| The northeast area of Sichuan province is one of most advantageous reserve block of exploration for oil and gas, has a lot of exploration targets and large oil and gas reserves, and become the force of exploration for oil and gas in Sichuan basin. The success in exploration for oil and gas has the great significance in relieving pressure of LNG supply in the city of Chengdu and ensure success of ambitious plan of"The gas from Sichuan province is supplied to other province". Therefore, this research has obviously economic benefits and social benefits.This article based on successful exploration experience in detrital rocks of west Sichuan, guided by the theory of geotectology, study of sedimentary basin, sequence stratigraphy, sedimentology and petroleum geology, followed the main line from evolution of basin, evolution of sequence to evolution of sedimentation. We put emphasis on Ziliujing formation and its correlated strata, combined with the research of outcrops in field, datum of well drilling and seismic exploration, combined micro measurement in field with indoor macro analysis, combined the research of integrity of basin with the research of important areas, established relatively isochronic framework of sequences, finished the correlation between sequence and sedimentary facies in framework of sequences. We utilized the system tract of third-order sequence as the unit for mapping, mapped sequence-based lithofacies and paleogeography map which had many advantages as follow accuracy, isochronism, origin-continuity, exploration practicability and so on. Combined the isopach map of each system tract period, We can comprehensively realize the characteristics of lithofacies paleography and evolution in framework of sequences, then we can try to discuss the factors of sedimentary filling. Ultimate objective is to provide theoretical support for searching and ascertaining potential reservoirs and regularity of distribution, in order to arrange the next program of exploration. We divided lower Jurassic into a tectonic sequence(second-order sequence), twothird-order sequences (SQ1 and SQ2) which can be divided into PST and RST. Through comprehensive research, we believe that : In period of SQ1-PST, affected by tectonic movement, great loads of sediment was carried into basin, shorter axis direction of basin developed braid river deltas, longer axis direction of basin developed (Meandering)deltas; In period of SQ1-RST, the provenance from both northwest and northeast of research area was on the decline, mainly developed alluvial plain and delta plain in boundary of the basin. From boundary to centre of the basin consecutively developed shore lacustrine - delta front, shallow lacustrine - prodelta, shallow lacustrine, shallow lacustrine -semi-deep lacustrine; In period of SQ2-PST, the provenance from both northwest and northeast of research area was a small amount, mainly developed shore lacustrine, shallow lacustrine, semi-deep lacustrine. In period of SQ2-RST, affected by slowly tectonic uplift in boundary of the basin, the provenance from both northwest and northeast of research area was increasingly rising. With depression in basin, it is obvious to zone between shore lacustrine, shallow lacustrine and semi-deep lacustrine. In supplying place of provenance developed deltas and in no-supplying place of provenance consecutively developed shore lacustrine, shallow lacustrine and semi-deep lacustrine towards basin.The control factors in framework of sequences of lower Jurassic in the northeast area of Sichuan province were various, but the factors were mainly tectonic activity and secondly climate change. Lifting or subsidence in boundary of the basin was related to sediment supply, while lifting or subsidence in basin affected migration of sedimentary facies zones. Both tectonic activity in boundary of the basin and in basin ensure migration of depocenter. The climate change decided the change of relative lake-level. In warm, wet climates, relative lake-level rised, water area expanded, water desalted, with mass stream sediment was carried to basin. While in dry climates, relative lake-level falled, water area shrinked, water salted, streamaction and deltafication were not relatively obvious. |
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