Model for Transient Temperature and Pressure Behavior in Commingled Vertical Wells
- Weibo Sui (Texas A&M University) | Ding Zhu (Texas A&M University) | A.D. Hill (Texas A&M University) | Christine Ehlig-Economides (Texas A&M University)
- Document ID
- Society of Petroleum Engineers
- SPE Russian Oil and Gas Technical Conference and Exhibition, 28-30 October, Moscow, Russia
- Publication Date
- Document Type
- Conference Paper
- 2008. Society of Petroleum Engineers
- 5.6.4 Drillstem/Well Testing, 4.1.2 Separation and Treating, 1.8 Formation Damage, 4.1.5 Processing Equipment, 3.3.1 Production Logging, 5.1.5 Geologic Modeling, 5.1 Reservoir Characterisation, 5.6.11 Reservoir monitoring with permanent sensors, 5.3.1 Flow in Porous Media
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Multilayer 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.
Multilayer formation properties are necessary information for reservoir development. Distinct layers in multilayer reservoirs usually have different thickness, porosity, permeability, and skin factor that tend to cause differential depletion during reservoir development. Therefore, multilayer reservoir characterization has been attracting interest for many years. Since the first rigorous mathematical model derived by Lefkovits in 1961, there have been numerous studies of the behavior of multilayer reservoirs. A complete literature review of the analytical model developed between the 1960s and the 1980s can be found in Ehlig-Economides (1987a). This study showed that individual layer properties in multilayer reservoirs cannot be determined from conventional drawdown or buildup tests.
Kuchuk et al. (1986) introduced a quantitative modeling and testing technique combining stabilized rate profiles with transient rate and pressure measurements described briefly in Ehlig-Economides (1987b) as "layered reservoir testing". The layered reservoir testing" models have been enhanced by some authors (Kuchuk et al., 1991; Spath, 1994; Larsen, 1999; Prats, 1999), and the testing method has proven effective during the past two decades. However, a series of step-wise surface rate changes are still required during the test, with the production logging tool stationed above each layer to be characterized to record the transient rate variations during each rate step. This method is time consuming and may involve significant errors depending on the accuracy of the transient flow rate measurements.
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