Abstract
The main components of the Ordovician carbonate reservoirs in the Tahe Oilfield are paleokarst fracture-cavity paleo-channel systems formed by karstification. Detailed characterization of these paleokarst reservoirs is challenging because of heterogeneities in characteristics and strong vertical and lateral non-uniformities. Traditional seismic analysis methods are not able to solve the identification problem of such strongly heterogeneous reservoirs. Recent developments in seismic interpretation have heightened the need to describe the fracture-cavity structure of a paleo-channel with more accuracy. We propose a new prediction model for fracture-cavity carbonate reservoirs based on spectral decomposition and a waveform cluster. By the Matching Pursuit decomposition algorithm, the single-frequency data volumes are obtained. The specific frequency data volume that is the most sensitive to the reservoir is chosen based on seismic synthesis traces of well-logging data and geological interpretability. The waveform cluster is then applied to delineate the complex paleokarst systems, particularly the fracture-caves in the runoff zone. This method was applied to the area around Well T615 in the Tahe oilfield, and a paleokarst fracture-cavity system with strong heterogeneity in the runoff zone was delineated and characterized. The findings of this research provide insights for predicting other similar karst systems, such as karstic groundwater and karst hydrogeological systems.
Highlights
The Ordovician carbonate paleo-water system in the Tahe Oilfield was mainly formed during the Hercynian period
This paper proposes a new model for predicting fracture-cavity carbonate reservoirs based on spectral decomposition and a waveform cluster
In the conventional spectral decomposition process, the considered appropriate single-frequency data are generally chosen by experience, and lack geological constraints
Summary
The Ordovician carbonate paleo-water system in the Tahe Oilfield was mainly formed during the Hercynian period. Influenced by multi-phase tectonic movement and multiple sea-level rises and falls, the karst superposition reformation was developed. Cracks, and weathering crusts, a pale karst reservoir with large caves as the main reservoir space was formed. The karst paleo-channel in the karst water system area is the core of the entire karst reservoir system. The caves, with different scales and forms, are closely related to the ancient river channel. It is generally thought that the Ordovician fracture-cavity carbonate reservoir was formed by dissolution, with an extremely heterogeneous internal structure and non-uniform lithological properties [1,2,3]. Because of the burial depth of the Ordovician carbonate strata, which exceeds
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