Volcano Edifices And Gas Pool Formation In Changling Faulted Depression, Songliao Basin, China

Volcanic is one of the three major exploration domains of oil and gas. Oil and gas reservoirs have been found in volcanic in many basins around the globe, but volcanic are still regard as a restricted exploration domains and blind domains for many years. In recent years, Xushen gas field and Songnan gas field are found in volcanic rocks in Songliao Basin, it set off a wave of exploration and research, but subsequently, the exploration of multiple volcanic traps have been lost. Exploration goes into the bottom. It shows that the volcanic gas accumulation is complex beyond human imagination. For example of volcanic oil and gas in Changling faulted depression, starting from both tectonic background and oil geological, Studying the volcanic edifice, volcanic reservoirs, gas pool formation by using the data of gravity-magnetic-electric-seismic and drillings in Changling faulted depression, I have established three models of volcano edifice, development a new understanding that the type of fault controls the type of volcano edifice, and that the different volcanic institutions have different reservoir laws, recognized the reservoir characteristics of“three-element control volcano reservoir-forming”, proposed it is important that the structural background and volcano institutional characteristics are key factor for forming a middle-large original volcanic gas field. It is important how to find out large volcanic gas field in the Mesozoic and Cenozoic volcanic rift basin, and how a Paleozoic volcanic gas reservoir were formed and destroyed.1. Changling depression had developed three kinds of volcano edifice models, which are polygenetic-volcano edifice like Yaoyingtai, shield-volcano in LS1 well area and caldera-volcano body in YS2 well area. Controlled by the fracture. They had been from three kinds of fracture which are inherited contemporaneous fault like Daerhan, early basement fault like Longfemgshan, late overburden fault like Chaganhua. They are located in the Yaoyingtai-Daerhan region on the ancient uplift in the middle of Changling fault depression, in the edge of the eastern slope around the depression, in the Chaganhua region at deeper parts of a secondary depression. Their lithology are mainly acidic volcanic rocks, intermediate-basic intrusive rocks or volcanic rocks, basic rocks, etc. They each has different reservoir characteristic and hydrocarbon accumulation features. Other volcanic edifices are regard as the combination of three model’s changing based on its controlling fracture characteristics.2. Effective volcanic reservoirs are controlled by three factors, namely, lithofacies, weathering transformation and tectonic. The acidic volcanic in both upper subfacies of overflow facies and hot debris subfacies of explosion facies had developed rich primary pores and cracks. At the same time, it had madden secondary pores and cracks that the stronger transformation to volcanic in the uplift areas by weathering dripping and tectonic. Both of them are mostly favorable for reservoir. To other types of volcanic, the key to effective reservoirs is a stronger weathering dripping on them.3. There are three sets of source rocks which are in Houshiling Formation, Shahezi Formation and Yingcheng Formation in Changling depression. Shahezi Formation in Chaganhua secondary depression is the main source rock of Songnan field, it is at the stage of maturity-high maturity evolutionary. On the other hand, the deeper central basin faults as a source of CO2 communicate mantle.4. Three-elements which are Source, phase and faults are the controlling factors of volcanic gas reservoir. Large deep rift basin has good conditions for hydrocarbon accumulation. With near-source, favorable phase and fault passing the source to eas in polygenetic-volcano edifices on the ancient uplift, the advantage is the most favorable to form large gas reservoir, where Songnan gas field has been discovered. Being far from the source rocks, reservoirs needing to be transformed by weathering, poor effectiveness of traps, and the traps in shield-volcano edifices are not found any oil and gas. Near by the source, but because of strong reservoir heterogeneity, a poor reservoir reconstruction, and damage to the trap by faults which makes Complex relationship between air and water, the caldera-volcano edifices often do not have the conditions for making large complete volcanic gas reservoirs.