Oil & Natural Gas Projects
Exploration and Production Technologies
Well Integrity Assurance for Subsalt, Near-Salt Deepwater Gulf of Mexico
This project is part of the Natural Gas and Oil Technology Partnership, Oil
and Gas Recovery Technology. The program partners the National Laboratories
with petroleum industry organizations to develop advanced technologies for improved
natural gas and oil recovery.
The goal of this Joint Industry Project (JIP) is to identify, quantify, and
mitigate potential well integrity issues associated with subsalt and near-salt
deepwater Gulf of Mexico (GoM) reservoirs.
Sandia National Laboratory (SNL)
The work conducted in this project modeled the timing and magnitude of salt
forces on well casings. Computer models were developed that enabled understanding
and prediction of the complex geomechanical behavior of subsurface formations.
From this work, identification of optimal well paths and locations of potential
borehole instability could be determined.
The improved casing design developed in this project has been applied in two
of the five largest oil fields ever discovered in the deepwater GoM-Thunder
Horse North and Mad Dog fields operated by BP America with multiple partners.
The more-efficient well casing design implemented in Thunder Horse North field
resulted in a well construction cost reduction of over $30 million. Applied
to other potential wells in the GoM, the improved understanding of well casing
design is expected to significantly reduce drilling and completion costs.
The cost of drilling and completing a single well in the deepwater GoM can be
as much as $50-100 million. Integral to the successful economic development
of the area is that the lifetime of a well spans 10-20 years. This research
has enabled development of a more-efficient casing design for oil and gas well
construction in the GoM that reduces the risk of well failures. Such innovative
technology will help to produce efficiently the vast remaining discovered and
undiscovered oil and gas resources in the GoM.
Significant cost savings result from efficient casing designs. The appropriate
design specifies what must be done for well casing stability but also what operations
do not add to the stability or longevity of the well and can be omitted. For
example, the analyses conducted in this project show that it is not always necessary
to cement the casing/borehole annulus through the salt because the subsequent
uniform loading is insufficient to substantially deform the casing. This poses
no threat to drilling operations or impingement on the inner casing string in
the long term and results in considerable cost savings. However, if hole quality
is poor, a cemented annulus is necessary, as the cement effectively transforms
the potentially nonuniform loading situation into one of uniform loading.
Other significant benefits can accrue from quantifying the magnitude and timing
of salt loading. Difficult cementing jobs and liner tiebacks can be omitted,
and a more aggressive well design adopted. The simplified well design and the
elimination of potentially troublesome operations leads to millions of dollars
in cost savings in individual wells.
The deepwater GoM is the most active deepwater region in the world and provides
some of the greatest challenges in scope and opportunity for the petroleum industry.
The region is estimated to contain undiscovered recoverable resources of nearly
30 billion barrels of oil. By 2005, as much as 67 percent of the daily oil production
and 26 percent of the daily gas production in the gulf will come from deepwater
Huge formations of salt, thousands of feet thick, underlie much of the deepwater
areas-and these salt formations deform plastically due to forces caused by sand
and shale formations. The complex salt tectonics, coupled with the extreme water
depths (as great as 10,000 feet) and reservoir depths, necessitate high development
costs, and innovative technology is required to bring these fields on stream.
Difficulties, such as collapsing a well during drilling, can be encountered
near salt formations because of the changing stresses associated with salt deformation.
Then, after a well penetrating a salt formation is cased and completed, the
slow movement of salt over the field lifetime may cause premature failure of
the casing through shears and twisting.
Although the behavior of salt is well described from a geologic standpoint,
our knowledge is poor of the influence of salt deformation at both the well
and reservoir scale (both temporally and spatially). However, the nature of
the deformation occurring during field life is considered more likely to be
detrimental than beneficial. In subsalt reservoirs in which the salt is laterally
extensive and in close vertical proximity to the reservoir formations, there
may a tendency for the salt to flow laterally to fill "subsidence bowls"
formed by compaction of the reservoir interval. This lateral movement could
jeopardize the integrity of well casings drilled through the deforming salt
because of anisotropic loading and induced shears at the bounding formation
Assuring the integrity of subsalt wells in the deepwater of the GoM throughout
the fields life is a major drilling engineering challenge. The consequences
of well failures may result in billions of dollars in remedial costs and lost
production. On the other hand, the costs associated with overly conservative
well design are significant, which motivates systematic analyses of casing loading
for scenarios of interest.
Simplified hole-closure and casing-design guidelines for salt, many developed
for the Western U.S. Overthrust Belt, are not appropriate for the relatively
pure, slow-moving halite found along the Gulf Coast.
The research was designed to enhance the understanding of the stress fields
associated with salt diapirs and the forces that subsurface salt bodies exert
on oil and gas wells. This work provides the basic research to develop technologies
that counter the effects of salt deformation. The project is designed as a JIP,
with cofunding by DOE and an industry consortium.
The study assessed the timing and magnitude of salt loading on well casings,
including the behavior of reservoir rocks during oil production, and on in-situ
stresses in formations adjacent massive salt diapirs. Laboratory experiments
were conducted to constrain the constitutive behavior of deepwater GoM salts
and to compare their behavior with that of salts encountered during oil and
gas exploration and production in the U.S. Western Overthrust Belt and in the
North Sea. Computer models were developed to understand and predict the complex
geomechanical behavior of subsurface formations and salt diapirs during oil
The computer modeling increased understanding of the geomechanical considerations
needed to drill through or next to massive salt sections, by identifying optimal
well paths and locations of potential borehole instability. The study also identified
forces on well casings over the field lifetime, resulting in a modified design
for well construction. The project performer examined the role of cement between
the casing and wellbore and made recommendations on when and how cement should
be used to alleviate casing stresses resulting from salt flow that could lead
Current Status (October 2005)
The project is complete.
Project Start: April 12, 2001
Project End: April 11, 2005
Anticipated DOE Contribution: $590,000
Performer Contribution: $1,175,000 (67% of total)
NETL - Paul West (firstname.lastname@example.org or 918-699-2035)
SNL -Joanne Fredrich (email@example.com or 505-844-2096)