Geochemistry Of Oil And Gas Accumulation In The Cretaceous In Mosuowan Area

Mosuowan Area is located in the interior Junggar Basin surrounded by three hydrocarbon-generating sags and filled with developed various faults resulting in predominant accumulation conditions.However,the active basin tectonic movement made the process of hydrocarbon accumulation complicated.And the test results reveal that the oil-water relationship is complicated in Cretaceous in Mosuowan Area for industrial oil flow in Wells Pen-5 and good oiliness cores but most of the water in Wells Pencan-2.On the aim of finding out the regularities of hydrocarbon distribution and provide effective guidance for exploration in the next step,it is necessary to study the origin and accumulation progress of hydrocarbon in the research area.This study,under the guidance of hydrocarbon geochemistry,is aiming at defining the source of Cretaceous hydrocarbons,defining main causes of differential accumulations by fine dissections of typical wells and defining main controlling factors of hydrocarbon accumulation to establish accumulaiton models for favorable further explorations associated with tectonic evolution,hydrocarbon generation and expulsion,hydrocarbon migration and preservation by fluid inclusion temperature measurement and microscopic fluorescence.Cretaceous hydrocarbons in Mosuowan Area are mainly derived from Permian and vary in distinct wells as Wells Pen-5 are sourced from western sags of Wells Pen-1 while Wells Pencan-2 are from Fukang sag in the south.The main causes of Cretaceous differential accumulations between Well Pencan-2 and Mo-24 include reservoir properties,pore structures,sandbody scales and sedimentary microfacies differentiations as Cretaceous bottom of Well Pencan-2 is characterized by bad properties,low permeability,high replacement pressures,bad pore structures and small sandbody scales showing up as underwater distributary channels,mouthbar and shunt bay with interbeded sand,silt and mudstone resulting in bad transverse connectivity but favorable for reservoirs after late reformations.Cretaceous of Mosuowan Area consists of two-stage accumulations in middle-late Early Cretaceous and main accumulation from Late Cretaceou to Oligocene respectively.It does exist strong biodegradations from late Early Cretaceous to early Late Cretaceous to the first hydrocarbons.And it characterizes complicated sources and multiple stages since late reversal movements of palaeohigh readjust previous reservoirs and formed scattered and small-scale reservoirs as well as four lithologic and stratigraphic oil reservoirs of low amplitude as thin sand-mud interbed,depositional filling,low-amplitude structures and stratigraphic pitch-out.For further exploration,the preferred exploration should be along secondary generations in updipping direction of primary reservoirs as well as in delta-frontal facies,southeastern Mosuowan and low-lying sedimentary filling sandbody controlled by ancient landfroms to the south of Wells Pencan-2.