| Adopting the classic and high-solution sequence stratigraphy as theoretical basis, this dissertation uses the seismic, well log, geologic log and core data to establish four-order regional chronostratigraphic framework by the characteristics of palaeotology, petrology, mineralogy, geochemistry, well logging response and seismic section in K2y1 in Gulong Region. Based on the study of sedimentary feature and source-reservoir-cap rock association within sequence framework, the dissertation discusses the formation mechanism of oil and gas reservoir through the relationship between the structure, sedimentary, diagenesis, fracture, migration and the reservoir, and comprehensively analyzes the main controlling factors of reservoir formation and petroleum distribution, and points to the favorable targets.Sequence research shows that the K2y1 layer in Gulong Region belongs to the LST (Lower System Tract) 2nd and/or 3rd-order sequence in Songliao Basin, which is controlled by tectonic subsidence, palaeoclimate and palaeogeomorphology etc. and can be divided into three 4th-order sequences SQ1, SQ2, SQ3, and the sequence boundary and system boundary can be determined by palaetologic, petrologic, mineral, geochemical, well logging response and seismic section features. The K2y1 sequence in research zone is filled by multi-provenance from the north, Qiqihaer and the west, the ring distribution of deposits is controlled by the ring slope-break zone at the edge of the basin. The underwater distributary channels of delta front are very well developed which is controlled by the accommodation of the lacustrine basin, but the thin blanket sands are almost unconnected laterally with interlayered mudstone vertically.Structure research shows that the nosing structures around Gulong Sag are the most favorable zone for oil and gas migration and accumulation, especially Longnan Anticline, located between Changjiaweizi Syncline and Talaha Syncline with high uplift, is favorable to the petroleum migration and accumulation, which has been confirmed by the exploration practices. A series of nosing structures on the west of Daqing Placanticline are close to the petroleum generative depression and considered as the favorable migration direction, but if there are not necessary factors forming the traps, such as fault and lithology, the oil and gas will pass by these nosing structures and accumulates in the structure traps upon the higher placanticline. The fracture serves as the channel in active period through which the oil and gas can migrate from the source rock to the reservoir, vise versa in repose period. Fault clay in the fracture turning and/ or in the intersection of fractures is favorable to the oil and gas accumulation.Sedimentary research shows that the change of base level of deposition controls the genetic type of sand bodies and their distribution in space, and that in LST develop stratigraphic overlap trap and sorts of combination traps, and in TST (Transgressive System Tract) develop composite lithologic trap, lithologic pinchout trap and lens trap, and in HST (High System Tract) lithologic upward pinchout trap and lens trap. Of all the three system tracts in the sequence stratigraphic framework develop the favorable reservoir, but they play different roles during the process of oil and gas reservoir formation. In the slope-break zone at the edge of basin is prone to form the stratigraphic overlap reservoir, stratigraphic unconformity reservoir and structural pinchout reservoir, while in the center of basin below the slope-break zone develop types of composite lithologic traps and in south of the research zone is the lithologic trap belt composed of sand bodies.Diagenesis research shows that the main controlling factors of secondary porosity in this region are the organic acid generated from organic pyrolysis, carbon acid corrosion and meteoricwater eluviation. Based on the result the dissertation predicts that Gulong Sag is the secondary porosity development area.Fracture research shows that in Xinzhan Region reservoir fracture is structure fracture, and that under the control of deposition the thin sand interlayer within mudstone is the lithologic basis for fracture formation, and that in the tectonic setting the special structural evolution leads to the fractured reservoir formation in Putaohua oil-bearing layer in Xinzhan Region, reservoir overpressure is another important factor in fracture formation.By analyzing the main controlling factors of oil and gas migration and accumulation, the dissertation considers that overpressure + buoyancy (driving force) and capillary force (resistance force) are the key in the migration of oil, gas and water to the pure oil accumulation in occluded oil reservoir with low porosity and permeability in syncline, the oil-water bearing layer formation in semi- occluded oil reservoir with middle porosity and low permeability in the slope of syncline and gravitational differentiation of oil and water in reservoir with middle porosity and permeability in high structure.The above research on the mechanism of oil and gas reservoir formation shows that the main controlling factors of the type of oil and gas reservoir and the distribution of oil and water in space include: (1) the type of sand body and the superposition in space determining the distribution of oil reservoir in space and the degree of oil filling the reservoir in Gulong Region; (2) the type of reservoir; (3) the type of structure and its location; (4) evolution and arrangement of faults. In the end the dissertation divides the K2y1 Putaohua oil-bearing layer in Gulong Sag into four oil reservoir belts from the boundary into the center of the sag—nosing structure reservoir belt, structural-lithologic combination reservoir belt in Talaha-Yingtai Region, complex lithologic reservoir belt in Gulong-Maoxing Syncline and upward pinchout-fault-lithologic reservoir belt in the slope of sag, and also points to the favorable stratigraphic-lithologic targets.
|
PDF Full Text Request