The Logging Response Characteristics And Identification Of Volcanic Rocks Phase And Gas Zone In Changling Sag, Songliao Basin

Volcanic reservoir has been the larger reserves discovered in Changling fault depression of Songliao Basin south by far. It has great exploration potential.In recent years, As the volcanic reservoirs have been found, the researching on the volcanic reservoir has become a focus of attention.The volcanic rocks as a special reservoir, it is more difficulty in studying on and forecasting the volcanic reservoir's distribution, because of its complex lithology and the inhomogeneity. By counting drilling cores,detritus data, we find out, there are mainly developing six kinds of volcanic rocks in the study area. In this paper, we use conventional logging data to summarize the frequency distribution of natural gamma logging,acoustic logging,density logging and neutron logging of these six kinds of volcanic rocks, for the volcanic rocks of different response characteristics of the different logging. We can qualitatively identify the basic rock, neutral to acidic rock, through quantitative analysis of the log response characteristics of each type of volcanic rock. In addition, we also apply the three-porosity and natural gamma logging of the intersection graph to identify volcanic rocks. The identification of volcanic facies is an important part of the study on the volcanicreservoir. The distribution of volcanic facies and the distribution of good reservoir have a close relationship. By counting drilling cores,detritus data and the establishment of the typical electrofacies of the volcanic facies,subfacies, we can carry out the division of the single well in Changling fault depression. Through the establishment of comparing with well profiles of volcanic lithology-lithofacies, we can analysis and research on the distribution of the volcanic lithology and lithofacies in the study area. The identification of volcanic gas is also an important part of volcanic rocks of oil andgas exploration. In this paper, we apply three-porosity cross plot and overlapping to carry out the identification of the gas zone, for the characteristics of volcanic rocks of complex,and get some good effectiveness. We use of characteristics of neutron porosity and acoustic jet lag cross plot, to avoid complex lithology influenting on the recognition results, increasing the accuracy of gas zone recognition. Acoustic logging has not great difference on non-hydrocarbon gas and hydrocarbon gas. It nakes the difference larger caused the density logging, because of the difference of volume density between mathane gas and carbon dioxide. We may accord to the difference of the porosity of acoustic travel time logging and density logging to identify non-hydrocarbon gas zone and hydrocarbon gas zone,by using three porosity overlapping methods.Following the results and the awareness were achieved:1,There are maily developing six kinds volcanic rocks in Changling fault depression: volcanic breccia,tuff,tuff lava,rhyolite,basalt and andesite, and rhyolite has the distribution of the maximum thickness in the study area. There are four volcanic lithofacies and ten subfacies:they are Volcanic conduit:Diatreme and Hydrothermal breccias; Explosive facies:Air-fall,Base surge deposit and Pyroclastic flow deposit; Effusive facies: Lower effusive subfacies, middle effusive subfacies and upper effusive subfacies; volcanogenic sedimentary facies:Epiclasts-bearing volcanogenic sediments and Reworked volcanogenic sediments. And, Explosive facies and Effusive facies are maily located volcanic facies in Changling fault depression.2,There are the different logging responses amang the different Volcanic rocks, natural gamma values are increasing rom the basic,neutral to acid rock, and in the acidic rocks, the natural gamma of pyroclastic rocks with high tuffaceous is greater than volcanic lava. the difference of acoustic logging is almost no difference, but the density logging value is reduced. The distribution range of the neutron porosity of Rhyolite is larger, the distribution range of the neutron porosity of andesite and basalt are more concentrated, while the distribution range of the neutron porosity of the tuff and tuffaceous are also larger.3,In this paper, we can use three-porosity and natural gamma logging cross plot to identify the volcanic, which, the effect of the acoustic and natural gamma cross plot is the best identifying volcanic rocks, it is easy to identify the basic rocks, neutral rocks and acid rocks, and it can also be better distinguished between pyroclastic rocks and volcanic lava in acid rocks. In addition, acoustic logging and density logging cross plot is the better, it is easily to identify basic rock, neutral rock and acid rock.4,It is the explosive facies of the tuff category in the top of the Yingcheng Formation, and then volcanic conduit and the effusive facies with each other layer This is the characteristic of the distribution of the volcanic lithology and volcanic facies in Changling fault. there are volcanic-sedimentary rocks-volcanic rocks of the "three paragraph" structure in some areas.5,Volcanic conduit with a high gamma,low density,higher acoustic; The explosive facies are of high gamma, the resistance of pyroclastic flow deposit is higher than the base surge deposit and the air-fall, all belong to middle density; The rhyolite of the effusive facies belongs to the high gamma, high resistance, the resistance of the upper effusive facies and the lower effusive facies is larger than middle effusive facies. The basalt of the effusive facies belongs to the low gamma, The andesite of the effusive facies belongs to the middle gamma, density logging are larger than rhyolite's, however, acoustic are smaller. The volcanogenic sedimentary facies belongs to the middle gamma, the distribution rang of the natural gamma values of the epiclasts-bearing volcanogenic sediments is larger, its resistance depends on the sedimentary rocks besides the pyroclastic debris, tuffaceous sandstone, its resistance is larger and density is lower, acoustic and neutrons are more latger. But the resistance of the reworked volcanogenic sediments is smaller, its density is lower,acoustic is smaller and neutron porosity is lower.6,By analysising neutron-acoustic cross plot, we can distinguish with gas zone. Relatively to oil and water layers, the acoustic porosity is more greater than neutron porosity at the gas zone. Because of methane gas and carbon dioxide gas volume density, three porosity overlapping can be applied to distinguish between hydrocarbon gas zone and carbon dioxide gas zone, the interval transit time porosity and density porosity difference is smaller at the hydrocarbon gas zone, and at the carbon dioxide gas zone, the difference is larger between the two.7,Pyroclastic flow deposit is the facies belt where the gas zone is the most development in Changling fault depression...