The Study Of Well Logging Evaluation For Coalbed Methane Of Region A

With the development of science and technology, the relative decrease of petroleum production, and the enhancement of people’s environmental protection awareness, coal bed methane, as a clean energy, has been attached with more and more importance. Coal bed methane exploration and development has become a worldwide hotspot and difficulty. Our country is rich in coal bed methane, which will enjoy a promising prospect in large-scale exploration and utilization. Since well logging data is accurate, continuous and reliable, it has an irreplaceable position in the exploration of coal bed methane.Coal seams are different from conventional reservoirs in both pore structures and fluid occurrence states. Compared with conventional reservoirs, coal seams are low in porosity and poor in permeability. And, in coal seams, the porosity is composed of cleat porosity and matrix porosity, the sum of which is coal seams’ total porosity. At the same time, compared with conventional natural gas, the coal bed methane’s absorption state and absorption method are different. The three basic occurrence states of coal bed methane are free state, absorbed state and dissolved state, of which the absorbed state is the main existence form. As a result, compared with conventional reservoirs evaluation, the evaluation techniques for coal seams are quite different. Furthermore, coal seams are characteristic of high resistivity, high acoustic slowness, high neutron porosity, low density and low natural gamma ray, therefore, if conventional well logging evaluation method, which usually uses acoustic-density or density-neutron crossplots, is to be utilized, the calculated porosity will be pretty large, which is obviously against the real situation. As a result, it is obviously not suitable to apply conventional well logging evaluation methods to coal seams evaluation and gas content calculation. So it is necessary to develop a set of well logging evaluation method suitable for coal seams evaluation. Based on collecting, sorting and analyzing a large number of previous research results and a lot of data about well logging, thin section analysis, cores and tests,(1) this paper summarizes the characteristics of coal seams and the factors influencing coal bed methane content, analyzes the influences of coal seams’thickness, micro constituents, coal quality and depth changes on coal bed methane content, determines the trend of gas content per ton coal increasing with coal seam depth, thickness, inert group content and coal rank;(2) coal seams’identification and classification methods are determined, based on the coal seams’conventional logging responses, which are high in resistivity, acoustic slowness, compensation neutron porosity, low in natural gamma ray, bulk density, and photoelectric absorption indexes, as well as coal seams characteristics in imaging logging data;(3)coal seams’industrial components are calculated with the volume model and probability statistics, coal matrix parameters in different coal ranks are estimated with the relationship between ash and other components, ash and the logging curves. Thus, the problem of low accuracy in coal industrial components calculation is resolved.(4) Coal seams’fracture porosity is calculated using dual laterolog data and with the consideration of the coal seams’ double pores characteristics;(5) Coal seams’permeability is calculated based on the F-S method and Darcy’s law;(6) Coal seams’theoretical gas content and actual gas content are determined on the basis of Langmuir equation and probability statistics, thus, coal seams’gas saturation estimation method is also determined;(7) the coal rank can be determined with vitrinite reflectance through the established relationship between the vitrinite reflectance and the depth;(8) coal seams’ roof and floor evaluation is through analyzing the physical properties of the lithology of coal seam’s roof and floor;(9) the research methods are applied to the coal bed methane well logging evaluation in Block A, corresponding well logging evaluation methods for industrial components, gas content, and coal rank are established catering for the actual situation. Great consistency can be observed when the result is compared with and analyzed with the actual core analysis data.In this paper, certain progress and understanding are obtained in the research of coal seams’industrial components and gas content calculation methods.(1)Coal matrix parameters in different coal ranks are estimated with the relationship between ash and other components, ash and the logging curves, which resolves the problem of low accuracy, as is the case with the volume model method.(2)Different coal bed methane content calculation methods are established catering for different coal ranks and geological conditions, and the regional analogy methods for the calculation of coal seams’maximum absorbed gas content, actual gas content, and coal bed methane saturation are proposed. This paper proposes a systematic well logging evaluation method for coal seams industrial components, gas content, porosity, permeability, and the properties of roof and floor, which has been successfully promoted and applied in Block A. The method introduced in this paper will also exhibit greater value in further promotion and application.