Long Term Well Monitoring
By Nathan Waldman |
Wed, 7 May 2008
Pressure
Transient Analysis (PTA) is the primary tool for reservoir management. To efficiently produce a reservoir, the
operator needs to determine Reservoir Pressure (P*), permeability, skin, reservoir
geometry and reservoir limits or boundaries. He also needs to know how these
values change as the reservoir is produced. However, downhole PTA is expensive,
interrupts production (cash flow) and runs the risk of loss of the tool string
in the well bore and even loss of the well.
For these reasons, management is reluctant to approve PTA unless the
well is experiencing an unexpected decline in productivity. Long Term Well Monitoring (LTWM) from
surface pressure measurements avoids the risk and expense of downhole testing
while providing the data necessary for PTA and efficient reservoir management.
The
rationale for LTWM with the SPIDR is that most wells experience unplanned
shut-ins during the course of normal operations. These shut-ins can be due to pipeline
problems, weather problems, control system upsets, etc. When these unanticipated shut-ins occur, an
un-scheduled build-up test occurs that might be analyzed provided a SPIDR was
in place to capture the build-up data. Normal SCADA systems do not sample with the
frequency or resolution required for PTA. In addition to capturing un-planned shut-ins, a
SPIDR installed for LTWM would be recording the decline in flowing well-head
pressures and production over time allowing calculation of reserves and
determination of reservoir limits. LTWM
is also used to identify communication between wells and can help evaluate the
need for additional wells in a reservoir or help avoid the drilling of
unnecessary wells.
When
multiple shut-ins occur over time, the reservoir engineer can determine the
accretion of skin, changes in reservoir permeability and changes in P*. If skin is increasing production rates can be
controlled to avoid excessive pressure drop across the completion which could
result in loss of the well. If skin is
significant, remediation could significantly increase production. As reservoir permeability changes, the
reservoir model can be updated to reflect the consequent reduction in
productivity. Changes in P* over time
permit creation of a very accurate and reliable Decline Curve for the
reservoir.
LTWM
using the SPIDR data acquisition system can be accomplished in a Static Mode or
Active Mode. In Static Mode, the SPIDR
is installed on the well and allowed to sample unattended. When a shut-in occurs, planned or unplanned,
data stored in the SPIDR can be downloaded and analyzed. In Active Mode, the SPIDR is connected to a
SCADA system and the data is automatically transmitted over the internet to a specified
distribution list. The transmitted data
file is updated on a pre-set interval, usually hourly. Active Mode allows changes in well operation
to be quickly detected allowing quick response and thereby minimizing
production loss.
In addition to these methods DRC is now offering a new
Internet communication option for the SPIDR.
If your wellsite has access to the Internet or an internal network, the
SPIDR can be placed online. This will
allow you to operate the SPIDR remotely using our Flowcom software. You will be able to download and view SPIDR
data in real-time.
We have placed a SPIDR online in our offices and if you
would like to test our system and see how it really works (as well as view
actual SPIDR data) please contact us and we can instruct you on how to connect.
