The Machine Learning analytic model concludes that the amount of frac proppant being injected into a shale well is the most influential factor to the well's future production. But more proppant does not always mean higher production.
The relationship between frac proppant injection amount and shale production rate is represented by a curve plot on a Cartesian Plane. X axis is the amount of frac proppant injection (tonnage). Y axis is the prediction of the first 12 month cumulative well production (boe).
Initially, with the increasing of frac proppant injection, the well production increases. Most production curve has a steep climbing slop. That steep slop starts from the moment when the frac pressure reaches target tight reservoir rock fracturing pressure point. Eventually the production reaches a relative peak. Three possible types of behaviours are observed after the peak:
- Type-I curve: production drops steeply, the reaches several higher peaks in sequence.
- Type-II curve: production drops, but eventually stabilizes at a certain level.
- Type-III curve: production stabilize at high level.
Type I: shale frac stimulations break lateral seals between boreholes and make the same drilling pad wells connected. This scenario potentially increase hydrocarbon recover rate and well production if the input frac proppant amount matches a peak production on the modeling curve. But since each lateral break would cause a pressure drop, often the frac procedure is terminated at this point in fear of breaching into a thief zone, therefore the frac proppant would match a production trough on the modeling curve. The ultimate outcome of this case would be a low production result.
Type II: shale frac stimulations established partial communication between horizontal boreholes or nearby permeable rocks or faulting. Highly heterogeneous geology and inadequate frac process design is often to blame.
Type III: No or very little communications between horizontal boreholes after frac. Large well spaces or single shale well frac often behaves as the Type III curve. The downside of Type III is that such well panning or geology will likely result in low hydrocarbon recovery rate, thus low economical return.