Calculating EUR Change for a Frac Hit Parent Well: Positive/Negative/Neutral
Data Science & Analytics

Calculating EUR Change for a Frac Hit Parent Well: Positive/Negative/Neutral

Rosemary Jackson  •  

In tightly spaced unconventional reservoirs, hydraulic fracture hits communicated from child (infill) wells to parent (existing) wells has become the norm. The effect of frac hits on productivity can be positive, increasing the EUR of the parent well, negative, decreasing the EUR of the parent well, or neutral, having no effect on the EUR. Kyle LaMotta, VP of Analytics, explains the Petro.ai answer to quickly determining this effect in the newly released investigative decline curve comparison in the Frac Hit app, “Petro.ai is comparing two decline curves, pre and post frac hit, and then looking at the EUR difference between those two. The area between the two curves becomes an accurate measure of the production difference.

“This concept isn’t used today because until now, people didn’t have a good way of doing it.

Operators should be re-declining or re-forecasting the wells after they’ve experienced the frac hit because it’s going to change the reserves.

“They’ve essentially booked the reserves at one decline curve but then that decline curve has changed because of the frac hit so operators should be updating their reserves to account for that new EUR forecast.”

LaMotta adds, “Frac hits fully affect the reserves that are in a pad and company-wide. Let’s say they drill 100 new wells in a year, then they would have to also update all their existing wells based not only on the decline area for those wells but also the results of the frac hits of those existing wells.

“One of the biggest questions about frac hits is what is the actual impact of an infill well. We know that we’re putting these wells relatively close together and there’s going to be interaction between wells. The question is, is there a material impact of these frac hits on a parent well? In some cases, the wells might be communicating but there’s no change in production. In other cases, the child well or the near wells could take resources from the parent well because they were completed too close together and the child well is actually draining some of the reservoir that was accessible by the parent well.”

LaMotta shares examples of the three types of frac hits on parent, or existing wells, when child, or infill wells, are added.

Below is an example of a negative frac hit. What initially looks like a neutral frac hit actually changes the decline of the well after the interruption.

Negative frac hit

“We’ve shown in other apps in the platform that there is an interaction between wells. Now what we’ve added is the ability to quantify the impact of the frac hit. In this case, we have a decline curve of the well which is the dotted green line.The actual production is the solid green line. What you notice is after the date when the child well was completed, which is indicated by the vertical dashed black line, the decline rate increases noticeably. The previous trend was continuing along the dotted green line which was forecast. But after the frac hit, we see that the decline rate changed and now it’s on a new trajectory which is a lower than the original one.

“The impact of the reduction in EUR is the area between the two curves. If you integrate and find this area, that is the total production this well no longer has access to because of that frac hit.”

Positive effect

In the graph above, we see that after the completion of the child well, there was a frac hit that resulted in increased production of the parent well. This is a positive effect. What you gain is the area between these two curves.

Neutral effect

“The graph above shows an overall neutral effect because it had a quick uplift which could be the result of a pressure uplift. When you shut these things in, the pressure’s building back up in the reservoir so that might be why the oil’s going back up.This is a neutral frac hit where you didn’t really gain that much. Neutral impact means no impact on the parent well. When we’re talking about positive, negative and neutral impact it’s always on the parent well because that’s the existing well.

An important way to use this kind of frac hit analysis is when applied to well spacing. We know that as you space wells closer, you are going to start affecting the parent wells. But the question is, is there a tradeoff to be made so that we know we’re impacting the parent well negatively? Maybe that parent well is later in its life and we’re only going to affect it a little bit. In that case, we may gain more by adding additional wells with closer spacing. You want to look at the tradeoff between adding an additional well that could affect the parent well, but you could offset that by adding the additional production from the new well. You’re looking at tradeoffs. There are always tradeoffs.

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