Natural Gas Accumulation Mechanism Spectra And Its Application

Accumulation mechanism is the foundation of natural gas accumulation research, but the research degree of different types of natural gases is disparate. At present, the accumulation mechanism of adsorption type of natural gas and the mechanism spectra relationship between different types of natural gases need further investigation. Therefore, the discussion in this aspect can further perfect theoretical knowledge of the natural gas accumulation mechanism, and provide theoretical basis for comprehensive exploration of basins which contain multi-type of natural gases. Through systemic research, main achievements are obtained as follows:The continuity of formation fluid is the factor which makes the migration pattern of nonassociated natural gas change, and the adsorption degree (adsorption ability) of medium is the factor which makes the occurrence of adsorbing natural gas change. Comprehensive considering of the above two kinds of factors, the natural gas accumulation (migration) dynamic continuous equation is built. According to the continuous equation, accumulation dynamic balance equation between coal-bed methane and shale gas under the condition of complex medium is established.The difference of accumulation mechanism between coal-bed methane and shale gas mainly reflect on the medium adsorption ability for natural gas, and it has the characteristics that adsorption ability of coal is intensive than shale. The difference of accumulation mechanism between source-contacting gas and conventional reservoir gas mainly reflect on fluid connectivity of medium, and it has the characteristics that fluid connectivity of conventional sand is better than tight sand. From coal-bed methane to shale gas, source-contacting gas, then to conventional reservoir gas, content of adsorption gas gradually reduce, and the natural gas accumulation (migration) dynamic balance is changed from adsorbing dynamical system to nonassociated dynamical system, and the migration pattern is changed from diffusion type to piston type, again to replacement type.Turpan-Hami basin and Eastern sag of Liaohe depression are respectively Mesozoic foreland basin and Cenozoic rift sag. Both of them are the typical representative of clastic basin in eastern and western regions of China. Both areas have characteristics of developing multi-types of gases. Different parts of the Turpan-Hami basin formed a variety of gas reservoir distribution spectra, but as a whole basin, it develops a type of gas spectra from coal-bed methane, shale gas, source-contacting gas to conventional reservoir gas from deep to pale and from sag center to sag margin. The Easten sag of Liaohe depression formed the gas reservoir distribution spectra with coal-bed methane and shale gas in lower part, source-contacting gas in middle part, and conventional reservoir gas in upper part. It also formed a bottom to up and center to margin type of distribution spectra with coal-bed methane, shale gas, source-contacting gas and conventional reservoir gas generated in different sets of source rocks. Moreover, in different formations, it formed a bottom to up ordinal descending spectra in total natural gas resource and various types of natural gas resource.Like the Turpan-Hami basin and the Eastern sag of Liaohe depression, many clastic basins have the characteristics of developing multi-types of natural gases in China; therefore, the research of accumulation mechanism spectra has a strong instruction function on natural gas integrated exploration in these basins.