Abstract
The successful interpretation of open-hole well logging data relies on jointly using all available petrophysical and geological information. This paper presents relevant case studies related to the integration of well logs with core measurements for exploration wells drilled in the Romanian continental shelf area of the Western Black Sea basin. The analyzed wells targeted gas-bearing sands and silts complexes of Early Pliocene (Dacian) age, developed in a deltaic to shallow marine sedimentary environment in two distinct fields. The wireline logging programs included conventional formation evaluation logs, pressure surveys, nuclear magnetic resonance, and borehole electrical imaging logs. The core dataset comprised routine and special measurements (porosity, grain density, permeability, water saturation, and Archie parameters) carried out at quasi-reservoir confining pressure. The wireline logging suites were interpreted via a deterministic workflow, including core-derived interpretation parameters. Other core-derived parameters were used for constraining and validating the log interpretations. The results show that a problem related to the ambiguity of formation water resistivity can be overcome through resistivity–porosity dependencies constructed to include potential aquifer zones in the proximity of the Dacian gas-bearing reservoirs. This study also revealed and quantified uncertainties regarding the estimation of gas–water contacts from formation pressure surveys, which can be mitigated by the confirmation or correction of pressure-derived fluid contacts via the well log interpretation results. Lastly, we identified a probable resistivity logs suppression effect related both to high contents of capillary-bound water and also to the limited resolution of electrical logging tools in the presence of sand-shale thin bedding or laminations.
Highlights
Considered as one of the most important hydrocarbon-bearing areas in SE Europe, the Western Black Sea basin has already demonstrated its potential through oil and gas fields discoveries in the continental shelf areas of Romania, Bulgaria, and Ukraine
Detailed studies regarding the geology, tectonics, hydrocarbon systems, and hydrocarbon plays from the Western Black Sea basin, including the Romanian offshore, have been carried out by Robinson et al [1,2], Moroşanu [3,4,5], Dinu et al [6], Bega and Ionescu [7], Crânganu et al [8], Georgiev [9], Tari et al [10], Nikishin et al [11,12], Oaie et al [13], and Boote [14]
This study aimed to present and discuss the main issues related to the petrophysical evaluation of two biogenic dry gas fields of Early Pliocene (Dacian) age from the Romanian continental shelf—Western Black Sea basin
Summary
Considered as one of the most important hydrocarbon-bearing areas in SE Europe, the Western Black Sea basin has already demonstrated its potential through oil and gas fields discoveries in the continental shelf areas of Romania, Bulgaria, and Ukraine. In the Romanian Black Sea shelf sector, the most important hydrocarbon fields are located in the central area, the Histria Basin/Depression (Figures 1 and 2). Ample geophysical investigations have been performed in this area starting in the 1970s, by means of seismic, gravity, and magnetometric surveys, for the identification of favorable geological structures and hydrocarbon accumulations. The volume of geophysical exploration and drilling activities in shallow water and deepwater perimeters is still limited.
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