ABSTRACT:

Vertical and horizontal resistivity, borehole image, NMR and conventional wireline log data were acquired in an exploration well in Northern Italy as part of a comprehensive evaluation program to quantify gas pay in a thick turbidite sand sequence. The highly porous turbidite pay sands in this High Adriatic basin occur as thick sequences of stacked sands and inter-bedded thin shales. Bed thickness of the turbidite sheet sands varies from a few centimetres to several decimetres thickness. More massive beds of graded, fining-upward sands occur as well. Traditional resistivity measurements that are made parallel to bedding planes are dominated by the highly conductive thin shales and fine-grained water sands, obscuring the presence of more resistive hydrocarbon bearing sands. The calculated water saturation from these measurements significantly under-estimates the producible hydrocarbon volume. Macroscopic electrical anisotropy is the direct result of a layered formation in which the thickness of the individual sand and shale beds are less than the vertical resolution of the logging instrument and resistivity measurement has directional properties. The vertical resistivity measurement, perpendicular to bedding, results in a series or volume-weighted resistivity response due to the formation components and is therefore dominated by the presence of resistive pay sands. In this analysis, the vertical resistivity measurement and resulting anisotropy ratio, Rh/Rv, are used together with conventional wireline data to more accurately quantify gas reserves and significantly reduce uncertainty in subsequent completion and production strategies. The integrated petrophysical analysis utilizing electrical anisotropy increased the accuracy of water saturation values and gas-water contact information over that of conventional analysis lacking vertical resistivity data. Results of this analysis are in good agreement with wireline pressure test data. Additionally, log measurements of electrical anisotropy identified new gas-bearing sands, which significantly increased field reserves. These sands could have been easily missed with standard resistivity measurement

This content is only available via PDF.
You can access this article if you purchase or spend a download.