Study on Microscopic Seepage Mechanism During Fracturing Process in Tight Reservoir

Abstract

Tight reservoirs usually have ultra-low permeability, so fracturing must be carried out during production. Due to different injection velocities and rock-fluid properties, in the fracturing process, oil-water migration law in the pore and throat is complicated. In this paper, to figure out oil-water microscopic seepage mechanism in the fracturing process, we establish two digital core models with and without fractures by using CT scanning method, based on a typical tight reservoir core. Then we study the interfacial position changes and micro-force characteristics during oil and water two-phase movement, using pore scale simulation method. The results show that: ① In the digital core model without fracture, the injected fluid does not advance along a fixed channel, it flows backward when encounters at the parallel channels under imbibition force. This phenomenon leads to the oil remaining in the pore and difficult to use. ② In the digital core model with fractures, a new phenomenon called “reverse imbibition” occurs near the injected fluid entrance. The reverse imbibition is a phenomenon that oil moves from low pressure to high pressure affected by capillary force. It is occurred when the displacement force less than imbibition force. Analysis shows that the reverse imbibition helps oil advance from micro-pore-throat to fracture space during fracturing process. This is the main microscopic mechanism of enhanced oil recovery by fracturing. Under quasi-static conditions, the reverse imbibition only occurs when wetting angle is less than 45°. Therefore, in the hydraulic fracturing process, adding water wetting surfactants is beneficial to increase imbibition capacity, and then can improve oil recovery effectively.

Copyright 2023, IFEDC Organizing Committee.

This paper was prepared for presentation at the 2023 International Field Exploration and Development Conference in Wuhan, China, 20–22 September 2023.

This paper was selected for presentation by the IFEDC Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the IFEDC Technical Team and are subject to correction by the author(s). The material does not necessarily reflect any position of the IFEDC Technical Committee its members. Papers presented at the Conference are subject to publication review by Professional Team of IFEDC Technical Committee. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of IFEDC Organizing Committee is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of IFEDC. Contact email: paper@ifedc.org.