Investigation of Oil Saturation Development behind Spontaneous Imbibition Front Using Nuclear Magnetic Resonance T2

Abstract

Spontaneous imbibition is a critical mechanism for the development of water-wet fractured reservoirs. In order to improve the ultimate oil recovery, it is important to understand the change of in situ oil saturation during the spontaneous imbibition process. In this study, spontaneous imbibition experiments of two ends open (TEO) are conducted using unconsolidated sand packs. The sand packs are filled with quartz sands of three different particle sizes respectively and are fully oil-saturated. Nuclear magnetic resonance (NMR) T2 is used to monitor the saturation development behind spontaneous imbibition front. For porous media of the same lithology, the imbibition speed and final oil recovery decline with the reduction of average pore size. As the imbibition front constantly moves forward, the change of oil saturation behind the imbibition front does exist, and the major decrease of oil saturation happens in the large pore space. In terms of a particular region behind the spontaneous imbibition front, with the progression of the front, the oil saturation gradient in the area declines. Specifically, the dramatic gradient descent occurs when the spontaneous imbibition front just passes by. The smaller the average pore size is (the larger the mesh of sand is), the more rapid the saturation changes behind imbibition front. For porous media of small pore size, even when the imbibition front has moved far away, oil saturation still changes a lot.

Investigations on the driving forces of the fluorocarbon surfactant-assisted spontaneous imbibition using thermogravimetric analysis (TGA)

“…3 ). 22 The oil sand was compressed to rock slices under the pressure of 30 MPa. The rock slices were then soaked in the aqueous phase with different concentrations of FS-30.…”

“…It can be seen from eqn (1) that IFT between oil and water should be reasonable so that the driving force of imbibition, i.e. capillary force, was sufficient.…”

“…Spontaneous imbibition refers to a spontaneous process in which the wetting phase is imbibed into the porous media under capillary pressure and the non-wetting phase is expelled at the same time. 1 It is a key process for oil recovery in naturally fractured reservoirs. 2 It is estimated that more than 50% of the reservoirs worldwide are natural oil-wet reservoirs where water always needs to overcome the capillary pressure in the secondary recovery process.…”

A Critical Review of Enhanced Oil Recovery by Imbibition: Theory and Practice

“…Recently, imbibition experiments have been conducted at the nanoscale. − For example, an imbibition experiment was carried out on a chip, which helps to understand the microscopic mechanism of imbibition. Besides, the multi-computed tomography (CT) and nuclear magnetic resonance (NMR) technologies are used in imbibition experiments, and thus, a fluid distribution and saturation change during the imbibition process can be directly observed and quantified. − Simulation is also an effective tool to study imbibition. Imbibition at the field scale or core scale can be simulated by some commercial software, ,, such as CMG, Eclipse, and COMSOL Multiphysics, but the theory or models in the software are not flexible and cannot be improved by individuals.…”

Interplay between Viscous Pressure and Capillary Pressure on Polymer Gel Dehydration and Water Shutoff in Hydraulically Fractured Reservoirs

“…Seright and Brattekas believe that the pressure-gradient-induced gel dehydration can enhance the water shutoff performance. − Another mechanism for gel dehydration is the capillary effect. In water-wetted porous media, water can be imbibed into the matrix under capillary force. − When the gel in fractures is in contact with a water-wet matrix with a large oil saturation, capillary imbibition will occur, and the gel undergoes loss of water and reduction in volume. Wang et al used capillarity tubes and cores to study the effect of capillary force on gel dehydration, suggesting that a smaller capillary diameter leads to a higher degree of gel dehydration .…”