Integrated Exploration And Resource Prediction Of Multitype Gas Reservoirs In Coal-bearing Strata In Linxing Area

Linxing area is located in the northern part of the Jinxi fold belt of the Ordos Basin.At present,natural gas resources such as tight sandstone gas,coal-bed methane and shale gas have been discovered.This paper analyzes the accumulation conditions,accumulation mechanism and main control factors of the three types of natural gas in the Carboniferous-Permian coal-bearing strata in Linxing area,and clarifies the distribution rules and characteristics of the gas content of the three types of natural gas.It predicts the three types of natural gas resources for exploration perspective and optimizes the favorable areas for integrated exploration.Linxing area has extensive overlying source rocks(such as coal rock,mudstone),which has a wide distribution range,large thickness,high organic matter abundance,and is in the stage of maturity to over-maturity.At the same time,different types of reservoir sand bodies,gas-bearing coal seams and gas-bearing shales are widely developed in the study area,and the cumulative thickness of various types of reservoirs is large,which provides favorable storage conditions for the three types of natural gas accumulation.In addition,sandstones,mudstones and coal beds in the area frequently overlap vertically,forming multiple sets of source-reservoir-cap rock combinations,which is conducive to the comprehensive exploration of multiple types of natural gas.It can be seen from the research on the accumulation period and evolution process of the three types of gas reservoirs in Linxing area that the main accumulation periods are all from Early Jurassic to Early Cretaceous,and the Early Cretaceous is the most important accumulation period.In the Early Cretaceous,due to the influence of elevated ground temperature and local magma baking,various source rocks entered a stage of high maturity.At this time,source rocks dominated by coal and mud shale began to generate a large amount of gas,and were abnormal under the action of high pressure,the eastern Zijinshan rock mass was migrated outward.Since the Late Cretaceous,the strata have continued to uplift,and the three types of gas reservoirs have also undergone secondary evolution.The primary gas reservoirs have been adjusted,lost,or even completely destroyed.They also received the supplement of remote source natural gas in the west of the study area.Formed the current state of natural gas distribution.The distribution of the three types of natural gas in Linxing area has a strong regularity.Among the three types of natural gas,coal-bed methane has the highest gas content,and there is a distribution law of "west high and east low";tight sandstone gas follows,and the distribution law of "west high and east low,north high and south low";shale gas has the lowest gas content,and the distribution law is roughly the same as that of coal-bed methane,but the center of high gas content is shifted to the southwest direction than coal-bed methane.The main controlling factors of three types of natural gas accumulation were analyzed by linear regression analysis and gray correlation method.It was found that the main controlling factor of tight sandstone gas accumulation in Linxing area was sandstone porosity,while the main controlling factor of coal-bed methane and shale gas were same,all of were organic abundance.The area abundance method was used to predict the three types of natural gas resources,and the total resources were calculated from the perspective of integrated exploration theory.The total predicted resources of the three types of natural gas before the integrated exploration is 2101.98 × 108m3,which the tight sandstone gas is 886.88 × 108m3,the coal-bed methane is 981.27 × 108m3,and the shale gas is 233.83 × 108m3.According to the integrated exploration theory,the total predicted resources of the three types of natural gas is 2430.41 × 108m3,which tight sandstone gas is 999.69 × 108m3,coal-bed methane is 1114.50 × 108m3,and shale gas is 316.22 ×108m3.The integrated exploration has increased the forecasted resources of the three types of natural gas by 328.16 × 108m3,up to 15.61%,which tight sandstone gas has increased by 112.81 × 108m3,up to 12.72%,coal-bed methane has increased by 133.23 × 108m3,up to 13.58%,and shale gas has increased 82.39× 108m3,up to 35.23%.Above all,the integrated exploration effect is remarkable.According to the three types of natural gas content,gas reservoir characteristics,and production methods are the same,the integrated development method is selected,and according to different types of gas reservoir combination of single production and integrated development resource standards,the single production and integrated development favorable areas are divided.The favorable areas of tight sandstone gas are T25-T13-L9 well areas,L4-L5 well areas,T24-T29 well areas;the favorable areas of coal-bed methane are T25-T13-L9 well areas,T3-T9 well areas,T24-T29 well areas and part of the south of Leijiaqi;the favorable shale gas areas are T25-T13-L9 well areas and T9 well areas;the integrated development of favorable areas of tight sandstone gas and coal-bed methane are T25-T13-L9 well areas,T24-T29 well areas;the integrated development of favorable area of tight sandstone gas and shale gas is T25-T13-L9 well areas;the integrated development of favorable areas of coal-bed methane and shale gas are T25-T13 well areas,T3-T9 well areas;the integrated development of favorable area of the three types of gas reservoirs is the T13-T25-L9 well areas.