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针对以往非平行地层γ测井研究多采用“上界面倾斜、下界面水平”的单一边界形式，且岩性背景集中于砂泥岩储层，对上、下界面不同倾斜组合所致响应差异及花岗岩、火山岩等高放射性目的层边界效应缺乏系统区分的问题，开展可分别控制上、下界面倾角的边界倾角响应研究，以提升放射性矿产测井的解释精度。构建可独立设定上、下界面倾角的非平行地层几何模型，基于MCNP程序，对两界面倾角各取0°至75°的36种边界倾角开展蒙特卡罗数值模拟研究，分别以砂岩、花岗岩和火山岩为目的层，从地层整体倾斜、单一界面倾斜及岩性效应三个层面分析响应特征。结果表明：地层整体倾斜时曲线关于目的层中心对称，倾角不超过45°时峰槽较窄且形态稳定，达到60°以上时目的层趋于陡倾，峰或槽展宽为平台，因视厚度恒定而真厚度随倾角余弦减小，按曲线宽度判读将系统高估目的层厚度；单一界面倾斜以固定侧倾角30°为临界呈现三种状态，固定侧小于30°时活动侧倾斜使一侧围岩读数升高、对侧降低并破坏曲线对称性，等于30°时各曲线收敛而近乎不敏感，大于30°时影响转移至另一围岩段并反向，上、下界面作用规律互为镜像。依据上、下围岩段计数率的不对称程度，可有效判别倾斜界面的空间情况。γ测井响应受边界倾角与目的层岩性背景共同控制并具有显著岩性效应，实际解释中在判定目的层中心、厚度与边界位置时须结合目的层岩性极性与上、下界面倾角及其相对大小，并对大倾角条件做视厚度校正。研究结果为复杂区放射性矿产的γ测井解释与地层厚度校正提供了理论支撑。
Abstract：Previous numerical studies of γ logging in non-parallel formations have mostly used a single boundary form, namely a tilted upper interface with a horizontal lower interface, and have concentrated on sandstone and mudstone reservoirs, rarely distinguishing the response differences caused by different dip combinations of the upper and lower interfaces or the boundary effects of highly radioactive ore layers such as granite and volcanic rock. To address this gap,we carried out a study of the boundary-combination response in which the dip angles of the upper and lower interfaces can be controlled independently,in order to improve the interpretation accuracy of radioactive mineral logging. We constructed a non-parallel formation geometric model in which the dip angles of the upper and lower interfaces could be set independently and, using the Monte Carlo N-Particle(MCNP) transport code,carried out numerical simulations of 36 boundary inclination,with each interface dip angle taking values from 0° to 75°. Using sandstone,granite,and volcanic rock as the target layer, we analyzed the response characteristics at three levels: overall formation dip, single-interface dip,and lithological effect. The simulations showed that,when the whole formation dips,the curve remains symmetric about the center of the target layer; at dip angles no greater than 45° the peak or trough is narrow and stable in shape,whereas at dip angles of 60° or more the ore layer becomes steeply inclined and the peak or trough broadens into a plateau. Because the apparent thickness stays fixed while the true thickness decreases with the cosine of the dip angle, reading the thickness from the curve width systematically overestimates the ore-layer thickness. For a single tilted interface,three states appear,with a fixed-side dip angle of 30° as the threshold: when the fixed side is less than 30°, tilting the active interface raises the reading of the surrounding rock on one side and lowers it on the other, breaking the symmetry of the curve; when it equals 30°,the curves converge and become almost insensitive; and when it exceeds 30°,the effect shifts to the other surrounding-rock section and reverses. The effects of the upper and lower interfaces are mirror images of each other, and the degree of asymmetry of the count rates between the upper and lower surrounding-rock sections can effectively identify the spatial situation of the tilted interface. The natural γ ray response is jointly controlled by the boundary dip angle and the lithological background of the target layer and exhibits a marked lithological effect. In practical interpretation, determining the center, thickness, and boundary position of the target layer requires combining the radioactive polarity of the target layer with the dip angles of the upper and lower interfaces and their relative magnitudes, together with an apparent-thickness correction under large-dip conditions. These results provide theoretical support for γ logging interpretation and formation-thickness correction of radioactive minerals in complex areas.
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基本信息:
中图分类号:P631.817
引用信息:
[1]肖程.地层边界倾角对γ测井影响的数值模拟研究[J].世界核地质科学().
2026-07-27
2026-07-27
2026-07-27