Pore-Scale Movability Evaluation for Tight Oil Enhanced Oil Recovery Methods Based on Miniature Core Test and Digital Core Construction

Abstract

The movability of micro-remaining oil in microscale pores in tight reservoirs directly affects the recoverability of a reservoir fluid. Currently, core displacement and digital cores have been applied for the reservoir fluid movability and microstructure visualization. In this study, we present a practical framework for the pore-scale movability of tight oil, which combines core displacement tests and digital cores on real tight core samples. In this framework, the core displacement tests and miniature core displacement tests using three different displacement methods (water flooding, CH 4 flooding, and CO 2 flooding) are first performed. Then, through a series of CT (computed tomography) scanning results on the core displacement tests, a digital core model is constructed, and a distribution of micro-remaining oil is experimentally investigated. By combining the results of the miniature core displacement tests and the digital core model, the types and movability of tight oil at different times for the three methods are obtained. These results indicate that the remaining tight oil at pore scale can be classified into three different categories according to a shape factor (S) of the remaining oil, including block-like oil (4.85 > S > 1), flat-like oil (12.22 > S > 4.85) and film-like oil (S > 12.22). From CT scanning results, the method of water flooding can effectively unlock the type of block-like oil, while CH 4 flooding and CO 2 flooding can produce flat-like and film-like oil. Furthermore, CO 2 flooding can significantly unlock more film-like oil than CH 4 flooding.

Study on Interpretation Method of Multistage Fracture Tracer Flowback Curve in Tight Oil Reservoirs

“…where, b is the equivalent diameter of the fracture, m. A is the seepage cross-sectional area, m 2 and V is the tracer injection volume, m 3 . The expressions for the injection and rejection rates are as…”

“…In recent years, tight oil reservoirs have become a focal point of global unconventional oil and gas exploration and development. , Due to their characteristics such as significant reservoir thickness, low porosity and permeability, poor connectivity, and high water saturation, multistage fracturing technology has emerged as a key technique for reservoir stimulation in tight oil formations. − With the widespread application of multistage fracturing technology in the development of tight reservoirs, accurately characterizing postfracturing fracture networks has become a challenging task in tight reservoir development. This characterization plays a crucial role in evaluating the effectiveness of fracturing and predicting production dynamics with a high level of accuracy. , Currently, the commonly used methods for describing postfracturing fracture networks include microseismic event monitoring, production analysis, and fracturing fluid flowback analysis. − During mining field operations, the injection and flowback technique of tracers is frequently employed .…”

“… 1 , 2 Due to their characteristics such as significant reservoir thickness, low porosity and permeability, poor connectivity, and high water saturation, multistage fracturing technology has emerged as a key technique for reservoir stimulation in tight oil formations. 3 − 5 With the widespread application of multistage fracturing technology in the development of tight reservoirs, accurately characterizing postfracturing fracture networks has become a challenging task in tight reservoir development. This characterization plays a crucial role in evaluating the effectiveness of fracturing and predicting production dynamics with a high level of accuracy.…”

Study on gas injection development effect of tight reservoir based on fluid occurrence state

“…It is important to describe the fluid occurrence mechanism accurately and comprehensively. The occurrence state of tight oil will be comprehensively affected by temperature, pressure, pore size, pore mineral composition, fluid composition and other factors (Liu et al, 2020). For unconventional reservoirs such as tight oil, the occurrence state of fluid in reservoirs is quite different from that of conventional oil and gas reservoirs (Kong et al, 2021).…”

N2 and CO2 Huff-n-Puff for Enhanced Tight Oil Recovery: An Experimental Study Using Nuclear Magnetic Resonance

“…Tight oil reservoirs are a strategic resource that can alleviate the contradiction between energy supply and demand. − The development of tight oil reservoirs by horizontal wells and stimulated reservoir volume fracturing has achieved some success, but the low oil recovery is still an unavoidable problem . The widespread distribution of nanoscale pores in tight reservoirs results in ultralow porosity and permeability, thus making it difficult to develop tight oil .…”