Well Spacing Design as Stacked Pay is Exploration in Shale
Data Science & Analytics

Well Spacing Design as Stacked Pay is Exploration in Shale

Rosemary Jackson  •  

Exploration in Conventionals: One well bore travels through multiple pay zones and is opened in one zone or comingled in several for long years of production

Exploration in Shale: The parallel to conventionals is important because stacked pay has been around a long time and needs to change to exploit shale stacked pay. No comingling— requiring multiple wells in each pay zone.

What determines well spacing design in unconventional plays? The placement of wells in a pad is based on vertical stress, ISIPs, drainage, microseismic data, fracture growth, parent/child interactions, stress shadow and acreage lithologyWell spacing design is exploration in shale. Exploration facilitated by using tools like the Pad Scenario Designer in Petro.ai which combines multi-variate calculations to produce an ROI value for each modeled pad configuration. 

Well spacing in unconventionals is anything but conventional. There are no matrix-expanding drainage boundaries. There’s shale. Shale has no real matrix and when you start draining, the boundary is already there. When you frac that well, you stimulate both the propped and the shear surface area, and you’re already at the maximum extent the well will drain. There is no midpoint analysis or round number of so many feet that needs to separate wells. There is no accurate reference to past drilling environments for predicting future well placement in shale. 

Shale well spacing is conceptualized as oil discovery through stacked pay. Shale is a laminar, dense rock. Pay or pay zone refers to the target interval the well is producing from. Kyle LaMotta, VP of Analytics, describes the process, “The challenge with unconventionals is that the landing zones they’re targeting are stacked meaning there are layers of pay, layers that they’re trying to produce from that are right on top of each other. So, they have to put multiple wells in each of those pay zones.”

Troy Ruths, CEO of Petro.ai continues, “Shale has been challenging because you do make money on every well. Each well will produce. It’s not like exploration in conventionals. This is shale exploration where economics balance with drilling and production in equal concern. With Petro.ai, we can be sure about what we’re putting in. We can understand vertical stress and we can understand the growth of the fracture that can be measured with microseismic data. The Midland basin is a great place to use this information because it has so many shear fractures. There are so many natural tilt meters in the subsurface telling you where the frac is growing.

“We have a lot of great information on where these fracs are growing. And at Petro.ai, what we’ve been able to show is that production is a zero-sum game.

“If you produced it by one well, it won’t be produced by another well regardless of the parent/child spacing. At the end of the day, you’re really thinking about how much you can extract from your stacked pay. It’s a volumetric question. Even though unconventionals is very different, we’ve managed to bring it to a volumetric and reservoir properties perspective.

“Stacked pay are the virtual boundaries that form naturally and through fracking in the hydro-carbon rich depositional environment of shale. In the stacked pay dynamic, wells are cooperating to drain the reservoir. You can confuse yourself and your assessment by using type curves and thinking about spacing as experiential. If you have a great parent well, it could be draining from multiple zones. Or you could create interference among the tightly spaced zones that lowers your productivity and ROI.”

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