Abstract

Accurate determination of oil, water, and gas production rates is an important element of oilfield management and optimization. Multiphase flow meters (MPFM) are being accepted more and more for well testing, reservoir management, production allocation, production monitoring, and fiscal metering. In addition to common MPFM applications, this study shows how a multiphase flow meter may be used as a valuable tool to evaluate water production problems of the well by imposing transient flowing conditions to the well and tracking characteristic parameters such as flowrates, water cut and gas oil ratio with the equipment during the test.

Representative curves are shown in this study in order to identify some common wellbore problems associated with water conformance. The curves were obtained through numerical reservoir simulation using a number of cases related to the most important problems: water channeling in stratified formations, mechanical wellbore integrity, water conning, and oil-water contact advance.

The flowrate at the well should be shortened to a half of the current flowrate with a choke for several hours then, the dimensionless pattern curves of the water cut and gas oil ratio gathered in this study should be matched with the measurement of the MPFM on site in order to characterize the nature of the water problem. This application represents a new tool used to identify the sources of water production. The tool is easy and quick to apply, and complements other analytical techniques being used like diagnostics plots based on production history, water-oil ratio performance and production logs. All of them are used to differentiate between the different mechanisms of water invasion, so that an appropriate treatment may be selected to control undesirable water production.

Introduction

During the petroleum exploitation, the production of water can come from an aquifer or from injector wells in a waterflooding process. When excess of water production exists, the costs associated to surface facilities, artificial lift systems, corrosion and scale problems increases. Besides, the recovery factor decreases as oil is left behind the displacement front. These factors reduce the economic indicators. The drastic influence of water production must be soon detected and the source of such problem must be identified in order to apply effective and suitable techniques to control this production. The sources of water production can be identified by several techniques. Production logs are one of the most confident techniques. A high level of expertise for logging analysis is required, but is only available in some cases. Analytical techniques such as characterizing the water-oil ratio and production history may be matched with diagnostic plots to distinguish between the different mechanisms causing water invasion. The quality of the production history data is poor in many cases, though. These techniques complement to each other and none of them by itself gives a high level of confidence to the conclusions.

It has been reported1 that the analysis of the fluctuating water-oil ratio, WOR, can provide valuable indications to determine the source of water production. It has been suggested to choke the production during short periods with several sizes of orifices and monitor the pressure along with the WOR with a three-phase flow meter to determine the resulting changes in WOR. However, the performance of the WOR for different pressures and rates is not described nor associated to the sources of water production, other than empirical experience.

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