Search

Macrolithotypes control the pore-fracture distribution heterogeneity in coal impacting the coalbed methane (CBM) production from the reservoir. However, few studies have focused on the characteristics of macrolithotypes. Here, the macrolithotype samples from the three continuous seams (No. 3, 5 and 11) in the Hancheng Block, Ordos Basin, China were quantitatively characterized by multiple length scales. The results indicate that the bright coal has the best development of micro-fracture than those of the other macrolithotypes, which with good openness and connectivity under the optical microscopy; N2 adsorption/desorption results reflect that the adsorption pores of the semi-dull and dull coal are more developed than the bright coal and semi-bright coal, and are dominated by plate-like and ink-bottle pores. The characteristics of the mercury intrusion/extrusion curves were determined by the mercury injection (MIP). From bright to dull coal the pore connectivity being worse, and the uniformity of pore and throats distribution becomes lower. The pore type that divided by NMR are recovered to be seepage type (the bright), comprehensive type (the semi-bright and semi-dull), and the type of adsorption (the dull). The behavioral differences would impact the porosity and permeability in coal. Thus, by the well logging evaluation approach, the relationship between coal macrolithotypes and select logging parameters were determined for coal macrolithotype identification, and with the petrel software included, the porosity-permeability models were built to investigate the permeability evolution with the coal macrolithotypes. Macrolithotypes are closely related to the permeability of coal reservoirs in this area. The greater contribution of permeability is typically from of the bright and semi-bright coal, and followed by semi-dull and dull coal, the better development of bright coal, the better permeability of the reservoir and vice versa. [ABSTRACT FROM AUTHOR]

Previous studies about factors on coalbed methane production cannot meet the need for refined development. This work attempts to study the impact of macrolithotype characteristics known before fracturing on well production, to enable the developer to predict the production potential of each well in advance and adopt a precise development strategy. Logging data of 216 wells were obtained to predict macrolithotypes distribution of No. 3, 5, and 11 seams in the Hancheng block. And macrolithotype characteristics were described from two aspects: the proportion of bright layers in thickness (PBLT) and the number of layers per meter (NLPM), and their impact on well productivity were evaluated respectively by analyzing the production data. The results show that PBLT value increases from No.11 to 3 seams. PBLT has a positive correlation with well productivity. Bright type has the highest productivity potential (771 m3/d), followed by semi-bright type (681 m3/d), and semi-dull type (436 m3/d). There is a negative correlation between NLPM and productivity. Stable type has the highest productivity potential (1049 m3/d), followed by relatively stable type (719 m3/d), and unstable type (405 m3/d). Thick coal seams with high NLPM may not have much production potential. Under multi-seam production, seams with high PBLT should be selected, and NLPM can be used as a critical index to estimate the inter-seam interference before fracturing. [ABSTRACT FROM AUTHOR]