The Ancient Geomorphological Features And Hydrocarbon Enrichment Patterns In Wunan Area

The southern Wuerxun depression is one of the important oil and gas area, the papertakes the southern Wuerxun as researching target, using balanced section principle to restoretarget layer ("special lithologic", the second section of Nantun group, the second section ofDamoguaihe group)palaeogeomorphology of during deposition and a large number of oil andgas migration and accumulation period(the end of Yimin group), combining with regionalsedimentary and tectonic evolution to analysis geomorphological features. Combined with theancient geomorphological morphological characteristics, it researches the depositionalsystems and hydrocarbon migration and accumulation by palaeogeomorphology controlledand forecasts favorable exploration zones.During the deposition of "special lithologic", palaeogeomorphology was half a zonaldistribution around the midwest Wunan subsags, which outward elevated as terrain ladder;settlement subsags of during the second section of Nantun group deposition was in themidwest, developed faulted uplift in the southern, slope zone in the eastern; the secondsection of Damoguaihe group deposition period, the settlement subsags developed steep slopefault terrace, subsags in the middle, slope in the eastern, uplift belt in the southern Bayantalaregion; in the end of Yimin group, which was a period of oil and gas substantial migration, theancient geomorphological features of this period was similar, which was dustpan rift basin ofwest off and east override, presented west and east banding pattern, the west of which wassteep fault step belt, subsags in the middle, slopes in the eastern and protuberant belt in thesouth.By the research of paleogeomorphology controlling depositional system duringdeposition period, the special lithologic developed braided river delta-lacustrine depositionalsystem, the Midwest subsags long-term controlled the development of lacustrine depositionalsystem, the low and slope had three braided river delta deposition in the east of Wuerxun, sodid Bayantala; the second section of Nantun group mainly developed braided river delta-lakedeposition system, eastern slope had a large area of braided river delta deposition; the secondsection of Damoguaihe group mainly developed meandering river delta-shallow lakedeposition, northern gentle slope in the east slope of Wuerxun and graben landscepecontrolled two large meandering river delta to extend to subsags.Through the research about ancient geomorphological controlling oil and gas migrationand gather, we can know that the influencing factors of hydrocarbon accumulation in south of Wuerxun derived from ancient geomorphological mainly have four aspects:(1) subsagscontrolled oil and gas reservoir distribution in deposition period.(2) the ancientgeomorphological features controlled favorable facies development.(3) the high parts of thepaleotectonic was favorable accumulation area.(4) fractures provided pathways and traps forhydrocarbon migration and accumulation. According to that we systematically research theaction about palaeogeomorphology controlling hydrocarbon accumulation in target layer,summarizing the hydrocarbon accumulation law and drawing the main mode.Finally, four kinds of maps (sedimentary facies maps, fractures development and distributionmaps, subsags range map and palaeogeomorphology topographic map) are superimposed,combining hydrocarbon accumulation model, the paper forecasts favorable exploration areaand gets favorable target area of the target layer.