Salt Sheets Research Articles

Structure and Stratigraphy of the Calcasieu Lake Salt-Withdrawal Minibasin, Onshore Louisiana

ABSTRACT The Calcasieu Lake salt-withdrawal minibasin, central Cameron Parish, Louisiana, forms an E-W elliptical shape of ~15 mi by 10 mi. Complex normal-fault systems occur along the basin's periphery, commonly down-to-the-basin and flanking adjacent salt-cored uplifts, including Hackberry, Big Lake, Sweet Lake and Creole. Calcasieu Lake salt dome, a comparatively small piercement structure, occupies the basin's center. Sub-salt exploration is currently a major play offshore, yet sub-salt production beneath prominent overhangs of the Calcasieu Lake salt dome was established nearly a quarter century ago in October, 1966, producing ~6.0 BCFG and 300 MBO. Calcasieu Lake minibasin formation was preceded by emplacement of an allochthonous salt sheet into Upper Eocene Jackson strata, probably similar to the modern salt canopy offshore. Rapid sedimentary loading in the Oligocene caused salt remobilization, forming or enhancing peripheral salt uplifts, and an eventual salt weld to form. The Middle Miocene marked renewed sedimentation and basin formation, likely related to formation of the now-detached Calcasieu Lake salt dome by remobilization of salt from a central residual mound. In particular, a sandrich depositional sequence, up to 3,000 ft or more in thickness, is confined to the basin itself, without equivalent strata on peripheral highs. Local upturning of Middle Miocene basinal strata by the Calcasieu Lake salt dome allowed for the sub-salt production at Calcasieu Lake. The paucity of wells drilled along the basin's flanks leaves open many exploration opportunities to test these sand-rich strata as they onlap and pinch-out up the flanks. End_of_Record - Last_Page 409-------

ABSTRACT: Emplacement, Inflation and Folding of an Extensive Allochthonous Salt Sheet in the Late Mesozoic (Ultra-Deepwater Gulf of Mexico)

ABSTRACT: Emplacement, Inflation and Folding of an Extensive Allochthonous Salt Sheet in the Late Mesozoic (Ultra-Deepwater Gulf of Mexico)

Evaporites, brines and base metals: Low‐temperature ore emplacement controlled by evaporite diagenesis

Salt beds and salt allochthons are transient features in most sedimentary basins, which through their dissolution can carry, focus and fix base metals. The mineralisation can be subsalt, intrasalt or suprasalt, and the salt body or its breccia can be bedded or halokinetic. In all these evaporite‐associated low‐temperature diagenetic ore deposits there are four common factors that can be used to recognise suitably prepared ground for mineralisation: (i) a dissolving evaporite bed acts either as a supplier of chloride‐rich basinal brines capable of leaching metals, or as a supplier of sulfur and organics that can fix metals; (ii) where the dissolving bed is acting as a supplier of chloride‐rich brines, there is a suitable nearby source of metals that can be leached by these basinal brines (redbeds, thick shales, volcaniclastics, basalts); (iii) there is a stable redox interface where these metalliferous chloride‐rich waters mix with anoxic waters within a pore‐fluid environment that is rich in organics and sulfate/sulfide/H2S; and (iv) there is a salt‐induced focusing mechanism that allows for a stable, long‐term maintenance of the redox front, e.g. the underbelly of the salt bed or allochthon (subsalt deposits), dissolution or halokinetically maintained fault activity in the overburden (suprasalt deposits), or a stratabound intrabed evaporite dissolution front (intrasalt deposits). The diagenetic evaporite ‐ base‐metal association includes world‐class Cu deposits, such as the Kupferschiefer‐style Lubin deposits of Poland and the large accumulations in the Dzhezkazgan region of Kazakhstan. The Lubin deposits are subsalt and occur where long‐term dissolution of salt, in conjunction with upwelling metalliferous basin brines, created a stable redox front, now indicated by the facies of the Rote Faule. The Dzhezkazgan deposits (as well as smaller scale Lisbon Valley style deposits) are suprasalt halokinetic features and formed where a dissolving halite‐dominated salt dome maintained a structural focus to a regional redox interface. Halokinesis and dissolution of the salt bed also drove the subsalt circulation system whereby metalliferous saline brines convectively leached underlying sediments. In both scenarios, the resulting redox‐precipitated sulfides are zoned and arranged in the order Cu, Pb, Zn as one moves away from the zone of salt‐solution supplied brines. This redox zonation can be used as a regional pointer to both mineralisation and, more academically, to the position of a former salt bed. In the fault‐fed suprasalt accumulations the feeder faults were typically created and maintained by the jiggling of brittle overburden blocks atop a moving and dissolving salt unit. A similar mechanism localises many of the caprock replacement haloes seen in the diapiric provinces of the Gulf of Mexico and Northern Africa. Evaporite‐associated Pb–Zn deposits, like Cu deposits, are focused by brine flows associated with both bedded and halokinetic salt units or their residues. Stratabound deposits, such as Gays River and Cadjebut, have formed immediately adjacent to or within the bedded salt body, with the bedded sulfate acting as a sulfur source. In allochthon/diapir deposits the Pb–Zn mineralisation can occur both within a caprock or adjacent to the salt structure as replacements of peridiapiric organic‐rich pyritic sediments. In the latter case the conditions of bottom anoxia that allowed the preservation of pyrite were created by the presence of brine springs and seeps fed from the dissolution of nearby salt sheets and diapirs. The deposits in the peridiapiric group tend to be widespread, but individual deposits tend to be relatively small and many are subeconomic. However, their occurrence indicates an active metal‐cycling mechanism in the basin. Given the right association of salt allochthon, tectonics, source substrate and brine ponding, the system can form much less common but world‐class deposits where base‐metal sulfides replaced pyritic laminites at burial depths ranging from centimetres to kilometres. This set of diagenetic brine‐focusing mechanisms are active today beneath the floor of the Atlantis II Deep and are thought to have their ancient counterparts in some Proterozoic sedex deposits. The position of the allochthon, its lateral continuity, and the type of sediment it overlies controls the size of the accumulation and whether it is Cu or Pb–Zn dominated.

Salt extrusion at Kuh-e-Jahani, Iran, from June 1994 to November 1997

Abstract Kuh-e-Jahani is one of the largest extrusions of salt currently active in the Zagros mountains. Salt rises from about 4 km below sea level to nearly 1.5 km, above, where, unable to support its own weight, it spreads over the surrounding scenery in a process responsible for present and past allochthonous salt sheets elsewhere. We report vertical movements and apparent horizontal displacements of 43 markers dispersed over this mountain of salt for 4.5 years in three consecutive intervals, the first of 18 months and two others of 12 months. The geometry and inferred flow rate of the salt changed between surveys emphasizing that the gravity spreading is not steady. Our field readings of the dimensions and velocities of the salt at Kuh-e-Jahani are used to tune a simple numerical model and constrain the viscosity of the salt to between 10 16 and 10 17 Pa s −1 , its rate of surface dissolution to 2–3 cm a −1 , and its rate of rise out of its orifice at 2–3 m a −1 for c. 55 ka. These results imply that vigorous extrusion of salt at Kuh-e-Jahani is probably close to evacuating its deep source and that this mountain will soon begin to waste as salt dissolution overtakes extrusion. This progress report is warranted because our results have significant implications for sophisticated engineering in salt.

Deepwater reservoir prediction using seismic and geomechanical methods

In deepwater exploration, due to a lack of well information, seismic data become the main means of predicting reservoirs and hydrocarbons. AVO is the most popular method to detect hydrocarbons. However, factors such as pressure, lithology, and thin‐bed effects can cause false AVO effects. The deepwater Gulf of Mexico, in addition to these complex factors, has simple‐to‐complex salt sheet morphologies. The evolution of these salt sheets through time significantly influences the accumulation and migration pathways of deepwater sediments. In this article, we propose that the hydrocarbon migration pathway and seal integrity can be better understood by combining information about pore‐fluid pressure, effective stress, lithology, and seismic energy attenuation.

Data Visualization Centers

Published in Oil & Gas Executive Report, Volume 2, Number 2, 1999, pages 32-35. Early December 1998, Veritas DGC Inc. unveiled its new, state-of-the-art Data Visualization Center in Houston. The center is designed to help Veritas' marine-data-library clients quickly evaluate massive amounts of 3D-seismic data in a collaborative environment, greatly decreasing the overall cost of processing and interpreting seismic images in critical deepwater Gulf of Mexico blocks. Designed to be a true working environment for teams of geoscientists, the center allows multiple groups to work simultaneously in the main visualization theater and four satellite workrooms to solve complex interpretation problems through sophisticated manipulation of 3D volumes. The result is improved interpretation, with higher confidence, in a shorter time frame. Deepwater Subsalt Plays Are the Driver The driver behind the investment Veritas has made in the Data Visualization Center is the subsalt deepwater Gulf of Mexico plays that pose special processing and interpretation problems for geoscientists. The acoustic properties of salt tend to distort the seismic images of geologic structures that lie below or adjacent to the domes and sheets of salt found in the deep waters of the gulf. To derive the best possible images, a technique known as prestack depth migration should be applied to the data. However, this technique is extremely time-consuming and computing-intensive and, therefore, quite expensive. As recently as 3 years ago, an internal study suggested that, with the then current computing resources available, applying prestack depth migration to an average-sized 3D survey could take several years to compute. Increases in processor speeds and improvements in supercomputing architecture have cut that time to months. Still, the cost in computing time alone makes application of this technique to proprietary data daunting for individual clients, not to mention the preparation and interpretation that also are required. These factors are complicated further by the fact that very few individuals have combined experience in prestack depth migration and subsalt interpretation.

Abstract: Numerical Models of Salt Sheet Deformation Driven by Various Rates and Patterns of Sedimentation 

Abstract: Numerical Models of Salt Sheet Deformation Driven by Various Rates and Patterns of Sedimentation 

Abstract: Spatial Variations in Formation Water Salinities, South Pelto and South Timbalier Areas, Eastern Louisiana Continental Shelf 

ABSTRACT Spatial variations in pore fluid pressure, temperature, and salinity were determined from borehole logs along a 100-km long north-south transect from the Louisiana coastline to the shelf edge in the South Pelto and South Timbalier outer continental shelf areas to help identify driving forces and pathways of regional fluid flow and solute transport, information potentially useful also in identifying pathways of hydrocarbon migration. The Pleistocene to Upper Miocene sediments were deposited in fluvial, deltaic, and open marine environments and hence contained waters of fresh to brackish to normal marine salinities, <1 to 35 g/L, at the time of their deposition. Most of these sediments, however, now contain hypersaline fluids having salinities of up to 140 to 170 g/L. Exceptions are shallow Upper Pleistocene fluvial and deltaic sediments that contain fluids less saline than sea water, even though this section is now overlain by seawater. These shallow brackish fluids probably represent the remnant of a regional freshwater lens formed during the last low-stand of sealevel. A regional plume of water having salinities in excess of 140 g/L dips gulfward to the shelf edge at depths of 3 to 5 km below the seafloor. The locus of this plume is within the sandier Pliocene section. Potential sources of dissolved salt within this plume include updip shallow salt structures and the underlying remnants of an allochthonous salt sheet at depths of approximately 6 km. Regional faults in the area may have acted as vertical conduits for upward transport of brines. Down-dip fluid flow was presumably in part gravity-driven. The distal end of this regional salinity plume near the shelf edge is now highly overpressured, and fluid flow should be in the opposite direction, i.e., updip. Hence, this part of the regional salinity structure was probably established prior to over pressuring. The results of this study establish the dynamic nature of formation water flow which has occurred in the outer continental shelf. Further work is now needed to quantify the magnitude of the driving forces and rates of these processes.

The Evolution of Allochthonous Salt Along a Megaregional Profile Across the Northern Gulf of Mexico Basin

Sequential restorations of a north-south megaregional cross section across the north-central Gulf of Mexico Basin from east-central Louisiana to the abyssal plain define a dynamic, complex history of sedimentation, salt flowage, and salt evacuation. Proprietary composite seismic profiles (590 km), 33 wells, and published depth-to-basement maps were used to constrain the section in depth. Thirteen sequential structural restorations, incorporating both decompaction and isostatic subsidence (thermal and tectonic), were then constructed from the Late Cretaceous to the Holocene. The restorations highlight and constrain a protracted history of deformation that is primarily controlled by gravity and the progradation of Cenozoic sediments over salt. Early stages of the tectonic history of the northern Gulf of Mexico Basin were related to differential thermal subsidence resulting from Early-Middle Jurassic rifting. During the Cenozoic, the evolution of the basin was dominated by the influx of large clastic depocenters, which caused the basinward evacuation of autochthonous Jurassic salt. Salt extrusion from the autochthonous layer was accomplished by inclined salt bodies, which flowed into salt glaciers or sheets near the sea floor. Evacuation of allochthonous salt layers provided significant sediment accommodation, and unusually thick sedimentary sections were deposited, such as the Terrebonne Trough of southern Louisiana (3-7 km of Miocene strata). Salt sheet formation and evacuation occurred progressively basinward through time in response to basinward shifts of major Cenozoic sedimentary depocenters. As a salt sheet neared complete evacuation, the underlying autochthonous salt layer would begin to evacuate, providing additional sediment accommodation that caused autochthonous salt flowage basinward, and the formation of the next allochthonous salt sheet basinward of the depocenter. The area of autochthonous salt progressively decreased through time and currently represents at most 45% of its maximum along this transect. The total area of salt through time was more stable, with variations of only 30% from its maximum. This relationship is a function of lateral salt flow into and out of the plane of section, and possible salt dissolution. The restorations indicate that very little translation or extension (1.46%) occurred at the autochthonous salt level during the evolution of the basin. The majority of translation or extension occurred above allochthonous salt sheets (25%) and was compensated laterally by salt flow. Displacements above allochthonous salt sheets were driven by gravitational instabilities caused by the slope gradient.

The Evolution of Allochthonous Salt Systems, Northern Green Canyon and Ewing Bank (Offshore Louisiana), Northern Gulf Of Mexico

The discovery that major episodes of subhorizontal, allochthonous salt flow have occurred in the Gulf of Mexico Basin requires a means of quantifying the evolution of allochthonous salt and associated structures to conduct both basin and petroleum systems analyses. Sequential structural restorations of allochthonous salt systems provide an evolving structural framework for integrating stratigraphic, geophysical, and geochemical data sets. In this study, interpretation of more than 10,000 km (6200 mi) of multifold seismic data, and sequential restoration of eleven profiles, were used to determine the geometry and evolution of allochthonous salt structures within Ewing Bank and northern Green Canyon protraction areas. The results illustrate the complex geometry of the multilevel salt system and the types of interactions between counterregional and salt-stock canopy models of allochthonous salt system evolution. Sedimentary loading is accommodated by salt sheet extrusion, gravity spreading, gravity gliding, extension, salt evacuation, and contraction. Salt geometry commonly changes dramatically through time because it provides much of the accommodation for sediments and absorbs much of the extension and contraction within its overburden. The positioning and kinematics of extensional and contractional structures are controlled by salt body geometries, salt system interactions, and, most importantly, the topography of the base salt or equivalent salt weld. The structural restorations also constrain the timing of salt sheet and salt weld formation and document the positive correlation among sedimentation rates, salt flow, and structural deformation. Cross-sectional salt area generally decreases through time in areas of salt evacuation and minibasin formation, but increases in sections crossing growing salt bodies. Three-dimensional restoration is required to determine the three-dimensional kinematics and balance of allochthonous salt tectonics.

Abstract: Subsurface Controls on Seafloor Vent/Seep-Related Geology, Deepwater Gulf of Mexico: Initial Results

ABSTRACT Within the deepwater Gulf of Mexico hydrocarbon province, improved seismic acquisition and processing have provided new comprehensive data sets for defining relationships between sediments, salt, and faulting. Sequential restoration techniques and physical modeling have advanced our understanding of how salt-sediment configurations evolve to their present configurations. Coincident with this emerging new subsurface framework, high quality data for determining surficial geology and the processes that impact it have also been collected, primarily for geohazard evaluations. The study reported here represents the initiation of the first comprehensive attempt to link high-resolution surficial geology to controlling subsurface geology and processes. Special attention is focused on seafloor responses forced by the surficial venting/seepage of hydrocarbons, other fluids, and sediment within a northern Green Canyon-Ewing Bank area covered by 2-D and 3-D seismic and previously studied extensively. Sixteen surface sites accompanied by high-resolution acoustic data and ground truth observations/samples (acquired by research submersible) represent the surface data set. Initial results of combining subsurface and surficial data sets indicate a first-order relationship with faults, conduits for gas and fluid flux to the seafloor. Faults linked to subsurface salt support the most numerous and active vent/seep-related features, perhaps because of frequent salt movements that open conduits to the surface by fault activation. Salt geometry and proximity to the seafloor are important factors. Salt stocks focus fluids and gases vertically while venting/seepage occurs around the edges of shallow salt sheets. Topography on the surface of deep salt sheets (>1.5s TWT) and other types of salt bodies is an important determinant of numbers and types of conduits to the seafloor.

Extrusions of Hormuz salt in Iran

Abstract This work illustrates that Lyell’s approach to inferring geological processes from field observations can be improved by using field measurements of their rates to scale dynamic models. A controversy in the 1970s about whether crystalline rock salt can flow over the surface echoed an earlier controversy resolved with Lyell’s help about whether ice could flow and carry exotic blocks. This work argues that the external shapes, internal fabrics and structures and rates of flow of current salt extrusions in the Zagros Mountains are keys not only to understanding past and future extrusion of salt, but also to the extrusion of metamorphic cores of orogens. Salt is shown to extrude first in hemispherical domes, which later spread to the shapes of viscous fountains until they are isolated from their source. They then rapidly assume the shapes of viscous droplets, which they maintain until they degrade to heaps of residual soils. Salt emerges as a linear viscous Bingham fluid, and strain rate hardens downslope to a power-law fluid ( n = 3) beneath a thickening carapace of brittle dilated salt. The velocities of salt constrained in emergent diapirs by measurements of extruding salt sheets in Iran are remarkably rapid compared with rates estimated for buried equivalents elsewhere in or under which it is planned to store nuclear waste or to extract hydrocarbons.

Abstract: Evolution of Extensive Salt Sheets in the Louisiana Shelf and Coast, Northern Gulf of Mexico

Abstract: Evolution of Extensive Salt Sheets in the Louisiana Shelf and Coast, Northern Gulf of Mexico

Physical Modeling of Structures Formed by Salt Withdrawal: Implications for Deformation Caused by Salt Dissolution

By creating 15 physical models, we investigated deformation above subsiding tabular salt, salt walls, and salt stocks. Dry quartz sand simulated a brittle sedimentary roof above viscous silicone representing salt. The modeled diapiric walls had linear planforms and rectangular, semicircular, triangular, or leaning cross sectional shapes; the stock was cylindrical. In models where the source layer (or allochthonous salt sheet) was initially tabular, a gentle, flat-bottomed syncline bounded by monoclinal flexures formed above a linear zone where the silicone was locally removed. Above all subsiding diapirs, the deformed roof was bounded by an inner zone of steep, convex-upward reverse faults and an outer zone of normal faults. Above subsiding diapiric walls, extensional and contractional zones were balanced. Above the subsiding salt stock, conical, concentric fault zones comprised inner reverse faults and outer normal faults. Sediments were added both before (prekinematic) and during (synkinematic) salt withdrawal. In entirely prekinematic roofs, reverse fault zones and normal fault zones both widened with time. Reverse faults propagated upward from the corners of the withdrawing diapirs. New reverse faults formed in the footwalls of reverse faults, each nearer the center of the deepening roof trough. Conversely, new normal faults formed successively outward from the sagging trough. Synkinematic deposition retarded faulting, but the pattern of inner reverse and outer normal faults was repeated; however, reverse faults formed successively outward, whereas normal faults formed inward. New conceptual models suggest that salt dissolution forms similar structures to those physically modeled for salt withdrawal. The appropriate physical models resemble natural dissolution structures above tabular salt. Extension alone above diapirs is not caused merely by salt withdrawal or dissolution, but by regional extension or active diapirism.

Abstract: Structural Overview of the Deepwater to Ultra Deepwater Northern Gulf of Mexico Area based on a Recent Regional Seismic Program

This interpretation project is based on an extensive 2-D seismic program (known in the industry as Phase 45) that consists of 60,000 line miles, covering the central and western parts of the deepwater and ultra deepwater northern Gulf of Mexico region. This paper concentrates on the central part of the project area (Garden Banks, Keathley Canyon, Green Canyon and Walker Ridge) covering 38,000 mi 2 and utilizing a 4 by 4 mile recently acquired seismic grid. Four horizons have been interpreted: top and base salt along with the Discoaster surculus (DS - approximate top Pliocene) and Discoaster berggrenii (MDB - approximate top Miocene) horizons. Abundant well data, in the form of electric logs, micropaleontology and velocity data, were available in the northern Green Canyon and Garden Banks regions. All interpretation was performed on a workstation. The mapping of these horizons shows how salt geometry changes moving from north to south. Around the continental shelf break a series of coalesced but discrete allochthonous sheets with significant intersalt basins occur. To the south a virtually continuous salt sheet, with numerous suprasalt basins, develops out to the edge of the present day northern Gulf of Mexico salt province, marked, in part, by the Sigsbee Escarpment. In these distal parts of the salt province, particularly in the Walker Ridge area, there is comparatively little sedimentary cover above the salt except where suprasalt basins have locally depressed salt. These basins have both symmetric and asymmetric geometries. The Mio-Pleistocene section is oilen railed above the allochthonous salt in these basins and seems to override deeper Mio-Pleistocene identified outboard of, and carried beneath, salt.

Subsalt Play, Gulf of Mexico: A Review

Exploration for deep-water sandstone reservoirs beneath allochthonous salt in the Gulf of Mexico represents a major new frontier play in North America. More than 30 wells thus far have been drilled with subsalt targets, resulting in 8 discoveries, at least 3 of which are commercial and 3 that have reserves of 100 million bbl oil equivalent or more. Reservoirs consist of Miocene-Pleistocene sandstones deposited in submarine fan channel system environments on the paleoslope, where salt deformation has a complex late Cenozoic history. Salt sheets exist at various stratigraphic levels and have overridden sandstone fairways on the present-day outer continental shelf and upper slope, where water depths are moderate and where pipeline and other infrastructure facilities already exist. Potential reserves for the subsalt play have been estimated at 1.2 billion bbl of oil and 15 Tcf* gas from 25 or more significant fields. Recent success in the subsalt play has depended upon (1) advances in 3-D (three-dimensional) seismic acquisition and processing (in particular, 3-D prestack depth imaging) and (2) improved geologic modeling of salt deformation and depositional systems. In addition, better understanding of the drilling risks frequently encountered in penetrating salt sheets has been important. Progress in all these areas ismore » certain to continue and will result in significant new tools and techniques for exploration as a whole.« less

Sedimentary Loading of Salt Sheets with and without Subsalt Extension: Results from Finite-Element Modeling: ABSTRACTS

Sedimentary Loading of Salt Sheets with and without Subsalt Extension: Results from Finite-Element Modeling: ABSTRACTS

Comparison and Results of a Borehole Gravity Survey with Core and Log Data through an Allochthonous Salt Sheet in Ship Shoal South Additions, Offshore Louisiana : ABSTRACTS

Comparison and Results of a Borehole Gravity Survey with Core and Log Data through an Allochthonous Salt Sheet in Ship Shoal South Additions, Offshore Louisiana : ABSTRACTS

Extensive Salt Sheet Provinces at Louisiana Shelf, Gulf of Mexico : ABSTRACT

Extensive Salt Sheet Provinces at Louisiana Shelf, Gulf of Mexico : ABSTRACT

Abstract :Gulf of Mexico Subsalt Deformation Zones: Weak Formation Integrity Rather than Anomalous High Pressure Zones

ABSTRACT A study of pressure gradient profiles, mudweights and drilling report data from subsalt wells in the Gulf of Mexico indicates that reported shale deformation zones underneath salt are not anomalously high pressure zones, but rather, low formation integrity zones. Pore pressure gradients were calculated from shale transit time and resistivity logs, and supplemented by detailed drilling reports and available wireline pressure test data for 23 subsalt wells located in the shelf and deepwater areas of the central Gulf of Mexico. The study indicates those pore pressure gradients beneath salt sheets remain constant from deformation zones into the deeper subsalt section and are moderate to high (16.5-20 kiloPascals/meter, kPa/m, 14-17 pounds/gal mud weight, ppg) but not anomalously high for the depth and age of the subsalt section. Unusually low shale resistivities found in sections beneath salt indicate higher pore pressure gradients, but sonic values from the same intervals do not corroborate the higher pressures, suggesting that the low shale resistivities may be caused instead by highly saline formation brines. Lost circulation and well flow problems encountered when drilling out of salt indicate that some subsalt deformation zones have low formation integrity. Results of this study do not support current subsalt exploration models that evoke hydrocarbon bearing fluids migrating upward to subsalt reservoirs through an undercompacted, high pressure shale deformation zone. Instead, some subsalt sections appear to be unstable zones of lower fracture strength with implications for both sealing capacity and subsalt well design. New models are needed to predict pressure and fracture gradient in subsalt deformation zones, to evaluate migration and seal risk, and ensure better design of subsalt wells.