The Detailed Study Of The Sequence Stratigraphy And The Reservoir Of The Feixianguan Formation In The Puguang Gasfield In The Northeast Of The Sichuan Basin

Based on the former study, by referring to the geological survey reports, observation of the outcrops, and the data of the wells, and so on, it is known that the sedimentary framework of the Feixianguan Foramation inherit the characteristics of Changxin Formation's in the northeast of the Sichuan Basin, the Kaijiang-Liangping "continental shelf links southwardly to the ocean, the platform in the east of which is isolated, and the main evolution feature of the sedimentary framework of the Feixianguan Formation in the northeast of the Sichuan Basin is the transformation of the Kaijiang-Liangping "Continental shelf to the platform, i.e. the platforms is rimmed during the 1st and 2nd section of the Feixianguan Formation, however, it is a whole epicontinental platform during the 3rd and 4th section of the Feixianguan Formation. Based on the knowledge of the sedimentary framework, using the principle and methods of the sequence stratigraphy, by means of the analysis of the lithology- sedimentary in the outcrops, the core, and the well-logging, the Feixianguan Formation in the northeast of the Sichuan Basin is divided into 2 3rd-order sequences, and each sequence includes LST, TST, and HST, which have the district characteristics in the different sedimentary, respectively, and the Feixianguan Formation is divided into 11 4th-order sequences, and 20 5th-order sequences in the Puguang area,. Furthermore, the frameworks of the 3rd-order sequence and the high-frequency sequence are built for the study area and the Puguang Oilfield, respectively. By integrating the outcome of the sequence stratigraphic study in the wells and outcrop sections, and the research on the seismic sequence and seismic facies in the Puguang area, which make it clear that the evolution of shoal is different between the bilateral platform margins of the Kaijiang-Liangping "continental shelf in the lower sequence, which is progradation in the west one, and is aggradation in the east one, the elaborate distribution of the shoals in the high-frequency sequence framework is figured out in the Puguang area. The development and distribution of the shoal is controlled by the high-frequency, which occur mainly in the middle and upper of the 4th-order and 5th-order sequence, moreover, some shoals are recognized in the lower and middle of 4th-order and 5th-order sequence in the middle HST of the upper sequence. By means of the modern analytical technology of rock and mineral, by integrating the study of the lithology and geochemistry, linking the diagenesis and the evolution of the reservoir with the study of the sequence stratigraphy, the change of sea level, and hydrocarbon accumulation, and so on, it is revealed that the reservoir of the Feixianguan Formation in the northeast of the Sichuan Basin suffered many kinds of the diagenesis, especially, the cementation, the dissolution, and the dolomitization influenced greatly on the formation and quality of the reservoir. The dissolution happened during the syngenesis and burial, the former occurs in the shoal mainly, which is controlled by the sequence, and, the latter occurs based on the former. The dolomitization mechanism include evaporation marine, refluxion, mixed meteoric-marine waters, and burial, thereinto, the development and distribution of the three formers are related to the evolution of the sequence and the distribution of the sedimentary framework, the last one influenced on the quality of the reservoir obviously. The formation mechanism of the reservoir of the Feixianguan Formation in the Puguang gas-field can be summarized as follows: the platform margin shoals and the platform interior shoals that are controlled by the sea-level change of the 3rd-order sequence are the most favorable sedimentary facies of the reservoir, the syngenesis dissolution by the meteoric water is the chief formation mechanism of the reservoir, the burial dissolution react greatly on the melioration of the dimensions and quality of the reservoir, and the dolomitization promotes the quality of the reservoir mainly. Furthermore, by recognizing the reservoir in well section and contrasting the reservoir sections between the wells, it is known that the reservoirs of the Feixianguan Formation occur mainly in the middle and upper of the HST in lower sequence and in the lower and middle of the HST in upper sequence, singularly in the TST, and all of them occur mostly in the middle and upper of the 4th-order and 5th-order sequence. By integrating the analysis of the physical property of the reservoir and the study of the reservoir parameters by the well-logging, it is known that the physical property of the reservoirs in Feixianguan Formation in the Puguang gas-field is excellent as a whole, and the physical property of the reservoirs in the lower sequence is better than in the upper sequence remarkably, furthermore, there are the prominent differences between the physical properties of the different kinds of the lithology, which deposited on the different sedimentary facies, i.e. the physical property of the oolite-dolostone deposited on the platform margin shoal is best, the crystalline-dolostone takes the second place, the third is the oolite-limestone deposited on the platform interior shoal, and the limestone and marlite are the worst. At the last, according to the discussion of the controlling factors of the physical property of the reservoir, the research on the distribution of the physical property of the reservoir in the Puguang area is achieved in the different 5th-order sequence cell, respectively.