Fine Description And Physical Properties Of Coal Reservoir In Eastern Junggar Basin

In order to accelerate the low rank coalbed methane exploration and development,and abundance the low rank coalbed methane geological theory, taking the coalof the middle-lower Jurassicin Eastern Junggar Basin(Zhundong)as an example to study the reservoir physical properties and evaluatethecoalbed methaneenrichment areas, along with the guidance of coalpetrology, coal geology, coalbed methane geology theorys,and further studied the Zhundong low rank coalbed methane reservoir characteristics and its controlling factors, and discussed the comprehensive evaluation of coalbed methane enrichment factors, finally established the comprehensive evaluation system to predict coalbed methane enrichment area which is dominated by coal reservoir, and preliminary forecast enrichment areaof coalbed methane in Zhundong. Main research achievements are acquired as follows:Lignite and long flame coalwere widely distributedin the Eastern Jungar Basin:The macrolithotype oflong flame coal composed of semibright coal and bright coal. The petrographic composition domianaterd by vitrinite, with secendary amounts of inertinite, and a small amount of exinite,occasionally with sapropelinite.The obvious differencesof coal quality characteristics between different kinds coal inzhundong area.Thecoal facies change dramaticallyin Zhundong, and the XishanyaoFormation coalswere deposited in dry and oxygen enriched awamp environment which isthe exposure peat swamp environment, and the coals were mainly in dry forest peat swamp environment, butparts of the Xishanyao Formation section deposited in herbaceous peat awamp and deep water forest peat swamp, indicating that the sedimentary environment of Xishanyao Formation caols were variable.It is complex thatthe genetic types of coalbed methane, in which both biogenic and thermogenic gashad beenfound. Generally,the adsorption capacibility of ZhundongJurassic coals were low. Thedegree of thermal evolution had a positively relationship with adsorption capacity of coal, that is meaning the adsorption capacity of long flame coal(VL=16.85~18.5 m3/t) was stronger than that of lignite(VL are all less than 10 m3/t). The methane adsorption capacity of coal also had relationship with vitrinite(or huminite) content, inertinite content, moisture content and so on;the influence of ash yield to adsorption capacity is not obvious. The coal reservoirs adsorption pore characteristics based on low temperature nitrogen adsorption are obvious contradictions with balance water isothermal adsorption results. Therefore, it is suggested that methane mainly in adsorbed and gas filling(free gas) state, and also contains a small amount of condensed gas and solution gas.The coal porosity was gradually decreases with the increase of coal rank of Jurassic coal in Zhundong. According to the mercury-injection test, the pore structure characteristics of coal are changed with the increase of coal rank. Nondestructive testing technology also reflects the characteristics as the result of mercury-injection test. Based on direct observation by scanning electron microscope(SEM) thatthermogenic poreare formed in the long flame coal, which hold less amount of pores and scattered distribution, however, primary pores are more common in lignite, larger than thermogenic pore and often linked with fracture.Taking the resources conditions, reservoir features and preservation conditionsas first level influence factors, which including 12 secondary influence factors, such as reservoir porosity, coal rank and maceral characteristics,et al.Finally established thecomprehensiveevaluation system to predict the low rank coalbed methane enrichment areawhich guide forCBM exploration and development in Zhundong,and the result shows as follows: west Wucaiwan area, Bogda Piedmont, Jimusaer sag and the middle part ofWutongwozi sag are more favorable areas; due to the buried depth of coal seamsaredeep than 3000 m in Fukang sag, which is not evaluated this time. The coalbed in the east of Wucaiwan—Dajing—Wutongwozi sag area had relatively shallow burial depth, and allin the position of methane oxidation zone, without further exploration and development value.