Working Paper Article Version 1 This version is not peer-reviewed

Characteristics and Control Mechanism of Low Resistivity Contrast Oil Pays in Chang 8 Tight Sandstone Reservoir of Longdong West Area, Ordos Basin

Version 1 : Received: 14 January 2021 / Approved: 15 January 2021 / Online: 15 January 2021 (13:02:42 CET)

How to cite: Bai, Z.; Tan, M.; Shi, Y.; Li, G.; Clark, S. Characteristics and Control Mechanism of Low Resistivity Contrast Oil Pays in Chang 8 Tight Sandstone Reservoir of Longdong West Area, Ordos Basin. Preprints 2021, 2021010294 Bai, Z.; Tan, M.; Shi, Y.; Li, G.; Clark, S. Characteristics and Control Mechanism of Low Resistivity Contrast Oil Pays in Chang 8 Tight Sandstone Reservoir of Longdong West Area, Ordos Basin. Preprints 2021, 2021010294

Abstract

The log interpretation and evaluation of Chang 8 tight sandstone reservoir in Longdong West area, Ordos Basin, is facing great challenges due to the existence of low resistivity contrast oil pays. To better guide the exploration of oil resources in this area, the characteristics and control mechanism of low resistivity contrast oil pays were studied in this research. Firstly, according to the relative value of apparent resistivity increase rate of the target formation, the reservoir was divided into two types: low resistivity contrast oil pay (LRCP) and high resistivity oil pay (HRP). Then, the reservoir characteristics were studied by comparing and analyzing the experimental data, formation water data and logging data collected from the two reservoir types. On this basis, the control mechanism of LRCP was studied and summarized into reservoir micro factors and regional macro factors, respectively. It is found that the reservoir rock composition between LRCP and HRP is basically the same. Compared with HRP reservoir, the average porosity and permeability of LRCP reservoir are relatively better, but the pore structure is relatively poorer because of the high content of micro pores. When the filling pressure of crude oil is sufficient enough, the high oil saturation can be formed in LRCP reservoir. The high irreducible water saturation and high formation water salinity are the main micro factors reduced the reservoir resistivity. Besides, the difference of hydrocarbon expulsion capacity of source rock and the regional difference of formation water salinity are the macro factors influenced the distribution of LRCP and HRP from vertical and horizontal of the region. The formation of LRCP is controlled by the comprehensive influence of reservoir micro factors and regional macro factors. And the comprehensive consideration of the influence of micro factors and macro factors on LRCP is suggested during the log interpretation and evaluation.

Keywords

Tight sandstone; Low resistivity contrast oil pay; Reservoir Characteristic; Control mechanism; Longdong West area.

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