An Analytical Approach to Utilize Temperature and Pressure Profile of a Multi-zone Well in Estimating Zonal Flow Contributions

Abstract

Oil and gas producers around the world face a major challenge in estimating zonal flow contributions in wells with multiple pay zones. This study develops an analytical approach that estimates zonal flow contributions from producing zones using the pressure and temperature profiles of the well. Such a method can assist operators to monitor wells and decide on workovers. This method can work best in an instrumented well that can provide real time pressure and temperature data.

This study develops a model that divides a multi-zone well into a series of producing and non-producing sections. Taking the mixing cup approach, energy and material balances are performed at the producing sections to quantify flow rate from each reservoir. Measured pressure and temperature data from a well are used as the input of the model along with sand-face fluid temperature of each zone. Sand-face fluid temperature, when unavailable, is estimated using an analytical expression that relates reservoir flowing fluid temperature change with pressure drop and flow rate. The model is used first in the forward mode for a theoretical conventional dry gas well with multiple pay zones to generate synthetic pressure and temperature profiles along the wellbore for a given flow profile. Then the model is verified by using it in inverse mode with the generated synthetic temperature and pressure profile to estimate rates and error bounds. An iterative solution method is used as calculating sand-face temperature requires flow rate from the zone. Sensitivity study of the model is presented to show the relative significance of each variable. Sensitivity studies show that this model is highly dependent on the accuracy of temperature measurements and that the model may not be useful for low producing zones.

Later, the model is applied to three field cases of gas wells from a conventional sandstone reservoir where producing zones are separated by impermeable shale layers. Spinner data from those wells are interpreted using a commercial software to generate a flow profile against which the model is validated. A recently developed analytical expression is used to estimate the unavailable sandface temperature. The quality of the match of the model estimates with spinner data is excellent. Limitation of the model in low producing zones is discussed.