The Research On Geochemical Characteristics Of Carboniferous Source Rocks In The Zhundong And Wulungu Location Of Junggar Basin

Zhundong and Wulungu location in the northeastern Junggar basin, in which predecessors had been carried out over 20 years of exploration work. In Zhundong location we had found a considerable geological oil reserves. However, from the exploration of the extent that the vast areas of the Zhundong and Wulungu is still in the regional exploration stage. As the complex geological features and the restrictions on availability of hydrocarbon source rocks in this area, oil and gas geochemistry is very weak, which severely restricted to the region's overall evaluation and exploration decision.In this paper, we have a lot of organizing and collecting information on previous studies, including the spread of hydrocarbon source rocks, geochemical analysis information, logging information and so on. At the same time we use the geochemical analytical techniques to analyse and evaluate the organic matter abundance, type and degree of thermal evolution of the Carboniferous source rocks in the study area, and then discussing the sedimentary environments and organic matter source of the hydrocarbon source rocks with the gas chromatography of saturated hydrocarbons, chromatography-mass spectrometry analysis. Combined with the analysis of the sedimentary facies in the source rocks, identified the Carboniferous hydrocarbon source rock characteristics, hydrocarbon potential, spatial distribution and other characteristics in the study area. The main conclusions obtained in this thesis are as follows:During Carboniferous the ancient tectonic environment of the Junggar basion is complex. It is a time when Central Asia-Mongolia slot tends to cut close. Fold movement and volcanic activity are very frequent. A series of fold mountain and numerous of small mountain depression and fault formed around the block area. Due to the rising mountain ranges the small closed area between the land and sea, bay or lagoon residual formed in some areas. Then uplift to erosion areas, low-lying areas begin to accept deposits. Junggar basin, dominated by marine deposits in the Carboniferous. There are also marine-terrigenous facies, and continental sedimentary. The Zhundong area deposited a set of a Lower Carboniferous clastic rocks-volcanic construction, to marine-based, some areas develop the continental facies, and thickness has changed dramatically, about 1000-3000m.Early Carboniferous, the oceanic crust of Kelameili continued northward subduction and formed some underwater island arc in the south side of th Arman suture zone. Wulungu depression and Wucaiwan on both sides of these island arcs. Late Carboniferous, Kelameili ocean basin closed, the early Carboniferous to Late Carboniferous deposits between the residual basin unconformably covered on the ophiolite, about 300Ma in the late Carboniferous granitic batholith intrusion, the gravel thick to 1600m of the Shanlianglishi group (C1sl) deposits in the south of the ophiolite belt and formed the Kelameili suture. In the north the Wulungu depression developed coastal sediments. From the point of view of the sedimentary evolution of features, the Wulungu region could be deposited shallow-bathyal sea clasitic rocks in the early Carboniferous.Through organic geochemical analysis, we know that most of the Carboniferous shale samples in the Zhundong and Wulungu are effective hydrocarbon source rocks. Among all of them, the mudstone of the Jiangbasitao mostly are general or well source rocks, and the shale samples of the Tamugang are good hydrocarbon source rocks. By drilling strata we know that the mudstone of the Batamayineishan is mainly volcanic rock which are poor-general hydrocarbon source rocks. The kerogen type of source rocks in Jiangbasitao and Batamayineishan groups are generallyⅢ1-Ⅲ2, only individual to typeⅡ1. The kerogen type of source rocks in Tamugang group areⅡ2-Ⅲ2 .The maturity of organic matter has entered the mature to the high mature stage. While part of the hydrocarbon source rock samples of the Jiangbasitao has reached over-mature stage.According to the geochemical characteristics of soluble organic matter of core samples from the Carboniferous source rocks in the Zhundong and Wulungu location, it is concluded that the organic matter of the Tamugang source rocks is mature, but has not reached a high stage of maturity. In the Dishuiquan profile bottom-up, the reduction of the source rock depositional environment enhanced. Section samples of the Carboniferous were formed under oxidizing environment and the lithofacies palaeogeography is marine-continental transitional facies. Organic matter was derived from hydrobiont such as algae and plankton or terrigenous. The CPI of the Batamayineishan group mudstone in Q1 well ranged from 1.47 to 1.94 range, OEP is between 0.91 and 1.66. The CPI of Q2 well is between 1.5 and 1.59, OEP is between 1.44 and 1.48. Based on biomarkers to judge the maturity of source rocks should be in the low maturity to maturity. Pr/Ph of the source rocks in Q1 and Q2 wells are more than 2, Pr/nC17= 0.77～1.0.Oil-source correlation results showed that oil and gas of the well L5 and well D1 kinship with the Carboniferous source rocks. The tectonic evolution analysis showed that the Suosuoquan Depression and Wucaiwan Depression differentiation in the Triassic, Luliang Uplift has been taking shape. The oil and gas accumulation of Wucaiwan Depression is mainly Yanshan period. A large number of oil and gas can not flow backward across the Luliang Uplift to Wulungu depression, so the oil and gas of D1 well could not come from Wucaiwan depression. Tectonic evolution of north-south direction shows that after the Triassic the Hongyan area had been already in the uplift, therefore, the oil sands of Lun5 wells should not be from the north. While the Wulungu depression experienced in the evolution of multi-stage tectonic movements, as the oil and gas migration provides the ideal venue for tectonic evolution analysis showed that oil and gas of the well L5 and oil sands of the well D1 indicate that it should have come from Wulungu depression.The biomarker geochemistry of Carboniferous oil in C27 well and C201 well have a certain similarity with the Carboniferous mudstone of C1 well that the crude oil of C27 and C201 wells mainly from Carboniferous source rocks.The reservoir of Batamayineishan group was covered above the source rocks of Tamugang group, under the pressure difference oil and gas generated in the source rocks are directly migrate to the internal reservoirs of Carboniferous and formed a self storage in the reservoir model in Batamayineishan group with cracks and corrosion in the pores.