Impacts of the Base-Level Cycle on Pore Structure of Mouth Bar Sand Bars: A Case Study of the Paleogene Kongdian Formation, Bohai Bay Basin, China

Xixin Wang,Ling Ji,Jian Sun,Jiagen Hou,Yuming Liu,Xun Gong

doi:10.3390/en11102617

Abstract

The pore structure of rocks can affect fluid migration and the remaining hydrocarbon distribution. To understand the impacts of the base-level cycle on the pore structure of mouth bar sand bodies in a continental rift lacustrine basin, the pore structure of the mouth bar sand bodies in the ZVC (ZV4 + ZV5) of the Guan195 area was studied using pressure-controlled mercury injection (PMI), casting sheet image and scanning electron microscopy (SEM). The results show that three types of pores exist in ZVC, including intergranular pores, dissolution pores, and micro fractures. The porosity is generally between 1.57% and 44.6%, with a mean value of 19.05%. The permeability is between 0.06 μm2 and 3611 μm2, with a mean value of 137.56 μm2. The pore structure heterogeneity of a single mouth bar sand body in the early stage of the falling period of short-term base-level is stronger than that in the late stage. During the falling process of the middle-term base level, the pore structure heterogeneity of a late single mouth bar sand body is weaker than that of an early single mouth bar sand body. In the long-term base-level cycle, the pore structure heterogeneity of mouth bar sand bodies becomes weaker with the falling of the base-level.

Highlights

Pore structure refers to the shape, size, distribution and the connective relationship of pores and pore throats [1,2]
Investigations of the factors controlling pore structure are critical to the exploration and development of an oil field [6,7,8,9,10]
The mercury mercury injection injection and and extrusion extrusion curves curves of of the the samples samples change change at at the the threshold threshold pressure, pressure, which is the pressure at which a wetting phase will begin to be displaced by a which is the pressure at which a wetting phase will begin to be displaced by a non-wetting non-wetting phase phase from a porous medium

Summary

Introduction

Pore structure refers to the shape, size, distribution and the connective relationship of pores and pore throats [1,2]. The pore structure of the reservoir is controlled by tectonic movement and diagenesis and by the influence of sedimentary factors (e.g., Ju et al [25], Tang et al [26], Wang et al [27], Wang et al [28]). The controlling effects of sedimentation on reservoir characteristics are mainly reflected by the changes of the base level. The influence of base level cycle on the reservoir characteristics can be divided into autocycles and allocycles [29]. Autocycles refer to the sedimentary cycles formed by the change of the internal factors of the basin under the condition of a relatively stable sedimentary background. Allocycles refer to the sedimentary cycles formed by the change of Energies 2018, 11, 2617; doi:10.3390/en11102617 www.mdpi.com/journal/energies

Methods

Results

Conclusion