Experimental Study on Spontaneous Imbibition under Confining Pressure in Tight Sandstone Cores Based on Low-Field Nuclear Magnetic Resonance Measurements

Abstract

Spontaneous imbibition (SI) is an important method to improve oil recovery in tight sandstone reservoirs. Commonly, the physical simulation of SI is performed at atmospheric pressure but the characteristics of spontaneous imbibition under confining pressure (SIUCP) is often neglected. In this study, oil distribution in tight cores was obtained in combination of high pressure mercury intrusion (HPMI) measurements and low-field nuclear magnetic (LF-NMR) measurements. After that, oil recovery for SI and SIUCP of tight core samples with all faces open (AFO) were obtained using LF-NMR measurements. Finally, a new scaling law for SIUCP was proposed to predict shut-in time in field scale. The results showed that 95.94–98.12 wt % of the oil was distributed in nanopores (0.1 ms < T 2 < 100 ms) of core samples, and the average amount of oil in nanomicro-pores, nanomeso-pores and nanomacro-pores were 34.04, 40.15, and 22.75 wt %, respectively. Ultimate oil recovery for core samples were 22.41, 44.41, 57.27, 61.84, and 62.82 wt %, respectively, as confining pressure increased from 0 to 2175 psi. The improved oil recovery for SIUCP was associated with the decline of effective pore radius as a function of confining pressure, which results in the effect of enhanced SI and compaction. Finally, a modified dimensionless time model was proposed in combination of Mason’s dimensionless time model and effective pore radius as a function confining pressure.

CO2 Huff-n-Puff after Surfactant-Assisted Imbibition to Enhance Oil Recovery for Tight Oil Reservoirs

“…Compared with the conventional CO 2 HNF experimental result in Figure , the total oil recovery factor increased 10.8% although the HNF efficiency decreased a lot. In the imbibition process, oil is preferentially displaced from relatively small pores by water and leaves a large amount of oil in relatively large pores . On the contrary, in the CO 2 HNF process, the produced oil mostly comes from relatively large pores, and these smaller pores contribute the oil production in the subsequent cycles .…”

“…In the imbibition process, oil is preferentially displaced from relatively small pores by water and leaves a large amount of oil in relatively large pores. 37 On the contrary, in the CO 2 HNF process, the produced oil mostly comes from relatively large pores, and these smaller pores contribute the oil production in the subsequent cycles. 17 Therefore, imbibition and HNF compensate each other to recover the remaining oil in the pore network, which makes them a perfect combination to enhance oil recovery.…”

An experimental study of imbibition process and fluid distribution in tight oil reservoir under different pressures and temperatures

“…Combined with the pore size classification method proposed by Loucks et al (2012), pores can be classified directly according to the T 2 value, and the specific areas are listed in Table 6. For convenience, 0.1∼1 ms is classified as nanomicro-pore, 1∼10 ms is classified as nanomeso-pore, and 10∼100 ms is classified as nano macropore (Jiang et al, 2018).…”

Experimental Investigation of the Pressure Decay Characteristics of Oil Reservoirs after Fracturing Operations

“…At the same time, the flow of the fracturing fluid will cause the decay of the well pressure. 6 , 7 In addition, salt ions in the matrix pores diffuse into the fracturing fluid, causing the salinity in the fracturing fluid to rise rapidly. When the imbibition front comes into contact with the pore wall, salt ions will dissolve and diffuse into the fracturing fluid.…”