending more and more just to stay even.

“They are pumping way bigger frac jobs in child wells to help compensate” for the problems created by parent well production, said Garrett Lindsay, a senior production reservoir engineering for Schlumberger, who delivered the paper. While the geology of these formations varies, the older-well advantage remains fairly consistent, ranging from a high of near 80% in the Wolfcamp and Haynesville to 60% in the Bone Springs, after normalization.

The problem is that the older wells are depleting the hydrocarbons and the reservoir pressure required to get them out of this ultratight rock. Fracturing plans aim to stimulate a limited area around a well, but the reality shown in multiple presentations at the fracturing conference show fractures regularly extending out thousands of feet.

New wells inevitably end up competing with older wells for oil and gas as fractures extend into the depleted pressure zone around that well.

Even when new shale wells are widely spaced, older wells outperform them when the results are adjusted according to a study by Schlumberger. Source: SPE 189875.

 

Time is not on the side of the younger generation of wells. When they compared the relation between well generations, where there is a 3-year gap, “there is still a significant chance a child well completion will perform better.” After 6 years, the completion for the child well “will need to be larger to perform on par with the parent well.”

This will become an increasingly important problem as dense development means more tightly spaced production. In the Eagle Ford, those lines already have crossed and a wide gaps has developed.

Limited Options

The paper considered a variety of ways to reduce this advantage, but there is no fixing the big problem: the depletion caused by older wells.

Lindsay cautioned that, in some cases, operators will need to focus on a “calibration of expectations” in line with what the availble technology can deliver.

Wider well spacing reduces the parent well edge, but not hugely. When wells spaced 1,000 ft or less apart, Bakken parent wells outperform the child wells 74% of the time, when production is normalized. When they are 2,000–2,500 ft apart, 71% perform better.

In retrospect, it would have been favorable if early developers concentrated development, leaving significant undeveloped sections for later drilling. But companies rushing to lock up leases by drilling wells had other priorities.

Improved completion designs could help, but unconventional recovery rates remain stubbornly low. Adding customized designs and incremental improvements might help, but they are hard to deploy in operations built to mass produce wells using standardized plans.

Tightly controlling fracturing using diversion, which is supposed to block off dominant fractures to allow more equal growth and effective stimulation, might be helping. But comments by engineers at the conference offered mixed reviews.

Given the fact that the industry is still producing less than 10% of the oil in the ground indicates that there is a lot of room for improvement.

Production-extending methods, such as refracturing older wells or adding chemicals able to enhance production, could push up ultimate recovery rates, but the discussion at the conference indicates the industry is still trying to find the right formula to consistently apply these approaches.

Experience shows they can deliver significantly more production in some wells, but not all wells, and the cost can sometimes be too high to justify the added output, Lindsay said.

They are not Drilling Shale Wells Like they Used To

Stephen Rassenfoss, JPT Emerging Technology Editor

25 January 2018


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