Sleipner Vest Research Articles

A Numerical Analysis of the Effects of Supercritical CO2 Injection on CO2 Storage Capacities of Geological Formations

One of the most promising means of reducing carbon content in the atmosphere, which is aimed at tackling the threats of global warming, is injecting carbon dioxide (CO2) into deep saline aquifers (DSAs). Keeping this in mind, this research aims to investigate the effects of various injection schemes/scenarios and aquifer characteristics with a particular view to enhance the current understanding of the key permanent sequestration mechanisms, namely, residual and solubility trapping of CO2. The paper also aims to study the influence of different injection scenarios and flow conditions on the CO2 storage capacity and efficiency of DSAs. Furthermore, a specific term of the permanent capacity and efficiency factor of CO2 immobilization in sedimentary formations is introduced to help facilitate the above analysis. Analyses for the effects of various injection schemes/scenarios and aquifer characteristics on enhancing the key permanent sequestration mechanisms is examined through a series of numerical simulations employed on 3D homogeneous and heterogeneous aquifers based on the geological settings for Sleipner Vest Field, which is located in the Norwegian part of the North Sea. The simulation results highlight the effects of heterogeneity, permeability isotropy, injection orientation and methodology, and domain-grid refinement on the capillary pressure–saturation relationships and the amounts of integrated CO2 throughout the timeline of the simulation via different trapping mechanisms (solubility, residual and structural) and accordingly affect the efficiency of CO2 sequestration. The results have shown that heterogeneity increases the residual trapping of CO2, while homogeneous formations promote more CO2 dissolution because fluid flows faster in homogeneous porous media, inducing more contact with fresh brine, leading to higher dissolution rates of CO2 compared to those in heterogeneous porous medium, which limits fluid seepage. Cyclic injection has been shown to have more influence on heterogenous domains as it increases the capillary pressure, which forces more CO2 into smaller-sized pores to be trapped and exposed to dissolution in the brine at later stages of storage. Storage efficiency increases proportionally with the vertical-to-horizontal permeability ratio of geological formations because higher ratios facilitate the further extent of the gas plume and increases the solubility trapping of the integrated gas. The developed methodology and the presented results are expected to play key roles in providing further insights for assessing the feasibility of various geological formations for CO2 storage.

Noble gases solubility models of hydrocarbon charge mechanism in the Sleipner Vest gas field

Noble gases are chemically inert and variably soluble in crustal fluids. They are primarily introduced into hydrocarbon reservoirs through exchange with formation waters, and can be used to assess migration pathways and mechanisms, as well as reservoir storage conditions. Of particular interest is the role groundwater plays in hydrocarbon transport, which is reflected in hydrocarbon–water volume ratios. Here, we present compositional, stable isotope and noble gas isotope and abundance data from the Sleipner Vest field, in the Norwegian North Sea. Sleipner Vest gases are generated from primary cracking of kerogen and the thermal cracking of oil. Gas was emplaced into the Sleipner Vest from the south and subsequently migrated to the east, filling and spilling into the Sleipner Ost fields. Gases principally consist of hydrocarbons (83–93%), CO2 (5.4–15.3%) and N2 (0.6–0.9%), as well as trace concentrations of noble gases. Helium isotopes (3He/4He) are predominantly radiogenic and range from 0.065 to 0.116RA; reported relative to air (RA=1.4×10−6; Clarke et al., 1976; Sano et al., 1988), showing predominantly (>98%) crustal contributions, consistent with Ne (20Ne/22Ne from 9.70 to 9.91; 21Ne/22Ne from 0.0290 to 0.0344) and Ar isotopes (40Ar/36Ar from 315 to 489). Air-derived noble gas isotopes (20Ne, 36Ar, 84Kr, 132Xe) are introduced into the hydrocarbon system by direct exchange with air-saturated water (ASW). The distribution of air-derived noble gas species are controlled by phase partitioning processes; in that they preferentially partition into the gas (i.e., methane) phase, due to their low solubilities in fluids. Therefore, the extent of exchange between hydrocarbon phases and formation waters – that have previously equilibrated with the atmosphere – can be determined by investigating air-derived noble gas species. We utilize both elemental ratios to address process (i.e., open vs. closed system) and concentrations to quantify the extent of hydrocarbon–water exchange (i.e., volumetric gas–water ratios). These data are discussed within the framework of several conceptual models: (i) total gas-stripping model, which assumes all noble gases have been stripped from the water phase, thus defining the minimum volume of water to have interacted with the hydrocarbon phase; (ii) equilibrium model, which assumes equilibration between groundwater and hydrocarbon phase at reservoir P, T and salinity; and (iii) open and closed system gas-stripping models, using concentrations and elemental ratios. By applying these models to Ne–Ar data from Sleipner, we estimate volumetric gas–water ratios VgVw between 0.02 and 0.07, which are lower than standard geologic gas–water estimates of ∼0.24, estimated by combining gas-in-place estimates with groundwater porosity estimates. Sleipner Vest data can be best approximated by an open system model, which predicts more than an order of magnitude more groundwater interaction during migration than geologic estimates, indicating a dynamic aquifer system and/or a hydrous migration pathway. In an open system, the extent of gas loss can be estimated to be between 8 and 10 reservoir volumes, which have passed through the system and been lost (i.e., filled and spilled).

Sequestration of CO<sub>2</sub> in Geological Media: A Case Study of the Saline Reservoir Using Parallel Computing for Multi-Well Injection

Carbon-Dioxide Capture and Storage (CCS) in deep saline aquifers is one of the most feasible techniques for reducing anthropogenic emission of carbon dioxide (CO2). In this paper, a high-performance parallel computing is used to simulate the large-scale and long-term CO2 geologic storage in the saline aquifer (Sleipner Vest field in the Norwegian) based on the ECO2N module of the flow/transport simulator TOUGH2-MP, which is the parallel version of TOUGH2 implemented by the MPI. We have developed a complex three-dimensional heterogeneous model to study the spatial and temporal distribution and storage of CO2 injection into the sands of the Utsira formation, at the Sleipner Vest field in the Norway. Simulation results demonstrate that the high-speed parallel computing enhanced the capability on handling the large-scale model and the long-term studies. Furthermore, in order to avoid the problems of overpressure in the saline reservoir, the case study employs multi-well (ten-well) injection model, which has been proven to be able to reduce the reservoir pressure effectively when compared to the single-well injection model.

Hydrocarbon system analysis in a rift basin with mixed marine and nonmarine source rocks: The South Viking Graben, North Sea

The South Viking Graben of the North Sea is a prolific oil and gas province that has recoverable reserves of approximately 176 x 109 Sm3 (standard cubic meters) (6.2 tcf) gas, 58 x 106 t (412 million BOE) natural gas liquids, and 12.5 x 106 Sm3 (78 million bbl) of black oil contained in the main fields Sleipner Vest, Sleipner Ost, and Volve. These fields are located primarily within Block 15/9 in the Norwegian sector and extend into neighboring Blocks 15/6 and 16/7. The principal source of black, nonvolatile oil is the Late Jurassic Draupne Formation, which has a predominance of marine algal organic matter. The lower section of the Draupne Formation together with the Heather Formation are organically leaner and contain a mixture of marine algal and terrigenous organic matter, resulting in a potential to generate both oil and gas. The Middle Jurassic Hugin and Sleipner formations contain humic coals and coaly shales with potential to generate gas and some light liquids. These coals contain, on average, 80-90% vitrinitic woody material with occasional enrichment of resinite. High resinite concentrations can lead to an overprediction of oil potential, as they contribute significantly to the hydrogen index (HI) but generate primarily low molecular weight aromatic compounds. All source rock facies types have reached maturities sufficient to generate oil and gas. Basin modeling suggests that onset of oil and gas generation started during the latest Cretaceous-early Paleocene. These source rocks have continued to yield oil and gas to the present day in many parts of the catchment area for the Sleipner fields. Detailed geochemical analyses identified five main oil and condensate families. Family A comprises condensates and oil located in the northernmost part of Sleipner Vest and Dagny, generated from a marine, clastic source with a predominance of type II algal organic matter. Family B is condensates in the middle to southern part of Sleipner Vest, generated from a source, or a contribution from several source facies, with mixed terrigenous higher plant organic matter and marine algal material. Family C consists of condensates reservoired in the Jurassic of Sleipner Ost (except well 15/9-A15), generated from a mixed algal/terrigenous source but with a higher contribution of hydrocarbons from a marine algal source as compared with the Sleipner Vest family B. Family D comprises condensates in the Jurassic-Triassic of Loke and Gungne, in well 15/9-A15 from the crest of the Sleipner Ost structure, as well as condensates within the Paleocene sands of Sleipner Ost. These condensates have a mixed terrigenous higher plant and marine algal signature and are derived from pre-upper Draupne Formation sources. Family E is the black oil present in the Jurassic Volve field, derived from a marine, calcareous shale with type II to II-S organic matter. The source rock for this oil is unique in the greater Sleipner area and is likely located in the isolated subgraben between the northern parts of Sleipner Vest and Sleipner Ost. The hydrocarbon gases are broadly similar and are interpreted to have been generated from coals and coaly shales of the Sleipner and Hugin formations, as well as those parts of the pre-upper Draupne section that have a predominance of terrigenous higher plant organic matter.

Full-scale measurements from a large deepwater jack-up platform

Abstract Analysis of full-scale measurements obtained from the instrumented Smedvig West Epsilon jack-up platform operating in the STATOIL Sleipner Vest field in the North Sea is described. This jack-up platform has a skirted spud-can foundation. The following topics are discussed in the paper: • Comparison between measured and calculated natural frequencies and modes of the platform based on modal analysis. • Comparison of measured foundation stiffness with the design stiffness. • Comparison between measured and simulated platform response by application of a nonlinear time domain analysis. Implications with respect to procedures and assumptions employed for design of the platform are addressed. The comparison between measured and simulated response is performed for a moderate sea state with a significant wave height of 9.3 m.

Fault controlled communication in the Sleipner Vest Field, Norwegian Continental Shelf; detailed, quantitative input for reservoir simulation and well planning

Abstract The Sleipner Vest field, located in blocks 15/6 and 15/9 on the Norwegian Continental Shelf, contains hydrocarbons (mainly gas condensates) within the marginal marine units of the Middle Jurassic Hugin Formation. The field is segmented into fault-bounded compartments, which exhibit differences in gas-water contacts of between 10 and 100m. Microstructural analysis of core samples has identified three principal fault types; cataclasites, developed from clean sandstones, framework phyllosilicate fault rocks created from impure sandstones and clay smears developed from phyllosilicate-rich units. The distribution of these has been linked to the phyllosilicate content of the undeformed Hugin reservoir at the time of deformation. Petrophysical property analysis has been used to quantify the representative permeabilities and threshold capillary pressures of the fault rocks and their undeformed equivalents. Juxtaposition/seal diagrams and detailed fault plane maps were also constructed and provide a basis for mapping sand-sand juxtapositions and the distributions of the different fault rock types with assigned permeabilities and capillary threshold pressures. The results provide an explanation of the mapped variations in gas-water contacts. An important correlation exists between the type of fault rock predicted to dominate the fault plane near the hydrocarbon-water interface and the difference in hydrocarbon depths across the faults. Compartments separated by faults with windows of juxtaposed clean sandstone cataclasites have small hydrocarbon-water level differences (7–11 m), suggesting that the low capillary threshold pressure (more permeable) cataclastic fault rocks control communication. Compartments separated by faults predicted to have extensive phyllosilicate-rich fault rocks (developed from impure sandstones and clay rich units) with high capillary threshold pressures correlate to larger hydrocarbon-water differences (>39 m), reflecting the reduced communication.

96/02178 Sleipner Vest CO 2 disposal - Injection of removed CO 2 into the Utsira formation

96/02178 Sleipner Vest CO 2 disposal - Injection of removed CO 2 into the Utsira formation

Sleipner vest CO 2 disposal - injection of removed CO 2 into the utsira formation

Production from the Sleipner Vest Field, containing up to 9,5% CO 2, starts October 1, 1996. The Sleipner Vest gas will be delivered under the Troll Gas Sales Agreements, and hence has to meet the sales specification of maximum 2,5% by volume CO 2 in the gas. The amount of removed CO 2 would be approximately 1 million metric ton per year. For environmental reasons the CO 2 will be injected into an underground aquifer.

Emission-free fossil energy from Norway

The Norwegian policy regarding CO 2 as a greenhouse gas is explained as a background for Statoils CO 2-removal and -deposition activities. The planned deposition in a subsea aquifer of 1 million tons of CO 2/year which will be removed from the Sleipner Vest offshore gas field is described. A brief description of the Norwegian R&D activities with respect to CO 2-removal and deposition is given. Several scenarios where CO 2-free energy in the form of electricity or hydrogen is supplied to continental Europe or UK are discussed. It is concluded that CO 2-removal and -deposition is a less expensive solution than the large scale application of renewable energy sources (other than hydropower) and probably also fusion energy. R&D in the area of CO 2-removal and -deposition is especially suited to international cooperation and burden sharing.