Processing, inversion, and interpretation of a 2D seismic data set from the North Viking Graben, North Sea

Abstract

Simultaneous elastic impedance inversion is performed on the 2D North Viking Graben seismic data set used at the 1994 SEG workshop on amplitude variation with offset and inversion. P‐velocity (Vp), S‐velocity (Vs), density logs, and seismic data are input to the inversion. The inverted P‐impedance and S‐impedance sections are used to generate an approximate compressional‐to‐shear velocity ratio (Vp/Vs) section which, in turn, is used along with water‐filled porosity (Swv) derived from the logs from two wells, to generate fluid estimate sections. This is possible as the reservoir sands have fairly constant total porosity of approximately 28 ± 4%, so the hydrocarbon filled porosity is the total porosity minus the water‐filled porosity. To enhance the separation of lithologies and of fluid content, we map Vp/Vs into Swv using an empirical crossplot‐derived relation. This mapping expands the dynamic range of the low end of the Vp/Vs values. The different lithologies and fluids are generally well separated in the Vp/Vs–Swv domain. Potential hydrocarbon reservoirs (as calibrated by the well data) are identified throughout the seismic section and are consistent with the fluid content estimations obtained from alternative computations. The Vp/Vs–Swv plane still does not produce unique interpretation in many situations. However, the critical distinction, which is between hydrocarbon‐bearing sands and all other geologic/reservoir configurations, is defined. Swv ≤ 0.17 and Vp/Vs ≤ 1.8 are the criteria that delineate potential reservoirs in this area, with decreasing Swv indicating a higher gas/oil ratio, and decreasing Vp/Vs indicating a higher sand/shale ratio. As these criteria are locally calibrated, they appear to be valid locally; they should not be applied to other data sets, which may exhibit significantly different relationships. However, the overall procedure should be generally applicable.

AVO inversion and Lateral prediction of reservoir properties of Amangi hydrocarbon field of the Niger Delta area of Nigeria

“…For a fixed lithology and porosity, V p /V s is 10% -20% lower for gas saturation than for water saturation, but there is some overlap in V p /V s ratio between brine sands and oil sands. Shales have higher V p /V s values than sands [6]. For water saturated and gas saturated sediments, the V p /V s ratio increases with increasing porosity, and also showed that V p /V s could effectively be used to separate water saturated and gas saturated sediments as porosity increases.…”

“…Ambiguities in lithology and fluid identification based only on the P-impedance can often be effectively removed by adding information about V p /V s related attributes at non normal incidence as described by [6]. The V p /V s ratio is a useful discriminant of lithologies and fluid content.…”

Estimation of quality factor based on peak frequency-shift method and redatuming operator: Application in real data set

“…To strengthen the conclusions from the interpretation of the seismic image shown in Figure 10, we chose three trace corresponding to CMPs 700, 1100, and 1500. Figure 11 depicts a remarkable amplitude gain and resolution of the Q-compensated seismic traces, mainly in the region where sand and intense fracturing gas is present (Keys and Foster, 1994;Madiba and McMechan, 2003).…”

Petro physical analysis of among hydrocarbon field fluid and lithofaciesusing Well Log Data

“…Thus, it is difficult to delineate hydrocarbon reservoirs directly on the separate inverted P-impedanceand S-impedancesections. Ambiguities in lithologic and fluid identification based only on the acoustic impedance can often be effectively removed by adding information about V p /V s related attributes at nonnormal incidence [22,23,24,25].…”