Sequence Stratigraphy Study And Exploration Target Forecast In The Suibin Depression Of Sanjiang Basin In Mesozoic

Suibin depression lies in the anterior margin of the newest Mesozoic Nadanhadamountain orogenic belt in China east. Its geotectonic position locates at the jointregion where central Asia and Mongolia structural domain and the littoral PacificOcean structural domain connect. The structural environment is particular,and thegeological structure is complicated. For its specific tectonic setting, and as the onlyMesozoic sedimentary depression that has marine facies and continental-oceanicinteraction facies in China east, it's so important in the research of the Mesozoic stratathat geologists and petroleum explorer pay lots of attention. Based on the theories of sequence stratigraphy, petroleum geology, andsedimentology, this paper adopts the method of combining field geologic survey withlab analysis, macroscopic view with microscopic view, and the way of combininggeology, well logging, seismic, and other subjects;meanwhile, with the main line ofthe sequence stratigraphy analysis and the sedimentary facies research, regionalcorrelation markers and local markers were founded out to establish correlationstandard.In addition, the strata sequence and system tract in the whole region weredivided and the framework of sequence stratigraphy was founded, with the theory ofcycle correlation and controlling step by step. Using the single well sedimentaryfacies analysis for foundation,combining the electrofacies and seismic faciesanalysis,the paper made researches of Mesozoic sedimentary facies, sedimentarysystem and the law of sedimentary evolution of Suibin depression. Through all theresearches above, the favorable exploration areas in Suibin depression were proposed. The structural evolution of Suibin depression can be divided into 4 stages. Byplotting Mesozoic group strata sequence, nine strata sequence interface, four tectoniclayers, and eight third order strata sequences were identified. Through the seismicequilibrium profile and Milankewhich cycle analyses, it is considered that faults werethe major dominating factor to Suibin depression strata sequence. Through thesequence stratigraphy framework, we can find out the sediment and tectoniccharacteristics of Suibin depression: the faults of depression's east ramp regiondeveloped very well;the faults in the center of the depression didn't develop and thestrata is stable;the strata in the north changes obviously. The interior of the stratasequence contains low systems tract (LST), transgression system tract (TST) and highsystem tract (HST). Based on the study of depression's strata sequence, thesedimentary facies and the sedimentary system, some depositional facies wereidentified, such as alluvial fan, fan delta, underwater fan, fluxoturbidite fan,deepwater turbidity fan, lacustrine and marine facies. Moreover, the characteristics ofsedimentary system in different system tract were illuminated which provided thefoundation for forecasting the favorable reservoir belt. This region has marine facies,transitional facies, continental deposit characteristics and the climate from Jurassic tothe early Cretaceous was warm and moist and the plant cover was abundant. In themiddle and later Jurassic, the marine transgression happened broadly, a set of marinestrata was deposited in the Suibin-Dongrong Formations. At the early Cretaceous, theregression happened, and then deposited a set of transitional strata called ChenziheFormation. By the time of the Muling Formation's deposition, seawater completelyretreated from the basin, then deposited one set of terrestrial strata. Suibin depressionmostly has nine sedimentary facies, including pluvial facies, fluvial facies, lacustrine,paludal facies, delta facies, tidal-flat facies, shore and neritic facies, neritic facies andbathyal sea facies, etc. The sediments of the upper Jurassic mostly were shales andsandstones which fast deposited near the provenance area. The reservoir suffereddiagenesis and compaction intensively, thermal metamorphism degree was so highthat it resulted in poor reservoir physical property. Therefore, Most Mesozoicreservoirs are low porosity and low permeability reservoirs. On the basis of overallevaluation, nine favorable exploration areas were pointed out in this area: in theframework of the Suibin depression Sequence stratigraphy trellis, the overlap beltsbetween the fault nose structure /fault block and the fan-delta front sandbodies at lowsystems tracts of Sq2 and Sq3, and high systems tract of Sq4 are the most favorableexploration areas。...