Sedimentary System Development Controlled By Sequence Stratigraphy And Seismic Geomorphology Of The Enping Formation,Baiyun Sag

The appearance of sequence stratigraphy, seismic sedimentology and seismic geomorphology enriched the study methods of sedimentology to various degrees. It has been verified that sequence stratigraphy is an effective theory and extensively applied to sequence analysis, fill patterns, spatial and temporal distribution of facies and reservoir description in sequence framework in marine basins and continental basins. Seismic geomorphology is defined as the application of analytical techniques pertaining to the study of landforms and to the analysis of ancient, buried geomorphical surfaces as imaged by 3D seismic data and then analyze distribution and developing regulations of depositional system. Based on sequence stratigraphy, seismic geomorphology method and theory and basin modeling software, development regulations of sedimentary deposits in different periods was described efficiently using the recent 2D and 3D seismic data of Enping Formation, Baiyun Sag, which has a certain reference on prediction of reservoir and lithologic traps.There are only nine wells mainly distributing on the structural high of sag edge and drilling only upper section of Enping Formation. But seismic data covered all the Baiyun Sag, including surrounding uplifted areas. Based on three-dimensional seismic data and classic sequence stratigraphy method, sequence boundaries were recognized and sequence framework was built. Depositional system and distribution regulation of facies belt was determined by applying of single well facies, seismic facies and attribution, and seismic geomorphology feature. Finally, developing regulation of depositional system in sequence framework was clear.The main results obtained in the papers as followings:1) Build a sequence framework of Enping Formation, Baiyun SagSeismic stratigraphic unites and characters were recognized according to terminal manners of seismic reflection and the differences of interior seismic facies. The sequence recognition of upper Enping Formation was synthetically used single well, paleontological and seismic data. Enping Formation was divided into three three-order sequence, SQ72, SQ71 and SQ70. Two three-order sequence boundaries, T71 and T72, were recognized. Both sequence SQ72 and SQ71 were divided into LST, TST and HST. Sequence SQ71 was divided into LST and HST.2) Describe seismic geomorphology feature of sequence boundariesGeomorphological map of sequence boundaries, T80, T72 and T71, of Baiyun Sag and surrounding areas reflected the characteristic of seismic geomorphology of every three-order sequence. During the deposition of sequence SQ72 and sequence SQ71, Panyu uplift and Dongsha swell in the north of Baiyun sag cut off the northern provenance by a series of north-dipping faults. The provenance was offered by surrounding uplift. During the deposition of sequence SQ70, because of extensive transgression, Panyu uplift was under water and accepted deposition. Paleo-Pearl River with a great quantity of detrital material of terrigenous origin of Southern China fold belt got over of Enping sag and entered Baiyun sag along NW-SE braided channel developed in Panyu uplift.3) Distribution of depositional system by control of seismic geomorphologyAccording to seismic facies and attribute analysis of sequence SQ72, fan delta developed in southern abrupt belt and short spacing braided delta and beach bar reformatted by delta developed in northern gentle slope belt. For sequence SQ71, small-scale fan delta developed in southern abrupt belt and beach bar in the middle of sag. For SQ70, three stage of braided delta developed from northern gentle slope belt to the mid of sag. By attribution of the time of half-energy, the distribution of the delta was recognized effectively.4) Matched relationship of seismic geomorphology and depositional system in three-order sequenceDuring deposition of sequence SQ72 and sequence SQ71, surrounding uplifts, including Panyu uplift, Dongsha swell, Yunkai uplift, South swell and Baiyun east uplift-northwest trench, northeast trench and south structural transfer zone-north gentle slope, south steep slope and sag, consisted of the main transport and deposition zone. During deposition of sequence SQ70, depositional areas obviously extended, and South China fold belt-northwest large-scale valley-sedimentary slope belt and sag consisted of the main transport and deposition zone of this period.5) Development regulations of depositional system in three-order sequence frameworkIn horizontality, sequence SQ72 developed nearly source fan delta, braided delta and beach bar. The quantity and scale of depositions followed a rule of increasing firstly and then decreasing. Sequence SQ71 developed trench filling complex and small-scale beach bars. The quantity and scale of two system tracts were equal. Sequence SQ70 developed braided delta and turbidity. The rule of quantity and scale were as the same as that of sequence SQ72. In verticality, the pattern of depositions varied, while the scale and quantity were equal.