EVALUATION OF NONSANDSTONE RESERVOIRS BETWEEN SALT BEDS OF THE PALEOGENE QIANJIANG FORMATION IN THE QIANJIANG DEPRESSION OF THE JIANGHAN BASIN

Based on Ⅳ-order rhythms as the basic scale (scale: several to dozens of centimeters), the authors have, for the first time, made a detailed description and study of nonsandstone reservoirs between salt beds distributed widely in the Qianjiang subbasin, Jianghan basin, in respect to reservoir rock types, reservoir pore spaces, physical properties of reservoirs and vertical distribution of reservoirs and draw the following conclusions: Ⅳ-order rhythms and their association in relatively diluted intervals are the most promising reservoirs in which accumulations with industrial oil could occur. Among all types of reservoir rocks, dolostones have the highest porosity (average 19%) and lowest permeability (average 25.3×10^-3μm²), mudstones have a medium porosity (average 13.4%) and the highest permeability (average 68.8×10^-3μm²), and glauberite rock has the lowest porosity average 10.6%) and a medium permeability (average 36.2×10^-3μm²). These data indicate that the permeability is not absolutely positive relative to the porosity but mainly relative to the pore texture and fractures. The porosity of reservoirs is influenced by the glauberite content. When the glauberite content is from 10% to 50%, the porosities of dolostones and mudstones decline with increasing glauberite content, and when the glauberite content is above 50%, glauberite forms glauberite rock and its porosity are maintained at about 10%. This suggests that the view that the porosity is positive relative to the glauberite content in dolostones is incorrect. Most nonsandstone reservoirs) between salt beds commonly have small pore throats and poor permeability. So if we want to develop) them effectively, it is necessary to improve their permeability according to the typical dissolution behaviors) of evaporite minerals.