Stratigraphic Trap Identification Based on Restoration of Paleogeophology and Further Division of System Tract: A Case Study in Qingshui Subsag

Abstract

The 1st and the 2nd numbers of the Oligocene Shahejie Formation(E3s1 and E3s2)in which several sets of reservoir-seal beds assemblage developed are the major target zones of hydrocarbon exploration and development in Qingshui subsag, Western sag, Liaohe Depression, Bohai Bay Basin in China. All over the structural traps in the area have been essentially drilled, and identification and delineation stratigraphic traps become the major issue for finding more reservoirs and improving petroleum reserve in this petroleum-richness area. In the basement of interpretations of variable data including well logs, core, and seismic, the restoration and analysis of paleogeomorphology allow us to learn the influence of structure transfer zone, fault slope break, sedimentation slope break, and trough and high, and shoreline in each of the deposition periods on the deliver direction of debris from various source areas and the distribution of sedimentation facies in the sag. Under the guidance of sequence stratigraphic context, the study on system tract is carried out to the faulted subsag and the initial flooding surfaces and maximum flooding surfaces in E3s1 and E3s2 are identified, and the major system tracts are further divided into several parasequence sets to improve the accuracy of lithologic traps identified. On the basis of palaeogeomorphology restoration and system tract further division, the extension and geometry of the lithologic traps identified are confirmed through interpretive data process, 90 phasing, waveform clustering, velocity analysis, multiple attributes analysis, spectral decomposition, forward and inverse modeling. Lots of lithologic traps have been identified in several sub-cycles in each of the system tracts of E3s1 and E3s2. Three of recognition have been gained through the study:1)Paleomorphilogy has controlling effect on the type of deposition system and their spatial distribution, and the paleomorphilogy restoration technique is the key to determine the deliver direction of the debris from various source areas and predict the distribution of deposition systems in the subsag;2)Further division technique of system tract in terms of sequence stratigraphy can further divide the major system tracts into several parasequence sets effectively, and it lays a solid foundation for fine lithologic trap characterization;3)Try to use geophysical techniques that can verify each other as many as possible to make the lithologic trap prediction more accurate.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015