Statistical Detection of Flow Regime Changes in Horizontal Hydraulically Fractured Bakken Oil Wells

Abstract

The application of horizontal and hydraulically fractured wells for producing oil from low permeability formations has changed the face of the North American oil industry. One feature of the production profile of many such wells is a transition from transient linear oil flow to boundary-dominated flow. The identification of the time of this transition is important for the calibration of models that forecast the wellÕs future production and the expected ultimate recovery. It is preferable that such models generally use data from the boundary-dominated flow regime for parameter calibration. Accurate well production forecasts are needed for operational decisions, long-term planning, commercial transactions, regulatory proceedings, and asset valuation. Petroleum engineers frequently make the call on the transition point based on subjective visual interpretations of log-log plots for individual wells. This is time-consuming and is generally not repeatable by other analysts. This note evaluates statistical approaches that can serve as alternatives to the subjective visual interpretations. Specifically, the predictive performance of production models calibrated with boundary-dominated data based on transition dates calculated with constrained nonlinear least squares and Bayesian regressions was very close to that obtained using the visual method, suggesting that statistical approaches may indeed be constructed to replace less objective visual approaches without loss of accuracy.

Price Responsiveness of Shale Oil: A Bakken Case Study

“…8 Further, only a few years after completion, they also have relatively lower production rates than most conventional wells. Among other factors, the change in flow rate is the consequence of the natural progression of a horizontal shale well’s production from transient flow to boundary-dominated flow (or some other flow regime), as described in, among others, Kabir et al ( 2011 ), Zhou et al ( 2017 ), Zhang et al, ( 2016a , 2016b ), Luo et al ( 2018 ), Yang et al ( 2019 ) and Attanasi et al ( 2019 ). The full history of horizontal wells drilled in the Bakken Shale and summarized in Table 1 demonstrates this revealing characteristic.…”

Statistical analyses of reservoir and fracturing parameters for a multifractured shale oil reservoir in Mississippi

“…For multifractured horizontal wells, two general flow regimes may be observed: transient linear flow and boundary‐dominated flow. Transient linear flow is the dominant flow regime in low‐permeability reservoirs and may last for a long time, depending on the matrix permeability and fracture spacing, etc The most common method to identify these two flow regimes is the use of a log‐log diagnostic plot of production rate versus time when only production data are available . For hydraulically fractured wells with infinite fracture conductivity, the log‐log plot follows a straight line with a slope of −0.5 during the transient linear flow period.…”