Abstract
The petrophysical properties of Miocene mudstones and gas bearing-heteroliths were the main scope of the work performed in one of the multihorizon gas fields in the Polish Carpathian Foredeep. Ten boreholes were the subject of petrophysical interpretation. The analyzed interval covered seven gas-bearing Miocene horizons belonging to Sarmatian and Badenian deposits. The water saturation in shaly sand and mudstone intervals was calculated using the Montaron connectivity theory approach and was compared with Simandoux water saturation. Additionally, the Kohonen neural network was used for qualitative interpretation of four PSUs (petrophysically similar units), which represent the deposits of comparable petrophysical parameters. This approach allowed us to identify the sediment group with the highest probability of hydrocarbon saturation. Then, the spatial distribution of PSUs and reservoir parameters was carried out in Petrel. The resolution of the model was selected to reflect the variability of log-derived parameters. The reconstruction of the spatial distribution of shale volume, porosity, and permeability was performed with standard parametric modeling procedures using the Gaussian random function simulation stochastic algorithm, while PSU distribution and hydrocarbon saturation (SH) required a separate approach. The distribution into PSU groups was carried out by facies classification. Predefined ranges of clay volume, effective porosity, and permeability were used as discriminators to achieve spatial distribution of the PSU groups. The spatial distribution of hydrocarbon saturation was performed by creating the meta-attribute of this parameter and then reducing the derived pseudo-saturation model to physical values. Results included the creation of maps of hydrocarbon saturation that show the preferable areas with the highest hydrocarbon saturation for each gas horizon.
Highlights
Research on hydrocarbons in Miocene sediments of the Carpathian Foredeep conducted in recent years has led to the discovery of many gas horizons located in thin-layer heteroliths, mudstones, and sandstones
The analyses of the results presented in the form of maps of average hydrocarbon saturation indicate best perspectivity for horizons XV and XVI showed high hydrocarbon
As was noted in the previous works, the favorable conditions for gas accumulations provide the thin layers of sandstones and mudstones sealing by the laminas of impermeable claystones with admixtures of calcite and dolomite
Summary
Research on hydrocarbons in Miocene sediments of the Carpathian Foredeep conducted in recent years has led to the discovery of many gas horizons located in thin-layer heteroliths, mudstones, and sandstones. Many geophysical and geological research has been performed to recognize the possibilities of hydrocarbon accumulation in Miocene sediments [1–7]. The main influence on the formation of gas accumulations was the structural and facies factors, which define the horizons lithological boundaries [1]. Baden-Sarmatian is dominated by heterolithic deposits formed in the environment of the basin plain. They consist of claystones and siltstones covered with thin layers of fine and medium-grained sandstones, the thickness of these sediments can be up to about 200 m
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