Seal Analysis Research Articles

Seismic attribute maps; application to structural interpretation and fault seal analysis in the North Sea Basin

Seismic attribute maps (dip magnitude, dip azimuth, reflective amplitude, etc.) are a relatively new tool for structural geological analysis (Bouvier et al. 1989; Dalley et al. 1989; Ruijtenberg et al. 1990;Hoetz and Watters 1992). They are being used increasingly in the hydrocarbon industry, both for regional structural 'lineament' mapping (Oudmayer and De Jager 1993; Demyttenaere et al. 1993), and also for the more detailed fault mapping undertaken during reservoir characterization (Hoetz and Watters 1992).

Early Identification of Reservoir Compartmentalization by Combining a Range of Conventional and Novel Data Types

Summary Reservoir compartmentalization (vertical and lateral) is often a major uncertainty at the field appraisal stage, impacting important investment decisions. Unfortunately, the most definitive compartmentalization data (dynamic production data) are not usually available so early in field life. This paper illustrates how early indications of compartmentalization can be achieved by integrating various types of conventional and novel data. Using an example from the Ross oilfield, U.K. Continental Shelf (UKCS), we demonstrate how integration of oil compositional data (molecular maturity parameters, gas chroma-tography [GC] fingerprinting, pressure-volume-temperature [PVT] data) with pressure, well test, and fault seal analysis revealed the presence of several sealing faults, and thus enabled the field to be described in terms of its likely segmentation. Vertical compartmental-ization was investigated using a combination of oil geochemistry (maturity, GC fingerprinting), water composition (residual salt analysis), and high-resolution stratigraphy, revealing a continuous shale that has a lateral extent of > 5 km; it divides the reservoir into two main layers. The results of this study helped to decrease uncertainty in field development planning. The key message is that there are many tools available to aid in assessing compartmentalization, but individually they each only give part of the picture. It is therefore important to use several tools in combination.

Trap and Seal Analysis in Carbonate Shelf Margin Stratigraphic Trap Exploration; Example from the Lower Miocene, Zhujiang Formation, Pearl River Mouth Basin, People's Republic of China: ABSTRACT

Carbonate shelf margin stratigraphic traps are a particularly risky play type because the same diagenetic factors responsible for secondary reservoir quality enhancement can be responsible for degrading seal quality and increasing trap risk. The Zhujiang Fm. prograded westward off the Dongsha Massif initially as a ramp which evolved into a prograding and aggrading shelf margin. Seismic interval velocity analysis, modeled with data from a nearby oil-bearing pinnacle reef, indicates a thick porosity zone at the shelf margin, wedging and pinching out eastward. Core data from the pinnacle reef indicated a short-term exposure event was responsible for significant early secondary porosity enhancement. This also may have influenced the adjacent shelf area; enhancing porosity in the shelf margin, but reducing seal capacity in the equivalent up-dip shelf sequence. The seal competency of the overlying Hanjiang shales was demonstrated by hydrocarbons sealed in the adjacent pinnacle reef. Seal risk was evaluated by mercury injection capillary pressure analysis in a shelf carbonate well updip from the margin. It was determined that the up-dip shelf seal is sufficient to hold an economically favorable 300-500 ft (90-150 m) hydrocarbon column. Seismic evidence revealed several large mega-slumped portions of the shelf margin producing scalloped areas extending severalmore » kilometers back into the shelf. Subsequent filling of these reentrants could produce lateral sealing by juxtaposing Hanjiang shales against the sides of the remnant Zhujiang carbonate salient. The slump scar on the south side of the salient did not downcut to a significant stratigraphic depth to provide a critical closure to trap a minimum hydrocarbon column to meet economic thresholds.« less

Compositional Limitations on Rock Types Contributing to Zones of Sealing Phyllosilicate-Rich Fault Gouge: ABSTRACT

A common approach to fault-zone seal analysis in siliciclastic strata involves analyzing the lithologic composition of the displaced stratigraphic interval along a fault as a means of predicting the spatial extent of sealing phylloilicate-rich gouge zones. It is often assumed that only the mudstones within the stratigraphic section contribute to the formation of this phyllosilicate-rich gouge. This study documents composition-dependent contrasts in natural deformational style of sandstones and mudstones that challenge this assumption. Faulting of phyllosilicate-poor (<20%), porous sandstones results in the formation of deformation bands. In contrast, the deformation of mineralogically less-mature sandstones generates gouge with a fine-grained, phyllosilicate-dominated matrix. Capillary-pressure tests indicate that this phyllosilicate-rich gouge is capable of sealing large hydrocarbon columns, whereas the deformation bands generally do not have small enough pore throats to serve as good seals. Most mudstones; deform by intergranular sliding and other grain-scale mechanisms to form [open quotes]scaly[close quotes] gouge typical of sealing [open quotes]shale smear[close quotes] fault zones. Other mudstones, however, deform by transgranular fracturing and brecciation, potentially leading to the formation of fluid conduits rather than seals. A transition in deformation mechanism from fracturing to intergranular sliding typically occurs when phyllosilicate content of the original mudstone exceeds 20-30%. At naturalmore » conditions suitable for petroleum preservation, faulting of sandstones and mudstones containing in excess of 20-30% phyllosilicates generally produces phyllosilicate-rich fault gouge. Thus, during fault-seal analysis in siliciclastic sequences, this compositional criterion can be used to distinguish between lithologies that do and do not contribute to the formation of high-quality sealing fault gouge.« less

The Internal Structure and Properties of Fault Damage Zones and the Impact on Sealing and Reservoir Behaviour: ABSTRACT

The concentration of sub-seismic deformation adjacent to larger faults forms a complex deformation volume or damage zone which is important to hydrocarbon migration, trapping and reservoir management. The results of a combined study of structural logging of cores, microstructural characterization and physical property measurement of deformation features preserved in cores, with analysis of fault populations from seismic and outcrop studies, are used to evaluate the properties and evolution of damage zones. The detailed internal structure of fault zones is dependent on the conditions of deformation, the lithological architecture present and the position in the fault array. Clusters of deformation within the damage zone are also surrounded by relatively undeformed volumes. Quantification of the geometry of the these zones is critical to understanding the fluid-flow and sealing properties of-the fault zone. Complete evaluation of the impact of the damage zone on reservoir properties requires knowledge of the petro-physical properties and spatial distributions of the fault rocks present. These range from quartz-rich cataclasites, developed from pure sandstones, to phyllosilicate smears developed from shales. An important class of intermediate fault rock is generated from impure sandstones. Localization of cement precipitation within the damage zone will remove the applicability of simple seal analysis basedmore » only on the host-rock lithology and displacement. Realistic prediction of the impact of faults on reservoir behavior requires integration of the detailed geometry with the petrophysical characterization of the fault rocks.« less

Radial Lip Seal Analysis—Finite Element Solution for a Body of Revolution

To deal with the complex geometry of radial lip seals, in particular the metal-to-rubber boundary and multiple lips, the elasticity equations for a body of revolution are an important step to improve the accuracy of the predicted solution. A nonlinear strain displacement finite element solution of the elasticity equations for a body of revolution is presented here. Following Zienkiewia. (1), the equations are derived from the work equivalence principle generalized to nonlinear problems. Realistic levels of Poisson's ratio present no difficulty when a technique of reduced integration is used (2), The elastic law is Hooke's law with thermal expansion. External forces can be volume forces or surface forces. Both are converted into consistent nodal forces. Boundary conditions can be any combination of forces or displacements on any given node. This paper presents the equations and the solution by the finite element method as well as an extensive verification of the program prediction for thermal shrinkage of the seal from mold to ambient temperature, showing remarkable agreement with experiments in a large number of cases. Comparison of the prediction of the program for radial load and axial movement of the lip against experiment are also given, as well as comparison with the results of the previous code for conical shells.

Integrating Pressure into Fault Seal Analysis, US Gulf of Mexico: ABSTRACT

Integrating Pressure into Fault Seal Analysis, US Gulf of Mexico: ABSTRACT

Integrated Fault Seal Analysis and Risk Assessment: Okan and Meren Fields, Nigeria: ABSTRACT

Integrated Fault Seal Analysis and Risk Assessment: Okan and Meren Fields, Nigeria: ABSTRACT

Fault Seal Analysis: Methodology and Case Studies: ABSTRACT

Fault Seal Analysis: Methodology and Case Studies: ABSTRACT

Rancidity in Packaged Nurs: End-Use Technical Service

This paper describes the method used by a technical sales organization in trying to determine the cause of rancidity occurring in packages of nuts. Tests included seal leak detection, oxygen and hexanal headspace analysis, film barrier testing, environmental exposure and visual examination of each package. The conclusion was that the cause of rancidity was an inadequate seal of the packages.

Trap and Seal Analysis in Carbonate Shelf Margin Stratigraphic Trap Exploration; Example from the Lower Miocene, Zhujiang Formation, Pearl River Mouth Basin, People's Republic of China: ABSTRACT

Trap and Seal Analysis in Carbonate Shelf Margin Stratigraphic Trap Exploration; Example from the Lower Miocene, Zhujiang Formation, Pearl River Mouth Basin, People's Republic of China: ABSTRACT

Timing of hydrocarbon generation and accumulation in fault-bounded compartments in the Norphlet Formation, offshore Alabama

Analysis of the variation in depth of the gas-water contacts in the Bon Secour Bay and Lower Mobile Bay-Mary Ann Fields of offshore Mobile Bay, Alabama, together with fault seal analysis, implies that some of the pre-Cretaceous faults in these fields must be sealing. It is also likely that the large, post-Cretaceous Lower Mobile Bay Fault is dip-leaking. The gas currently reservoired in the Norphlet Formation has most likely been produced by thermal degradation of oils generated in the overlying Jurassic lower Smackover Formation. For a range of heat flow models appropriate for this area of the Gulf Coast, the onset of gas generation (defined as the time at which 10% of the maximum possible amount of gas has been generated) occurs at 104 −5 +10 Ma. The error bounds in this estimate are the 90% confidence limits, which were calculated by assuming that the times of onset of gas generation are log-normally distributed. The time of onset of gas generation is younger than the age of the sealing faults in the area, hence it is likely that gas generation occurred in situ in the Norphlet Formation, with re-migration occurring during the development of the post-Cretaceous Lower Mobile Bay Fault.

Thermo-Hydrodynamic Solution of Floating Ring Seals for High Pressure Compressors Using the Finite-Element Method

This paper describes the finite-element solution of the nonlinear and coupled hydrodynamic and thermal equations for pressure and temperature profiles in an oil seal including misalignment. Fluid properties are evaluated at the center of each element. For centered seals, results obtained are in good agreement with previous finite-difference analysis with approximate temperature distribution. For eccentric or axially tapered seals, use of the true temperature profile gives significantly different results. This analysis shows that the circumferential temperature variation should be considered in oil seal analysis and that reducing clearance taper produces a stabilizing effect.

Thermal Effects in Cryogenic Liquid Annular Seals—Part I: Theory and Approximate Solution

A thermohydrodynamic (THD) analysis is introduced for calculation of the performance characteristics of cryogenic liquid annular seals in the turbulent flow regime. A full-inertial bulk-flow model is advanced for momentum conservation and energy transport. The liquid material properties depend on the local absolute pressure and temperature. Heat flow to the rotor and stator is modeled by bulk-flow heat transfer coefficients. An approximate analytical solution is obtained to the governing equations when the seal operates at a steady-state and concentric condition. The temperature-rise in the fluid film of a cryogenic liquid seal is found to be composed of four sources due to viscous dissipation, pressure extrusion work, surface heat transfer and kinetic energy variation. For incompressible adiabatic flows, the fluid temperature rises linearly along the axial direction. The approximate analytical solution provides a useful tool for preliminary design and a better understanding of seal performance. Full numerical predictions of load, leakage, temperature, and rotordynamic coefficients for a high speed liquid oxygen seal are given in Part II to show the importance of thermal effects on seal performance. The accuracy of the approximate concentric seal analysis is then demonstrated by comparison to the results from the full numerical solution.

Fault Seal Analysis in the North Sea

The majority of North Sea structural traps requires that at least one fault be a sealing fault. Over 400 faults from 101 exploration targets and 25 oil and gas fields were analyzed in a regional study of the North Sea. The faults cut clastic successions from a variety of depositional environments (marine, paralic, and nonmarine). The emphasis of the study was on fault-related seals that act as pressure or migration barriers over geologic time. Parameters such as fault strike and throw, reservoir thickness, depth, net-to-gross ratio, porosity, and net sand connectivity were plotted against seal performance to define trends and correlations to predict fault seal characteristics. A correlation appears to exist between fault orientation and sealing, although this is not stati tically significant. Sealing is proportional to fault throw normalized as a fraction of the reservoir thickness. The great majority of faults with throw greater than the thickness of the reservoir interval were sealing faults. The most useful parameters in fault seal prediction are fault displacement, net-to-gross ratio, and net sand connectivity. The conclusions of this study have general applicability to fault seal prediction in exploration, development, and production of hydrocarbons in clastic successions in the North Sea and perhaps other areas as well.

Advanced Analysis of Multi-Ring Liquid Seals

The equilibrium position of multi-ring seal assemblies is of major importance to the designer of high pressure centrifugal compressors. Typical computer codes now use a curve-fit of the Short Bearing Sommerfeld Number for eccentricity evaluation with the assumption that all rings in the assembly will always operate at the same eccentricity. The results from the recently developed seal analysis program, SEALS, have shown that the equal eccentricity assumption for multi-ring seals is questionable. This paper will review the analysis procedure used in SEALS, and present the results of an eccentricity evaluation comparison with a seal analysis program currently being used in industry.

Self-syphonage in plumbing drainage systems: Effects of surface tension and viscosity

Self-syphonage is a major problem in plumbing design and so has been addressed in various codes by building services experts. This paper reports the results of experimental investigations carried out to determine the effect of viscosity and surface tension on the formation of vortices and eddies on flow characteristics within the trap and pipe, and most especially on trap seals. Within the range of the experimental results, viscosity and surface tension are insignificant factors for self-syphonage and residual seal depth analysis.

Fault-Zone Seals in Offshore Trinidad Oil Fields

Hydrocarbon columns in Pliocene sands of offshore SE Trinidad occur in 3-way closure, primarily in the footwall of normal faults. Multiple reservoir sands and numerous fault blocks result in a large number of individual hydrocarbon accumulations. Fault-plane sections demonstrate that fault sealing is unrelated to juxtaposition of intercalated shales. These fault-zone capillary seals were studied by (1) inferring their fluid-flow properties from the pattern of trapped hydrocarbons and (2) direct examination and measurement of cored faults. Buoyancy pressures for hydrocarbon columns were calculated from fluid property data for each reservoir and fault block. Buoyancy pressures range widely, increasing nonlinearly with fault displacement and percent shale in the faulted section, but do not vary systematically with stratigraphic position or depth. Small-displacement faults observed in core are narrow zones of cataclasis within porous sandstone. Mercury injection tests indicate fault-zone displacement pressures that coincide with buoyancy pressures calculated for hydrocarbon columns sealed by large-displacement faults. The agreement between measured displacement pressures and calculated buoyancy pressures indicates that (1) the reservoirs are filled to their capacity, dictated by the displacement pressure of the fault zones, and (2) the fault-zone seals are primarily the product of deformation of the sands, with some enhancement by incorporation more » of argillaceous material into the fault zones. The observed relationship between fault displacement and calculated buoyancy pressure of the hydrocarbon columns implies that fault-zone continuity is a factor that needs to be assessed in fault-zone seal analysis. « less

Detailed Seal Analysis, Lower Cretaceous Rocks of the North Sinai Basin, Egypt: Effects on Hydrocarbon Migration and Accumulation in Overpressured Regimes

The filling mechanism of petroleum traps in the North Sinai basin has been studied, taking into account the area's maturation history, the hydrodynamic parameters, and the seal efficiencies. The purpose of this study was to ascertain whether or not sizeable accumulations of hydrocarbons could be expected and to investigate the origin of the oil discovered to date. Formation pressure regimes in the North Sinai basin include highly overpressured reservoirs with undercompacted shale, starting at relatively shallow depths. In particular, the deeper closed hydraulic systems usually exhibit abnormally pressured regimes in individual fluid compartments. The pressure regimes are separated from each other by seals that are of particular interest to explorationists, as they frequently support oil and gas pools. The fracture pressures as well as the formation pore pressures were used together in some wells to evaluate seal quality. This detailed seal analysis has identified many regional seals and pressure compartments and their lateral and areal extent. These seals seem to control the hydrodynamic regime in the underlying permeable Lower Cretaceous reservoirs, and along with source maturation strongly affect the migration of hydrocarbons from source rocks and their accumulation in reservoirs. The water chemistry of the undercompacted sediments and overpressured reservoirsmore » agrees with the different hydrodynamic systems mapped. Water chemistry zones clearly define different hydraulic systems. Originally, they are the freshwater aquifer of Lower Cretaceous overlain by higher salinity formations.« less

An Annular Gas Seal Analysis Using Empirical Entrance and Exit Region Friction Factors

Wall shear stress results from stationary-rotor flow tests of five annular gas seals are used to develop entrance and exit region friction factor models. The friction factor models are used in a bulk-flow seal analysis which predicts leakage and rotor-dynamic coefficients. The predictions of the analysis are compared to experimental results and to the predictions of Nelson’s analysis (1985). The comparisons are for smooth-rotor seals with smooth and honeycomb-stators. The present analysis predicts the destabilizing cross-coupled stiffness of a seal better than Nelson’s analysis. Both analyses predict direct damping well and direct stiffness poorly.