Oil production from the Bakken formation has been active for 60 years and has applied three well completion design strategies in three different eras: mainly hydraulically fractured vertical wells before 1987, horizontal wells before 1991, and mainly multiple transverse fracture horizontal wells since 2006. Reported production data enables comparisons of well performance during these eras.

This study employs the log-log graph of rate (q) versus material balance time (Q/q) to diagnose transient (slope −¼ or −½) and boundary dominated flow (BDF) (slope −1) behavior. Wells from the 3 eras show mainly 3 types of flow regime sequences seen as straight trends on the log-log graph of rate versus material balance time: −¼ to −1, −½ to −1 and −¼ to −½ to −1. Flow geometries corresponding to various flow regime sequences are related to specific well and formation characteristics. Then we extrapolate the BDF behavior to estimate the EUR for each well when possible.

We observed that both the average well EUR and the average well rate at start of BDF behavior is highest for the multiple transverse fracture horizontal well completion design. This project also investigates the behavior of the GOR versus material balance time (MBT). Three types of GOR behavior were observed: constant, constant followed by sharp increase, or scattered. In all three eras, the EUR was highest in wells with constant GOR behavior followed by sharp increase. The sharp increase likely signals flow below the bubble point pressure. The lower EUR in wells that did not produce below the bubble point pressure shows that solution gas drive behavior enhances the EUR. Lower EUR in wells with scattered GOR behavior may be attributed to unstable well production.

This study shows how to use long term production behavior to gain important insights about well designs and why some wells have higher EUR and rate behavior.

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