Study Of Coal Core-Scale Logging Technique And Log Response Character

CBM, as the unconventional natural gas, is generated by coal and mainly adsorbed in the coal reservoir. The complexity of heterogeneity in CBM reservoir and the difficulty while exploring are far beyond those in conventional reservoir. The technique of coal core-scale logging is the important basis and prerequisite of logging evaluation for CBM reservoir, which is implemented according to the property of CBM reservoir and the characteristic of insensitive logging response of absorbed gas. Basing on the experiment analysis of coal core, this paper analyzes the coal quality, coal rank, and gas content. By combining the logging response, the logging characteristic parameters of CBM reservoir are extracted and the corresponding interpretation model is established.By referring to the coal core experiment data in Heshun, the distribution characteristics of coal quality, coal metamorphic grade and gas content are summarized, and the relationship between lithology, physical properties and gas-bearing properties is analyzed. Then the linear relationships between ash content and foxed carbon content, water volume and volatile matter, coal metamorphic grade and component of coal are obtained. Using logging response characteristic, logging parameters of CBM reservoir, sensitive to reservoir parameters such as DEN, GR, tri-porosity and resistivity curves, can be extracted. With statistical regression, the reservoir recognition methods, logging evaluation methods of component content of coal, coal rank and gas content are found. And the suitability of these methods in Heshun is validated, also with their limitation in this region being pointed.According to the development characteristic of fracture in CBM reservoir, the response of dual laterolog is systematically simulated with three dimensional finite element method. Numerical simulation of dual laterolog response under conditions of single fracture, cross fracture and fracture group is proceeded. It is found that the response of dual laterolog reduces with the increasing fracture openness, larger invasion diameter or borehole size, increases with the increasing block resistivity, and shows a relationship of linearly declining with the increasing fluid conductivity in fracture and fracture porosity. The characteristic while fracture dip is changing is also studied. The changing rules of dual laterolog under different influencing factors are generalized in this paper.Calculation method of fracture porosity and permeability using dual laterolog is outlined through lots of numerical simulations of dual lateolog of fracture. The accuracy is proved by comparing the calculated fracture porosity and the porosity from model. And the practical logging data processing result is consistent with coal core description. As coal core experimental measurement is very difficult, there is no data collection of coal core porosity and permeability from this region for quantitative validation. Therefore, the practical effect of this method needs to be further verified.