Abstract:

 Tight oil exploration in Qaidam Basin started relatively late, but with great potential. Under the influence of saline lacustrine basin, the tight oil reservoir of the upper Ganchaigou Formation in Zhahaquan district is characterized by thin single layer, distinct vertical overlap and significant lateral change, and thus the prediction of reservoir “sweet spot” has become the key and difficult point in this research. Based on the established high resolution sequence stratigraphic framework and the application of phase inversion, of strata slicing and of quantitative seismic sedimentology techniques, the seismic sedimentology study was conducted on the sand bodies composed of four parasequence sets in the upper Ganchaigou Formation, Zhahaquan district with the guidance of seismic sedimentology, which plays an important role in the deposition system research and thin layer sandstone prediction. Furthermore, combined with drilling and logging data, typical strata slices were precisely interpreted, as well as calibrated, and the distribution and evolution of thin beach bar sand bodies was predicted. This research suggests that shoreshallow lacustrine facies was dominated in the study area, where beach bar sand bodies were widely distributed. Also, on the basis of controlling factors analyses on tight oil reservoir performance, gamma inversion technique was proposed for prediction of reservoir “sweet spot”, and the favorable exploration area was determined. In addition, the prediction results tallied with the actual drilling situations, which effectively guided tight oil exploration in the study area and can be applied to prediction of reservoirs with comparable geologic characteristics in the future.

Key words: seismic sedimentology, saline lacustrine basin, tight oil, reservoir “sweet spot”, beach bar sand body