| Junggar basin, one of large oil and gas basins in China northwest. Major tectonic units in China-part of the Junggar block. The Tianshan orogenic belt, East and west Junggar and Altai mountains surrounded the Hercynian fold. An area of130,900square kilometers. Above Junggar Triassic basin is Mesozoic and Cenozoic unified continental sedimentary basins. Composite overlay with the underlying Paleozoic Partition of Sea-land transition of sedimentary basins, therefore, This is a large composite superimposed basin.Karamay oil field is located near the city of Karamay in the northwest of Junggar Basin of Xinjiang Uygur Autonomous Region, Southeast from Urumqi, about400km.The oil field was the NE-SW trending, and about50km long and a width of10km. Ground was covered in the Gobi and alkali Beach, the terrain is relatively flat, dry climate, large temperature difference between day and night, more sand, water source shortages. Structure located in the Junggar Basin thrust belt, by the fault zone control. Thrust belt is NE trending, composed of hong-che fault zone, ke-wu fault, wu-xia fault. Karamay Oilfield in the southwestern tip of the ke-wu fault, or Karamay-Baijiantan segment, fault development in the oil region. According to the cutting of the fracture, the oil field is divided into10development zones:one, two, three, four, five, six, seven, eight, nine and Black Oil Hill District.This study area is located in the Baijiantan region, which is35km northeast from the city of Karamay, Regional tectonics in the South Baijiantan fracture footwall of the ke-wu fault zone in the northwest edge in the Junggar Basin, the terrain gently, average surface elavation of about265m, the target layer is Upper Karamay formation of Triassic. Karamay formation reservoir in this area is a sandy conglomerate reservoir with low porosity and low permeability, it is the main reservoir of the eight districts of the Karamay Oilfield, and the type of the reservoir is monoclinic teservoir which is blocked by fracture. Reservoir depth of about2040m, the total sediment thickness of about218meters, the oil-bearing area of11.5square kilometers. This reservoir exploration began in the mid-fifties, had industrial oil flow in1965, by the continued exploration of thesixties and seventies, it began development in March1982, and in September1983, it was explorated comprehensively with water injection, after four stages:the capacity building stage, high and stable production stage, descending phase and comprehensive management of mitigation decreasing. Years of development practice shows that the complex geological features,making the reservoir stable and tapping potention being more and more difficult, the most promiment is the reservoir which controled by sedmentary facies in the eight districts changes of the vertical and horizontal, and strong heterogeneity. Now, the northwestern margin entered a fine exploration stage, there is an urgent need for new theoretical guidance, many problems need to be examined for the weak basic geological research.Predecessors have done the research work at different levels about stratigraphic division、sequence stratigraphy and sedimentary reservoirs、sedimentary facies of Upper Karamay formation in the study area. And made many achievements and understanding. About sedimentary facies, predecessors reaserched that is fan-delta deposition formed by alluvial fan into the lake in eight districts, and had more than one material source, the main source is from the northwestern margin. Identified two subfacies, fan delta plain and fan delta front. This paper has different understanding of the research about subfacies and microfacies. The study area mainly composed of two subfacies, fan delta front and the front fan delta, also developed small range of bay, can be identified underwater distributary channel and seven microfacies like, fan delta plain does not appear.During the deposition of the whole karamay formation, the dominated subfacies in the study area is fan delta front, and the underwater distributary channel deposition is the most developed.This paper on the basis of previous research, combined with the geological background of the study area, mainly analyse the core data and logging data, based on high resolution sequence stratigraphy theory, through the selected profile, combined with the contrast of adjacent wells, we divised and correlated the single layer of105new wells and adjusted the layer division of274old wells. The lithology, electrical cycle in the study area is obviously, and has many levels, within a certain range, its distribution is stable, basically able to control the sand group, sand layer and single sand. So the stratum is divided into five sand group, ten sand layer and19single sand. And on the basis of the layer division, we tracked the single sand body of the production reservoir S4and S5in the study area.At the same time, on the basis of previous research, this paper take the theory of sedimentology, structural geology, sequence stratigraphy and petroleum geology as guidance, combined with regional background, coring data, logging data, seismic data, and analysis of laboratory data, studied the variety of sedimentary facies markers comprehensively. Combined with the analysis of single well phase, associated wells phase, researched the law of microfacies profile and planar distribution on the upper karamay formation in the eight districts, then established the sedimentary facies model of the study area.The law of sedimentary evolution at different stages is obviously in the study area of upper karamay formation, lake level overally experienced a process of rise-down-rise. During the deposition from S5to S3, the lake level was increasing, at S31deposition period, the lake level reach the highest. After that, the lake level declined quickly, and to a minimum at Si2, since then to S11, the lake level had a rising trend.By the research of the upper karamay formation in the study area, we obtained the following knowledge and conclusions:1. Triassic karamay formation is divided into five sand groups,10sand layers, and further divided into19small layers.2. The number of single sand body is large, and had a large range of thickness, profile connectivity is poor, plane often has scattered or connected into a sheet, narrow strips.3. Upper karamay formation is the depositional system of fan delta into lake in eight districts, fan delta plain facies does not appear, mainly composed of two subfacies, fan delta front and the front fan delta, also developed small range of bay, can be identified seven microfacies.4. The main microfacie is underwater distributary channel deposits, in which there are debris streams and tributaries bay deposition. The main rock type is coarse sandstone and sandy conglomerate and conglomerate.5. The sedimentary evolution experienced of a lake level rise-fall-rise process of upper karamay formation. |
PDF Full Text Request