Abstract

In this continuation work, we expand upon the Nagoo et al., SPE-190921 [1] seminal paper that unveiled for the first time a simple and direct analytical critical gas velocity diameter-and-inclination-dependent equation for predicting the onset of liquids loading in horizontal wellbores. Using this equation, we now introduce a new analytical method for quantifying lost liquids production in liquids-rich horizontal gassy oil and gas wells undergoing liquids loading. Case studies of in-operation horizontal wells from the Permian and Delaware basins are used to highlight and validate the methodology.

For horizontal liquid-rich wells in unconventional plays, liquids loading can severely impair production in gassy oil or gas wells with significant oil or water production. Currently, there is no reliable, field-focused, simple-to-use, analytical method for quantifying the lost (or deferred) liquids production because of the liquids loading happening in the wellbore. We propose that the downhole wellbore gas velocity and the critical gas velocity profiles can be superimposed on the traditional wellbore lift curve to yield a varying unloading point on the wellbore lift curve that is very sensitive to and dependent on the predictive reliability of both the diameter-and-inclination-dependent critical gas velocity model used and the wellbore multiphase flow model used. In looking at the new gas velocity-based lift curve results for several horizontal wellbores, the lost liquids production can now be quantified and compared to the actual liquids production drop in the well history before and after the onset of liquids loading. Furthermore, it is demonstrated that as opposed to prior ad hoc recommendations of bottom-of-lift-curve or tangent-of-lift-curve demarcation points for liquids unloading, the new analysis presented provides an analytical intersection point between the downhole wellbore gas and critical gas lift curves as the basis for the unloading point (onset of flow liquids flow reversal point). This signifies that the combination of analytical multiphase flow wellbore and analytical critical gas velocity calculations will now change and define the range of unloading producing rates according to diameter, inclination and fluid property changes.

For the first time, a practically useful and simple analytical method for quantifying lost liquids production in liquids loaded horizontal gassy oil and gas wells is presented in the form of gas velocity-based lift curves. This signifies a new powerful arm of horizontal well artificial lift modeling for life-of-well lift optimization (i.e., incorporating rate declines) for keeping wells flowing at flow rates to avoid liquids loading. Both the lost liquids and lost gas production can be predicted on a well-by-well basis and wells can now be prioritized for artificial lift needs according to their downhole "loading proximity". Various relevant field case studies are used to validate the method in practice.

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