Daba Mountain, The Front Edge Of The Lower Triassic Feixianguan Off The Reservoir And Control Factors Study

Based on sedimentology, reservoir geology, log well geology to deposit, seismogeology, and latest relevant research develop both at home and abroad for the theoretical foundation .With the open-air section, drill and log well and the earthquake materials are research objects, adopt macroscopic and microcosmic , determine the nature and the ration , in the room and outdoors, routine and modern research approach to combine together, Mixed with test means and technology with advanced analysis, This paper have researched Triassic Feixianguan Formation stratum , rock, sediment ,diagenesis and the character of reservoir in detail in the front of Daba mountain which is in the northeast of Sichuan Basin; have probed into its main factor in controlling of its character of reservoir and the law of development . has made the following understanding and progression:1. According to stratum thickness , lithology , extinct plants and animal, sedimentary cycle , eustasy and electrical property ,etc. combining with the situation of areal geology .Have solved the difficulty in dividing stratum of Feixianguan Formation in the research district and have divided it into Fei 1 member , Fei 2 members Fei 3 member, and Fei 4 member from the bottom to the top . The achievement have set up reliable time standard for the sedimentary facies of the district and the research and contrast for reservoir.2. Through the drill core of well drilling and the sectional macroscopic and microcosmic research correctly, we have made a system partitioning on Feixianguan Formation in this district on its rock type and its feature systematacially for the first time and have summed up its rock as more than 20 kinds of three big classes. Although its gray rock is distributed in a large amount in every stratum , storage and collection performance is bad; Dolomite is mainly in Fei 1 to Fei 2 , storage and collection performance differs greatly ,Among them the best in its storage and collection performance is oolith dolomite ,secondly is crystal grain dolomite ; Gyprock is mainly distributed from Fei 1 to Fei 2 in some well district, can only be regarded as the cover rock; Fragmentary rocks is distributed in Fei 1 and Fei 4 distribute lesser quantity, storage and collection performance is extremely bad .3 . According to the open-air section, bore logging well and earthquake materials, combining with the geological characteristic and study progress of the forefathers,this paper thinks, the depositional environment of Da ba mountain foreordained affinity and the most part of Sichuan Basin has comparatively obvious difference.The author has proposed that Da ba mountain foreordained affinity is a relatively isolated tableland environment of carbonate which is surrounded by deep water—half deep water sea trough or slope during Fei 1—Fei 3 , faced with carbonate tableland of east of Sichuan which is connected with land each other across the sea . Such isolated tableland environment of carbonate, according to environment and the characteristic of sediment, can be divided into the inferior environments : tidal flaU lagoon , beachu tableland edge and slope .etc. Up to the lapse of time and the decline of the sea level, this isolated tableland is expanding to the hyperplasia all around constantly, the sea trough range shrinks gradually; till Fei 4 , it has connected with carbonate tableland of east of Sichuan as a whole , and has evolved into tidal flat - lagoon environment inside tablelandSedimentary facies is the base of the development of reservoir. The favorite facies belt is oolite beach at the tableland edge in every facies belt . during Fei 1—Fei 3, up to regional decline of sea level, tableland edge beach moved with clitellum form to the peripheral deep water district, horizon rised gradually , had obvious diachronekity. during Fei 1, oolite beach at the tableland edge distributed with clitellum form along with Pol - Du 5-Luojia5-Manyue-Hekou; till Fei 2, it moved to district of deep water ,along with Po2-Du2-Luojia2-Shatuo-Jichang-Shuanghe; When Fei 3, this beach body swiftly moved to Huanglong 2- Tiandong 23-Merman 1-Ningchang-Chengkou ; till Fei 4.it only distributed on a small quantity in regions of Zhenping of the northeast corner.4. Diagenesis is the key of the development of reservoir, primary porosity disappeared basically after welding ? pressure solution > cementation of three calcite and one dolomite, induced porosity is mainly formed through dolomitization and corrosion of many stages,but packing action of calcite and one dolomite for many stages made them smaller greatly .Dolomitization is one of the key factors of the development of good reservoir .There are three types Dolomitization in Feixianguan Formation stratum in this district . Admixing water dolomitization functioned mainly in oolite beach at the tableland edge ,and related with the influence of fresh water .had great contribution to improvement of physical property of reservoir .formed oolite dolomite and crystal powder dolomite with relic texture or not which had the best physical property .Reflow-penetrate dolomitization functioned in lagoon in the tableland, and related with the influence of barrier and strong evaporation, ,had less contribution to improvement of physical property of reservoir formed dolomite and sandcutting gypsum dolomite which had less good physical property ,crystal powder dolomite has some property of reservoir ; bury dolomitization also functioned mainly in oolite beach at the tableland edge , but its intensity is weak , and its origin is related with argillutite compaction water in trough ,has little contribution to physical property of reservoir . According to dolomite character difference in sedimentology -, petrology ^ geochemistry ,this paper has brought forward dolomitization mode to explain the cause of dolomite .Corrosion function is another key factor for the formation of induced porosity in Feixianguan Formation ,had identified four corrosion function in stratum and member we study . Syngenesis - penesyndiagenesis corrosion function is related with the reconversion of admixing water and fresh water of the sedimentary in oolite beach at the tableland edge exposed in sea level atmosphere when or after deposit ,had relatively heavy corrosion, filled with high degree, so its validity is not big; Corrosion function formed in the period of liquid hydrocarbon had a close relationship with organic acid produced by mature source rock in Permian System, regarding there is no pitch to fill withing as the characteristic in the hole produced, had heavy corrosion , filled with a low degree , its validity is great; Corrosion function formed in the period of gaseous hydrocarbon had a relationship with hydrogen disulfide produced in the course of reduction of thermal chemical sulfate, regarding there is no pitch to fill withing as the characteristic in the hole produced, had the heaviest corrosion , filled with a low degree , its validity is the greatest . Corrosion function in the period of fabric uplift is related to the fact that different density H2S groundwater is redistributed and adjusted to lift to construct, the corrosion is low in intensity, filled with a high degree, validity is small. Every corrosion function connect with each other as well as differ with each other, The geographical position of oolite beach at the tableland edge is favorable to liquid hydrocarbon issue and gaseous state hydrocarbon corrosion function, at the same time, syngenesis - penesyndiagenesis corrosion function can be regarded as foundation , reservoir developed very much. According to these characteristics , put forward the function mode of bury and corrosion when liquid hydrocarbon and gaseous state hydrocarbon formed.5. Tectonic process is the condition of the development of reservoir . It not only determines Kaijiang- Liangping sea trough and the entrance of the city -sea trough of west place in Hubei emergence and development, but also influences its sedimentary framework of furrow - stand in reservoir in the front of Da ba mountain , make favorable reservoir (oolite beach at the tableland edge) ,surround by sea trough edge distribute to present to bring to preserve;Meanwhile , determines that oolite beach at the tableland edge had strong mixing water dolomitization and every strong corrosion function also. Physical propert) of reservoir differed greatly at both sides of h because of its dissymmetry character of dustpan fault depression of sea trough, Physical propert} of reservoir of oolite beach at the tableland edge in abrupt slope of sea trough is better than that gentle slope bring.Mountain foreordained affinity fly to celestial being imprison group As to two group of the tectonic system of Feixianguan Formation in the front of Daba mountain , the northeast fabric physical property of reservoir is better than that of northwest, this is because that the direction of organic acid fluid is paralleled with its extend direction of northeast fabric. Fissure produced by tectonic process is not only related with the intensity of tectonic strain ,but also had a obvious negative relationship with development degree of pore, the existence of fissure can release tectonic stress effectively.6.Today.s Feixianguan Formation reservoir in the district is the final result for a long time which has influenced by interaction of sediment n lithogenesis and tectonic process among more than 200 million years -long geological history, distributed mainly in Fei 1 -Fei 2 in vertical , in oolite beach at the isolated tableland edge in landscape orientation, the major rock is oolite dolomite , reservoir space mostly are intergranular dissolved pore formed by redeposit , intragranular dissolved pore n pore between crystallite and solution opening between crystallite , Physical property of reservoir is good , pore structure is in condition ,mostly formed reservoir7.According to control factor for the development of reservoir, reservoir distribution rule in vertical and landscape orientation and the character of seism anomaly ,this paper has put forward two favorable facies belt of Feixianguan Formation reservoir in the northeast of Sichuan Basin .