Prediction And Evaluation On The Subtle Reservoirs Of Lower Tertiary, Subei Basin

With the relatively higher degree of prospecting, the subtle reservoir in Subei basin was considered as an important exploration direction. Forecasting subtle traps by sequence stratigraphy and 3D seismic data is a sensitive topic in hydrocarbon exploration. In this paper, using sufficiently 3D seismic data, drilling data, log data and core data, stratum sequence Lower Tertiary Subei basin is partitioned by using sequence stratigraphy theory. Each sediment sequence system mode is built. Integrated using geology, log, drilling data, special seismic processing technique, interpretation technique, including high resolution seismic data processing method, high precision horizon calibration technique, 3D seismic visualizing interpretation, seismic coherence analyze, attribute analyze, logging-constrained inversion, subtle trap objects were identified and interpreted .Finally, advantage objects of subtle trap in this area were determined.Based on the analysis of seismic data, borehole and well logging and core of Lower Tertiary Subei Basin, two second level sequences and 8 third sequences have been identified. System tracts were also identified within each sequence. Each of the 8 sequences consists of either complete lowstand, transgressive and highstand system tracts or one or two of them. Based on sequence stratigraphy and structural analysis , sequence pattern in Gaoyou sag may be described as the west part with fault break and east slop without break.There are a couple of favorable conditions to form subtle trap reservoirs in Subei basin. Fault is the key factor of subtle traps to oil accumulation, and has the function of linking reservoir and lateral sealing. The favorable oil bearing facies belts include sublacustrine fan, delta front, fan delta front and the central part of subaqueous fan.Guided by the theory of sequence stratigraphy, a suite of techniques for identification and description of subtle traps have been developed based on modern new technologies of seismic exploration such as high resolution seismic processing , multi attribute extraction , 3D visualization , coherence analysis , well constrained seismic inversion , reservoir lateral prediction. A number of subtle traps have been found during the 3D seismic interpretation on data in Majiazui & Lianmengzhuang 3D seismic project Gaoyou sag and Liuzhuanbei Jinghu sag 3D seismic project. With the data mentioned above and analysis on the petroleum geologic conditions, 6 favorable areas for subtle trap exploration are put forward.Production from fractured reservoirs is controlled primarily by the shape, orientation and concentration of the fractures. In this paper, evidence of fractures from cores and borehole image logs were integrated with 3-component seismic converted wave data in different directions, 9-component VSP, and 3D seismic reflection data, to develop an understanding of how the seismic data relate to the fracture. AVO, seismic inversion data, and other attributes of seismic reflection data was used to detect and characterize fracture density and dominating fracture azimuth in Yancheng sag.