Reservior Characteristics In Paleogene And Favorable Lithologic And Stratigraphic Traps In Western Tanhai Sag, Liaohe Oilfield

Guided with sedimentology, reservoir geology, high-resolution sequence stratigraphy, together with the technical methods of the observation and description of cores and specimen, drilling and logging data analysis, 3D seismic data volume tracking, reservoir’s seismic reproduction, this research focuses on the Paleogene clastic reservoir’s origin, types, controlling factors, reservoir characteristics in West Tanhai Sag, Liaohe Oilfield. 3D seismic data volume is also applied to track and describe the main sand bodies, which form the lithologic and stratigraphic traps in the research area. The achievements and understandings are as follows:The main seven types of sedimentary facies in Paleogene reservoir in West Tanhai Sag are: braided fluvial delta, fan delta, delta, nearshore subaqueous fan, lacustrine, beach, and sublacustrine fan, the microfacies with the best original properties is distributary channels, followed by mouth bar, subaqueous distributary channels, distal bars, the worst is sand sheets.The main lithological types are feldspathic lithic sandstone, lithic feldspar sandstone, lithic sandstone and greywacke with low compositional and textural maturities in the Paleogene reservoir in the west sag of the beach area, Liaohe Depression. The sedimentary environment is near-source and multi-source depositional system. The pore types are primary pores, secondary pores and composite ones.The porosity and permeability alter regularly with the burial depth and the abnormal high values of porosity and permeability appear at the depth scale of 1400 to 2600 meters and 2800 to 3400 meters. The research shows that the diagenetic stage of this reservoir is from B substage of Early Diagenesis to A substage of Late Diagenesis and the primary types contain mechanic compaction, cementation, dissolution and replacement. In detail, the replacement is constructive with prevalence and strong degree, and the other three are detrimental with medium degree.The main controlling factors are the intensity and stages of diagenesis. These two abnormal high porosity zones are attributable to the composite effects of various diagenesis activities. The first zone is related to the organic maturity in acid diagenetic environment and the second one in alkaline environment, in which the dissolution of silica components contribute the formation and reservation of secondary pores to a great degree. In the research area, the lithologic and stratigraphic traps can be divided into four categories: sandstone lenses, pinch-out upward reservoir, turbidite, and buried highs. The four genetic types of sand bodies, which forms the lithologic and stratigraphic trap, are LST(Low System Tract) slope fan, sublacustrine fan, pinch-out upward, and HST(High System Tract) slump fan. Based on the tracking of 3D seismic data volume, several sand bodies and their primary criteria are recognized and described.