The Identification And Evaluation About Volcanic Reservoir Of Fault Depression Layer In Southern Songliao Basin

The studies of volcanic reservoirs have become a difficult and hot issue in oil and gas geology research in recent years. And volcanic reservoir also has become the most important target for exploration where volcanic rocks are rich; therefore the studying of which is obviously valuable and meaningful in theory research and practical exploration. Taking the fault depression layers of southern Songliao Basin as an example, based on the study of the existing literatures on volcanic reservoir at home and abroad, we have done a lot of work on geologic field survey, core observation, testing and analysis, mapping and comprehensive research to analyze the tectonic and sedimentary features. On the basis of the above results and latest data acquired in recent years, this dissertation have use geophysical joint inversion to identity and evaluate volcanic reservoirs. After a series of efforts, this dissertation have got the conclusion and progress as follows:(1)Songliao Basin developed on the basement of Hercynian-Indosinian fold orogenic belt which was formed after paleo-Asiatic Ocean closed. Strikes of three sets of faults developed in the basement are NNE, NNW and EW, and their genesis is related to sinistral strike slip of Tanlu fault system in the period of Yanshan. The early yanshannian movement of NNE fault highly reconstructed the basin's basement, and induced NNE, NNW conjugate shear fractures and SN tracking tension fracture system played an important role in controlling the structural geometry of rifted basin. In the period of fault depression the majority of NNE, NNW and EW faults formed in the extending and decoupling action of early Crataceous along early fracture plane. Structural evolution stages of Changling and Shiwu fault depression are totally consist of rifting stage, depression stage and the stage of tectonic inversion. In the period of rifting Changling fault depression developed syndepositional nomal faults which strikes are mainly NNE, NNW and EW with strongly extending movement, and the activity of NW trending fault was extremely obvious in Huoshiling period, which probably was caused by the sinnistral strike slip of NNE basement faults; and in the period of Shahejie and Yingcheng the movement turned to NWW-SEE trending extending and decoupling, the extension rate of crust exceeded 20% and the average amount of extension was 15km. So the distribution of volcanic rocks was obviously controlled by deep faults.(2)Fault depression layers of Changling and Shiwu Depression were composed of Huoshiling (K1h), Shahezi (K1sh), Yingcheng (K1yc) and Denglouku formation (K1d), which the first three layers formed in the three phases of depression, and the last layer formed in the transition from rift to sag. There were varieties of depositional system associated with the fault depression setting in these layers, such as fan-deltas and subagueous fans in steep slope region, braid deltas in gentle slope belt, and between them was lake depositional system; In early phase it developed alluvial fans and later was alluvial plain of braided river which were rational distributed in space. It indicates that the margins of normal faults and gentle slope in rifted basin determined the distribution and development of depositional systems, and formed a complete cycle of basin development.(3)The main types of volcanic rocks in Changling rift depression were rhyolite, tuff, andesite, basalt, volcanic breccia and irruptive rocks. And there were two types of eruption ways–eruption of central type and fissure type, which happened in multiple phases. Volcanic facies mainly contained effusive and explosive facies, and they overlapped in the vertical. Acid rocks such as rhyolite reservoirs was the best in reservoir property, then was rhyolitic tuff, andesite and other neutral-basic rocks were bad. The main reservoir pore space included dissolved pore, primary air void and structural fracture, and the combination type is mainly fractured–porous. With the porosity range of 4% to 6% and the permeability range of 0.06μm2 to 0.26μm2, the volcanic reservoirs in the basin are medium-low porosity and low, extra-low permeability reservoirs. Generally, the porosity and permeability of the reservoirs are determined by lithology-facies, cycles of eruption, diagenesis and tectonic movement. The upper and lower of effusive facies, hot detrital flow of explosive facies and the aisle subfacies of volcanic rocks are relatively better favorable reservoir facies belt.(4)Studying from three different angles, volcanic apparatus, volcanic facies and seismic attributes, to predict volcanic reservoirs in Yaoyingtai area of Changling rift depression, identity 18 relatively definite exploration targets, and form a set of volcanic reservoirs identification and evaluation technology of Songnan rift depression layers. Based on the analysis of regional tectonic setting, we have determined the macro distribution of volcanic rocks utilizing seismic integrated interpretation. Using seismic, well logging data to identity volcanic massif, analyze and interpret single well facies, then study the volcanic massif itself, the lithological and facies characters for accurately describing the exploration targets. We have carried out the prediction of volcanic reservoirs to find effective reservoirs through making use of geophysical technology, such as attribute analysis, waveform analysis, seismic inversion, hydrocarbon detection and so on. Because the deep volcanic rocks have complex lithology and dual media, we utilize the advanced technologies of micro- resistivity scanning imagery (FMI), nuclear magnetic resonance (CMR-PLUS), element capture service (ECS), dipole sonic imager (DSI), array lateral electric-logging (HRLA) etc. to classify the volcanic rocks lithology and evaluate reservoirs physical property and gas potential.