Shallow Dome Research Articles

Deep-Seated Salt Sheet: Eastern Calcasieu Parish, Louisiana

ABSTRACT Interpretation of recent seismic and well data in the Gillis-English Bayou and West Manchester area of Calcasieu Parish, Louisiana, supports a complex structural history involving allochthonous salt, erosion and faulting. Since its discovery in 1934, Gillis-English Bayou has produced over 195 BCFG and 18 NMBL from Oligocene and Miocene age sands. Unlike the aerially small, shallow salt dome fields along trend, Gillis-English Bayou covers approximately eighteen square miles, by area the largest field in the parish. West Manchester, to the south, has produced over 120 BCFG and 2 MMBL from Oligocene Lower Hackberry sands. The associated salt sill underlies at least thirty square miles at depths of 15,000 to 20,000 and can be indirectly related to hydrocarbon accumulation in the area. Associated with this vertical and lateral movement of salt is a significant Vicksburg erosional event underlying West Manchester Field. In this area of thick Vicksburg sediments, over 1,200 of section is absent.

ボール接合単層ラチスドームの座屈実験及び弾塑性座屈解析 : 中央集中荷重を受ける部分球形ドームについて

The purpose of this paper is to examine the elasto-plastic buckling behavior of a single layer reticulated dome subjected to a static load at the center of the dome. The nonlinear analytical and the experimental study of a shallow dome were carried out. The type of buckling concerned here is the snap-through of the dome. The results of the experimental study were compared with the numerical analysis. It is emphasized that the joint characteristics as well as the material non-linearity have significant effects upon the buckling behavior of a dome.

Germination of Monocolpate Angiosperm Pollen: Evolution of the Actin Cytoskeleton and Wall during Hydration, Activation and Tube Emergence

The monocolpate pollen grain of Narcissus pseudonarcissus L. has two preferred sites for tube emergence, one at each end of the colpus. While the cellulosic microfibnls of the inner layer of the intine are disposed circumferentially in the centre of the grain, the microfibrils in these terminal sites are shorter and randomly oriented Soon after the beginning of hydration, inclusions of the vegetative cell begin movement, firstly in a rotatory manner, and then in a pattern focused on one or both germination sites, where the intine bulges as hydration progresses. These changes are associated with the evolution of the actin cytoskeleton. Actin is present in the unactivated grain in the form of fusiform bodies. During hydration these dissociate to form finer fibrils, initially randomly disposed. Then, correlated with the change of the pattern of movement in the vegetative cell, the actin fibril system becomes polarized towards the germination sites, where shorter fibrils accumulate. Callose, absent from the ungerminated grain, is deposited within the cellulosic wall in these locations, forming a shallow dome which eventually develops into an annulus subtending the inner callose lining of the emerging tube. The transition to cylindrical growth is associated firstly with the development of zonation in the cytoplasm of the vegetative cell, with the tip occupied by a population of wall precursor bodies (P-particles) and a dense aggregate of short actin fibrils; and then with the establishment of the ‘inverse fountain’ pattern of movement characteristic of the apical part of the extending tube.

Geometrically Nonlinear Analysis in the Vicinity of Critical Points by the Generalized Inverse

In the geometrically nonlinear analysis for equilibrium paths, the determinant of the tangent stiffness matrix at the critical point becomes zero so that a numerically unstable situation appears in the vicinity of critical points. To avoid such a situation, many numerical methods including the arc-length method and the perturbation method have been developed. In this paper, an analytical method to pursue the geometrically nonlinear equilibrium paths in the vicinity of critical points such as limit point and bifurcation point is presented by using the generalized inverse. In the first part, the perturbation equations for the incremental equilibrium equations are derived. Then, critical points on the equilibrium path are classified into limit point and bifurcation point by using the existence condition of solution. In the second part, an analytical method for post-critical paths beyond critical points is presented by means of the generalized inverse. In the final part, the application of the present method to the post-buckling analysis of a shallow arch and cable domes subjected to the symmetrical loads is shown.

Single Layer Shallow Lattice Domes: Analysis, General Behaviour and Collapse

This paper discusses some aspects of the pre- and post-collapse analysis and behaviour of shallow lattice (reticulated) domes. Use is made of a nonlinear computer program to study the behaviour associated with changes in both structural geometry and material properties, as well as that associated with bifurcation and limit point buckling. This program has been described in detail elsewhere, and apart from a discussion of the use of static condensation in the nonlinear range, only a brief summary of the theory used in the program is given here. The program is used to predict both the pre- and post-buckling response of a 42-member shallow braced model dome under two types of loading and the numerical results are compared with those of an experimental study. The influence of initial imperfections on the general behaviour is discussed briefly, and some guidelines are set out to aid the numerical determination of the true load-deflection response of shallow lattice domes.

An integrated approach to the synthesis of geometrically non‐linear structures

AbstractAn integrated approach to the minimum weight design of geometrically non‐linear three dimensional truss structures with geometric imperfections, subject to inequality constraints on static displacements, stresses, local buckling and cross sectional areas, is investigated. The integrated structural synthesis problem involves design and response quantities as independent variables and equilibrium equations, describing the finite element model, as equality constraints. The non‐linear structural analysis and the optimization are thus merged together into a single process. A computer program developed to compute the contraint values and analytical gradients is coupled with a generalized reduced gradient algorithm to solve the integrated problem. Numerical results for a geometrically non‐linear shallow dome example problem are presented for various types of imperfections. Furthermore, it is found that the algorithm is capable of detecting and guarding against system as well as element elastic instability using equilibrium information only, that is, without imposing system and local buckling inequality constraints.

Collapse of Shallow Lattice Domes

A numerical and experimental study of the collapse and postcollapse behavior of shallow lattice domes is presented. The numerical analysis is based on an updated Lagrangian, materially and geometrically nonlinear, displacement‐based finite‐element program. The formulation incorporated in the program can detect plasticity, instability, and finite deflection effects in the dome structure. Warping effects are ignored. The solution of the nonlinear stiffness equations is designed so that critical points on the equilibrium path are identified in the results. A method is used to obtain the lowest bifurcation path of a perfect lattice dome, once it is established that there is a bifurcation point on its primary equilibrium path. Limit point behavior is detected automatically. A shallow model dome was tested experimentally in a purpose‐built test rig. The experimental results presented are compared with the corresponding numerical predictions and good agreement between them is demonstrated.

Recovery of Cellar Oil By Water Injection

Summary The effect of operating and reservoir parameters on cellar flooding were evaluated by use of a commercially available reservoir simulator. The parameters were representative of Miocene reservoirs and operating conditions in south Louisiana. Cellar flooding is a one-well injection/production process that exploits the density difference between injected water and in-place crude to recover oil from the "cellar" of a steeply dipping pressure-depleted reservoir by a gravity-segregation mechanism. The cellar of a reservoir is the volume located downdip of the most downdip well that produced from the segment. The results of computer simulation show that the most significant operating parameters are injection volume and migration time. The most significant reservoir parameter is well location. Criteria to select cellar flood candidates and guidelines to operate a cellar flood are presented. Introduction Reservoirs associated with shallow or piercement salt domes and other highly faulted areas are often small, with steeply dipping beds. The reservoir size is often such that only one well can be justified economically to recover primary oil. Some of these reservoirs produce by depletion drive, while others produce by a full or partial water drive. The drive mechanism may be supplemented, under certain conditions, by gravity drainage as discussed by Dykstra1 and Hagoort.2 Isolated reservoirs of the type under evaluation are produced by a combination depletion drive/gravity segregation mechanism. A high residual oil saturation remains down structure of the producing well as a result of gravity effects at the end of primary production. The drilling of additional wells or sidetracking of existing wells is usually not economical. The location of existing wells eliminates conventional waterflooding or other conventional methods to displace the down structure oil. Cellar flooding is a possible method to recover the down structure reserves. Cellar flooding is a single-well injection/production process that exploits the density difference between the injected water and in-place crude to recover oil from the "cellar" of a steeply dipping pressure depleted reservoir by a gravity segregation mechanism (Fig. 1). The "cellar" of a reservoir is the volume located downdip of the most downdip well that produced from the reservoir. Implementation of cellar flooding could increase oil recovery from developed fields and extend the utility of existing injection facilities as mature waterfloods reach an economic limit. Implementation of cellar flooding also could produce a profit from what otherwise could be operating expense associated with the eventual mandatory subsurface disposal of all produced brine. (In some areas produced brine is discharged to surface water bodies after treatment to remove oil.) Intermittent and continuous cellar flood processes were evaluated by Gaskell and Lindley3 in 1961 by use of a physical reservoir model. Intermittent cellar flooding is a cyclic process with three distinct phases: an injection phase, a shut-in/segregation phase, and a production phase. Continuous cellar flooding differs from an intermittent process in that there is no shut-in period. Production is maintained from the reservoir during water injection by completing the project well with a dual setting. A thicker pay zone and higher reservoir pressure are required to use continuous cellar flooding than to use intermittent cellar flooding. Gaskell and Lindley's model showed that either process could recover cellar oil. In addition to the model studies mentioned, work by Texaco U.S.A.4,5 and Humble Oil and Refining Co.6,7 has resulted in various patents on the cellar flood process.

Geothermal Patterns and Petroleum Traps, Louisiana: ABSTRACT

End_Page 590------------------------------Published literature documents varying degrees of correlation between geologic structures and geothermal highs (halos) of several petroleum fields. In conjunction with these fields, additional structures and associated productive trends have been evaluated in order to develop certain predictive criteria. The studies attempted in this regard include structural and stratigraphic traps, rollover anticlines, and salt domes with productive horizons of various ages in Louisiana. As part of the characterization of the subsurface temperature regime of the regions studied, the following broad generalizations seem to be in order. (1) Geothermal halos observed near faults appear astride the fault, or clearly confined to one fault block or the other. (2) A single geothermal halo in a deep section may be overlain by multiple halos, generally of lower relief, in shallow sections. (3) Geothermal halos associated with deep-seated salt domes are located in the sedimentary section on or near the top of the dome, near the perimeter or on the flanks. Such halos are not discernible on shallow domes. (4) In the interior basin, a salt dome with productive horizons appears to have a geothermal halo of higher relief than those in the vicinity with no petroleum accumulations. (5 Even some petroleum traps, created by sedimentary facies changes with no distinct structural closures, are marked with geothermal halos. The observed characteristics of the subsurface thermal regimes are generally explicable in terms of thermal properties of rocks and pore fluids and by hydrodynamics. End_of_Article - Last_Page 591------------

The stabilisation of low oxidation state transition metal complexes. Preparation and electrochemistry of cobalt(II) unsaturated macrocyclic complexes and the stabilisation of a cobalt(I) derivative. Crystal and molecular structures of [CoII(L)(CH3OH)2][BF4]2and [CoI(L){P(OCH3)3}][BF4

A series of seven cobalt(II) complexes [CoII(L)X2]2+, based on the planar macrocyclic ligand L derived from 2,9-di(1-methylhydrazino)-1,10-phenanthroline and 2,6-diacetylpyridine have been prepared with varying axial ligands X[X = H2O, pyridine(py), 4-aminopyridine (apy), 4-cyanopyridine (cpy), 4-dimethylaminopyridine (dap), imidazole (im), 1-methylimidazole (mim), quinoline (quin), pyrazine (pyz), or 1,4-diazabicyclo[2.2.2]octane (dabco)]. The single-crystal X-ray structure of the bis-methanol adduct [CoII(C23H21N7)(CH3OH)2][BF4]2, which crystallises in space group P21/n with a= 12.110(8), b= 17.205(9), c= 15.411(8)A, β= 112.62(3)°, and Z= 4, was solved by a combination of Patterson and Fourier techniques, and refined by blocked full-matrix least sauares to R= 0.088 for 1 754 observed diffractometer data. The structure confirms the seven-co-ordinate geometry for this complex with the cobalt ion in the plane of the macrocyclic ligand. Cyclic voltammetry of the complexes in acetonitrile at a platinum microsphere shows a reversible reduction wave near E½=–1.4 V which may be tentatively assigned to the initial formation of a highly unstable cobalt(II) ligand radical species. Addition of P(OCH3)3 to a solution of [Co(L)(H2O)2][BF4]2 in acetonitrile shifts the reversible reduction wave from E½=–1.43 to –1.199 V; electrochemical reduction of such a solution by controlled potential electrolysis yields the metal-reduced cobalt(I) complex [CoI(C23H21N7){P(OCH3)3}][BF4]. The single-crystal X-ray structure shows it to crystallise in space group P21/n with a= 10.745(4), b= 10.721(5), c= 24.722(8)A, β= 92.57(2)°, and Z= 4. The structure was solved by a combination of Patterson and Fourier-difference techniques, and refined by blocked-cascade least squares to R= 0.069 for 2 519 observed diffractometer data. The cobalt ion is displaced out of the plane of the five donor nitrogen atoms by 0.36 A towards the phosphorus atom. The macrocyclic ligand is not planar but has the shape of a shallow dome, the distortion being away from the axial ligand. The stabilisation of the metal-reduced cobalt(I) complex is attributed to the combined π-acceptor properties of the unsaturated macro-cyclic ligand and the axial P(OCH3)3 ligand.

Geothermal Trends in Petroliferous Regions of Louisiana: ABSTRACT

End_Page 1361------------------------------Published literature documents varying degrees of correlation between geologic structures and geothermal highs (halos) of several petroleum fields. In conjunction with these fields, additional structures and associated productive trends have been evaluated to develop certain predictive criteria. The studies attempted in this regard include structural and stratigraphic traps, rollover anticlines, and salt domes with productive beds of different ages in Louisiana. As part of the characterization of the subsurface temperature regime of the regions studied, the following broad generalizations seem to be in order: (a) geothermal halos observed near faults appear astride the fault, or clearly confined to one fault block or the other; (b) a single geothermal halo in a deep section may be overlain by multiple halos, generally of lower relief, in shallow sections; (c) geothermal halos associated with deep-seated salt domes are located in the sedimetnary section on or near the top of the dome, near the perimeter or on the flanks. Such halos are not discernible on shallow domes; (d) in the interior basin, a salt dome with productive horizons appears to have a geothermal halo of higher relief than those in the vicinity with no petroleum accumulations; an (e) even some petroleum traps, created by sedimentary facies changes with no distinct structural closures, are marked with geothermal haols. The observed characteristics of the subsurface thermal regimes are generally explained in terms of thermal properties of rocks and pore fluids, and fluid migration induced by changes in the density, viscosity, and pressure potential of the subsurface fluids. End_of_Article - Last_Page 1362------------

Petroleum Accumulation Trends in East Texas Salt Dome Area: ABSTRACT

Three main genetically related classes of salt domes can be recognized relative to the regional structures in the East Texas basin--anticlinal, synclinal, and flank domes. The anticlinal domes are deep seated while the synclinal and flank domes occur at shallow and intermediate depths. High dome maturity and associated flank bed configurations were achieved in the synclinal domes such as Hainesville and Bethel, only partly achieved in some flank domes such as Grand Saline, while other flank domes such as Keechi and presumably the anticlinal domes are immature. The largest oil and gas accumulations in the east Texas dome region occur in crestal anticlines of the deep-seated anticlinal domes. The shallow domes on the regional flanks and synclines have all been nonproductive from their crestal anticlines probably because they do not uplift adequate sedimentary sections. The synclinal and flank domes therefore appear to have poor potentials except for entrapment beneath overhangs and porosity pinch-outs on the flanks when the evolution of the domes promotes these features. Patchy carbonate porosity and sandstone pinch-outs may develop around elevated dome flanks during the immature earlier history of the mature synclinal domes and throughout the history of the immature flank and anticlinal domes. Salt overhangs appear to be better developed in he more mature domes. This model highlights the potential targets around salt domes in east Texas and can be used to reevaluate both the producing and nonproducing domes in the basin. The genetic basis for the model also underscores its applicability in other halokinetic basins. End_of_Article - Last_Page 668------------

Stability predictions through a succession of folds

For a discrete, or discretized, conservative gradient system, such as is envisaged in catastrophe theory and arises throughout the physical sciences, it is often necessary to assess the stable regions of an equilibrium path that exhibits a succession of folds. At each fold the degree of instability changes by one, so that as the system evolves from a region of known stability the first fold must represent a loss of stability. At a second fold, however, it is not clear whether the system is suffering a further loss, as we shall see in some examples, or is regaining its original stability as is more common in elasticity. A new theorem involving a conjugate parameter allows all such stability changes to be readily assessed on the basis of the form of the equilibrium paths themselves. The application of the general theory to the external and internal stabilities of an elastic structure under dead and rigid loading is demonstrated. Under the former, the load is the control parameter and the corresponding deflection plays the role of the conjugate parameter, while in a direct analysis of rigid loading these roles are reversed. A supplementary study of rigid loading which uses Lagrange multipliers supplies further theorems relating the dual concepts of external and internal stability. The use of the theorems is demonstrated in the buckling of elastic arches and shallow domes, and in the incipient gravitational collapse of a massive cold star. The possible stabilization of bifurcations by rigid loading is examined, and shows how the results can also be of value in bifurcational instabilities.

Transverse vibrations of viscoelastic shallow shells

A method for the time history of motion of shallow shells of viscoelastic material under arbitrary time-dependent transverse load is presented. The method is based upon the concept of iso-amplitude contour lines on the surface of the shell. It is shown that the time behavior can be found by using the frequency of free vibration of the associated elastic shallow shell. As an illustration of the technique, the problem of a shallow dome upon an elliptic base is discussed, all details of which are explained by graphs.

Approximate Methods for the Linear and Nonlinear Analysis of Plates and Shallow Shells

Abstract Berger's equations for the large amplitude deformation of membranes are used to produce a simple approximate expression for the large amplitude deflection of plates. The deformation of shallow shells is also considered and two approximate methods are outlined. Several important problems are discussed, the obtained solution being in good agreement with both experimental data and other approximate results. The main advantage of this technique is its ease of application, as it requires comparatively little computational work. A simple approximate formula for computing the fundamental frequency of a vibrating shallow shell is also presented and is shown to yield very accurate values in the case of a shallow dome and a rectangular panel.

Remarks on the Approximate Analysis of the Nonlinear Behavior of Shallow Shells

Abstract Berger's equations for the large amplitude deflection of shallow shells are analyzed in detail and a simplified theory obtained for small deformations. As an illustration the bending of a uniformly loaded shallow dome is discussed and the obtained results compared with experimental data.

Geometric Nonlinearity

ABSTRACT The nonlinear behavior or structures has attracted considerable attention in the last decade. This paper is specifically concerned with three-dimensional skeletal structures wherein nonlinearities are attributable to change of geometry. The frameworks that are considered possess particular relevance to roofing systems. The outline theoretical analysis incorporates: (a) effects of finite joint deformation; (b) change of member lateral stiffness; (c) change of member length due to bowing. Cable systems are discussed simply as a particular case of the more general solution. Theoretical and experimental results are compared for a relatively complex rigid jointed structure. An example of a shallow dome is presented in which the salient design considerations that must be made for this form of structure are clearly demonstrated.

Salt Piercement in Shallow Gulf Coast Salt Structures

Data from 16 salt structures of the Gulf Coast province have been analyzed to (1) document some of the piercement features on shallow Gulf Coast salt structures and (2) investigate some of the mechanisms and controls of the salt-piercement processes. The process of piercement by vertical displacement of overburden by salt has been the primary subject of this study. Accordingly, the investigations have concerned mainly the upper section of alternating sandstone and shale beds that are in contact with the salt and show a discordant relation with the salt core. The two general types of piercement processes recognized on shallow Gulf Coast salt domes are (1) piercement by rupture of the overburden through fracturing, faulting, and tilting of the overburden upward and outward in segments, with rise of the salt being enhanced by erosion, and (2) piercement by vertical displacement of overburden ahead of the growing salt mass, accompanied by peripheral faulting surrounding the salt dome. The discordant relation commonly observed in the upper parts of shallow salt structures between the salt plug and the enveloping strata is the result of piercement by vertical displacement of overburden by salt. The discordant relation can be produced by piercement of each bed contemporaneously with deposition or by postdepositional piercement of a thick section of overburden. Postdepositional piercement and vertical displacement of overburden as much as 2,400 ft thick can be documented in the Gulf Coast. Piercement by vertical displacement is most likely where the salt has a plug shape and is growing by a process of plug flow. The plug shape evolves from a broad salt mound or pillow in the later stages of salt dome growth. Piercement by rupture and outward tilting of segments of overburden is most likely in the earlier stages of salt-dome growth, when the salt mass is in the broad mound or pillow shape or is changing from the pillow to the plug shape.

Evaluation of prestressed post-tensioned forces on the shallow dome of containment structures

The resultant radial, circumferential, and meridional pressures and anchorage forces of a three-layer tendon pattern for a shallow prestressed dome are presented. A constant horizontal or inplane tendon spacing is used in the analysis. The anchorage forces are given in terms of the X, Y, and Z coordinates of the containment vessel. Typical results of the variation of pressures and forces are presented.

Experiments on the snapping of a shallow dome under a step pressure load.

Abstract : The dynamic step pressure loads required to produce snapping are determined experimentally for two shallow spherical shell models. The resulting critical step pressures are compared with static buckling pressures that were obtained from the results of a nondestructive buckling test. The comparison reveals that the critical step pressures were between 55 and 58% of the static buckling pressure for one model and between 63 and 64% of the static buckling pressure for the other model. The measured supercritical response of the shells was similar to the predictions of theory. (Author)