Relationship Between Palaeogeomorphic Of The Erosion Surfaces And Oil And Gas Accumulation Of Yan An Formation In Zhen Jing

Zhen Jing structural location southwest in Erdos Basin. Petroleum exploration demonstrate: There are realationship between Pre-Jurassic paleo-geomorphology and reservoir. On the basis of analysis of Yan an and Yan chang formation ,the palaeogeomorphic form was reconstructed by the method of mold and disclosure palaeogeomorphic form to influence Yan an and Yan chang formation reservoir,so our research discover:1. Because Yan an and Yan chang formation have some differences of depositional system tract and salinity of formation water, mud stone have differences of resistivity log,. Yan an mud stone have high resistance but Yan chang mud stone have low resistance.2. Pre-Jurassic paleo-geomorphology form of Zhen Jing was was reconstructed by the method of mold. The paleo-geomorphology was divided into highland,slope , ridge, mountain valley and low-lying land. Because different height of paleo-geomorphology ,divergence deposition thickness of erosion surfaces generate differential compaction of structure and differential sandstone and mudstone sequence; because of differential rock have differentia compaction, it generate divergence deposition form. That is main reason about low amplitude structure of Yan an formation.3. The paper establish different structure of unconformity in the area and divide into 6 type of unconformity, analysing response characteristics of logging and porosity and permeability. There are the best structure of unconformity :sandstone above the unconformity interface, lithology of hydrolytic zone is weathered mudstone, lithology of eluvial zone is sandstone;there are the only second to the best structure of unconformity : sandstone above the unconformity interface, lithology of eluvial zone is sandstone too,lack of hydrolytic zone.At the same time,the paper research distribution law of eluvial zone in Zhen Jing area; eluvial zone distribute in northeast and eastern in research area and there is characteristics of large and deep.4. Under the erosion surfaces develop eluvial zone and eluvial zone develop thicker sandestone;the thicker sandstone is characteristics of high-porosity and low-capillary. Oil and gas is easy to go into reservoir and form lithology reservoirwithout more close-height. Hydrolytic zone is cap rock and if hydrolytic zone have high-capillary pressure,oil and gas can accumulate under erosion surfaces.5. The paper summarized 2 types of accumulation models in above erosion surfaces of Yan-an and under the erosion surfaces of Yan-chang formation:vally line—slope,high land—gntle slpe. Chang 7 source rocks through middle Jurassic and began to get hydrocarbon generation processe ,the peak of oil and gas generation occurred about 128.4Ma. Hydrocarbon migration dynamics is high preusurer(< 1900m) and water pressure. It migrated through connectivity pore reservoirs. If chang 6 reservoirs is good,oil and gas accumulated. If chang 6 without reservoir-cap rock assemblages,oil and gas migrated upward and migrated lateral near the erosion surfaces. Yan an especially Yan 9 and Yan 8 sandbodies developed witch sandstone with cross bedding on plane. It can supply well reservoir. Early Cretaceous is key hydrocarbon accumulation moments.6. Above Yan'an erosion surfaces of the oil and gas accumulation is controlled by sand thickness and structure high. Study results showed that (4) anticline which has structural high of the thick sand and a good potential for oil and gas exploration. According to the characteristics of the study area above the surface erosion and under the erosion of Yan'an formation of the favorable exploration area to predict. Yan'an formation favorable exploration area I in the northeaster direction S2 Well, favorable exploration area II in the study area northeast HH102 that is well; favorable exploration area III in the study area's largest incised valley HH101 and ZJ12 wells within.