Logging Evaluation Technology Of Coal-bed Methane Content

Coal-bed methane is different from conventional coal and natural gas because of its absorption station in coal. Components of coal-bed methane, the formation mechanism, storage media are essentially different from conventional natural gas, so the logging technology for coal-bed methane exploration and development will be essentially different from conventional natural gas, resulting the traditional evaluation of conventional natural gas reservoir will never suitable for the evaluation of coal-bed methane.The most important base of evaluation for coal-bed methane reservoirs is the content calculation of coal component. The coal components will be divided into four parts: fixed carbon, volatile matter, ash and moisture, the first two parts are pure coal components. As the calculation of component content of coal in lots of literature at home and abroad, the coal is generally divided into pure coal (fixed carbon and volatile matter), ash and moisture.Then using bulk density and compensated neutron logging, or acoustic time and density logging curve, combined with the balance equations ,we can calculate the bulk content of these three coal components, and then converted into weight percentage.When in the calculation of fixed carbon and volatile matter content in next step,we need to use the linear statistical relationship to calculate both content based on the core experiment analysis. As the liner relationship between ash and the other coal components are different with areas,but the relationship between ash and moisture are not much different because of the small content for moisture.Which become necessary to use coal analysis data in caculating fixed carbon and volatile matter content respectively.In terms of bulk density and compensated neutron logging curves,the response of fix carbon and volatile matter is different in coal component.While volatile matter and moisture are belong to volatile,and they have the same logging response.Therefore, the author of this article divided the coal into another three parts:fixed cabon,ash and volatile substances (volatile matter and moisture).As the lack of experimental data, we use the relationship of ash and moisture in another areathe which its liner relationship of ash and fixed cabon is similar with the study area.So we can obtain the four components of coal,and obtain coal components content in non-core analysis situation. The calculation of coal-bed methane content is the most important aspect in coal-bed methane reservoirs evaluation.Summarizing and contrasting various methods evaluation of of coal-bed methane applying geophysical techonolygy:statistical analysis, the background value method, neural network and adsorption isotherm. Statistical analysis and neural network need to have many samples to do the experimental data, so it's fitble for the study area which has adequate experimental analysis data; the background value needs to know the logging value when there is no gas, but it's hard to get precise value on logging curve. Langmuir adsorption isotherm can not only characterize seam gas absorption features, but also does not require analysis of many experimental data as a basis,so it's considered as the most appropriate means by many scholars consider, it has been widely applied to coal-bed methane evaluation.Adsorption isotherms as the input for reservoir simulation, it using two regular array, that is, Langmuir volume and Langmuir pressure. Because of the lack of industry standards, many existing isotherm data appear inconsistency situation, and in many cases is not suitable for reservoir simulation.Logging data can help explain the isotherm precision which is determined by coal core data.Now it has derived the general relationship of adsorption isotherm using logging data to estimate the dry coal base, it used Langmuir equation, the equation using fixed carbon and volatile matter weight percentage content ratio to derive the Langmuir constants (VL, PL), and moistrue and ash to be corrected. But the general Langmuir isotherm equation are derived under a certain temperature by methane adsorption isotherm experimental data and obtained methane adsorption isotherm equation which are applicable to this temperature,and the other temperature should not be predicted. To solve this problem, this paper put forward a adsorption isotherm equation which suitable for different temperature conditions and varies with formation temperature for bituminous coal and anthracite coal.In addition,we try to obtain coal components content under without coal core analysis data in coal logging component analysis.As a result of the adoption of isotherm equation which varies with formation temperature and pressure,it can reflect a actual amount of coal-bed methane under actual formation temperature and pressure. In addition, this article also evaluate seam cleat cleat porosity and cleat opening preliminarily, this is a great help for coal penetration research.In additional, inverse convolution is used in this thesis to enhance the along track resolution,so the real formation value could be recovered.