Oil & Natural Gas Projects
Exploration and Production Technologies
Autonomous Monitoring of Production
This project was selected in response to DOE's Natural Gas and Oil Technology
Partnership Upstream FY 2001 call for proposals on oil and gas technology to
increase U.S. production.
The project goal was to demonstrate a semi-autonomous system that delivers data
of sufficient quality to monitor small changes resulting from production over
time without additional drilling or intensive investment of manpower. Key project
elements were to produce time-dependent maps of changes in formation resistivity
caused by production or stimulation, utilizing existing infrastructure without
interruption of field production/stimulation activities.
Lawrence Livermore National Laboratory (LLNL)
Results from this project were the construction, testing, and demonstration
of a data-acquisition system for electrical resistance tomography (ERT) that
would allow remote operation. The system works through a combined land-and-satellite
communications link that allowed remotely set system parameters, data collection,
monitoring of system health, switching the system to waiting mode, and retrieving
data for processing.
One goal of this work was to reduce the cost of long-term (3-10 years) geophysical
monitoring of oilfield operations by using a single measurement system that
could be operated remotely to produce data for a large (hundreds of acres) area.
The project accomplished this by control of the data-acquisition system, through
a land-and-satellite communications link, that allowed researchers to remotely
set system parameters, initiate data collection, monitor system health, switch
the system to waiting mode, and retrieve the data for processing. The system
could be left in place for several years, saving considerable travel and manpower
costs, and yet allows frequent sampling of the reservoir. A demonstration of
the system was accomplished as part of the work at Buckeye, NM, a relatively
remote site where frequent data acquisition, requiring frequent site visits,
was rather expensive.
Technical improvements include:
- Decoupling the downhole casing from surface piping (using insulating subs
at the surface) and improving signal-to-noise ratio.
- Establishment of a data-acquisition system (permanently installed in the
field and designed to operate autonomously). When information is desired,
the operator calls the system up, initiating an acquisition sequence.
- The system acquires data in an unattended mode, stores and transmits the
data stream, and shuts itself down. Alternatively, the system can be programmed
to obtain data periodically on its own.
- The most important benefit of this technology is a new and better method
for monitoring stimulation during oil production.
Oil production is commonly assessed by measuring bulk oil produced at the wellhead.
Operators want to know what portions of the reservoir are being drained or swept
and where significant oil-in-place remains. Some survey techniques can be field-deployed
but provide low-quality information and are expensive relative to the knowledge
gained. These techniques often require interrupting production to acquire data.
Electrical methods such as ERT are well-suited for monitoring processes involving
fluids in exploration and production activities, as electrical properties are
sensitive to the presence and nature of the formation fluids.
Recent communication and computational improvements have made it possible to
obtain high-quality 3-D electrical tomographs providing the equivalent of electrical
logs deployed every few feet between existing wells. Thus formation characterization
and monitoring of subsurface fluid movement are possible, even over time where
fluid saturations can be used to map swept and unswept zones and can help guide
infill development to recover hydrocarbon from these areas. This project demonstrated
a semi-autonomous system that delivers data of sufficient quality to monitor
small changes resulting from production over time without interrupting production
or drilling or requiring intensive investment of manpower.
A semi-autonomous monitoring system was designed and installed in an oilfield
undergoing CO2 injection and waterflood. Issues addressed included system design,
worker safety, signal-to-noise ratio, and remote access. Numerical simulations
were performed to aid in system design and to assess signal strength under realistic
injection scenarios. Multiple hardware types in the field enabled the assessment
of system impacts under different operating conditions.
The remotely operated system successfully monitored operations over a year.
Time-lapse data correlated with the production history. Changes in electrical
properties correlated with displacement of oil by water and movement of water
and gas in the production intervals.
The methodology is quite straightforward. Using well casings as electrodes
for electrical imaging permits long-term and relatively inexpensive surveys
of stimulation or production. While this field-monitoring capability is new,
it constitutes an extension of already proven technology and has a high expectation
for success. Although ERT imaging is usually performed in a crosswell configuration
using arrays of electrodes placed along insulated casings, project researchers
developed a means for acquiring and interpreting data using existing metallic
casings as long electrodes, requiring no downhole modification. Data are interpreted
using existing tested computer codes that treat the fully 3-D case. The products
are time-dependent maps of the horizontal changes in formation resistivity caused
by stimulation or production (if horizontal casings are available, some vertical
resolution may be provided as well). These data can be interpreted to infer
fluid behavior during production.
The general-purpose communication system that was developed has the flexibility
to support different kinds of remote experimentation or data-gathering activity;
this system is called GET-NET. The remote local area network (LAN) has a data-acquisition
and control laptop computer that front-ends the long-electrode electrical resistance
tomography (LEERT) instrumentation. Through the firewall/virtual private network
device, the remote LAN is connected to the satellite network using an internet
protocol-enabled satellite modem.
The most important benefit of this technology is a new and better method for
monitoring stimulation during oil production-a direct result of the fact that
the electrodes used for ERT are already scattered throughout the reservoir (the
cased wells). No new "monitoring" wells are needed. Any well casing
can be used as an electrode if it reaches to the depth of the formation of interest.
This means that the capital cost for doing LEERT is very small. Considering
that the cost of a monitoring well can be as high as $1 million, this advantage
can make the difference between a method being practical or impractical and
thereby the difference between used or not used.
Well casing can be used irrespective of what else the well is used for or what
it contains. It may be a production well, an injection well, or even a monitoring
well and still be used as an LEERT electrode. The only real restrictions are
that the casing must be steel (no insulators such as fiberglass) and in good
electrical contact with the formation. If it is a production well, then production
tubing need not be removed for the casing for it to be used as an electrode.
Production can continue uninterrupted, another significant cost benefit. Similarly,
if it is an injection or monitoring well, its original function is unaffected.
LEERT requires minimal field personnel to operate, thereby minimizing survey
costs. Moving sondes in boreholes for logging or crosshole tomography, or moving
sources and receivers on the surface for reflection seismology, is time-consuming
and expensive. The cost of a 3-D surface seismic survey can run $1 million or
more. Conventional borehole geophysics is less expensive but has an upfront
cost as well as a downtime cost. In contrast, steel well casings used by LEERT
are all connected to a central multiplexer and are chosen automatically as a
current source or for voltage measurement by an appropriate switching algorithm.
It's all done automatically and with no moving parts.
For any monitoring method, the time interval between surveys is generally limited
by the survey costs and the reluctance to remove wells from production. In contrast,
LEERT can be used as a truly long-term monitoring tool, capable of nearly continuous
imaging but not limited by mobilization, survey, downtime, or demobilization
costs. LEERT can provide on-demand, real-time continuous imaging.
Current Status (October 2005)
Project funding was terminated during the field demonstration. As a result,
final field testing and sensitivity analyses were not completed, which prevented
transfer of the technology and training of a commercial partner(s). However,
a company that provides ERT services could quickly make this technology commercially
available. Equipment and software used in the project are at LLNL.
Daily, W., Ramirez, A., Newmark R., and Masica, K., Low-Cost Reservoir Tomographs
of Electrical Resistivity, The Leading Edge, May 2004, V. 23, I 5, 472-480.
Ramirez, A.L., Newmark, R.L., Daily, W.D. Monitoring Carbon Dioxide Floods
Using Electrical Resistance Tomography (ERT): Sensitivity Studies, Journal of
Environmental and Engineering Geophysics, September 2003, V. 8, No. 3, 187-208.
Newmark, R.L., Ramirez, A.L., Daily, W.D., Monitoring Carbon Dioxide Sequestration
Using Electrical Resistance Tomography (ERT): A Minimally Invasive Method, 6th
International Conference on Greenhouse Gas Control Technologies (GHGT-6), September
30-October 4, 2002, Kyoto, Japan, UCRL-JC-148146.
Newmark, R.L., Ramirez, A.L., Daily, W.D., Monitoring Carbon Dioxide Sequestration
Using Electrical Resistance Tomography (ERT): Sensitivity Studies, First National
Conference on Carbon Sequestration, Washington, DC, May 14-17, 2001, UCRL-JC-140527.
Project Start: June 12, 2001
Project End: June 11, 2004
DOE Contribution: $560,000
Performer Contribution: $0 (0% of total)
NETL - Purna Halder (firstname.lastname@example.org or 918-699-2084)
LLNL - Robin L. Newmark (email@example.com or 925-423-3644)
Illustration of long-electrode electrical resistance tomography.