RATE TRANSIENT ANALYSIS
Clients: IWFS, LLC Contact Information:

Mario A. Salazar, Integrated Well Flow Solutions LLC
e-mail: mario.salazar@inwellflowsol.com
phone: 1-512-363-0822
IWFS SERVICES
Rate Transient Analysis

The worldwide installation of permanent downhole gauges (PDGs) in wells in recent years
and the capture of terabytes of static and flowing bottom hole and well head pressure and
production rates  in SCADA systems and databases has added an important big data
component to the area of well production data analysis and performance optimization
making available accurate and dependable well data to the desktop of engineers who no
longer have to rely on manual readings, conversions and allocations to make informed
decisions.   

In that scenario, rate transient analysis or RTA emerges as a powerful tool to take
advantage of relatively large volumes of data and provide the answers needed to improve
the accuracy in the estimation of reserves; the characterization of the well-reservoir
system and if implemented thru any rate transient analysis software package, the ability to
facilitate an updated report of the reserves and production forecast at the well level.

Traditional decline curve analysis (DCA) uses reservoir engineering empirical methods to
estimate reserves and forecast production, while rate transient analysis (RTA) based in the
same theory of pressure transient analysis (PTA) uses a more dynamic approach that
includes flow rates and flowing pressures to understand the well, the wellbore, the
reservoir and boundaries.   Rate transient analysis is also known as modern decline curve
analysis.

Advantages of Rate Transient Analysis

Rate transient analysis provides many advantages by enabling engineers to:

•  Estimate the reserves of a well and forecast production with a higher degree of certainty
•  Gain reservoir understanding thru the characterization of the well-reservoir system
•  Operators do not need to shut-in the well to analyze its system performance.
•  Perform more efficient updates.  
Accurate estimation of reserves

DCA has been used for years as a valuable tool to estimate well proved
developed reserves and forecast production, however, DCA cannot be
effective early on the life of a well when it has been in decline for a short
period of time, in that context DCA can produce many EURs that look
apparently acceptable but not unique introducing a high degree of
uncertainty since we can easily over estimate or under estimate the value
of EUR.  Moreover, DCA cannot be used when the well rate is restricted
and kept constant.  Operational changes in the well can also become a
drawback since forecasts are no longer valid and a new DCA analysis is
required.
The drawbacks mentioned above are a good reason to start using RTA
instead of DCA.

Reservoir Characterization

Rate transient analysis can be used effectively in the determination of key
parameters enabling engineers to characterize the well-reservoir system
thru better understanding of:
Original oil in place and reserves
Pressure support
Drainage volume
Permeability
Flow regimes
Damage Factor
Deliverability potential

Analysis and Interpretation based on on-going data

RTA relies on on-going flowing bottom-hole pressure and rate data either
recorded permanently or consistently acquired from timely well tests to
determine well-reservoir system parameters. This means a well does not
have to shut down and stop production to build up the pressure in order
to obtain an analysis and interpretation of the performance of its
well-reservoir system. This is an excellent selling point for RTA.
RTA Modelling

RTA follows a pattern of compatibility with PTA as far as modelling is
concerned. The analytical model is the combination of four sub-models
representing the wellbore, the well, the reservoir and the limits or
boundaries.  

Finding the right analytical model is finding a solution not necessarily
unique to the interpretation. The following tables describe the optional
analytical sub-model types available in Rate Transient Analysis.
Well Model Type
- Finite Radius
- Infinite Conductivity Fracture
- Finite Conductivity Fracture
- Limited Entry
- Horizontal
- Fractured Horizontal
- Fractured Horizontal + SRVB
- Fractured Horizontal + Trilinear
Wellbore Storage Type
- Constant
- Variable
Reservoir Model Type
- Homogeneous
- Double porosity (PSS)
- Double porosity transient
- Double permeability
- Radial Composite
Boundary Model Type
- Infinite
- Single fault
- Leaky Fault
- Intersecting faults
- Channel
- Closed Circle
- Rectangle (Centered)
- Rectangle
- Weak constant pressure
- Strong constant pressure
Blasingame type curve
Log-Log Normalized Pressure and Derivative
Blasingame Plot