Abstract

Generalized empirical correlations have been developed to predict (1) critical oil rate and (2) water breakthrough time in vertical and horizontal wells. Water coning is a serious problem in many producing oil wells, which increases the cost of producing operations and reduces the overall oil recovery. A numerical simulator was used to analyze the most relevant fluid properties and reservoir parameters that affect water coning using a 3-D radial vertical well model and a 3-D Cartesian horizontal well model.

A stepwise procedure was developed to determine the average oil column height below perforations at breakthrough (hwb) for various water oil ratio, fluid properties, and reservoir parameters. Several simulation runs were performed to determine the effect of the various parameters on water coning. Regression analysis was used to develop relationship between (hwb) and the various variables. Results of the simulation runs showed that coning tendency is more severe in heavy oil reservoirs and less severe in reservoirs with low water-oil mobility ratios. Furthermore, results showed that the use of horizontal wells can significantly reduce water coning, improve ultimate oil recovery, and increase water breakthrough time compared to vertical wells.

An extensive parametric sensitivity analysis was performed to provide input data for developing a predictive correlation needed to calculate breakthrough time and height as function of fluid properties and reservoir parameters. The simulation outputs were used to develop empirical water coning correlations to predict critical oil rate and water breakthrough time for vertical and horizontal wells. The parameters were grouped based on the regression analysis. The developed empirical correlations are illustrated with several field examples from Hassi R'Mel oil field in Algeria.

Introduction

Water and gas production from a thin oil reservoir is a common occurrence due to water and gas coning problems. These problems increase production cost reduces the efficiency of the depletion mechanism, and the overall recovery. One of the main reasons for coning is the high-pressure drawdown. A vertical well exhibits a large pressure drawdown near the wellbore, whereas a horizontal well exhibits low-pressure drawdown due to its long lateral. Thus, horizontal wells provide an option whereby pressure drawdown and coning can be minimized resulting in high oil production rates. Two forces are responsible for water coning:

  1. dynamic flow force (applied force), and

  2. gravity force. In waterconing systems, the upward dynamic force due to wellbore drawdown causes water at the bottom of the oil zone to rise to a certain height at which the dynamic force is balanced by the weight of water beneath this point.

As the radial distance from the wellbore increases, pressure drawdown and upward dynamic force decrease, and the height of the balance-point decreases along the radial direction. Therefore, the locus of the balance point is a stable cone-shaped water oil interface. Oil flows above the interface, while water remains stationary below the interface. As the production rate is increased, the height of the cone above the original oil-water contact also increases, until at a certain production rate, the cone becomes unstable and water is produced into the well.

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