Research On Sequence Stratigraphy And Subtle Reservoir Target Assessment Of Shahejie Group In Qibei Slope

Most of the subtle pools in sequence existed in low fan of deep water, slope fan, or special lithology lens deposited on the top of the paleohigh. The key to prediction of subtle pools by sequence stratigraphy lies in the division of the 3rd sequences and related system tracts. In sequence studies, the tectogenesis occurred after deposition was "stripped off ", and the deposition model was built on base of ancestral structure, ancient landform, and controlled by syndepositional structure, paleoclimate and deposits sources. Based on integrated analysis of the distribution of depositional system and the development of combination of source rocks, reservoirs and seal rocks, as well as geological, geophysical and geochemical study of sedimentary environments and types and transformation of facies, the strata patterns of different sequences in the basin were clarified. The study of the vertical evolvement processes and horizontal distribution of all types of sedimentary facies, sedimentary systems and system tracts, is very important to scientifically predict the condition and characters of combination of source rocks, reservoirs and seal rocks, followed by exact prediction of favorable exploration targets. After more than 2 years of 3-D seismic data interpretation and high frequency sequences study of well-seismic combination, and on base of large amount of integrated studies, the sequence framework, structure, reservoir, hydrocarbon occurrence and accumulation in north Qikou area were analysed, including the sequence development model in north Qikou slope, and the findings can be described as follows: 1. The development of sequence in this area was controlled by paleo-structure, climate, variation of lake level and supply of deposits, and the former two were the main factors. 2.Through the muti-well synthetic seismogram repeated calibration and transverse comparison, problems of multiresolution in P-wave synthetic seismogram and seismic interval velocity variation in transverse direction are resolved by calibrating horizon using some soft wares like Jason,Landmark,MPRP, on this basis marked bed IFS2 is found in this region. 3.By sedimentary facies study the main target stratum (parasequence) has the following characteristics: etang hirst, coastal sand, coastal mud, etang mud, Organic bank facies develop well in the target section; arenaceous material from large coastal sand body of the near delta, fan-delta and subsea alluvial apron was carried here by lake wave or fluid. Organic bank facies is composed of constructional detritus and shells and can be recognized easily in the core without well marked bedding. 4. The main factors controlling the formation of lithologic deposit: a.the rich oil sources of the S1 and S2 sections of Qikou sag is the substance basis for the formation of lithologic deposit; b.sand of S3 and bioclastic limestone of S1 with good reservoir bed is also the important condition of formation of lithologic deposit; c. the arrangement of the advantageous reservoir body and tectonic slope position is the key to the formation of lithologic deposit;d. the thick mudstone developed in the upper and middle section of No.2 stratum (S1) and stable cap rock in transverse direction provide good seal condition.