Study On Oil And Gas Reservoir Forming Rule For The South Of Changling Sag In Songliao Basin

Changling Sag is situated in the south of the center depression of Songliao Basin, its east and west sides are Honggang Bench and Huazijing Bench respectively, it is a huge sag which crosses the southern of the center depression in Songliao Basin, the area is about 8,400Km2. It possesses very rich oil and gas resources, the total resources are 2,863 million tons, of which oil is 676 million tons and gas are 2,187 billion m3. It is a long time developing sedimentary basin which possess double composite structure of rift and depression. The founded oil and gas fields in Changling sag mostly lie in Huazijing Bench, eastern of the basin, they are respectively Dalaoyefu oil field, Shuangtuozi oil field and Dongling gas field from the northern to southern of the basin.The basement is metamorphite and granite from Permo-Carboniferous,the sedimentary caprocks are from upper Jurassic, Cretaceous, Tertiary and Quaternary from lower to upper. The upper Jurassic is major coal-bearing pyroclast terrestrial deposit formation, the Cretaceous is major terrestrial clastic deposit formation, the Tertiary is major terrestrial clastic deposit formation which distributes in the western of the basin, the Quaternary usually distributes the whole basin. The strata are Huoshiling formation, Shahezi formation, Yingcheng formation, Denglouku formation, Quantou formation, Qingshankou formation, Yaojia formation, Nengjiang formation, Sifangtai formation and Mingshui formation from lower to upper. According to Changling sag structural active characteristics and strata forming and existent situation, the strata is classified into three large structure zones which are the basement, rift and depression structure. The structural evolution is quite similar between Changling sag and Songliao Basin, the feature of the thermal evolution history determined the characteristics of the basin structure and sedimentary evolution, the evolution stages are divided into 5 sections of the forming of rifted basin, rift, transition between rift and depression, depression and compression overturn, the stress field had undergone a full tectogenetic cycle from pullapart to extrasion to levorotatory expanding and wresting to non-stress period to levorotatory expanding and wresting to squeezing.There are 4 huge nose-structures in Changling sag which are Shuangtuozi nose-structure, Daliaoyefu nose-structure, Xixiliga nose-structure and Qianan huge nose-structure from south to north. Of which Shuangtuozi nose-structure, Daliaoyefu nose-structure and Xixiliga nose-structure are all huge nose-structure controlled by long time growing basement palaeohigh. The rudiment of Qianan nose-structure had begun to appear under the effect of the forth Yanshan tectonic movement at the end of Nenjiang formation sedimentation period, and formed completely under the effect of the fifth Yanshan tectonic movement at the end of Mingshui formation sedimentation period.There are 4 sets of major hydrocarbon source rock in Changling sag, namely deep lake facies mudstone of Jurassic-Cretaceous, mid-deep lake facies mudstone of Denglouku formation, lakes facies mudstone of Qingshankou formation and Lake Facies mudstone of Nenjiang formation. Accordingly, the oil and gas reservoir forming assemblages can be divided into 5 sets types in Changling Sag: Type I is that oil and gas stored in fracture and hole of lava in Huoshiling formation. Typeâ…¡is that oil and gas produced and also stored in Yingcheng formation. Typeâ…¢is that oil and gas produced from the lower formation and stored in the above Denglouku formation, Typeâ…£is that oil and gas produced from the lower formation and stored in the above Quantou formation, Typeâ…¤is that oil and gas produced from the shallow formations including Qingshankou-Yaojia- Nenjiang formations and stored in themselves. The 4 petroleum systems can also be identified in Changling sag, they are J3h- K1yc (J3h-Kld+Klqn) (!) petroleum system, Kld (J3h-K1yc+Kld+Klqn) (!) petroleum system,K2qn (Kld+Klqn) (!) petroleum system, K2n (Kld+K2qn+K2n+K2s) (!) petroleum system.Oil and gas reservoir forming in Changling sag is controlled by the various essential factors of reservoir forming and the organic matching relationship, it was considered that the oil and gas reservoir forming was mainly controlled by 3 factors of hydrocarbon source rock, favorable storage phase belt and migration pathway conditions by the result of research. There are 5 major oil and gas reservoir forming models, which are autogeny and auto-store, proximal source, far lateral source, bench and vertical way.Autogeny and auto-store is one kind of model which oil and gas migrated and stored into source rock inside or near the reservoir trap ,the reservoir usually be formed after oil and gas first time produced without second migration in a large scale.Proximal source is another kind of model which oil and gas produced from deep lake facies mudstone and migrated vertically or laterally short distance into near reservoir traps and formed oil and gas reservoir. Far lateral source is the third kind of model which oil and gas produced from the center of Changling sag and migrated long distance along reservoir or unconformable interface into the ramp area of Changling sag and formed oil and gas reservoir.Bench way is the forth kind of model which oil and gas produced from deep source rock, and migrated laterally along updip direction into favorable reservoir by means of all kinds of dynamics, it would migrate vertically into upper trap along fault face when oil and gas met with opening faults, and formed oil and gas reservoir.Vertical way is the fifth kind of model which oil and gas produced from deep stratum and migrated into upper stratum along certain vertical ways which include fault and diaper, and formed oil and gas reservoir. This is an ordinary oil and gas reservoir forming model in multiple oil and gas play of faulted basin.According to the above results of our study, Changling sag should be divided into 5 petroliferous favorable structural areas which are Suotuo, Yaoyingtai- Daqingzijing, Dongling, Huachangqianqihao and Huaxingzhen- Yangjiadian area.Suotu structure zone: It locates in the northern of deep area of Changling sag and southern of Qianan sag, the main source rocks were distributed in the northern and southern of the sags, and formed the most potential oil and gas accumulation plays. There are a few low height structures developed in the sag sediment of Suotu area, and formed structure-lithological reservoir. The advantageous traps and vug-fracture reservoir of volcanic of deep sedimentary Yingcheng formation are matching in the effective source rocks, and high production natural gas could be acquired in this formation.Yingtai-Daqingzijing structure zone: This zone is a large scale nose structure controlled by the basement, Dalaoyefu and Xixiliga nose-structures are controlled by Yaoyingtai-Daqingzijing large scale blind palaeo-uplift at the same time. The advantageous sedimentary face of the frontal delta zone in the sag depression of this area is the potential area which could form large lithological-structure complex reservoir, the Huazijing fault prominence of fault depression is structure highland between Chaganhua fault depression and Fulongquan fault depression, and could accumulate natural gas from the above two fault depressions.Dongling structure zone: Dongling gas field locates the most southern of Dongling sag, there are fault traps developed in Denglouku formation and below in this area, most of the traps are developed in the west area of regional fault, and lots of wells in this area have already found high production. The distribution framework of western gas and eastern oil is distributed in Dongling. The characters of traps in fault depression are small area, high height and buried deep.Huachangqianqihao structure zone: The fault depression petroleum system of J3-K1 is developed in this zone, natural gas is the major target.it is the most popular developing area of structure traps in Changling sag, the volcanic diaper, fault-nose structure and fault block structure are developed widely in the fault depression of this area sag depression locates in the southern part of central structure zone in Changling sag, and also develops widely fault-nose and fault block traps.Huaxingzhen-Yangjiadian structure zone: There is few fold structure developed in the sedimentary rocks of this play, this play shows wide-low slope, the faults developed in this play distribute inclined major along north-north-east direction, and show small fault distance, short extension, so only a few small fault block traps and few anticline, nose-structure are developed in this play.