Compaction Subsidence Research Articles

Origin and late quaternary tectonism of a western Canadian continental shelf trough

Analyses of high resolution and multi-channel seismic profiles from the central continental shelf of western Canada ascribe a late Quaternary glacial origin to large-scale troughs. Along the margins of Moresby Trough, one of three large-scale cross-shelf bathymetric depressions in Queen Charlotte Sound, seismic profiles within Quaternary sediments show a divergence of reflectors, thickening and folding of seismic units, and concavity of reflectors suggestive of drag. Compactional subsidence, growth faulting, and compaction faulting are also observed. Fault traces commonly terminate below the seabed. Deformation of Quaternary sediments due to faulting is plastic in nature and maximum offset of reflectors is 2.5 m. The observed Quaternary deformation appears to be a product of rapid deposition, loading and subsidence of late Quaternary sediment, which is unrelated to seismic activity. In addition, Quaternary faulting was probably activated by post-glacial loading and isostatic rebound of consolidated Tertiary strata along the margins of continental shelf troughs. The presence of mass movement (slump or debris flow) deposits overlying lithified Tertiary strata along the flanks of Moresby Trough provides the only evidence of seismic activity in the study area. The lack of a mud drape over these deposits implies a late Holocene age for the timing of their emplacement. The Quaternary troughs are incised into Tertiary-aged sedimentary fill of the Queen Charlotte basin. Previous workers had interpreted seafloor escarpments paralleling the trough margins to indicate that the location of Moresby Trough was controlled by renewed or continued activity on Tertiary-aged faults. A multi-channel seismic line across Moresby Trough shows that such an escarpment on the seafloor does not correlate to faults either in the Tertiary basin fill or the underlying basement. Tertiary reflectors are continuous underneath Moresby Trough; the seafloor escarpment is an erosional feature and was not created by reactivation of Tertiary structures. Trough erosion and subsequent fill (up to 175 m thick) are entirely of Quaternary age.

Reservoir Compaction of the Belridge Diatomite and Surface Subsidence, South Belridge Field, Kern County, California: ABSTRACT

Abstract Surface subsidence due to reservoir compaction during production has been observed in many large oil fields. Subsidence is most obvious in coastal and offshore fields where inundation by the sea occurs. Well known examples are Wilmington field in California and Ekofisk field in the North Sea. In South Belridge field the Belridge diatomite member of the late Miocene Reef Ridge Shale has proven prone to compaction during production. The reservoir, a high porosity, low permeability, highly compressive rock composed largely of diatomite and mudstone, is about 1000 ft thick and lies at an average depth of 1600 ft. Reservoir compaction within the Belridge diatomite due to withdrawals of oil and water in section 12, T28S, R20E, MDBM the estimated peak subsidence rate reached -7.50 ft/yr in July 1985, after 1 yrs of production from the Belridge diatomite reservoir. Since production from the Belridge diatomite reservoir commenced in February, 1984, the surface of the 160 acres producing area has subsided about 12.50 ft. This equates to an estimated reservoir compaction of 30 ft in the Belridge diatomite and an average loss of reservoir porosity of 2.4% from 55.2% to 52.8%. Injection of water for reservoir pressure maintenance in the Belridge diatomite began in June, 1987, and has been effective in mitigating subsidence and repressurizing the reservoir to near-initial pressure. An added benefit of water injection has been improved recovery of oil from the Belridge diatomite by waterflood. The operation of four other water injection projects in South Belridge Field in the Belridge diatomite reservoir suggests that reservoir compaction and surface subsidence is a common occurrence in the field.

Evolution of Atchafalaya lacustrine deltas, south-central Louisiana

The entrenched Pleistocene/Holocene Mississippi alluvial valley was cut during the last low sea-level stand, and alluviation of the entrenched valley occurred during the Holocene sea-level rise. Regional Gulf Coast structures (salt domes and faults) have strongly influenced the morphology of the valley. Valley paleotopography has controlled depositional patterns and locations of major river courses, as well as partially isolated large interdistributary basins within the alluvial/deltaic plain. Interdistributary basin formation is further enhanced by distributary channel progradation, switching, and abandonment, in conjunction with compactional subsidence of the alluvial plain surface. Geomorphology and sediment cores from the Atchafalaya Basin, Louisiana, revealed that this basin has alternately accumulated fine-grained organic-rich sediments and terrigenous clastic-dominated meander-belt and lacustrine deposits. Basin subsidence and the presence of an active distributary channel in the basin are major determinants of the lithology of the sedimentary-fill. Prograding lacustrine deltas of the Atchafalaya River are the primary mechanism for filling the Atchafalaya Basin. These upward-coarsening deltas are relatively thin (3 m) but are areally extensive (tens to hundreds of kilometers), and because they occur so frequently during the infilling process, they account for a significant volume of the basin sequence. The Atchafalaya Basin sequence documents lacustrine deltaic episodes dating from the early Holocene (Maringouin and Teche deltas) to the present (Atchafalaya delta). Continued development of the Atchafalaya River will rework portions of the backswamp and lacustrine deposits into meander-belt deposits. Upon complete filling of the Atchafalaya Basin, sediment will mostly bypass the basin and become deposited in the marine delta in Atchafalaya Bay.

Controls on peat accumulation in the Permian Vryheid Formation in a part of northern Natal, South Africa

The early Permian Vryheid Formation is a fluviodeltaic tongue of sediment deposited on the passive northern margin of an asymmetric, intracontinental linear trough (Karoo basin). In the study area these strata attain a maximum thickness of about 270 m, comprising three informal lithostratigraphic members (Lower zone, Coal zone and Upper zone). The Coal zone is characterized by arkosic, coarse to very coarse, pebbly sandstones and subordinate fines arranged in upward-fining sequences, many of which are coal-capped. These units are interpreted as distal outwash fan deposits. Sedimentation patterns in the Upper and Lower zones are dominated by superimposed upward-coarsening sequences representing repeated wave/fluvially-dominated fan delta progradation. Peat accumulation in the cool, seasonal climate which prevailed during Vryheid Formation sedimentation was slow. Significant peat thicknesses were deposited only in areas of low basin/compaction subsidence in the Coal zone during a period of general stability. Extensive upper delta plain and alluvial plain peats formed on broad platforms created by abandonment of braided channel systems. The thickest peats accumulated in raised swamps where vegetation-stabilized contemporaneous channels promoted a high water table. Peat erosion by later channel activity was slight since channel widening rather than stream-bed erosion prevailed. Coals thin, split and contain more ash near loci of contemporaneous channel activity. Upper delta plain coals were not marine-influenced. Some lower delta plain coals also formed on broad abandoned deltas and are likewise extensive. Rapid compaction subsidence rates attracted channel activity or marine incursions and the seams are thin. Peats also accumulated in restricted emergent interdistributory bays during delta construction. These coals are thin, discontinuous, marine-influenced and contain numerous clastic partings.

Subsidence Measurements Around Geopressured-Geothermal Test Sites in Southwestern Louisiana: ABSTRACT

First-order elevation surveys of benchmark networks established around geopressured-geothermal test sites in southwestern Louisiana have been conducted before, during, and after testing to determine the potential for growth fault activation and compactional subsidence due to depressurization of geopressured-geothermal reservoirs. Subsidence increased to the south along the line from Lafayette, Louisiana, to the Parcperdue test site as expected as this line descends the flank of the Iberian structural axis. Subsidence varied for benchmarks around the site and by yearly rate although the yearly pattern was consistent. During the period from 1980 to 1982, the benchmarks on the site may have subsided more than other benchmarks due to compaction of soils by drilling and testing equipment. Motion rates for benchmarks around the Sweet Lake geopressured-geothermal test site south of Lake Charles, Louisiana, were highly variable during the period from 1980 to 1984 and were less variable from 1984 to 1986. These rates and patterns of motion may reflect the instability of the Sweet Lake salt dome located south of the prospect but do not correlate with the subsidence expected from geopressured-geothermal development. Relevelings of the benchmark network around the Gladys McCall geopressured-geothermal test site on the coast illustrate generally decreasing subsidence frommore » west to east and slight variations among benchmark motions. The greatest subsidence occurred along the well access road and at the well site from 1981 to 1984 coincident with well-site preparation and drilling.« less

Sedimentary Environments, Evolution, and Stratigraphic Framework of Laterally Prograding Transgressive Barrier Complex: Timbalier Island, Louisiana: ABSTRACT

Timbalier Island is a beach-ridge barrier flanking the abandoned late Lafourche deltaic lobe on the south-central Louisiana coast. Twenty-five vibracores (5-9 m) and 12 short cores were acquired in a variety of sub-aerial, intertidal, and subaqueous environments of this barrier complex. These cores, coupled with detailed shoreline change maps, indicate that the island's migration, evolution, and stratigraphy are complex and variable. Since 1887, Timbalier Island has laterally migrated approximately 6 km to the northwest, while the adjacent inlet (Cat Island Pass) migrated 2.5 km. Due to this extensive lateral progradation at the western end of the island, the following sequence is found: (1) bay/lagoon, (2) lowerspit platform/shoreface, (3) upper spit platform/shoreface, (4) foreshore, (5) backbeach, and (6) dune. An upward decrease in burrowing and increase in physical sedimentary structures, grain size, percent sand, and sorting are observed. None of the cored sequences resemble the tidal inlet channel-spit platform models observed elsewhere but, instead, mimic regressive shoreface sequences. During the island's evolution, the interior beach ridges subsided in response to compactional subsidence and became vegetated by a Spartina and Avicennia (mangrove) marsh. In this central-interior part of the island, the progradational sequence is capped by an aggradational (0.5-1 m thick) marshmore » deposit.« less

A coal depositional model for the Durham Coal Measures of NE England

The Upper Carboniferous (Westphalian) Coal Measures of the Durham coalfield were deposited on a broad, flat, deltaic plain. In early Westphalian A times, a lower delta plain setting prevailed, evolving through southward deltaic progradation into an upper delta plain by mid-Westphalian A. Detailed facies analysis of large, opencast exposures, supported by extensive subsurface data, has shown that a hierarchy of depositional controls operated across the Durham area during Westphalian times; (i) on the large scale, depositional geometry was controlled by patterns of major delta progradation and switching; (ii) on the medium scale, by a combination of structurally and compactionally induced subsidence, and (iii) on the small scale, by local sedimentary processes and subsidence patterns. These observations form the basis of a coal depositional model for the Durham Coal Measures, which predicts that the thickest coals are to be found in upper delta plain domains controlled by compactional subsidence and not underlain by substantial channel sandstones. This model may also be applicable to other coalfields of northern England, and to ancient delta plain sequences elsewhere in the world.

Monitoring Local Subsidence in Areas of Potential Geopressured Fluid Withdrawal, Southwestern Louisiana: ABSTRACT

ABSTRACT Growth faulting, rapid deposition, and deep burial of sediments in south Louisiana have resulted in the abnormal pressurization of pore fluids within some sedimentary units. Fluid production from geopressured sandstones may result in pore-pressure reductions, clay compaction, and land-surface subsidence Subsidence is being monitored at the U.S. Department of Energy's Sweet Lake, Parcperdue, and Rockefeller Refuge geopressured-geothermal prospects in southwestern Louisiana. Reservoir-defining growth faults were extrapolated to the land surface, surface lineations were mapped from aerial photographs, and historical elevation surveys were compared to obtain base-line subsidence rates. Data from the Sweet Lake prospect indicate that no correlations exist between subsidence anomalies and lineations or fault projections. Subsidence here is probably a result of normal sediment compaction, salt domerelated land-surface adjustments, and/or historical subsurface fluid production. Conversely, a good correlation exists between the Parcperdue subsidence profile and the extrapolated updip extensions of mapped subsurface faults. Historical land-surface subsidence north of the Parcperdue prospect may have resulted from down-to-the-coast slumping along these growth faults which define the prospect. Subsidence at the Rockefeller Refuge prospect ranges from virtually zero on the eastern end of the prospect to 50 mm on its western end. The gradation may be due to oil- and gas-associated fluid withdrawals or land management variations. A subsidence analysis near Lake Charles, Louisiana, suggests that a more extensive historical record of leveling data could provide a more qualifying subsidence record. Repeated leveling surveys at the geopressured-geothermal prospects should aid in determining the causes of subsidence before and after depressurization of the geopressured aquifers.

Multiple Barrier-Island and Deltaic Progradational Sequences in Upper Cretaceous Coal-Bearing Strata, Northern Kaiparowits Plateau, Utah: ABSTRACT

The Kaiparowits coalfield, Utah, contains reserves of 20 billion tons of coal which are confined to three major coal zones within the John Henry Member of the Straight Cliffs Formation (Upper Cretaceous). Mapping and subsurface work in the northern part of the coalfield End_Page 796------------------------------ indicates that the coal-bearing strata accumulated during seven minor progradations of the shoreline of the Cretaceous seaway. The lower and middle coal zones consist of eight and six seams, respectively, and were deposited in a swamp 20 km wide on the landward side of a barrier-island complex. The upper coal zone consists of a single seam that accumulated in interdistributary swamps in a deltaic setting. The three coal zones were deposited during the three of the seven progradations that are completely developed. The remainder are incompletely developed and do not contain significant coal seams. Complete vertical sequences of barrier-island and deltaic progradation are present in the Straight Cliffs Formation. Incomplete progradational sequences are usually composed of transition, shoreface, and foreshore deposits. The repetitious nature of the several progradations and transgressions of barrier-island deposits and the local incompleteness of their development suggest periodic fluctuations in the quantity of sediment supplied by longshore transport currents from deltas northwest of the study area. Delta-lobe abandonments probably resulted in the periodic interruption of sediment supplied to the barrier-island complex and allowed sufficient time for compactional subsidence in the barrier complex to cause minor transgressions. End_of_Article - Last_Page 797------------

Seaward Primary Dip of Fall-in Beds, Lower Seven Rivers Formation (Permian), Guadalupe Mountains, New Mexico: ABSTRACT

Fall-in beds are shelf carbonate rocks which exist adjacent to the Capitan Limestone in a belt about 1 km wide, and which have basinward dips of 5 to 15°. Sedimentologic and structural-geopetal data gathered in field studies of the lower Seven Rivers Formation in North McKittrick Canyon show that tectonic tilting and/or compactional subsidence can account for only part of the basinward dip of fall-in beds, the remainder being primary depositional dip. The dominant lithologies of fall-in beds are stromatolitic algal oncolite rudites and sand-sized, mixed skeletal-peloid grainstones. Rocks are tightly cemented with marine phreatic isopachous fibrous magnesium calcite. Fall-in beds lack features of the adjacent, shallower, but generally submerged shelf-crest facies such as fenestral fabric, pisolites, tepees, erosion surfaces, and shoaling cycles. An inferred energetic, subtidal marine depositional environment for fall-in beds is compatible with their significant basinward depositional dip. Primary geopetal fabrics, although scarce in fall-in beds, have dips not exceeding a few degrees. The dip divergence between bedding planes and geopetal surfaces averages 8 ± 2°, a value which is inferred to be equal to the original depositional dip. Proof of primary seaward dip in fall-in beds lends support to Dunham's marginal-mound hypothesis for the Capitan shelf. Also, primary dip in beds adjacent to the Capitan supports recent interpretations that the Capitan Limestone formed in a relatively deep (30 to 50 m), continually submerged shelf-edge position, and was not a true barrier reef. End_of_Article - Last_Page 471------------

Mechanical and Chemical Effects of Pore Fluids on Rock Properties: ABSTRACT

The disposal of wastes underground involves injection of fluids into a rock mass that through natural processes has probably attained a state of at least metastable equilibrium. Injected fluids tend to disrupt this equilibrium mechanically and chemically. The primary question concerns what effect this disruption will have on the rock body. Fracturing, faulting, or the reactivation of old faults could lead to earthquakes and to the creation of fractures that may provide permeability channels through which injected fluids could escape from the intended disposal beds. Accelerated compaction, brought about by chemically weakening the load-bearing framework of the rock or by reducing fluid pressures upon withdrawal, can cause surface subsidence. At depths of 3-4 km most rocks are brittle, and fracture and rigid-body rotation are the dominant mechanisms of deformation. The most important physical parameter in this regime is the effective confining pressure Pe, defined as the difference between the confining pressure Pc and the pore-fluid pressure Pp. Both the breaking strength and the compaction of rocks are dependent upon the magnitude of Pe regardless of the absolute values of Pc and Pp. Increases in Pp produced by injection of fluids decrease the normal stresses but do not change shear stresses across potential failure surfaces. This could lead to fracturing, faulting, or the reactivation of pre-existing faults. Decreases in Pp produced y withdrawal of fluids from a reservoir can lead to compaction and surface subsidence as the Pe is increased. The second important aspect of the problem is the role of the pore-fluid chemistry. Significant reductions in rock strength have been shown to result from the lowering of the surface energy of solids that occurs from adsorption of pore fluids and associated modification of bonding. Triaxial compression tests on sandstone show that the coefficient of internal friction is not altered by pore solutions of 0.002 to 2 ppm of FeCl3. The lowering of the breaking strength is due rather to the reduction of the intragranular cohesive strength as a function of the concentration of the electrolyte solution. The frictional characteristics of already broken rocks may be significantly altered by the introduction of surface-active fluids. In light of man-made earthquakes, such as those near Denver, Colorado, the influence of pore-fluid pressure and chemistry suggests that more sophisticated tests of rock properties should be made if problems caused by unexpected rock failure are to be eliminated. End_of_Article - Last_Page 2090------------

The Nigerian continental margin: Bottom sediments, submarine morphology and geological evolution

Two series of Late Quaternary sediments occur on the surface of the Nigerian continental shelf and slope overlying the Nigerian Coastal Plain geosyncline. The earlier series, the Older Sands, is a quartzose sheet sand which originated at a transgressive strand during the late Pleistocene-early Holocene eustatic rise of the sea. Terraces and rises capped by local ridges occur on its upper surface parallel to shore, which is crossed locally by shallow valleys with channeled floors. The rises with local ridges are interpreted as drowned barrier beach or island complexes, their present depth variation being seen as recording tectonic and compactional subsidence of the continental margin. The later sediments, refered to as the Younger Suite, locally bury the Older Sands very deeply, comprising sands near shore, silts in moderate depths and clays in deep water. They have been deposited during the seaward growth of the modern Niger delta. River mouth bars and an inshore terrace and rise are the principal morphological features of the modern continental shelf underlain by the Younger Suite. The continental margin is notched by three submarine canyons and by numerous large and small gullies. It has been an essentially depositional feature since the inception of the Nigerian Coastal Plain geosyncline in the early Cretaceous.