Characteristics And Log Evaluation Of Carbon Dioxide Reservoirs In Songliao Basin

Based on forming origin, classification, characteristics, and log evaluation of carbon dioxide(CO2) reservoirs in the deep Songliao basin, this paper develops several researches. The achievements are as follows:(1) The researches show that there are two forming origin of CO2 reservoirs: organic and inorganic. The organic origin means the gas is formed from living things. Inorganic origin gas have two sources: degassing from magma and from carbonates. Through the analysis of geochemistry features of CO2 gas, the forming origin in the area is determined, which is the base of the next research for the source of CO2 reservoirs.It is also showed that δ13C is different for the gases from different sources. So that δ 13C can be used to determine the forming origin. Almost all the values of δ 13C in Songliao basin are greater than -8%. therefore the CO2 gas in the area is inorganic and from mantle.(2) Through the research for the geological conditions of the existed CO2 reservoirs in the area, the forming conditions of those reservoirs are summarized and the main controlling factors are found.Based on the distributions of CO: reservoirs and developing wells in Songliao basin, the distribution relation with the deep big faults and the igneous rocks, and geochemistry characteristics of the CO2 reservoirs, we can get the following conclusions: The conglomeration of C CO2 gas is controlled by these deep big faults inside the basin . meanwhile is also related to igneous bodies, favored preserve conditions and the developing times of trap. The deep big faults provide CO2 with flowing paths, control the spatial distribution of the CO2 reservoirs. These faults are the most important controlling factor.(3) The CO2 reservoir modes are summed based on the researches of reservoir forming mechanisms.Through the analysis of origins of CO2 gas, their distribution rules, the lithology of base rocks, igneous rocks, faults, evolution feature of basin formation, The following modes of CO2 reservoirs are predicted:a. gas renegaded from deep earth . this mode is formed due ton the geothermal and structure change in the deep Earth, inorganic gases are produced, the fluid with the gases moves up through the deep big faults, is preserved and entrapped in the favored conditions.b. Gae from the earth disengaging. These gases are formed from shear and disengage upper crustc. Gases from metamorphic process. The base of Songliao basin C-P formations are carbonates, when heated they are decomposed and CO2 gas are escaped. The CO2 reservoirs are formed after moving up.(4) Qualitatively distinguishing the CO2 and hydrocarbon formation. Based on the physical and log response features, beds bearing CO2 are recognized. Which is realized by combining three porosity logs: first sonic log and neutron log are used to recognize gas-bearing beds, then density log are used together to distinguish CO2 and hydrocarbon-bearing beds.(5) The CO2 proportion is predicted. The difference of the porosity-calculated from sonic log and from neutron log is related to the effect of CO2 in gas-bearing beds. Using BP neural network the proportion of CO2 is predicted The predicted proportion can be compared with well test results very well.(6) The reserve computation of the area of Well Fang 9 in Songliao Basin.Through the reservoirs description, it is verified that the reservoir is igneous lithologic reservoir. The proving reserve of the area is computed using volume method The result shows that: the total reserve is about 65.18X108m3 . the CO2 reserve is about 58.01x108m3 based on the proportion of CO2 in the reservoirs.