Research paperPrediction of ultrathin lacustrine sandstones by joint investigation of tectonic geomorphology and sedimentary geomorphology using seismic data

- Paleogeomorphologic elements on Cretaceous unconformity were reconstructed.
- Seismic lithology of 1-7 m thick sandstones was realized using 90° seismic traces.
- Amplitude stratal slices illustrate lobate sedimentary geomorphologic patterns and sandstone thickness trends.
- The agreement between above elements reduces uncertainties of mapping ultrathin sandstone reservoirs.

Weak seismic signals from ultrathin (1-7 m) sandstones increase uncertainties of thickness estimation, imposing a significant challenge for accurate prediction of subtle hydrocarbon reservoirs. These types of uncertainties, however, can be reduced by a combined use of kinematic (travel time) and dynamic (amplitude) information extracted from 3D seismic data. In this case study in the Kuqa Depression of the Tarim Basin, China, we conducted an investigation of seismic-based tectonic geomorphology and then sedimentary geomorphology in four steps: (1) reconstruction of basin-floor paleogeomorphology using a residual structure map of a closely underlain erosional unconformity, (2) study of seismic lithology by seismic modeling and 90° phase adjustment of seismic traces, (3) mapping of geomorphologic patterns of depositional systems on stratal slices, and (4) combined analysis of tectonic geomorphology and sedimentary geomorphology for a better understanding of depositional history and reservoir distribution. Results show a good match between valley and lowland systems on the basin floor, sandstone thickness trend, and lobate sedimentary geomorphologic patterns, indicating a widespread, yet laterally highly variable, ultrathin sandy fan-delta system.