Model for Transient Temperature and Pressure Behavior in Commingled Vertical Wells
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AbstractMultilayer transient testing is designed for determining individual layer properties (permeability and skin) for multiple layers commingled in a well. Traditional multilayer transient testing requires a combination of rate profiles from production log and transient rate and pressure measurements acquired at multiple surface rates. This method can be time consuming and may involve significant errors depending on the accuracy of the transient flow rate measurements. Today, many wells are equipped with downhole sensors that provide distributed or multipoint temperature measurements along the wellbore. Using these data to determine formation properties can minimize time and disturbances in well production. This paper presents a forward model to investigate the possibility of evaluating formation properties from transient temperature and pressure measurements. The model couples wellbore and reservoir models for simulating transient temperature and pressure for single-phase flow.The wellbore model was developed based on mass, momentum, and energy balance. The reservoir model consists of a reservoir thermal model and a pressure/flow-rate transient model. Besides heat conduction and convection, it considers viscous heating and temperature variation due to fluid and rock expansion/compression. Wellbore and reservoir models are solved numerically to predict transient temperature and pressure behavior.Comprehensive experiments reveal the sensitivities of transient temperature to individual layer permeability and skin values in multilayer systems. The results indicate that there are two main mechanisms governing wellbore transient temperature behavior; formation heating/cooling and wellbore fluid mixing at entry points, and that permeability and skin affect transient temperature and pressure differently. Examples in the paper show that the transient temperature response can distinguish between low permeability and high skin factor as reasons for low productivity in any layer. Additionally, this work revealed that the transient temperature behavior is sensitive to the radius of the damaged zone, suggesting for the first time a mechanism to quantify the damaged radius. The observations show promise of using transient temperature and pressure to determine multilayer formation properties.
