Study On The Accumulation Of Coalbed Methane And Action Of Fluid In Western Guizhou And Eastern Yunnan

Based on the rich exploration data on coal geology and geological information relating to coal bed methane in Western Guizhou and Eastern Yunnan, this paper analyzes the geological conditions and accumulation regular of the coalbed methane reservoir comprehensively, establishes the coal reservoir pore types, and also illustrates the relationships between fluid activitie and coalbed methane accumulation, with the study of coal macerals, coal rank, porosity and permeability testing, the mercury injection analyses, low temperature nitrogen adsorption/desorption and fluid inclusions, The results show that,(1) There are favorable geological conditions of Coalbed methane reservoir in the study area, including the separated Late Permian coal-bearing formation hosted in a number of independent sub-syncline units with the feature of a syncline-controlled -gas structural, transitional facies with wide distribution of thick coal seams, and locating in the stagnation pressure water sealing zone with a superposed confining reservoir of multiple sets of cap rock in vertical.(2) Development of coal porosity and permeability is significantly influenced by regional tectonic diversity, with the porosity—increasing first and then decreasing and increasing again—in bimodal feature from northeast to southwest of the study area, and permeability increasing with increasing of porosity. The porosity is significantly affected by regional metamorphism, with the growth of R_O(R_O 0.68%-2.3%) first and then followed by a gradual decline (R_O 2.3%-3.31%).(3) The pores are dominanted by transition pores and micropores. The development of macrppores and mesopores is relatively bad. The BET surface area and BJH total pore volume is relatively high, which indicates the good adsorption capacity in the coal reservoir. Then the pore system in the study area is divided into four mercury-injection curves types and three liquid nitrogen isotherm types. As the result, it is proved that the ability of accumulation and deliverability of the coal reservoir is best in Panguan syncline, followed by Zhina Coalfield. The Gemudi syncline and Eastern Yunnan is good at accumulation but does badly in deliverability. The adsorption and desorption capacity is best in Zhina Coalfield, while it is weak in the rest of areas owing to the adverse pore structure or pore types, which brings about "bottleneck problem" for the recovery of coalbed methane.(4) The results show that the coal metamorphism is mainly controlled by deposition depth, magmatic hydrothermal fluids, tectonics and some so on, which lead to the nonuniformity of the coal metamorphism.(5) The mineral inclusions in coal are rich in liquid hydrocarbon, and at relatively low levels of gaseous hydrocarbons in Enhong Mining, Eastern Yunnan. The distribution of homogenization temperature is wide, which ranges between 81℃-192℃; the fluid flow of Late Permian coal-bearing strata can be divided into two periods: the first one occurred from the Early Triassic to Late Jurassic with the injection of the in-situ fluid experiencing the early stage of bio-gas and moisture, which is the main generation phase of coalbed methane. The another one corresponds to the large scale tectonic movement in late Jurassic, with the injection of the high temperature fluid in lower strata.