Abnormal pressure conditions and spatial variations have direct and powerful influences on the aggregation, dissipation, accumulation and development of hydrocarbons under subsurface conditions, and they are extremely important aspects that must be focused on for safe coal mining and oil and natural gas development. The Ordos Basin, located in the western part of the North China Craton (NCC), contains significant reserves of oil, gas, coal and other mineral resources and is a typical low-pressure basin. This paper conducts an overall analysis and comprehensive comparison of the spatial and temporal variations in the pressure coefficients of oil and gas areas in the Ordos Basin. The analysis is based on a dataset comprising 589 sets of pressure coefficient–depth data from hydrocarbon layers that are uniformly classified in the basin's main oil and gas fields. Notably, high-pressure features develop in the basin only in the gas fields located in the centres of areas with high gas generation intensity, in individual sections of lithological seals and in the gas layers beneath the gypsum salts of the Ordovician Majiagou Formation. The Mesozoic oil layers and Paleozoic gas layers throughout the basin, which are buried at depths up to 4500 m and within a stratigraphic era spanning 3 × 10 years, generally dominate low pressures, and these abnormal pressure features are not noticeably affected by spatial or temporal variations. Additionally, the ranges of the pressure coefficients and the distributions of the peak values of the oil and gas layers in the upper-oil and lower-gas areas (UOLGAs) generally resemble each other. The pressure coefficients for gas reservoirs only slightly exceed those for oil reservoirs. These unique features are rare in many large- and medium-sized petroleum bearing-basins worldwide. Excluding the high abnormal pressure data of the subsalt gas layer in the basin, based on the magnitudes, proportions, and distributions of the pressure coefficients of the gas layers, as well as the geological background, it is possible to classify the 10 gas fields in the basin into five distinct categories: (1) weak low-pressure dominated; (2) weak low-pressure dominated, mixed with high-pressure; (3) weak low-pressure dominated, supplemented with normal pressure; (4) normal and weak low pressures coexisting; and (5) abnormally high pressure dominated. Regarding the spatial distribution, the pressure coefficients of the gas layers exhibit a macroscopic pattern of gradual increase from the northern to the southern regions. Furthermore, the unique characteristics of the generally low pressures in the basin, in the coalfield (mine) gas pressure coefficient, in the gas content, and in the gas explosion frequency correspond to the performance and can be corroborated by each other. This study provides a scientific basis and theoretical foundation for a profound understanding of the accumulation (mining) effects of evolution-modification and the unique features of hydrocarbons and coal seams (mines and fields) in the Ordos Basin, which can help to promote and guide the further exploration and development of energy minerals in different regions of the basin; furthermore, a new type of pressure system has been added to global energy basin pressure systems.

中文翻译：

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鄂尔多斯盆地含油气层低压时空分布特征

异常压力条件和空间变化对地下条件下油气的聚集、消散、聚集和发育具有直接而有力的影响，是煤炭安全开采和石油天然气开发必须关注的极其重要的方面。鄂尔多斯盆地位于华北克拉通西部，蕴藏着丰富的石油、天然气、煤炭等矿产资源，是典型的低压盆地。本文对鄂尔多斯盆地油气区压力系数时空变化进行全面分析和综合比较。分析基于包含盆地主要油气田统一分类的烃层的 589 组压力系数深度数据的数据集。值得注意的是，盆地内仅在高产气强度区中心气田、个别岩性封闭剖面以及奥陶系马家沟组膏盐下气层发育高压特征。整个盆地中生界油层和古生界气层埋藏深度达4500 m，地层时代跨越3×10年，普遍以低压为主，异常压力特征不受时空影响。变化。此外，上油下气区（UOLGA）油气层的压力系数范围和峰值分布也大体相似。气藏的压力系数仅略高于油藏的压力系数。这些独特的特征在全球许多大中型含油盆地中都是罕见的。剔除盆地内盐下气层高异常压力资料，根据气层压力系数的大小、比例、分布情况以及地质背景，可对盆地内10个气田进行分类。将盆地分为五类：（1）弱低压为主； (2)弱低压为主，高压夹杂； (3)以弱低压为主，常压为辅； (4)正常低压和弱低压并存； (5)异常高压为主。从空间分布来看，宏观上气层压力系数呈现出由北向南逐渐增大的规律。此外，盆地普遍低压、煤田（矿井）瓦斯压力系数、瓦斯含量、瓦斯爆炸频率等独特特征与其表现相对应，可以相互印证。该研究为深刻认识鄂尔多斯盆地油气与煤层（矿、田）演化改造的聚（采）效应及独特特征提供了科学依据和理论基础，有利于促进和指导盆地不同地区能源矿产的进一步勘探和开发；此外，全球能源盆地压力系统中还增加了一种新型压力系统。