International audienc

Tertiary injectites, which are re-mobilized sandstones, represent commercially attractive targets for near-field, long-reach tie-backs to existing field infrastructure above and adjacent to producing reservoirs. Injectites exhibit exceptional porosity-permeability and productivity, such that discoveries can add incremental reserves and lift production decline in mature fields. Abundant injectites are visible on seismic data in the Tertiary of the Viking Graben, but, as some disappointing wells have established, not all are hydrocarbon-charged. The challenge is to reliably distinguish hydrocarbon-filled high porosity-permeability features from tight or dry reservoirs in a cost-effective way. Regional rock physics analysis of injectite reservoirs, using well data from fields in Norway and the UK, reveals that a combination of elastic attributes can effectively discriminate lithology and hydrocarbon presences in these reservoirs. After pre-stack conditioning, broadband seismic data correlate reliably with wells, giving confidence that pre-stack seismic is faithfully imaging the elastic properties of the subsurface in lower Tertiary target intervals. Informed by rock physics analysis, a combination of broadband seismic elastic attributes is used to predict sand presence and de-risk hydrocarbon presence in reservoirs v. water-wet targets. Hydrocarbon sand distribution predicted from relative acoustic impedance and V P /V S matches to known accumulations and identifies remaining near-field opportunities.

No abstract

The giant sub-salt discoveries from the conjugate Brazilian margin give encouraging support for analogous hydrocarbon potential offshore Angola. The challenge is to image the deep geology beneath complex salt geometries to confidently predict reservoir properties and distribution. Pre-stack relative inversion was performed on dual-sensor broadband 2D data from the Kwanza Basin and was correlated to the pre-salt carbonate succession in a discovery well. Well log analysis and rock physics confirm what is observed on the relative acoustic impedance volume. Two distinct types of carbonates with significantly different reservoir properties can be discriminated on the inversion volumes. This result demonstrates that the additional bandwidth from acquired deep-tow broadband seismic can reliably map reservoir properties even in deep challenging geological environments.