Sequence Stratigraphy Of Wen’an Slope Belt In Baxian Depression

Wen’an slope is located in the east of Baxian sag, in which west is hydrocarbon kitchen of Baxian sag, having found Ng, Ed, Esl seven hydrocarbon reservoir assemblages, those demonstrated reserves mainly concentrated in the middle of the slope. In the recent years, research expresses that the middle-shallow layer in the outside of Wen’an slope has a beneficial sediments construction background and gets close to hydrocarbon kitchen. At the same time, its sand body develops well, has a bigger potential exploration, therefore re-know slope is significance for the stabilization in Huabei oil field.This article devoted upper-Shayi section and Dongying formation to the study. Because the exploration in the outside of slope is lower, on the basis of comprehensive analysis of core, well logging, test of petrology and sequence stratigraphy, by the means of computer technology, studied sequence stratigraphy, it provide beneficial criterion for further exploration strategy in the area. The main achievement of this study is:1) High-resolution sequence stratigraphy division and contrastAccording to the theory of high-resolution sequence stratigraphy and sedimentlogy, this paper studies the sequence stratigraphy and depositional systems of upper-Shayi section and Dongying formation in Baxian sag, by geology, well logging, and well testing.By geologic strata sign, carry out division and contrast with118wells in the framework of cyclic sequence inside the zone, then subdivided purpose layer into15middle-term base-level cycles. For the most wells, upper-Shayi section is lost, so this paper mainly studies MSC5～MSC16.First of all, according to comprehensive analysis of outcrop, core, well logging, identify middle, long-term base-level cycle of upper-Shayi section and Dongying formation in Wen’an (amount to III and IV sequence).According to the corresponding relations of sequences and base-level cycle, draw up a division criterion of high-resolution sequence levels. The structure of middle-term base-level cycle could be subdivided into asymmetric up-deepening, asymmetric up-shallowening symmetric basic structure types. Base on long-term base-level cycle in the high-resolution sequence equitime stratigraphic framework, contrast middle-term base-level cycle one by one.According the variation of the middle-term base level cycle stacking patterns and accommodation space (A) and sediment supplication (S) ratios, analyzing the change of the long-term base-level to study the division of high resolution sequence strati graphic in Esls-Ed formations。Establishing the Esls～Ed equitime stratigraphic framework, adopt middle-term base-level as sequence units。In the contrast framework of middle-term base-level cycles to do the Esl s～Ed sand body contrast and forecast the sand body space distribution in the research area.2) The sediment microfacies in upper-Shayi section and Dongying formationOn the base of region geological background, according to the systems analysis of the facieses, studied characteristic of sedimentary facieses of upper-Shayi section and Dongying formation in detail, by identifying fluvial facieses, subdivides types of sediment microfacies.First, analyzes provenances.By researching palaeo-geomorphology, heavy mineral character, lithologic composition, and variation of clastics content, this paper points out that the provenances of upper-Shayi section and Dongying formation in Baxian sag are mainly derived from tow directions:NE, southeast. Overall characteristics of sedimentary facieses and distribution of sedimentary facieses have been discussed in this article based on core and log data study, and the sedimentary facieses of the study area was determinated as fluvial facieses. Base on the core, mud log and conventional log, the sedimentary facieses of braided river of upper-Shayi section, and meandering river of Dongying formation have been recognized.According to various phase sign, identify seven sediment microfacies:point bar, channel bar, meandering channel sand-body, and braid channel sand-body.The core deposition phase demonstrate:meandering river is positive cycle in the vertical sequence, which palaontological section shows character of "sand more, mud less"; Braid River shows character of "sand more, mud less" in palaontological section. We can get conclusion like this:braided deposits is rougher than meandering deposits.In the process of studying sediment microfacies, in addition to core phase search, this paper emphasis on logging phase, because core phase at study overlay is not high in the zone, single well phase search also rely on logging phase. Logging phase analysis makes use of logging phase sign to describe the sedimentary facieses division, and phase sign and rock-electricity convert pattern is certainly a key.3) Sand body spreading regularityThrough the search of core, single well phase, logging phase and deposition plane in the high-resolution sequence stratigraphy framework, expatiate sand body spreading regularity in space, and point bar and channel bar are excellent reservoir for this zone.With the research of provenances and sand body distribution, the paper studies characteristics of distribution and vertical evolution of sedimentary faces in each term cycle of Wen’an slope belt in Baxian sag.It is indicated that there are two main river with parallel pattern distribution in the plane, and that the phenomenon of divarication and aggregation between the river channels is very common.