Известия Томского политехнического университета: Инжиниринг георесурсов (Sep 2020)
COMPARATIVE PETROPHYSICAL CHARACTERISTIC OF THE JURASSIC SECTIONS OF THE OSTANINSKOE AND DVURECHENSKOE FIELDS (IN RELATION TO PETROLEUM POTENTIAL OF PRE-JURASSIC DEPOSITS OF THE TOMSK REGION)
Abstract
The relevance of the research is caused by the importance of reproduction and expansion of the resource base of hydrocarbons in Western Siberia based on the assessment of prospects and development of the horizon of the contact zone and the Paleozoic, where the deposits belong to hard-to-recover reserves. The aim of the research is to consistently justify the criteria for forecasting and prospecting Paleozoic hydrocarbon deposits based on the hypothesis of anomalies in the petrophysical characteristics of Jurassic formations – the uniqueness of the «reflection» of Paleozoic deposits in the geophysical parameters of the overlapping Mesozoic-Cenozoic section. This hypothesis was formulated and reasoned earlier by the results of studying the well sections of the Gerasimovskoe field with Paleozoic oil deposits and the Krapivinskoe fields with Jurassic oil deposits. The objects: geophysical and petrophysical parameters of the Jurassic reservoir layers and intervals of the Bazhenov suite at the Ostaninskoe oil and gas condensate field, which has deposits in the pre-Jurassic base, and at the Dvurechenskoe oil field with only Jurassic oil deposits. Methods. To characterize the Jurassic reservoirs, petrophysical calculations of electrical resistivity were performed, the data of induction logging and resistivity logging were used along sections of 28 wells of the Ostaninskoe and Dvurechenskoe deposits. To characterize the petrophysics of mudstones of the Bazhenovsuite, a qualitative and quantitative (statistical) analysis of the readings of the methods of potentials of spontaneous polarization, apparent resistence, and gamma-ray logging were carried out. The carbonate content of reservoir rocks was estimated using the volumetric gasometric method. Results. It was established that Jurassic reservoirs of the Ostaninskoe field have resistivity of 11...21 om·m for oil-saturated reservoirs and resistivity of 5...9 om·m for water-saturated reservoirs. Jurassic reservoirs of the Dvurechenskoe field have a resistivity of 6...12 om·m for oil-saturated formations and a resistivity of 2...5 om·m for water-saturated formations. The Jurassic reservoirs of the Ostaninskoe field are abnormally, two times higher, resistive than the Jurassic reservoirs of the Dvurechenskoe field. The total carbonate content of the Jurassic strata of the Ostaninskoe field is 5,4 %, and the Dvurechenskoe field is 1,1 %. It was shown that at the Ostaninskoe field, variations in the readings of the PS method are ±(0,5...2,5) mV, the resistivity level is 32...42 om·m, and the level of natural radioactivity is 36...44 mkR/hr. At the Dvurechenskoe field, variations in the PS readings are ±(5,0...8,0) mV, the resistivity level is 95...111 om·m, the level of natural radioactivity is 40...59 mkR/hr. The results of the research at the Ostaninskoe and Dvurechenskoe fields are fully consistent with the previously expressed and reasoned hypothesis of the anomalous petrophysical characteristics of the Jurassic section, overlapping deposits of the pre-Jurassic oil and gas condensate field.
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