Experimental Investigation on Cyclic Huff-n-Puff with Surfactants Based on Complex Fracture Networks in Water-Wet Oil Reservoirs with Extralow Permeability

Abstract

The injection from a well to other wells can be difficult in extralow-permeability oil reservoirs. In order to address this issue, a method of cyclic huff-n-puff with surfactants based on complex fracture networks for a single horizontal well was proposed and then investigated in terms of the effects of injection and fracture parameters on the oil recovery in water-wet extralow-permeability models. Firstly, the interfacial tension (IFT) and contact angle with different surfactant concentrations were measured to determine the basic properties of the surfactants. Then, the experiments of huff-n-puff with surfactants at different threshold injection pressures and soaking time were carried out to determine the oil increasing effects and analyze the pore-scale (micropores, mesopores, and macropores) mechanisms by combining the technology of nuclear magnetic resonance (NMR), which showed that the recovery increased with threshold injection pressure mostly in mesopores and macropores, while that increased with soaking time mostly in micropores. Eventually, the experiments of cyclic huff-n-puff based on different fracture distributions were conducted in six plate-fractured models to investigate the effects of surfactants, primary fracture, and secondary fracture on each cycle of huff-n-puff. Cyclic huff-n-puff with surfactants assisted by complex fracture networks including both primary and secondary fractures would bring to a higher oil recovery. However, other methods should be taken after several cycles of huff-n-puff due to the rapid reduction of oil recovery of each cycle. The findings for the proposed method should provide a meaningful guide to the development of extralow-permeability oil reservoirs.

Water- and Surfactant-Based Huff-n-Puff Injection into Unconventional Liquid Hydrocarbon Reservoirs: Experimental and Modeling Study

“…22 According to Sheng, 2 huff-n-puff surfactant technology is awaited to have a better effect on oil production than surfactant flooding in the ULR. Cao et al 32 conducted a series of surfactant huff-n-puff laboratory tests using water-wet artificial cores with extra low permeability similar to Dagang Oilfield. The authors used cylindrical cores and six different plate-fractured models to study the oil-increasing effect in micro-, meso-, and macropores.…”

Oil Production Mechanism of Water Injection Huff-n-Puff for Enhancing Oil Recovery in Tight Sandstone Reservoir

“…Cao et al proposed a single horizontal well surfactant cyclic huff-n-puff technology to improve oil recovery based on a complex fracture network for ultralow permeability reservoirs. Nuclear magnetic resonance (NMR) technology and numerical calculation methods were utilized to analyze the pore-scale oil increase mechanism and seepage characteristics. , …”

“…Nuclear magnetic resonance (NMR) technology and numerical calculation methods were utilized to analyze the pore-scale oil increase mechanism and seepage characteristics. 37,38 A large number of experiments were carried out on water huff-n-puff experiments using physical simulation methods. Bai et al proposed a new core-scale fracture laboratory simulation method using eight different fracture models to understand the impact of different injected fluids on enhanced oil recovery.…”

Pore Structure and Permeability Variations during Gas Displacement in Unconsolidated Sandstone Reservoirs through CT Reconstruction Analysis

“…And the macroscopic investigation will not provide a revealing insight into the microscope evolution. The general ways to investigate the pore structure include centrifuge, mercury intrusion, nitrogen adsorption, nuclear magnetic resonance (NMR), and computed tomography (CT) [23][24][25][26][27]. All of them can reflect the pore size distribution but cannot physically present the spatial pore structure except CT [28].…”