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 thewell-log and seismic data for the research of Carbonera formation. The majorsubdisciplines of reference contain tectonic geology, sedimentology, seismicstratigraphy, sequence stratigraphy and so on. The author use the landmarkworkstation and other software of petroleum geology.According to research result, the evolutionary process of Llanos basin isTriassic-Jurassic synrift, Cretaceous back-arc subsidence, Paleocene-early Eoceneaccretion of western Cordillera and early foreland basin, middle Eocene-earlyMiocene pre-andean foreland basin, middle Miocene-recent Andean foreland basin.According to sequence stratigraphy (P.R Vail),the sequence stratigraphicclassification in Llanos contains1megasequence and5supersequences. The sequenceclassification is controlled by sea level and erosion unconformable surface at most.The deposition of Carbonera formation which belong to SSQ4is controlled bycompression of pre-andean foreland.The well-log and seismic data can indicate theshelf facies and the delta facies.There are4sequences (SQ1-SQ4)which have theunconformable top surface. Every sequence can be delimited by mfs to2systemstracts (TST, HST). The study area lack LST due to exposure, so there are8planegraphs of sedimentary.The corner of study area deposit mass of delta plain in HST. level.The study areawas submerged by sea that rose up quickly and can not deposit mass of delta plain inTST. Delta front deposits are the important reservoir in the study area. Underwaterdistributary channel and underwater interdistributary channel can be read. Thelithologic character of underwater distributary channel is medium sandstone and finesandstone,. Single lay of sand thick is5m~10m. SP is low value and the shape is boxor gear box-the bell. The lithologic character of underwater interdistributary channelis mudstone. Single lay of mudstone thick is3m~5m. SP is high value and the shapeis flat-the tooth shape, GR is middle-high value. Delta front deposition is most widelyin HST and the total time is the longest. Delta front deposition can be identified sheetsand and mud foredelta. The lithologic character of sheet sand is Gray siltstone andfine sandstone. Single lay of sand thick is less than5m. A part of SP is high value andthe 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 iscalm.The tectonic action and sea-level is the main control factors for the sequence andsystem tract.At first the tectonic action have the2effects. Firstly the tectonic action madesupersequence unconformity interfaces, moreover it controlled paleogeomorphologyTectonic uplift and the Sea-level drop formation the interface of supersequence. Someone must be lacuna. Such as the SSQ4coverd the SSQ2.The paleogeomorphologycontrol the deposition. Such as the mountain which was extruded by Cordillera cut offthe seawater from the western Pacific in middle Eocene-early Miocene. Main materialsources still came from the eastern Guyana shieldDifferent systems tracts deposit the different depositions. TST deposit the mudof shelf and prodelta. HST deposit sand of delta front. Therefore the Sea-levelcontrolled the systems tracts so that controlled the deposition.