ABSTRACT
Most authors have concentrated on correlations for critical rate and breakthrough time in vertical and horizontal wells. WOR (water-oil ratio) has also been addressed in vertical wells. However, WOR performance in horizontal wells has not received much attention. The purpose of this work is to develop a method suitable for either hand calculation or simulation to predict (1) critical rate, (2) breakthrough time, and (3) WOR after breakthrough in both vertical and horizontal wells.
An extensive sensitivity analysis of water coning was performed using numerical simulation. From this analysis, an empirical coning correlation was developed based on the basic flow equations and regression analysis. The format of the correlation is similar to Addington’s gas-coning correlation. It predicts critical rate, breakthrough time and WOR after breakthrough.
WOR performance at variable rate production conditions has also been evaluated in this work. It was found that WOR has hysteresis, (i.e., WOR not only depends on the current production rate, but also the previous production history). However, given sufficient time after rate changes, hysteresis disappears. At such conditions, the correlations can also give a good estimation of WOR for variable rate cases.
This correlation provides a hand calculation method of coning prediction for both vertical and horizontal wells. It can also be used as a coning function for 3-D coarse grid reservoir simulation. The correlation was tested and found to be reliable and accurate in predicting WOR, as well as critical rate and breakthrough time when water-oil mobility ratio is smaller than 5 or viscous forces are not dominating.
