Nuclear Magnetic Resonance Measurement of Oil and Water Distributions in Spontaneous Imbibition Process in Tight Oil Reservoirs

Xiangrong Nie,Junbin Chen

doi:10.3390/en11113114

Abstract

Spontaneous imbibition of water into tight oil reservoirs is considered an effective way to improve tight oil recovery. We have combined testing techniques such as nuclear magnetic resonance, mercury injection capillary pressure, and magnetic resonance imaging to reveal the distribution characteristics of oil and water during the spontaneous imbibition process of tight sandstone reservoir. The experimental results were used to describe the dynamic process of oil–water distribution at the microscopic scale. The water phase is absorbed into the core sample by micropores and mesopores under capillary forces that dry away the original oil phase into the hydraulically connected macropores. The oil phase entering the macropores will drive away the oil in place and expel the original oil from the macropores. The results of magnetic resonance imaging clearly show that the remaining oil accumulates in the central region of the core because a large amount of water is absorbed in the late stage of spontaneous imbibition, and the water in the pores gradually connects to form a “water shield” that blocks the flow of the oil phase. We propose the spontaneous imbibition pathway, which can effectively explain the internal mechanisms controlling the spontaneous imbibition rate. The surface of the core tends to form many spontaneous imbibition pathways, so the rate of spontaneous imbibition is fast. The deep core does not easily form many spontaneous imbibition pathways, so the rate of spontaneous imbibition is slow. This paper reveals the pore characteristics and distribution of oil and water during the spontaneous imbibition process, which is of significance for the efficient development of tight oil.

Highlights

IntroductionTight oil has become a hot research topic in the petroleum industry [1,2,3,4]
In recent years, tight oil has become a hot research topic in the petroleum industry [1,2,3,4].Horizontal drilling and multi-stage hydraulic fracturing are the key technologies for exploiting the tight oil to enable economic production [5,6,7]
Equation (4) shows that C is a key parameter for establishing the relationship between the Equation (4) shows that C is a key parameter for establishing the relationship between the transverse relaxation time (T2) and pore radius (r)

Summary

Introduction

Tight oil has become a hot research topic in the petroleum industry [1,2,3,4]. Horizontal drilling and multi-stage hydraulic fracturing are the key technologies for exploiting the tight oil to enable economic production [5,6,7]. The production of tight oil is rapidly decreasing, and the elasticity recovery efficiency is low [8]. Spontaneous imbibition (SI) of water into a tight oil reservoir is considered an effective way to improve tight oil recovery [9,10,11]. It is necessary to conduct in-depth research on SI. The SI mechanisms involve a complex interaction between capillary [12], gravity [13], viscous forces [14], and wettability [15]. Many experimental studies on SI have been reported in the literature

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Conclusion