Studies On Hydrocarbon Accumulation Conditions And Mechanism Of The Gudao Buried Hill In Jiyang Depression

This dissertation pays a main research on Gudao buried hill, one of the biggest buried hill in Jiyang depression. This paper integrates geology, geophysics and geochemistry, depicts the factors of petroleum accumulation, reconstructs the process of petroleum accumulation, figures out the relationships between the chron and the distribution of process of petroleum accumulation such as hydrocarbon generation, migration, accumulation, conservation and so on, and studies their control actions on the process of petroleum accumulation of the Gudao buried hill pool. On the basis of the whole studies, this paper gives the comprehensive geological evaluation and the analysis of petroliferious geological conditions of the Gudao buried hill, and has predicted the favorable places for prospecting, and acquires main scientific issues and achievements as follows:(1) The Lower Paleozoic of Gudao buried hill in Jiyang depression has many rock types such as limestone, dolostone, mudstone, karst limestone and so on; Sedimentary system can be divided into carbonate ramp,carbonate platform, platform-shelf and eluvial deposits; This paper has studied the evolution of the Lower Paleozoic sedimentary and set the identification mark of the Lower of Paleozoic sequence boundary of Gudao buried hill in Jiyang depression; On the basis of well gugu 2, The Lower Paleozoic is divided into one Super-sequences, two first-order sequence, three second-order sequences, five para-second-order sequences, and twenty third-order sequences.(2) This paper accomplished the detail seismic interpretation of the bottom of Cambrian(Tg2), the top of Ordovician(Tgl), the bottom of Carboniferous, the bottom of Cretaceous, the bottom of Tertiary(Tg), the top of Shahejie Formation and the top of Dongying Formation and the isopach map of Cretaceous, Shahejie Formation Dongying Formation and Neogene and the burial depth map of the top of Ordovician and the paleo-geological map in the four key geologic epoch after Cretaceous, and the interpretation and the map of typical structure, volcanic intrusive bodies, eroded channel-vale; Gudao buried hill is a block-gebirg, fault zones being its borderlines, main block of the buried hill being a dome fold, and is a succeed arched structure with multi-period structure. Tectonic styles of Gudao buried hill are plane fault, listric fault, rollover anticline, thrust faulted anticline, imbricated fault, fault horst, graben, sheaf structure, reversal fault, volcanic intrusive bodies along faults; The evolution of Gudao buried hill can be divided four stages: rifting stage(between the last phase of J and the early phase of K ), downfaulting stage(Es), downfaulting- downwarping stage(Ed) and downwarping stage(N-Q), and the depositional characteristics of stages have being studied; Gudao buried hill has undergone seven stages: compress stage(T) , extensional stage(T), faulted depression and compress stage(K), early stage of tension(end of K) ,stage of extreme tension(Es), transitional stage of fault sag(Ed) , stage of stage(N); Guxi fault is earlier than Gubei fault and Gunan fault; The characteristics of Guxi fault, Gunan fault and Gubei fault and their controlling to Gudao burial hill are different to each other.(3)The reservoir space types of lower Paleozoic of Gudao buried hill are divided into intercrystal pore , intercrystal dissolved pore , intergranular pore, intergranular dissolved pore, moldic pores, vug, dissolved fracture and structural fracture; There are six carbonatite genesis fracture-cavity types: sedimentary period fracture-cavity system, penecontemporaneous fracture-cavity system, diagenetic fracture-cavity system, hypergene fracture-cavity system, catagenesis fracture-cavity system, anadiagenetic fracture-cavity system; Sedimentary period fracture-cavity system is controlled by the depositional system and compiled types of sedimentary facies; Penecontemporaneous fracture-cavity system is controlled by the third-order and fouth sequences surfaces; Diagenetic fracture-cavity system is indirectly controlled by depositional system; hypergene fracture-cavity system is controlled by the first-order, second-order and para-second-order sequences surfaces; Catagenesis fracture-cavity system is indirectly controlled by hypergene fracture-cavity system; Anadiagenetic fracture-cavity system is controlled by anadiagenetic solution and multi-stage anticline and faults; System of vug-fracture is controlled by lithology ,weather-worn surface and sequence boundary; Forming and reforming of the carbonatite vug-fracture are controlled by the uplift movement of latest Cambrian, latest-Ordovician, the compressional movement of Yanshan chron, the estensional movement of Himalayan chron; The top of Badou formation as eroded sequence surface(SB2) is easy to form karst reservoirs; Depositional sequence surface is an advantage to the solution during catagenesis and anadiagenetic stage and easy to form the fracture-cavity system; Diagenetic sequence surface is an advantage to hypergene function and anadiagenetic solution fracture-cavity system.(4)There are at least four brine charging events in Gudao; There are at least six fluid charging events according to the A-group～F-group Sr isotope samples; The serials from old to young is D-group→F-group→B-group; The first fluid charging to the third fluid charging occurred in late Paleozoic or Mesozoic; The fourth fluid charging occurred before Cenozoic during the uplift movement with the fracture and faults opening and fresh water seeping; The fifth fluid charging is similar to the fourth fluid charging but with more fresh water taking part in; The sixth fluid charging occurred in Minghuazheng stage, and the mixture fluid is from Shahejie formation water and fresh water.(5) Karst reservoirs nearby the ancient karst surfaces are controlled by the freshwater-rock interaction during hypergene stage and acid-water-rock interaction during burial stage; Layered reservoirs are controlled by anadiagenetic solution; The reservoir matrix permeability varies a large range, and is nothing with the burial depth, and is positive correlation to porosity up 2%; The Lower Paleozoic reservoirs(fracture-cavity intervals) are related to diagenesis and karstification and close correspondence to karst serials; Formations of the Lower Paleozoic bear high angle fracture in Gudao burial hill; Carbonatite reservoirs(fracture-cavity intervals) mainly occur in Badou formation, Shangmajiagou formation, Yeli-liangjiashan formation; Uconformity surface is one key element to control the Carbonatite reservoirs(fracture-cavity intervals); I grade reservoirs(fracture-cavity intervals) mainly bear in carbonatite reservoirs concerned with weathering crust, from Badou formation to Shangmajiagou formation controlled by the weathering surfaces; Physical property of reservoirs in fault-zones is better than that in monocline zone; I grade reservoirs(fracture-cavity intervals) rarely bear in layer-reservoirs in Gudao burial hill, and II grade reservoirs(fracture-cavity intervals) mainly bear in in layer-reservoirs in Gudao burial hill; Layer-reservoirs (fracture-cavity intervals)in Gudao burial hill is controlled by the depositional zones(sequence or karst zones), and faults improve the Physical property of layer-reservoirs, and layer-reservoirs (fracture-cavity intervals) bear in Fengshan formation and Yeli-liangjiashan formation.(6)The quality of layered cap-rock of Gudao buried hill without fracture is good. By means of studies of fault sealing of fault zone around Gudao buried hill, west, south north faults action last a long time, are lateral sealing and no vertical sealing; According to geochemistry indexes, there are two hydrocarbon charging events in Gudao burial hill carbonatite; Due to the bad oil preservation condition, the first stage oil pool was broken down; Because of the amount of the second hydrocarbon charging being small, there is no contribution to the pool; There are local pools due to the fault lateral sealing with the local caprock in Dongying formation;(7)The researches on geochemistry show that hydrocarbon comes from distinct stages, formations and sag, there are two stages hydrocarbon charging, and are two petroleum systems, namely, Bonan sag petroleum system and Gunan sag petroleum system.(8)Characteristics of petroleum accumulation of Gudao buried hill are two hydrocarbon sources from south and north, complex hydrocarbon transporting pathway, migration to the eminence of buried hill, mixed sources charge, being controlled by the faults, fracture-cavity reservoir, leakage by "top window", local petroleum accumulation. The wildcats aiming at main block of Gudao buried hill and east-north monocline are not success because of the absence of caprock and layer trap.