Abstract
Using 2D/3D seismic data and a large number of drilling and logging data and applying sequence stratigraphy, seismic sedimentology, and petroleum geology concepts, the characteristics of the sedimentary sequence of the forced regression have been analysed, the migration trajectory of the coastline have been reconstructed, the evolution model of the forced regression have been presented, and the significance for petroleum geology of the forced regressive sandbodies have been discussed. The falling stage systems tract (FSST) of the Zhujiang Formation present offlap high-angle oblique foreset reflection structure in the seismic profiles of the depositional trends and turbidite fan deposits with strong amplitude mound reflection structure are developed in the downdip direction of its front. The trajectory of migration of the shoreline shows a terraced downtrend in the direction of basin. The FSST is characterized by the shelf-edge delta without topset beds. The FSST was formed in the fall of relative sea-level. Five sets of foreset beds controlled by high-frequency relative eustatic were developed, therefore ordinal regressive overlap can be observed for the five sets of shelf-edge deltas in the depositional trends. The favourable reservoirs which were located close to the upper boundary of the falling stage systems tract and the basal surface of forced regression are sandbodies of the shelf-edge delta front and wave-dominated shoreface sands and the sandbodies of the turbidite fan. Those sandbodies favour the formation of lithologic oil–gas reservoirs by means of good trap sealing conditions, excellent oil–gas reserving performance, and effective oil source communication of fracture system.
Highlights
Sequence stratigraphy is widely used in the predictive exploration of petroleum, coal, and placer deposits, which is the third of a series of major revolutions in sedimentary geology [1]
Hunt and Tucker [3] reconsidered the lowstand shoreline sandbodies of forced regressive deposits, and put forward the concept of forced regressive wedge systems tract (FRWST), highlighting that, after the relative sea level began to fall, the FRWST formed until it fell to the lowest point, and the sequence boundary forms when the relative sea level falls to the lowest point
Considering that the forced regression wedge system tract was formed during the period of relative sea-level fall, Plint and Nummedal [4] proposed the concept of falling stage systems tract (FSST) and further stated that the FSST is the offspring according to the transgressive systems tract
Summary
Sequence stratigraphy is widely used in the predictive exploration of petroleum, coal, and placer deposits, which is the third of a series of major revolutions in sedimentary geology [1]. In the process of the development and application of sequence stratigraphy, there are some new views, including the position of sequence boundary, the division of system tracts, and the definition and nomenclature of units and bounding surfaces. Considering that the forced regression wedge system tract was formed during the period of relative sea-level fall, Plint and Nummedal [4] proposed the concept of falling stage systems tract (FSST) and further stated that the FSST is the offspring according to the transgressive systems tract. Catuneanu [5,6] re-defined the concept of FSST, pointing out that the FSST occurred in the period when the base level (relative sea-level) fell. Catuneanu [8] pointed out that stratal stacking patterns provide the basis for the definition of all units and surfaces of sequence stratigraphy. With the continuous improvement of sequence stratigraphy theory and method, it has been widely used in reconstructing the paleogeographic setting, climatic conditions, and tectonic setting which, in turn, are important for the petroleum industry [9,10,11]
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