Identification And Sedimentary Reservoir Comprehensive Research Of Reef-Bank Complex Of Xiaohaizi Formation In Bamai Area,Tarim Basin

Reefs is a special kind of carbonate structure that were mainly built with biology, it is belonged to hydrocarbon bearing sedimentary type with a broad hydrocarbon potential. Since1980s, home and abroad experts have made great achievements on extensively research of the reefs geological formation, structure, type, facies classification, diagenesis, growth evolution rules in different period. In recent years, some of the geophysicist also did exploratory research on seismic identification of reef, but the regional hydrocarbon potential of reef and its prediction research are relatively few. Therefore, based on geological, ground geology survey data, logging, core,3D seismic, analysis of samples and previous research as the foundation, using petrology, petroleum geology, tectonic geology, geophysics, sedimentology, such as seismic stratigraphy of interdisciplinarity advantage with3D seismic processing and interpretation techniques and reservoir prediction techniques, the reef and bank complex reservoir in Tarim Basin was found and its hydrocarbon prediction has been studied in details.Tarim Basin is surrounded on north, east and south three sides by the uplift southwest openings and darker craton basin during Carboniferous, bioclastic limestone, standard limestone and Xiaohaizi limestone developed in most parts of the whole basin. Bamai area stands for Bachu uplift-Maikit slope in south-western regions of Tarim Basin with the platform margin-slope ancient tectonic paleogeographic background. A few to ten meters of high-energy shallow bank sparry particles carbonate was revealed by drilling in Xiaohaizi formation which are markedly different from low-energy micritic limestone in Tazhong and Tabei area. This platform margin and typical shallow bank sedimentary implies a reef development environment. Through the difference thickness method, the underside flattened method, seismic attribute method and forward and inverse model method in three-dimensional seismic exploration area of600km2in Bamai area, a nearly east-west platform margin barrier reef was identified, its east-west direction extends more than25km which beyond the scope of3D seismic work area, neighboring two-dimensional seismic line also had special response. Reef core limestone in Xiaohaizi formation is62m thick the most, surrounding with50m thick of limestone outside the reef core area. Platform margin slope is a south tilting steep slope, horizontal width1-2km. organic bank behind reefs is a north tilting slow slope, horizontal width3-6km. This barrier reef and bank complex contains6reef cores which take the shape of moniliform in3D seismic work area, inlets are in between. Outside Reef is shallow bank composed mainly bioclastic and oolitic limestone. Reefs body were eastern lift up and western dropped down by the Indo-China and Himalayan tectonic movement and were cut by a NNW fault on the up-tilt direction. Nonetheless, wells near reefs show that reef-bank complex related reservoirs are possibly exist, and its discovery reveals a new field of oil and gas exploration in Bamai area.The main research results are as follows:(1) Through long distance and large-scale sequence stratigraphic correlation using well and seismic combination, salt rock of was found developed only between the Mid-mudstone Formation and the Standard Limestone Formation in Manjiaer depression and Tahe area, which was named Karratha Formation in Bachu area, in fact, the two should belong to the same layer. The research has important reference value to the regional stratigraphic correlation, and oil and gas exploration.(2) Identification of the reef-bank complex of Xiaohaizi Fromation in Bamai area in Tarim Basin was made at the first time, its evidence was mutual confirmed by the paleogeographical paleostructure outcrop, core, geophysical forward modeling, inversion and attribute analysis.(3) Through the fine seismic interpretation, the quantitative of the distribution characteristics of the reef-bank complex was studied. Six reef abnormal distribution area of the group of up to153.34km2, accounting for25.6%of the area in3D work area, the average thickness of the reef is20m. It was beaded NEE narrowing across the southern part of the3D work area, north east wider than north west.(4)Geology and Geophysics combination research can be a reliable method of reef study. Using paleotectonic and paleogeographic environment to analyse the location of the reef-bank complex development, and a qualitative understanding of the reef can be achieve by outcrop, core and seismic reflection, then quantitative study of morphological characteristics and distribution of the reef can be carried out through the combination of geophysical well seismic inversion, forward and attribute analysis. This study suggests that the RMS(root mean-square) amplitude attributes can effectively reflect the area and form of reef-bank complex; coherence attributes can accurately identify faults and borders between reef steep slope and slow slope. (5) Facies and microfacies characteristics of Bamai area were studied, and the development model of reef-bank complex was summarized. Site reconnaissance and rock structure, type, structure, bio and profile structure characteristics, combined with regional lithofacies paleogeography and seismic attribute analysis data, three sedimentary facies were found in Xiaohaizi Fromation, reef-bank platform margin, restricted platform and tidal, bank on the east of the reef was meticulous divided into calcarenite bank, oolitic bank, bioclastic bank, semi-restricted platform of oolitic bank, beans bank and open platform inter-bank marine.(6)Reservoir characteristics and controlling factors of the reef-bank complex in Bamai area were identified, combined with the hydrocarbon accumulation model, the exploration potential was pointed out. According to the well core observation of XBZ3D work area, reservoir space was mainly cracks and dissolving type, reservoir property and the hydrocarbon enrichment regularity study shows that this reef-banks reservoir had complex characteristics of controlling by both structure sealing and reservoirs; although the uplift process in Bachu area may occurred some damage to reef and its possible traps, but the facies transformation of before, after reef, inlets and fracture reservoirs relevant traps are still may partly be reserved, it can be a new field of oil and gas exploration in the future.From hydrocarbon accumulation conditions comprehensive analysis, the abnormal body reefs in this research area possess the basic condition of forming large reservoirs.