Historia termiczna a generacja węglowodorów w rejonie struktury Dobrzycy (Pomorze Zachodnie)

Paweł Henryk Karnkowski



Thermal history and hydrocarbon generation in the area of Dobrzyca Structure (Western Pomerania, Poland) The Dobrzyca Structure is located between Koszalin and Kołobrzeg and it is built mainly by Devonian rocks. The discussed structure is placed in the transition zone between the Pomerania Anticlinorium and the Pomerania Synclinorium (Fig. I). In the vertical structural subdivision five complexes were distinguished; all complexes and their tectonic styles are shown on Fig. 2. Seismic line T0030594 joining the Sarbinowo-I, Daszewo-16/Daszewo-17 wells and crossing throughout the Dobrzyca structure has been chosen for analysis. In the case of the Dobrzyca Structure the most important - from petroleum point of view - are Devonian formations. The author supposes that there is located the Frasnian coral reef within the Dobrzyca Structure. Coral limestones (Koczafa Formation) interfinger with the Strzeżewo Member (Fig. 3). Younger Upper Devonian members and formations observed along the elaborated section (22 km long) are strongly differentiated in facies and thickness characteristics. The obtained data (Fig. 4, 5) were used for computer simulation. The result of several simulations was the numerical and geological model of heat flow along the Daszewo—Sarbinowo line (Fig. 6). Heat flow model (Fig. 6) and hydrocarbon generation processes (Fig. 7) indicate that in the Daszewo region a hydrocarbon generation took place in the Zechstein and Buntsandstein time while the Dobrzyca structure was in the immature stage or later, in the late Mesozoic time, it was in the "oil window" (Fig. 8). The Laramide inversion only slightly changed the existing hydrocarbon-bearing image. This picture indicates assuming good source and reservoir rocks oil-field possibility within the Dobrzyca Structure. Maturity zones of organic matter in the Dobrzyca Structure can be compared with the Daszewo region where the oil field was located within the Zechstein sequences (Ca2) and the gas field within the Lower Carboniferous series (Fig. 9). The computer-aided simulations indicate also the stratigraphic traps below the Zechstein seal and structural traps bounded by faults (tilted blocks) in the tectonic contact zone between the Ordovician/Silurian and Devonian rocks.

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