Geophysical Characteristics And Prediction Of Thin Sandstone Reservoir Of Paleogene In Yudong Area,the West Of North Uplift, Tarim Basin

North uplift is one of three positions in oil and gas exploration in the Tarim Basin, It is one of the richest oil and gas regions. In recent years, the oil and gas exploration in Tarim north uplift have made obvious progress, especially in the Mesozoic and Cenozoic continental clastic achieved good results that found large-scale oil and gas reservoirs. Years of research confirmed that the thin sandstone reservoir in the sandstone section of Paleogene in Yudong region near the western part of Tarim north uplift region has a very favorable reservoir conditions. In recent years, QL1, YD1 and many other major lithologic reservoirs were gradually discovered, the lithologic reservoir about the thin sandstone at the thin sandstone section exploration gradually become the main object of research and exploration target. Previous studies focus only on the macro of Paleogene Kumugeliemu group and the related studies of large sets of strata sequence, formation, deposition, reservoir and reservoir conditions, at the studies of fine genesis phase with deposition and reservoir, sand body configuration, spatial distribution, hydrocarbon potential and other aspects about the main producing reservoir in the thin sandstone at the sandstone section which is thin, buried deep, rapid lateral changes is ignored, that leading to the causes phase whit thin sandstone is not clear, the spatial distribution of the thin sandstone, the sandstone configuration and the Oil-bearing Properties of thin sandstone are difficult to accurately determine. They are making the exploration and development of the north tower have some challenges.For these reasons, decided to carry out in the Yudong region of north uplift genetic mechanism and sands body conformation study,Geophysical response characteristics of the thin of sandstone and inversion of high-resolution study about sand body, the fusions of seismic data information study, and sand visualization about seismic sedimentology and evaluation of thin sandstone hydrocarbon study. At the same time, making clear the causes of thin sandstone and sand body configuration, to determine the spatial distribution of a thin layer of sandstone and sand body configuration.Search thin sandstone lithologic traps and evaluate its effectiveness, lay the theoretical foundation for thin sandstone lithology exploration research and take shape technical method about thin sandstone seismic analysis and forecasting, also provide guidance for the same type of thin sandstone lithologic reservoir exploration.In this paper, through a comprehensive study of cores, logs and seismic data, from analyze the diagenesis sign of thin sandstone to implement genetic mechanism and causes of diagenesis microfacies; from analysis of ancient water, heavy minerals and Palaeogeomorphology, etc. to implement the thin sandstone provenance and distribution direction; base on sequence stratigraphic division, sand comparative analysis combined with seismic data and so on, the thin layer of sandstone deposition configuration is established, the distribution and scale development of thin sandstone is predicted. Analysis of thin sandstone speed, density, porosity and pore fluid properties, fluid saturation and other parameters,various combinations of thin sandstone forward model like wavelet type, wavelet phase, wavelet peak frequency, top and bottom interface reflection coefficient combined model, fluid filling, etc. is established; by analyzing the influence of the thickness variation of seismic reflection characteristics, variation of reflectance characteristics of the thin sandstone, the characteristic reflection and characteristics of property are summarized; the use of high-resolution seismic inversion, seismic data fusion to improve the resolution of seismic data, through the use of feature reconstruction inversion, spectrum inversion, geostatistical inversion, BGR～HIS, strata slice, seismic data fusion, fusion of seismic attributes and thin sandstone thickness decision fusion, etc. to comprehensive analyze and predict of thin sandstone distribution; through the use of thin sandstone spatial distribution and sand body configuration analysis as high-resolution seismic inversion about sand finely portray. High-resolution inversion fuse with three-dimensional characterization of space, seismic slice analysis, thin sandstone lithologic traps are predicted and evaluated; Through the use of seismic multi-attribute fusion analysis, time-frequency analysis, ABV absorption anomaly, frequency attenuation gradient anomaly and amplitude attenuation gradient anomaly, hydrocarbon potential about thin sandstone lithologic traps is analyzed and evaluated.Through analysis of the ideas and technology, following several aspects of understanding and conclusions can be drawn:(1) The thin sandstone section of Yudong area developed a complete third-order sequence, includes the lower transgressive systems tract and the upper highstand systems tract, further divided 1 parasequence formations and 3 parasequence formations. The provenance of the thin sandstone was from Western WenSu bump recycled orogeny rapid uplift zone. The parent rock consist of intermediate basic magmatite and corresponding metamorphic rock, while the heavy mineral was a five kinds of stable mineral assemblage which includes magnetite, epidote, zoisite, leucexene, garnet. The pre-depositional ancient landforms was a steep slope which tilted to the inside basin and the paleocurrent flowed to the internal basin from west to east.(2) The fan delta front and the shore shallow lake are mainly developed in the thin sandstone section of Yudong area. The thin sandtone section mainly developed underwater distributary channel, mouth bar, sand sheet and shore 4 sedimentary microfacies sand body. While the microfacies sandbodies full of fine-siltstone of underwater distributary channel sand, sand bar and sheet sand superimposed on the longitudinal and transverse coalesced. It’s middle prosperous and middle permeable reservoir, and is the favorable facies of Yudong area. Phase 4 class 14 level 4 configurational unit were identified from the flagstone of the thin sandstone. The phase 4 configurational unit was shore shallow lake sand dam microfacies configuration, underwater distributary channel, sheet sand and river mouth bar microfacies of fan delta front configuration. The sandbodies of underwater distributary channel microfacies and the river mouth bar microfacies of the fan delta front is fully connected. And the all connected sandbody of underwater distributary channel microfacies of fan delta front is the favorable reservoir in the flagstone of third sands group.(3) Two rock combination type named Yudong Ⅰ and Yudong Ⅱ were developed in the flagstone of Yudong area. The rock physical parameter of Yudong Ⅰ flagstone of third sands group is totally different from the mudstone of the overlying interbedded intbd second sands group and the underlying third sands group and the transverse Yudong Ⅱ flagstone of third sands group. It has a bigger density and velocity of p-wave、low water saturation and shale content、the largest porosity and permeability. On seismic section, the flagstone of third sands group has the reflection characteristics of weak amplitude, high frequency, and fan to southward extension on the plane and slice.15 kinds of seismic attributes along with the change of thickness of thin layer sandstone is most sensitive.11 kinds of properties such as arc length, average instantaneous frequency, average reflection strength, effective bandwidth, maximum peak amplitude, the maximum trough amplitude, root-mean-square amplitude, slope at energy half-time, slope of instantaneous, slope of reflection strength、relative reflection coefficient have an linear positive correlation with the thickness changes; 2 kinds of properties such as average instantaneous phase, perigram component are negatively related to the thickness change linearly; the quadrature is exponential negative correlation with thickness changes; thin bed index factor has a logarithm positive correlation with thickness changes.(4) The rule of Peak amplitude and peak frequency changing with the thickness changes is different when Types of wavelet, wavelet phase, peak value of frequency, the combination of models top and bottom reflection coefficient changes. When Ricker wavelet achieves resonance, thin layer thickness is minimal and the ability to recognize thin layer is strongest when the frequence achieve highest.90 degree phase wavelet model of peak amplitude is best for thin layer distinguish because of its change speed and rate of change is big, waveform center is corresponding to the wedge thin sand body center. The frequency of seismic response increased when the peak value frequency became higher and it’s better to explain the thin layer. Continuous grading and continuous metrical model of peak amplitude, peak frequency variation is the largest, thin layer identification is the most favorable. If the model full of gas, the peak amplitude of the seismic record most affected and smaller influence on peak frequency. Layer thickness is larger than 1/8 wavelehgth the seismic data can determine its position, layer thickness is less than 1/8 wavelength can be detect by seicmic response micro variation.(5) Seismic reflection characteristics is effective, high credibility to predict thin layer plane distribution of sand body, but for the internal structure of the thin layer, the reflection ability of evolution law is limited. Geostatistical inversion is accurate effective, high credibility to predict internal structure and evolvement rule of the thin sandstone, but horizontal sand body prediction ability and reliability is general. Feature reconstruction inversion is accurate and reliable to predict plane distribution of thin layer sandstone, but is a bit poor to reflect internal structure and evolvement rule of the thin layer. Though it can reflect structure and evolution law of sand body of sands group, the inversion relatively complicated. Constrained sparse spike inversion and spectrum inversion the resolution of a single set thin sand body is bad, can’t solve the problem of internal structure of thin sand body.(6) Seismic reflection characteristics and seismic inversion multi-source information fusion, seismic sedimentology 90 degree phase and slice of thin layer sandstone predict thin layer sandstone of third sands group mainly distributed in the north YT5-YD1-YD4, fan to the south, east, south west distribution. It developed three periods of underwater distributary channel, sand bar and sand sheet overlay in vertical and superimposed each other in the plane, and also mutual lateral cut pile. And body in longitudinal and transverse connected to each other.(7) Seismic predict a lithologic trap developed in the thin layer sandstone of third sands group, covers an area of 306 km2, range 590 m. Hydrocarbon predicts identified the lithologic trap of third sands group in Yu Dong region is rich in hydrocarbons. The area which saturation is above 50% covers an area of 232 km2 is the favorable exploration target in Yudong region. It has deployed 3 exploration appraisal wells as YD101, YD102, YD103, of which TD101, YD102 have drilled, both prolific hydrocarbon flow are obtained.