Study Of Rupture System And Fracture Development Of Zhuangxi Paleozoic Buried Hill And Its Application In Oil Field

Zhuangxi Paleozoic Buried Hill locates in Dongying City of Shandong Province, and its geotectonic position lies in Hehuai syneclise in Southeast of Huabei platform, which is subordinate to south of Bohai Bay basin. Pre-Sinian of Huabei Platform was in the phase of geosyncline development and became stabilized in Sinian, then turned to platform development phase. Extensional big Tan Lu rupture developed toward NNE direction traversed Huabei platform. Zhuangxi Paleo Buried Hill belongs to secondary sag in the north of Jiyang depression in south of Bohai Bay basin, which is one of the most complicated Lower Paleozoic carbonate oil field in the world.After crystallization basement was formed in Tai Shan group in the end of Archaean, it suffered long term denudation and deposited to marine and land interbedded formation with stable lithology and thickness. Buried Hill is a large size fold nappe which was uplifted, compressed, folded, denudated and settled in Indosinian period, deposited in Mesozoic formation, then wholly advanced to the west in the late of Yan Shan movement. The force acting on internal structure of buried hill was complicated, and fault block was broken up. The buried hill not only experienced the early fold reversal faulting movement which resulted in serious denudation of formation, and also experienced the large size nappe movement and extensive distributed normal faulting movement in the medium and late period, thus formed into very complicated rupture system and various reservoir space with big vertical and horizontal change and 7 sets of oil bearing formation.Lower Paleozoic buried hill of Zhuangxi was comprised by Cambrian of Lower Paleozoic and carbonate rock of Ordovician. The buried depth of top surface is 3500 ~ 4600m, and total thickness is 1300 ~ 1500m. The basement is granite gneiss of Archaean. The whole is a large size nappe which advanced from east to west. Taking the reversal fault in the middle part as the limit, generally it can be divided into arched and extensional anticline in the hanging wall and bend folding—reverse running—gentle monoclinal structural configuration in the lower all, the internal of which was complicated due to cut by several faults of various period. The study indicated that there had 25 faults in total, among of which there had 1 nappe fault, 4 reversal faults, 3 faults with obvious paralleling displacement, and 17 normal faults. It can be divided into 13 fault block areas.The reservoir space was mainly secondary with many reservoir space type and complicated structure. The reservoir space type was fall into 3 types and 7 kinds. The reservoir type is mainly divided into big fracture and cavern and fracture —solutional void with porosity of 5% -0.1%. The fracture development was influenced by structural movement, lithology, structure position, rupture and igneous intrusion etc factors. The solutional void was related to denudation degree, paleo-topography, natural water and high mineralized water, different weathering action, rock property and top igneous intrusion etc factors.Main oil bearing formations are Upper Majiagou, Lower Majiagou, Yeli-Liangjiashan ~ Fengshan, Fujunshan—Pre-Sinian. Every oil bearing formation has no uniform oil-water contact, and the oil-water contact between different fault block of every formation is also different. The reservoir is normal temperature and normal pressure system, and reservoir type is fracture. There have 50 proven units with reserves in place, 22.7km2 proven oil bearing area and 4598xl04t reserves in place.Recommend the 1st plan. To drill 9 wells, the net present value would reach 14.9 billion dollars after 16 years. Currently there are 2 wells being drilled.