Challenges and enablers for large-scale CO2 storage in chalk formations

https://pure.hw.ac.uk/ws/files/15146951/1_s2.0_S187551001730104X_main_1_.pdf

Seismic assisted history matching using binary maps

This paper presents a history matching scheme that has been applied to production data and time lapse seismic data. The production data objective function is calculated using the conventional least squares method between the historical production data and simulation predictions, while the seismic objective function uses the Hamming distance between two binary images of the gas distribution (presence of gas (1) or absence of gas (0)) sequenced over the different acquisition times. The technique is applied to a UKCS (United Kingdom Continental Shelf) field that has deep-water tertiary turbidite sands and multiple stacked reservoirs defining some degree of compartmentalisation. Thirty five parameters are perturbed in this history match, they can be classified as volumetric parameters (net-to-gross, pore volume), transmissibility parameters (permeability, transmissibility), and end points of the relative permeability curves (critical saturation points). An initial ensemble of fluid flow simulation models is created where the full range of uncertain parameters are acknowledged using experimental design methods, and an evolutionary algorithm is used for optimization in the history matching process. It is found that permeability and critical gas saturation are key parameters for achieving a good history match, and that the volumetric parameters are not significant for this match in this particular reservoir. We also observe that matching only to production data marginally improves the seismic match, whilst matching to only seismic data improves the fit to production data. Combining both sets of data delivers an improvement for the production data and seismic data, as well as an overall reduction in the uncertainties. A unique feature of this technique is the use of the Hamming distance metric for seismic data history matching analysis, as this circumvents the use of the uncertain petroelastic model. This approach is easy to implement, and also helps achieve an effective global history match.

Seismic Assisted History Matching Using Binary Image Matching

Binary 4D seismic history matching, a metric study

In 2012, a repeat time-lapse seismic survey was acquired over the Halfdan oil field located in the Danish North Sea. The main oil reservoir is the Cretaceous chalk Tor Formation, and the field is developed with a line-drive water flood. The reservoir saturation changes due to water injection and gas breakout lead to large changes in acoustic impedance, which can be imaged with 4D seismic. The 4D acoustic-impedance changes, in conjunction with production and geologic data, were analyzed on a well-by-well basis and resulted in several interesting correlations between the geology and the 4D response. The 4D was used to update the seismic interpretation of some important layers within the static and dynamic model. In some areas, the impact of local porosity variations on the lateral sweep could be seen. The 4D also provided evidence that some faults serve as potential pathways for formation-water entry into the oil-producing layers. In addition, numerous well-intervention opportunities were identified through integrating the 4D with the production, geologic, and dynamic data. Examples from the two-vintage and three-vintage 4D acoustic-impedance data illustrating these key 3D and 4D learnings and a successful well intervention are shown.

Halfdan 4D workflow and results leading to increased recovery

The quick turnaround of seismic processing of a 4D time lapse survey over the Halfdan oil field allowed for interpretation and integration of the new 4D results seven weeks after completion of the seismic acquisition. Analysis of the first fast track 4D dataset led to improved processing parameters and an additional demultiple application which yielded a significantly improved fast track dataset 11 weeks after the seismic acquisition was completed. The repeat 4D seismic survey was acquired in the summer of 2012 in order to provide a better understanding of the sweep efficiency from the line drive water flood, guide future well interventions and improve the reservoir model. The baseline 3D seismic data was acquired in 1992/1993, prior to field development, and the first monitor 3D seismic was acquired in 2005. The rock physics model shows that
increased water saturation due to the water flooding along the injectors in the Tor oil-bearing reservoir dominates the 4D change in acoustic impedance yielding a hardening response. The rock physics model was used to convert the reservoir model pressure and saturation changes from the three time-steps to modelled acoustic impedance changes. Examples will be shown from the 4D time lapse and the reservoir model acoustic impedance changes.

The impact of a quick 4D seismic survey and processing over the Halfdan Field, Danish North Sea

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The impact of a quick 4D seismic survey and processing over the Halfdan Field, Danish North Sea