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Stimulation of Watered-out Inactive/Marginal Wells With Dual Completions |
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Based on a workshop sponsored by PTTC's Central Gulf Region in Shreveport, Louisiana on May 23, 2006.
Over 340,000 wells are inactive (shut-in) in the United States, of which 34,000 are in Louisiana. These wells were generally temporarily abandoned because they were no longer economical to produce, often because of high water cut. Many of these wells, particularly in the Gulf Coast, suffered premature high water production rates due to coning, channeling, or both and left 40 to 90 percent of the oil in place behind. For those wells, the technology now exists to recover those reserves, the Downhole Water Sink, utilizing a dual completion to create a sink in the aquifer while producing from the oil zone above.
The Downhole Water Sink (DWS) has been demonstrated to be an effective stimulation approach for certain high watercut wells that have prematurely watered out. The problem addressed is to understand the reservoir mechanisms, identify candidate wells, simulate the results, and design an optimum completion.
Aquifer, Channeling, Coning, Downhole Water Sink, Dual Completion, Reservoir Simulation, Water Cut
Marginal Well Upgrade Concept and Project for Louisiana
Reservoirs; and Dual Well Completion with Downhole Water Drainage,
Andrew K. Wojtanowicz, Louisiana State University
Assessment of Added Value to Wells in Louisiana - A Case Study; and
Identifying Reservoir/Well Candidates - A Method and Software;
William C. Kimball, Kimball and Associates
Understanding the Mechanism of Bypassed Oil in Water-Drive Reservoirs,
Juan Hernandez, Louisiana State University
SONRIS - Source Data on Reservoir/Well Candidates in Louisiana,
Chris Sandoz, Louisiana Department of Natural Resources
Watered-Out Well Stimulation Concept and Project
for louisiana Reservoirs
Many of the temporarily abandoned (shut-in) wells have become
uneconomic due to the high cost of producing and disposing of the water. Many of
these wells became uneconomic prematurely, leaving valuable oil in place. The
problem to be addressed is to identify those wells and derive a method for
assigning economic value to them. The cost of water can be considerable. Shell
Oil estimates the world average at $0.67/bbl. U.S. costs range from $0.17 to
$2.50/bbl. The components of this cost include lifting, pumping, separation,
de-oiling, filtering, and injecting. With known costs, those related to the
volume of water and those relatively fixed, and known revenues, the water-cut at
the economic limit can be calculated as well as the profit margin for an assumed
cost and price of oil for the purpose of deciding to produce, shut-in, or plug.
Given the age of the average on-shore well and the substantial fraction of the
domestic production coming from marginal wells, it is critical that the
productivity and valuation of marginal wells be assessed using technological
advances in downhole water control.
LSU has had a long-standing joint industry research effort to quantify and
optimize the technology of downhole water sinks (DWS) to enhance the value of
inactive wells with bypassed reserves. This includes modification of DWS
technology for removal of water damage, building a system for candidate
screening, developing a technical performance model and software for computing
the incremental recovery and the dollar value associated with those barrels. DWS
is a well completion and production technique for bottomhole water control in
reservoirs with bottom/edge water coning, cresting and under-running. It
controls water by diverting the water inflow pathway to the well using dual
completion and hydrodynamic mechanism of forced bottomhole water drainage.
LSU has constructed a pie-shaped sand pack physical model of a well with bottom
water drainage that visually demonstrates the displacement of the water with
forced downhole water drainage. It never gets back to the pre-breakthrough oil
saturation, however, due to the hysteresis of the oil/water relative
permeability.
Dual Well Completions with Downhole Water Drainage—DWS
Technology
The DWS technology requires a dual completion with the upper perforations in the
upper section of the oil zone, the lower perforations in the water zone below
the original oil-water contact. Oil is produced up the annulus. Water is
produced up the tubing, creating a reverse coning effect. Reservoir energy is
from the aquifer water drive. A variation would have a third set of perforations
in a lower water zone not in communication with the producing formation. The
water from the producing formation would be pumped by a downhole pump to the
lower zone, rather than to the surface.
Several early field tests of DWS (with no rigorous design) were published in the
mid 90s in Canada, East Texas, and Indonesia. In the Indonesia example, oil
production improved from 241 bbl/day and a water cut of 84% to 298 bbl/day and a
water cut of 18% in the oil stream, by draining 2,610 bbl/day of water. In a
designed application in Bakersfield, California, a computer model was used to
predict the oil recovery at various water withdrawal rates. The 10 year old well
was originally producing 6 bbl/day of oil at a water cut of 99%. Using a
designed DWS, water was withdrawn at 900 bb/day and the oil stream improved to
25 bbl/day at a 58% water cut. Similar results were achieved in Louisiana and
Venezuela.
Assessment of Added Value to Wells In Louisiana—A
Case Study
There are numerous shut-in wells in Louisiana, many of them
deemed not profitable due to high water cut. Implementing newer technology has
the potential to make a number of these profitable again and recover bypassed
oil. This was the case with the West Delta Block 84 field in Plaquemines Parish.
The field was discovered in 1955 at a depth of 14,500 feet. Ultimately the field
produced 9.8 million barrels of oil and 21 BCF of gas from 25 producing wells.
While there were several producing horizons, half of the production was from the
KEKF-R1 reservoir. The field was shut-in in 1990 and remained so through 2000. A
study and simulation was then done to evaluate the reserves and economics that
could be achieved with modern technology. The original plan was that the KE-1
and KF-1 formed a single communicating reservoir, the KEKF-R1, but the
waterflood of the KF-1 was ineffective in the KE-1 and reserves were bypassed.
A thorough reservoir study and characterization was conducted with engineering,
geological and geophysical data to quantify the original oil in place and where
and how much was remaining. The BOAST reservoir simulator was then used to run a
number of scenarios, including the remaining primary reserves from the one
producing well, secondary reserves recoverable through a new waterflood design
with existing wells, and enhanced reserves through a downhole water sink. The
optimum recovery was predicted by re-completing two producing wells in their
upper perforations, reinstating the flood in the KF-1 zone and instituting a
flood in the KE sand. The model predicted a future recovery of 1.7 million
barrels under this design. The last run compared the single well primary
recovery with and without DWS. Without DWS, the forecast oil was 27,700 barrels
while with DWS, recovery increased to 82,000 barrels.
Understanding the Mechanism of By-passed Oil in
Water-Drive Reservoirs
Early breakthrough of water, resulting in bypassed oil, occurs in bottom-water
systems and edge-water systems. This study examines the reasons for oil bypass
in edge-water systems and possible solutions. Frequently the problem is the
result of heterogeneities and the resulting viscous fingering. It can also be
caused by stratification and high horizontal permeability relative to vertical.
Even in relatively homogeneous reservoirs, water can under-run the oil and cause
coning. A reservoir model was built to study the effect. It became clear that in
situations of unstable flow from high production rates, there is a much higher
likelihood of early breakthrough and bypassed oil. Then possible solutions were
simulated, including a well penetrating the oil and water section and a dual
completion DWS. The study concluded that oil can be bypassed even in homogeneous
reservoirs, that water under-running and coning could cause as much as 62% of
the oil to be bypassed. Further, that oil bypassing is mainly stimulated by high
end point mobility ratios, low dip angles, and large well spacing and that the
best completion strategy in edge-water systems is the use of deep-penetrating or
dual-completed wells.
SONRIS—Source Data on Reservoir/Well Candidates in
Louisiana (Strategic Online Natural Resources Information System)
The Louisiana Department of Natural Resources has developed a very robust and
user friendly oil and gas well database and mapping system (very similar to that
developed by the Kansas Geological Survey). There are versions for users with
fast and slow internet connections that are publicly available at no charge
through their website
www.dnr.statela.us. The website provides
access to the electronic database, document images, and interactive GIS maps.
The type of information available includes well data and histories, well
engineering and tests, production, injection, operator information and lease
records. It allows the user to screen and sort the database by a number of
criteria from operator to field. Documents available include unitization orders,
well files, well logs and production reports. Data can be downloaded in
spreadsheet format. In the GIS mode, the selected wells can be spotted along
with geological features and political boundaries and the usual GIS features and
downloaded to the user.
Identifying Reservoir/Well Candidates—A Method and
Software
The objective of this methodology and software is to identify, screen and
prioritize worthwhile and economic marginal wells, even with incomplete or
missing information. This screening and "expert" system follows others that have
been used to screen for CO2-miscible displacement and selecting an
EOR method. It is designed to be a knowledge-based system "getting its power
from the expert knowledge that has been coded into facts, rules, heuristics and
procedures." The screening program is modeled after the PROSPECTOR program, an
expert system used to identify ore deposits and is designed to reduce the risk
of overlooking unfamiliar possibilities. The basic procedure is
Data input includes production, well tests and pressures, perforation depths,
core data, log data, seismic and geological models. Possible uncertain analysis
includes original oil in place, drive type, water problem, the cost of restoring
production, oil prices and ultimate recovery. Tools of analysis include
traditional discounted cash flow and risk assessment with Monte Carlo
simulation, decision tree, and options valuation using the Black-Scholes method.
Andrew K. Wojtanowicz
Louisiana State University
CEBA Building Room 3525
Baton Rouge, LA 70803-6417
Phone: 225-578-6049
Email:
awojtan@lsu.edu
Juan C. Hernandez
Louisiana State University
CEBA Building Room 3525
Baton Rouge, LA 70803-6417
Phone: 225-578-6691
Email:
jhern14@lsu.edu
William C. Kimbrell
Kimbrell & Associates
8867 Highland Rd. #106
Baton Rouge, LA 70808
Phone : 225-346-4700
Email :
lucror@aol.com
Chris Sandoz
Louisiana Department of Natural Resources
P.O. Box 94275
Baton Rouge, LA 70804-9275
Phone : 225-342-5540
For information on PTTC’s Central Gulf Region and its activities contact:
Mr. Robert H. Baumann, Managing Director
Center for Energy Studies, Louisiana State University
Energy, Coast and Environment Building
Nicholson Drive Extension
Baton Rouge, Louisiana 70803
Phone 225-578-4400 Fax 225-388-4541
E-Mail
rbaumann@lsu.edu
Disclaimer: No specific application of products or services is endorsed by PTTC. Reasonable steps are taken to ensure the reliability of sources for information that PTTC disseminates; individuals and institutions are solely responsible for the consequences of its use.
The not-for-profit Petroleum Technology Transfer Council is funded primarily by the US Department of Energy’s Office of Fossil Energy, with additional funding from universities, state geological surveys, several state governments, and industry donations.
Petroleum Technology Transfer Council, 16010 Barkers Point Lane, Ste 220, Houston, TX 77079
toll-free 1-888-THE-PTTC; fax 281-921-1723; Email hq@pttc.org; web
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