Vertical Flow Barriers Research Articles

The influence of heterogeneity on coastal groundwater flow - physical and numerical modeling of fringing reefs, dykes and structured conductivity fields

Abstract Geological heterogeneity of the subsurface, caused by both discrete features and spatially distributed hydraulic conductivity fields, affects the flow of coastal groundwater. It influences the shape and the position of the interface between saltwater and freshwater, as well as the location and flux rate of freshwater discharge to the ocean. Fringing reefs lead to a bimodal regime of freshwater discharge, with discharge at the beach face and through deeper, submarine springs. Impermeable vertical flow barriers (dykes) lead to an impoundment of fresh groundwater and a compartmentalization of the aquifer but also to a delayed expulsion of saline water. Spatially distributed conductivity fields affect the shape of the interface and the geometry of the saltwater wedge. Higher effective conductivities lead to a further landward intrusion of the wedge toe. These flow characteristics can be important for groundwater extraction, the delineation of protection zones and the assessment of contaminant transport to coastal ecosystems.

Chemical compaction features as potential barriers in the Permian-Triassic reservoirs of Southern Iran

Chemical compaction features are important diagenetic imprints that generally interrupt reservoir quality in most carbonate reservoirs. In the Permian-Triassic reservoirs of South Pars Field, they are recorded in various types and intensities. High- to low amplitude stylolites and solution seams are concentrated within the K1–K4 units of the upper Dalan and Kangan formations, depending on their facies characteristics, diagenetic alterations and dominant lithology. In these units, there are some meaningful trends between the chemical compaction zones and sequence stratigraphic positions including the systems tracts of third-order sequences. Control of chemical compaction on reservoir characteristics is evaluated by using the results of petrographic studies, petrophysical logs and core poroperm measurements. Internal reservoir architecture of the studied reservoirs is determined using the both hydraulic flow units and stratigraphic modified Lorenz plot approaches. Identified baffle and barrier units show close correspondence with chemically-compacted zones. This indicates that zones with high concentration of stylolites and solution seams can be considered as small-scale vertical flow barriers in the Permian-Triassic reservoirs of South Pars Field.

Predicting Vertical Flow Barriers Using Tracer Diffusion in Partially Saturated, Layered Porous Media

Sudden changes in isotopic tracer concentration in pore waters have been interpreted as indicating barriers to vertical advective flow through porous rocks in the subsurface, e.g. step changes in $$^{87}\hbox {Sr}/^{86}$$ Sr ratio are often used in the oil and gas industry as a signature of reservoir compartmentalisation. This study shows that this is not necessarily the case. It can take millions of years for such step changes to equilibrate by diffusion if there is no flow resulting from pressure or density gradients even in high permeability, high porosity rocks, particularly if the water saturation is low. Changes in tracer concentration gradients can be good indicators of changes in porosity (or water saturation) between layers. In contrast changes in sorption without a change in porosity are almost impossible to identify. The time taken for concentration gradients to equilibrate is affected by the layer properties but can be quickly estimated from the harmonic average of the effective diffusion coefficient for each layer and a simple analytical expression for a homogeneous system. This was achieved by performing a sensitivity analysis on different layer properties (porosity contrast, saturation contrast, sorption contrast, thickness ratio) using existing analytical solutions for diffusion in layered systems.

Integrated approach to geomodelling and dynamic simulation in a complex mixed siliciclastic–carbonate reservoir, N'Kossa field, Offshore Congo

Abstract The Lower Sendji Carbonate (Albian age) of the N'Kossa field is a mixed siliciclastic–carbonate reservoir exhibiting very heterogeneous reservoir properties and the development of extensive vertical flow permeability barriers. The reservoir is a succession of interstratified dolomite, limestone, sandstone and shale lithologies of sabkha, tidal flat and lagoonal origin. Early, synsedimentary dolomite cements are extensively developed, particularly over local palaeohighs. Challenges to hydrocarbon production include: (1) the vertical variability of reservoir properties; (2) the presence of many, laterally extensive vertical flow barriers; and (3) variable connectivity between fault-bounded compartments. This complexity was underestimated at the appraisal stage, the initial development plan calling for a relatively simple scheme of pressure support to the critical reservoir fluid via injection into the gas cap and the water leg. This decision was supported by the identification of a single hydrocarbon column (>400 m thick) over the entire structure which suggested a lack of vertical compartmentalization. Recent studies, which include a geological synthesis of more than forty wells and a dynamic data synthesis to determine the production mechanism and identify key heterogeneities, show a lack of pressure support to the oil leg from both water and gas injector wells. Today, integration of static and dynamic data together with an improved geological understanding of the stratigraphic control on vertical flow barriers and mapping of high permeability sandstone layers is the key to identifying unswept zones of the field and future infill drilling targets.

Pool Description And Performance Analysis Leads to Understanding Golden Spike's Miscible Flood

Abstract Reservoir description was a key factor in analyzing the performance of the Golden Spike vertical gravity controlled miscible L.P.G. bank scheme. Understanding the performance of the pool was enhanced by including a detailed reservoir description in a computer model study of the miscible scheme. The originally designed 7% pore volume L.P.G. bank was injected between the gas and oil zones from 1964 through 1975. Extensive monitoring of fluid distribution in this 1,385-acre, 480-foot-thick reef complex indicated that the miscible flood improved the oil recovery until 1979. A geological study, incorporating data from infill wells drilled during the 1970's, shows that the reservoir contains many local barriers to vertical flow. Located in the interior of the reef, these barriers range in size from less than 5 to over 600 acres. The barriers were not recognized prior to infill drilling, because the early development wells were drilled mainly in more homogeneous sections of the reefcomplex. Recent performance analysis indicates the barriers resulted in by-passing of oil and loss of miscible flood benefits after 1978. As a result of the loss of miscibility, the pool is currently under gas drive and the miscible scheme has been terminated. Performance analysis results are confirmed by a cross-section computer model study of the pool. The cross-section model also indicates that the vertical flow barriers combined with the designed bank size results in poor sweep efficiency by solvent. However, future sweep efficiency by gas is predicted to be high due to continued drainage of oil off the barriers. Introduction THE GOLDEN SPIKE D3 "A" Pool, located 18 miles southwest of the City of Edmonton in Central Alberta, was discovered in 1949 (Fig. 1). The pool is located on the western, seaward side of a trend of productive Leduc reefs. This limestone reservoir is a Leduc-age Woodbend reef complex, covering an area of 1,385 acres. Within the crestal area of 1,000 acres, average oil pay thickness is 550 feet. Initial oil-in-place was 319 MMSTB, with no gas cap or water leg present. As indicated in Figure 2, the Leduc Formation at Golden Spike is divisible into three members, designated Lower, Middle and Upper Leduc, Oil occurrence in the Golden Spike D3 ‘A’ Pool is restricted to the Middle and Upper members which, together, make up the reef complex, The underlying Lower Leduc is a shallow-water carbonate bank, more extensive in area than the reef build-up, but limited in reservoir development. This carbonate bank is not in communication with the oil zone. Initial production of this reservoir by fluid expansion resulted in a rapid pressure decline. Pressure maintenance by gas injection commenced in 1953. Analysis of the available well data and gas flood performance up to 1963 indicated a relatively homogeneous reservoir. The apparent good quality of the reservoir and the availability of a suitable, inexpensive hydrocarbon solvent (LPG) prompted installation of a miscible flood in 1964 (Fig. 3).

Thermal Separation Column with Vertical Barriers. I. Analytical Studies on the Thermal Separation Column Having Vertical Barriers

Abstract The effect of installing a couple of vertical flow barriers inside a double cylinder-type thermal separation column has been studied analytically. The method of analysis is entirely similar to that developed by Jones and Furry. The only change is that an additional parameter, which specifies the location of the barriers, has been introduced. The results indicated that the installation of barriers retards the convectional velocity and leads to a remarkable increase in the equilibrium separation. With the optimum design, which is achieved by locating barriers at 5/8 parts of the half-width of the wall spacing, the logarithmic equilibrium separation will become 4 times greater than that in the open column.