The Forming Condition And The Key Controlling Factor Of The Upper Carboniferous Volcanic Oil Pool In Malang Sag Of Santanghu Basin

Prospecting breakthrough had been achieved one after the other in the volcanic reservoir of Kalagang unit and Haerkawu unit of the upper Carboniferous formation in Malang sag of Santanghu basin, and biggish reserves scale had been obtained, whereas the understanding about the forming condition and the key controlling factor of the volcanic oil pool is insufficient owing to the volcanic reservoir's multiplicate controlling factors. Aiming at the difficulty in research about the tectonic characteristic, the reservoir property, the post-reconstructive process, the volcanic trap characteristic, the forming condition and the key controlling factor, adequately using the data of geophysical prospecting, drilling, well logging and general geology , integrating the traditional theory , new technic and method of basin tectonic analysis, petroleum geology, sedimentology and volcanic lithology, taking the research of reservoir's property and influencing factor as the masterstroke, this disquisition anatomizes the charact-erristic of the volcanic reservoir's structure and trap, and analyzes the controlling process of volcanic lithology facies, fracture and unconformity to the trap's forming, and elucidates the volcanic oil pool's forming condition and the key controlling factor, and indicates the advent-ageous zones and aims for volcanic oil pool prospecting. Primary summing-up:â‘ Santanghu basin, lying the coalescent position of Siberian plate and Kazakhstan plate, is a complicated multigyration superposition hydrocarbon bearing basin. The basin's floor comes into being during early Carboniferous epoch, and goes through four evolutive phases. Malang sag can be divide into five technic zones that from north to south respectively are Mabei technic zone, Niujuanhu-niudong technic zone, Mazhong technic zone,Madong technic zone and the south thrust technic zone.â‘¡In Carboniferous system formation, a suite of sea-to-land transient facies stratum, in which interbedding of clasolite and volcanic deposits,develops. A suites of hydrocarbon resource and three suites of reservoir-cap compounding grow, thereinto industrial oil flow has been achieved in two suites of reservoir-cap compounding in C₂k and C₂h.â‘¢In the upper Carboniferous formation in Malang sag ,fracture richly grows, and fissure eruption is volcanic's main eruptible mode, and vol- canic breccia of eruptive facies grows near the crater, and slag of spillover facies ,like basalt and andesite, grows median far from the cater and within incline, and volcanic tuff and tufaceous clastic rock grows far from the crater.â‘£Primary porosity, corrosion porosity and fracture grow in the upper Carboniferous for- mation in Malang sag.Effective matching of porosity and fracute engenderes diversiform modalities of reservoir interspace, such as blowhole corrosion porosity corrosion fracture type, corrosion porosity fracture type, corrosion porosity contractive fracture intergranular porosity type. The reservoir as a whole belongs to low-porosity low-permeability grade, and its Petrophysical property can reach medium- porosity low- per meability grade after reconstruction. The key controlling factors of reservoir's Petrophysical property include volcanism, structural process, and epigenetic diagenesis,etc.⑤The forming of volcanic lithology trap lies on volcanic lithology, lithology facies and the reservoir's post- reconstructive process, thus lithology - stratum trap, lithology trap and lithology-tectonic trap grow. Three representative types of volcanic oil pool such as lithology-stratum oil pool in Niudong zone, lithology oil pool in well block Ma36 and lithology-tectonicoil pool, come into being depending on the spatio-temporal matching of all conditions as ascendant reservoir of Kalagang unit and Haerkawu unit of the upper Carboniferous,potent trap, plenitudinous hydrocarbon resource of Haerkawu unit of the upper Carboniferous, hydrocarbon resource frature and cap condition from terminal Hercynian period to terminal Indo-China period. The key controlling factors of volcanic oil pool include volcanic lithology, lithology facies, fracture, erosion zone, hydrocarbon resource and age-old tectonic background, and the forming of volcanic reconstructive reservoir is the key factor of oil pool forming.â‘¥According to the hydrocarbon distributing order- liness of Kalagang unit and Haerkawu unit of the upper Carboniferous stratum in Ma lang sag that hydrocarbon distributes along three erosion lines( namely erosion line of mid- upper Triassic, erosion line of Tiaohu unit of upper Permian, erosion line of Lucaogou unit of upper Permian) and two sur-faces(namely unconformity surface and interim surface of volcanic outburst), henceforth hydrocarbon prospecting should proceeds with three zones in Malang sag (namely volcanic airslaked leached zone, volcanic inside story zone, and clasolite lithology zone), and expandsactively with new domain and new position.