A Study On Sedimentary Facies And Sequence Stratigraphy For Carbonera Formation In A Area Of The Llanos Basin,Colombia

Based on the depositional setting of Llanos Basin, Colombia, the author use the well-log and seismic data for the research of Carbonera formation. The major subdisciplines of reference contain tectonic geology, sedimentology, seismic stratigraphy, sequence stratigraphy and so on. The author use the landmark workstation and other software of petroleum geology.According to research result, the evolutionary process of Llanos basin is Triassic-Jurassic synrift, Cretaceous back-arc subsidence, Paleocene-early Eocene accretion of western Cordillera and early foreland basin, middle Eocene-early Miocene pre-andean foreland basin, middle Miocene-recent Andean foreland basin.According to sequence stratigraphy (P.R Vail),the sequence stratigraphic classification in Llanos contains1megasequence and5supersequences. The sequence classification is controlled by sea level and erosion unconformable surface.at most. The deposition of Carbonera formation which belong to SSQ4is controlled by compression of pre-andean foreland.The well-log and seismic data can indicate the shelf facies and the delta facies.There are4sequences (SQ1-SQ4)which have the unconformable top surface. Every sequence can be delimited by mfs to2systems tracts (TST, HST). The study area lack LST due to exposure, so there are8plane graphs of sedimentary.The corner of study area deposit mass of delta plain in HST. level.The study area was submerged by sea that rose up quickly and can not deposit mass of delta plain in TST. Delta front deposits are the important reservoir in the study area. Underwater distributary channel and underwater interdistributary channel can be read. The lithologic character of underwater distributary channel is medium sandstone and fine sandstone,. Single lay of sand thick is5m-10m. SP is low value and the shape is box or gear box-the bell. The lithologic character of underwater interdistributary channel is mudstone. Single lay of mudstone thick is3m-5m. SP is high value and the shape is flat-the tooth shape, GR is middle-high value. Delta front deposition is most widely in HST and the total time is the longest. Delta front deposition can be identified sheet sand and mud foredelta. The lithologic character of sheet sand is Gray siltstone and fine sandstone. Single lay of sand thick is less than5m. A part of SP is high value and the shape is the tooth, and other of SP is low value and the shape is flat.GR is low value. The lithologic character of mud foredelta is argillite and single lay is10m～50m. SP is high value and the shape is flat-the tooth.GR is high value. The water in shelf is calm.The tectonic action and sea-level is the main control factors for the sequence and system tract.At first the tectonic action have the2effects. Firstly the tectonic action made supersequence unconformity interfaces, moreover it controlled paleogeomorphology Tectonic uplift and the Sea-level drop formation the interface of supersequence. Some one must be lacuna. Such as the SSQ4coverd the SSQ2.The paleogeomorphology control the deposition. Such as the mountain which was extruded by Cordillera cut off the seawater from the western Pacific in middle Eocene-early Miocene. Main material sources still came from the eastern Guyana shieldDifferent systems tracts deposit the different depositions. TST deposit the mud of shelf and prodelta. HST deposit sand of delta front. Therefore the Sea-level controlled the systems tracts so that controlled the deposition.