Abstract
Chang-10 reservoir in Wuqi–Ansai oilfield of Ordos Basin is restricted by its strong microscopic heterogeneity, complicated microscopic pore structure and unclear oil–water movement rules. The technology of nuclear magnetic resonance (NMR) is an excellent method to quantitatively evaluate the reservoir fluid of different pore structure types, and the microscopic experiments such as cast thin slices, scanning electron microscope (SEM) and high-pressure mercury injection were also used to analyze the differences in the occurrence features of fluid of different pore structure types and their influencing factors. The experimental results show that the sandstone types of Chang-10 reservoir in Wuqi–Ansai Oilfield are mainly medium-fine arkose and lithic arkose. The pore types are mainly intergranular pore, feldspar pore, turbiditic zeolite pore and cuttings pore. The combination type of pore-throat belongs to mesopore–micropore and microlarynx–microlarynx. By mercury injection experiment analyzed the characteristic of capillary pressure curve, Chang-10 reservoir in Wuqi–Ansai Oilfield pore structures is classified into Type I, Type II, Type III and Type IV due to the different movable fluid occurrence features. The occurrence features of movable fluid are obviously controlled by the pore-throat, and the orders of control effect from strong to weak are from Type I, Type II, Type III to IV The saturation of movable fluid gradually becomes low when the pore-throat radius decreases.
Highlights
In Ordos Basin, Wuqi–Ansai Oilfield is in the central and eastern part of the northern Shaanxi slope
The Chang-10 reservoir in Wuqi–Ansai Oilfield is taken as the study object, and the core samples in study area are tested and analyzed by multiple tests including cast thin slices observation, X-ray diffraction experiment, scanning electron microscope (SEM), nuclear magnetic resonance (NMR), high-pressure mercury injection, etc., to compare and analyze the effects of different pore structure types on the occurrence features of movable fluid
Rock core characteristics observation data show that Chang10 reservoir sandstone in Wuqi–Ansai Oilfield is mainly composed of gray and gray-green sandstone
Summary
In Ordos Basin, Wuqi–Ansai Oilfield is in the central and eastern part of the northern Shaanxi slope. The Chang-10 reservoir in Wuqi–Ansai Oilfield is taken as the study object, and the core samples in study area are tested and analyzed by multiple tests including cast thin slices observation, X-ray diffraction experiment, scanning electron microscope (SEM), NMR, high-pressure mercury injection, etc., to compare and analyze the effects of different pore structure types on the occurrence features of movable fluid. NMR is a technology to study pore structures of rocks by means of measuring the amplitude and relaxation rate of NMR relaxation signals of hydrogen nuclei in pore fluids and establishing T2 spectrum based on the magnetic properties of hydrogen nuclei and their interaction with external magnetic fields (Chen et al 2006; Talabi et al 2009; Megawati et al 2012; Gao et al 2015) This technique can accurately and rapidly determine the parameters of reservoir fluids.
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