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Results
Abstract Information obtained from 4D gravity and subsidence monitoring provides improved decision-making in the exploitation of offshore reservoirs. Field cases demonstrate the impact of this technology in the estimation of hydrocarbon volumes, the evaluation of risk of water breakthrough, understanding of drive mechanisms and identification of undrained compartments. The additional information provides increased hydrocarbon recovery in later phases of the projects, through the identification of infill-well targets or by the optimization of compression facilities. The cost of this technology, which is typically 10๏นช of that of 4D seismic, makes it feasible in a large range of offshore fields. The technology has been used in eight fields on the Norwegian continental shelf (NCS). 4D gravity is sensitive to changes in the mass distribution in the reservoir. Gas depletion and water influx from surrounding aquifers produce an observable time-lapse gravity signal. The observed signals are independent of seismic velocities, which makes this technology complementary to seismic monitoring. In addition, gravity provides a more precise quantification of mass changes than 4D seismic, and it can provide a better sensitivity to the movement of the gas-water contact. Seafloor subsidence is also sensitive to important reservoir and overburden properties. It is directly related to compartmentalization, and it can be a key factor for the safety of installations. It is an observable effect of geomechanical changes. Seafloor subsidence has been used to identify non-depleted compartments; determine the drilling-window for in-fill wells; understand aquifer properties; and improve the geomechanical model hence the interpretation of seismic time-shifts. In this abstract, we review the principles of the 4D gravity and subsidence monitoring technology. We then discuss some of the case studies from the NCS that illustrate the value these data provide for reservoir management. Finally, we discuss the main cost drivers of the technology, and which steps are taken by the industry to reduce cost and hence extend its feasibility to a wider range of fields. Introduction Optimizing hydrocarbon recovery in offshore hydrocarbon fields involves decisions involving costly investments, like drilling infill wells or installing compression facilities. A good understanding of the dynamical behaviour of the reservoir over the lifetime of the field is of key importance to support and reduce the risk related to such investments.
- North America > United States (0.69)
- Europe > Norway > Norwegian Sea (0.16)
- Geophysics > Time-Lapse Surveying > Time-Lapse Seismic Surveying (1.00)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Gravity Surveying > Gravity Acquisition (1.00)
- Europe > Norway > Norwegian Sea > Mรธre Basin > PL 442 > Block 6305/8 > Ormen Lange Field > Springar Formation (0.99)
- Europe > Norway > Norwegian Sea > Mรธre Basin > PL 442 > Block 6305/8 > Ormen Lange Field > Egga Formation (0.99)
- Europe > Norway > Norwegian Sea > Mรธre Basin > PL 442 > Block 6305/6 > Ormen Lange Field > Springar Formation (0.99)
- (81 more...)
Abstract Seafloor subsidence is a matter of concern in areas with offshore hydrocarbon exploitations relatively close to the coast, like the central and northern Adriatic Sea. Traditional bathymetry methods provide sensitivities to seafloor deformations of the order of tenths of centimetres, which is often insufficient to determine subsidence patterns and rates. We propose a new, patented method for regional subsidence monitoring with an absolute accuracy of 2 to 5 millimetres, based on a technology developed for offshore reservoir monitoring. The method uses water pressure measurements as a starting point and reaches accuracies much better than pressure sensor specifications. The new method will allow distinguishing natural from anthropogenic subsidence in the Adriatic, and monitoring the extension of the anthropogenic subsidence bowls. The new measurements can cover the gap between the fine grid of land measurements and the sparse measurements obtained by GPS on offshore hydrocarbon platforms. In particular, the new information will allow to determine how close to the coastline the effects of hydrocarbon production extend. The method can also be used to enable accurate real-time subsidence monitoring in the area by using pressure sensors on the seabed. Regional subsidence monitoring can provide value to hydrocarbon exploitation itself. A good understanding of compaction processes is required for an optimal management of oil and gas reservoirs. Compaction depends on key properties of the reservoir like lateral compartmentalization and pore compressibility. In documented field cases, for instance, the analysis of subsidence patterns above producing fields have allowed to identify non-depleted compartments and have been used to identify target locations for infill wells. Introduction The context of the main Adriatic fields offshore is represented by young unconsolidated terrigenous sediments, where hydrocarbon production is likely to cause seafloor subsidence. The area features shallow water depths and a naturally subsiding sedimentary basin (Teatini et al., 2005). The coast presents large areas with elevations below 2 m above mean sea level. The Italian Adriatic coast features important natural sites and cities, including Venice and Ravenna. Italian authorities require that offshore development projects include a subsidence monitoring plan. ENI, the major operator in the area, has implemented a monitoring network since the beginning of the 90's (Dacome et al., 2015). The network includes onshore measurements with several technologies, and a network of 48 continuous GPS measurement stations placed on offshore platforms.
- Europe > Norway > Norwegian Sea > Mรธre Basin > PL 442 > Block 6305/8 > Ormen Lange Field > Springar Formation (0.99)
- Europe > Norway > Norwegian Sea > Mรธre Basin > PL 442 > Block 6305/8 > Ormen Lange Field > Egga Formation (0.99)
- Europe > Norway > Norwegian Sea > Mรธre Basin > PL 442 > Block 6305/6 > Ormen Lange Field > Springar Formation (0.99)
- (75 more...)
An Innovative Approach for Offshore Subsidence Monitoring: Technology Scouting, Feasibility Studies and Realization
Miandro, R. (Eni Upstream & Technical Services) | Dacome, C. (Eni Upstream & Technical Services) | Mosconi, A. (Eni Upstream & Technical Services) | Roncari, G. (Eni Upstream & Technical Services)
ABSTRACT Young unconsolidated terrigenous sediments represent the general geological context where the main offshore Adriatic fields are located. In such geological environment, sea floor subsidence, caused by hydrocarbon extraction, could eventually occur. In Italy in order to prevent any possible impact of the hydrocarbon production activities on coastal areas environments and infrastructures, before starting-up a new hydrocarbon off-shore development project, a monitoring plan to measure and analyse total subsidence evolution has to be submitted to the Italian Authorities. Though many tools are available for subsidence monitoring onshore, few are available for offshore monitoring. ENI, in order to fill the gap, conducted a research program, with different suppliers, to generate a monitoring system tool to measure seafloor subsidence. Advanced feasibility studies have been carried out with three different companies: Company 1; Company 2 and an Italian company, AGISCO, operating in the field of geotechnical instrumentation and consulting. Company 1 and Company 2 proposed the use of interesting technologies (respectively based on fiber optics and electrical tiltmeters), but with a technology readiness level lower than AGISCO's one, that proposed an advanced solution based on already available industrial components and easily implemented up to desired size. The AGISCO proposed tool was based on the internal cable altitude-dependent pressure changes, measured using pressure transducers. The AGISCO tool had already several applications on shore in dry/semi-dry places, but has never been applied to offshore subsidence monitoring for oil and gas industry. The company, in 2015, built for ENI the first prototype of the tool. The tool, according to ENI technical specifications resulted as a robust cable, with variable outside diameter (from 40 to 140 mm) and 100m interval spaced measuring points. The paper, through the design of instruments from the three companies, describes the process that has led to the choice of Agisco tool and outlines the future steps that will have to be taken towards the installation of the tool. INTRODUCTION ENI Upstream & Technical Services, as any others Oil Company involved in hydrocarbon exploration and production projects in Italy, particularly for the offshore fields located in the central-northern Adriatic sea, is obliged, by authorities to define a monitoring plan able to foresee, measure and analyse in semi-real time probable subsidence evolution before any gas production. The plan must manage any possible impact, direct or indirect, of the production project on the coastal areas and on the adjacent inland.
- Europe > Italy (0.75)
- North America > United States (0.68)
Abstract Channel sandstones have a particularly important place among sandstone reservoirs. Their exploitation is especially challenging because of the impact of reservoir heterogeneities, channel connectivity and well position. Understanding which channels are drained or swept during water flooding would greatly improve the possibility to increase oil recovery. Although ground movements induced by pressure sinks generated in the reservoir by production are generally very limited, surface deformation is known to reflect the pressure distribution in the reservoir. Thus, deformation monitoring of onshore reservoirs can provide useful information about which portions of the reservoir are actually being produced or where pressure is supported by water encroachment, or by water injection in the case of oil reservoirs. Standard ground surface monitoring techniques (such as: levelling campaigns, tiltmeters or GPS) are usually time-consuming in providing accurate measures for a limited set of benchmarks. However, the Interferometric Synthetic Aperture Radar (InSAR) has proven to be a cost-effective tool to measure surface displacement with millimetric precision over wide areas. The possibility to measure surface effects due to reservoir exploitation depends chiefly on the depth and extension of the reservoir, magnitude of pressure depletion within the reservoir, formation heterogeneity and geomechanical properties. This paper presents the results of a study aimed at assessing the effects of these parameters on the surface deformation pattern and magnitude for fluvial reservoirs. Since meandering and braided rivers often generate poorly connected reservoir sand bodies of different size and sinuosity, the approach taken was to build a number of geological models representing fluvial depositional environments at different depths. Then production and water flooding in alternating channels was simulated. Eventually, three-dimensional geomechanical models were developed for each reservoir so as to calculate the vertical and horizontal (longitudinal and transversal) components of the displacements. In order to assess whether these displacements could be detected via InSAR, the three different components of displacement were combined to calculate the Line Of Sight (LOS), to simulate the corresponding satellite displacement measurement; the latter was then compared with the sensitivity of the InSAR technique. Results show that, depending on reservoir depth, extension and pressure decline, a correspondence between the distribution of sand bodies within the reservoir and the surface displacement pattern can be established. Conversely, for the typology of reservoir under analysis, geomechanical properties turn out to play a minor role in the clear detection of surface deformations.
- Asia > Middle East (0.47)
- North America > United States (0.28)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Sedimentary Geology > Depositional Environment > Continental Environment > Fluvial Environment (0.74)
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Lifecycle > Disposal/Injection (0.34)
- Oceania > Australia > Northern Territory > Timor Sea > Bonaparte Basin > Petrel Basin > Sahul Platform > Block WA-6-R > Petrel Field > Torrens Formation (0.98)
- Oceania > Australia > Northern Territory > Timor Sea > Bonaparte Basin > Petrel Basin > Sahul Platform > Block WA-6-R > Petrel Field > Pearce Formation (0.98)
- Oceania > Australia > Northern Territory > Timor Sea > Bonaparte Basin > Petrel Basin > Sahul Platform > Block WA-6-R > Petrel Field > Cape Hay Formation (0.98)
- (9 more...)