Predicting High Volume Lift Perfonnance In Wells Coning Water
Authors: Blades D.N. , Stright D.H. 
Published: March 2010

This paper presents the results of a study of the water coming behaviour of under saturated, high viscosity crude oil reservoirs being pressure maintained by bottom water drive. Crude oil viscosities of 3, 10 and 60 cp are considered. The multi-rate performance of two wells is matched with a three phase, two-dimensional coning model to investigate the sensitivities to the pertinent reservoir fluid and rock properties. Of particular significance in this phase of the study is the need to recognize oil-water capillary pressure to obtain a match with reasonable reservoir and fluid property adjustments.

Approximately 45 computer runs were made with the coning model to develop a set of type curves, which are used to predict coming behaviour and ultimate recovery. The type curve are defined by oil zone thickness and crude oil viscosity. The performance of wells producing from several heavy gravity crude oil reservoir is matched with the type curves. The curves are used to determine the influence of rate on ultimate recovery. It is shown, that, for the reservoirs' studied, increased rates of production result in significant increase in ultimate recovery.

INTRODUCTION

THE PURPOSE of this study was to develop a method for predicting water coning behavior and the effect of production rates on water-oil ratios and ultimate recoveries from crude oil reservoirs with bottom water. The study was directed to heavy gravity crude oil reservoirs such as those found in southeastern Alberta. In many of these reservoirs, water coming is the mechanism controlling performance and there is sufficient coming history to match with predictive methods. As there is very little difference in the density of water and oil in heavy crude reservoirs, gravity forces are low compared to viscous forces. This effect, coupled with an unfavorable mobility ratio, results in a very low critical rate (the production rate at which the stabilized cone is maintained below the perforations) in this type of reservoir. The critical rate would decrease as the oil-water contact rises with production. The effect of pressure decline and excessive gas production on water coning behavior r was not included in the investigation. Only reservoirs which were being depleted in an undersaturated condition and which exhibited a low rate of pressure decline due to natural water influx or water injection were used for performance comparisons.

Several investigators(1–6) have studied the coning phenomena by the use of models and laboratory studies. The model studies have generally demonstrated that models can match coning performance effectively. The correlations have been developed to predict breakthrough times, critical rates and water-oil ratios after breakthrough. The previous correlations were not used in this study, because they excluded the effect of capillary pressure and did not permit a ready analysis of the effect of rate changes. We found it necessary to include capillary pressure in the model to predict coning behavior in heavy crude oil reservoirs which have significant oil-water transition zone thicknesses.