(INNOVATIVE APPROACH TO BOREHOLE SEISMIC SURVEYS, PROCESSING AND INTERPRETATION OF 3D SEISMIC DATA FOR SOLVING CHALLENGING GEOLOGICAL PROBLEMS)
The relevance of this study is determined by the need to improve the accuracy and reliability of solving the problems applicable to shallow zones through the use of a set of geophysical methods and processing of the resulting data. Over 70 % of hydrocarbon reserves are concentrated in the fields with complex geological structure featuring tectonic faults, shallow pay zones, varying reservoir quality in terms of area and thickness. The operational efficiency of the underground gas storage facilities based both on depleted fields and on aquifer reservoirs largely depends on the completeness and detailing of the challenges associated with the complex geological structure.
The article outlines practical application of borehole seismic surveys at Stepnovskoye underground gas storage facility (Saratov Oblast), as it may be useful in developing hydrocarbon fields as well.
From a geological viewpoint Stepnovskoye underground gas storage facility is one of the most complicated facilities in PJSC Gazprom system. It was created on the basis of a depleted gas and oil field. Stepnovskoye underground gas storage facility includes two gas storage facilities: D2V + VI of Vorobievsky horizon and D2IVa + IVb of Ardatov horizon. Until now, due to insufficient data on geological exploration, it has been assumed that the area has a plicative structure, although the evidences of tectonic faults were identified during the field development.
The reservoirs of Stepnovskoye underground gas storage facility vary in their characteristics: operating modes, areas of reservoir zones stretching, properties thereof, and fluid saturation patterns. Each reservoir is no more than 10 m thick.
Five wells of Stepnovskoye underground gas storage facility were subjected to borehole seismic surveys (vertical seismic profiling, including offset and walkaway vertical seismic profiling) in order to clarify the storage structure. Comprehensive use of the results obtained, as well as re-processing and re-interpretation of the data gathered by 3D seismic, field and geophysical borehole surveys for the first time clarified structural and tectonic configuration of the gas storage area in question by each target horizon.