A Research On The Relationship Of Oil-gas And The Ancient Structure Evolution In Akekule Area

The breakthroughs for exploration has been made on Ordovician,Devonian,Carboniferous and Triassic in Akekule lobe, which presents a perfect conditions in the study area with the formation of large and medium oil-gas field. Under the theme of tectonic research, the author has detailedly analyzed the forming and evolutions of Akekule lobe,the tectonic characters of fractures,unconformity and traps. On the top of that, the author sums up the ancient tectonic features of the three major unconformity(T74,T50,T46) during several major tectonic movement, especially the local structural features. And then the author probes into the evolution of the local structural features and establishes the ancient tectonic evolution model in Akekule area. Afterward, combining with condition and process of forming hydrocarbon reservoir, the author sums up the relationship of the ancient tectonic evolution and hydrocarbon. Finally, the author simply forecasts the target and gets some knowledge. A few points are following:1.Akekule lobe is a tectonic unit which is early formation, several stages of succession and development, change and shape the late tilted. By the regional tectonic setting, Akekule lobe is the underwater slope of extensional context in the early Caledonian. And in the Caledonian mid-night curtain, the underwater slope transforms into the nose convex shape by the structure. In the Early Hercynian, the nose convex shape transforms into flattened nasal convex by strong compression. And then to Late Hercynian, the structure continuous extrusion and the faults strongly form the convex broken nose job. In Indo– Yanshanian, the convex broken nose job is the Settlement-type nose under the tilted background. And then in Himalayan, the large double raised falls into a pattern. 2. The faults in the study area are highly developed, whose developmental stages are divided into Caledonian, Early Hercynian, Late Hercynian, Indo–Yanshanian. The development of the faults not only is the important channel for oil and gas vertical migration, but also controls the formation and development of the structure trap in the study area.The multi-stage tectonic movements in the study area develop the unconformity, such as T74,T70,T60,T50, etc. The unconformity crosses cutting, overlays and connectivity with oil and gas transportation system, such as fault and the transport layer, which constitutes three-dimensional network transporting of oil and gas migration in the study area.3. Under the influence of the factors such as regional stress, karst, fracture, not integration, salt body plastic flow, the study area develop the structure type, non-structural and composite type traps, whose plane distribution presents zonation and vertical distribution presents different types of overlay and reconstruction4. Akekule area presents good conditions for hydrocarbon accumulation. The formation of the oil-gas pool is a continuous process that stars at the Caledonian and extends Himalayan. The continuous process is divided into four stages such as Early Hercynian, Late Hercynian, Indo–Yanshanian, Himalayan. The formation of traps is in Late Hercynian and Indo-Yanshanian, which match well with the accumulation. The primary reservoir that formats in Caledonian-Late Hercynian suffers varying degrees of damage by later modified. And the secondary reservoir that formats in Indo-China and the subsequent period suffers less damaged by later modified. In Mid-Late Himalayas, the strata in Mesozoic and Cenozoic regionally dip towards north, which reforms the preliminary reservoir and oil-gas readjusts. Shallow oil and gas migtation from north to south formats the new oil and gas reservoir.5. On the top of it, the author believe that the Lunnan area and salt bodies covered area are the favorable oil and gas zone for finding carbonate reservoir, and the structural reservoir and lithology reservoir are the favorable oil and gas zone for finding clastic reservoir.