As an increasing percentage of the world’s production comes from
mature fields, there is a growing need for production enhancement techniques
that are both rapid and easy to use for the practicing production engineers.
For mature waterfloods, the ln(WOR) versus Np plot enables rapid well screening
on the basis of incremental recovery factor, where WOR is the producing Water
Oil Ratio and Np is the cumulative oil production. Published in-depth
information on application of this tool is sparse. Yet, this is often the only
tool available to the production engineer for evaluating development options,
where a history-matched simulation model has not been maintained.
In this paper, the theoretical basis for the use of the ln(WOR) versus
Np is reviewed and studied, and is used to arrive at practical guidelines for
interpreting production data. Its applicability as a forecasting tool to
single-layered and multilayered clastic, waterflooded reservoirs of varying
heterogeneity is demonstrated. Numerical simulation models then predict the
behavior of this plot for a wide range of heterogeneities.
Production data is then analyzed to show the applications of the theory
for multilayered reservoirs. The ln(WOR) versus Np plots are analyzed, and the
impact of various factors is observed. The authors also demonstrate that, where
applicable, this plot is the preferred decline curve for the following
- Ln(WOR) versus Np does not require any pressure data; only surface
well test production history is required.
- It can be assumed that the ln(WOR) versus Np function is an
approximate function of the reservoir only, and is decoupled from the outflow
and facility constraints. This is especially useful when comparing artificial
lift and drawdown strategies.
- It is a decline curve model that provides a forecast of water cut,
which is indispensable on waterflood projects.
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