Experimental Study on Oil Drop Discharge Behavior during Dynamic Imbibition in Tight Oil Sandstone with Aid of Surfactant

Yan Xin,Fei Ding,Li’Nan Wei,Ang Chen,Wenxun Zhao,Yanchao Fang,Yongpeng Sun,Caili Dai

doi:10.3390/en15041533

Abstract

The pore and throat structure of tight oil reservoir cores is complex, and the resistance of oil drop to discharge from the core is very high during dynamic imbibition. Surfactant has good ability in interfacial tension reduction and wettability reversal. It can reduce oil drop discharge resistance and enhance oil recovery effectively during dynamic imbibition in tight reservoirs. Here, we first analyzed the pore throat structure and mineral composition of tight core, and then the oil drop visualization instrument was used to study the discharge behavior of oil drop during dynamic imbibition. The oil drop discharge form was analyzed, and the influence of various factors on the oil drop discharge behavior was explored, and then the dynamic imbibition performance of surfactant in tight cores was obtained. The core throat diameter was mainly distributed in 0.07–1.1 μm, and the hydrophilic mineral content in core reached 50.8%. In the case of fluid flow in fracture, the oil drop discharge from near fracture matrix was faster, and its growth rate in height and width was faster than that without external fluid flow. Within a certain range, with the increase of IFT, the rate of core imbibition increased gradually. When the IFT increased from 0.32 mN/m to 0.59 mN/m, the oil drop rapture time decreased by 66.3%. The growth rate of oil drop discharged from the top and side of the core was faster than that from the bottom surface. Furthermore, it was easier to discharge. With the core thickness reduced by half, the rapture time of oil drop was reduced by 74.7%. For tight reservoirs, hydraulic fracturing can create more fracture surfaces and reduce the size of matrix blocks, which contributes to reduce the oil drop discharge resistance during imbibition and improve the oil recovery. This study provides a basis for surfactant to improve dynamic imbibition and oil production performance of tight sandstone oil reservoir.

Highlights

This study provides a basis for surfactant to improve dynamic imbibition oil recovery performance of tight sandstone reservoir
Dynamic imbibition effect of tight reservoir is influenced by pore structure and mineral
The core pore throat structure of tight oil reservoirs was complex, and the pore throat radius was mainly distributed in the range of 0.07–1.1 μm, and the oil drop had a relatively large resistance during the process of imbibing and discharging from the core

Summary

Introduction

Tight oil resources in the world are very rich and have great economic value. The proportion of tight oil reservoirs in China is gradually increasing, and the efficient development of such oil and gas resources is an important task in oil field [1,2]. Due to poor physical properties, low permeability, small pore throat, and poor pore connectivity of tight oil reservoirs, it is difficult for injected water to enter deep strata and the oil recovery is low in the process of conventional waterflooding development [3–5]. Improving the production of matrix crude oil is the key to waterflooding development of tight oil reservoirs. Imbibition has obvious effects on the development of lowpermeability, ultra-low-permeability, and even tight oil reservoirs and has become one of the important measures to improve the recovery of tight sandstone reservoirs [6–9]

Methods

Results

Discussion

Conclusion