Characteristics and displacement mechanisms of the dispersed particle gel soft heterogeneous compound flooding system

Abstract: Considering high temperature and high salinity in the reservoirs, a dispersed particle gel soft heterogeneous compound (SHC) flooding system was prepared to improve the micro-profile control and displacement efficiency. The characteristics and displacement mechanisms of the system were investigated via core flow tests and visual simulation experiments. The SHC flooding system composed of DPG particles and surfactants was suitable for the reservoirs with the temperature of 80−110 °C and the salinity of 1×104−10×104 mg/L. The system presented good characteristics: low viscosity, weak negatively charged, temperature and salinity resistance, particles aggregation capacity, wettability alteration on oil wet surface, wettability weaken on water wet surface, and interfacial tension (IFT) still less than 1×10−1 mN/m after aging at high temperature. The SHC flooding system achieved the micro-profile control by entering formations deeply and the better performance was found in the formation with the higher permeability difference existing between the layers, which suggested that the flooding system was superior to the surfactants, DPG particles, and polymer/surfactant compound flooding systems. The system could effectively enhance the micro-profile control in porous media through four behaviors, including direct plugging, bridging, adsorption, and retention. Moreover, the surfactant in the system magnified the deep migration capability and oil displacement capacity of the SHC flooding system, and the impact was strengthened through the mechanisms of improved displacement capacity, synergistic emulsification, enhanced wettability alteration ability and coalescence of oil belts. The synergistic effect of the two components of SHC flooding system improved oil displacement efficiency and subsequently enhanced oil recovery. Key words: soft heterogeneous compound flooding, dispersed particle gel, surfactant, synergistic effect, displacement mechanism, high temperature and high salinity reservoir

Investigation of the profile control mechanisms of dispersed particle gel.

Dispersed particle gel (DPG) particles of nano- to micron- to mm-size have been prepared successfully and will be used for profile control treatment in mature oilfields. The profile control and enhanced oil recovery mechanisms of DPG particles have been investigated using core flow tests and visual simulation experiments. Core flow test results show that DPG particles can easily be injected into deep formations and can effectively plug the high permeability zones. The high profile improvement rate improves reservoir heterogeneity and diverts fluid into the low permeability zone. Both water and oil permeability were reduced when DPG particles were injected, but the disproportionate permeability reduction effect was significant. Water permeability decreases more than the oil permeability to ensure that oil flows in its own pathways and can easily be driven out. Visual simulation experiments demonstrate that DPG particles can pass directly or by deformation through porous media and enter deep formations. By retention, adsorption, trapping and bridging, DPG particles can effectively reduce the permeability of porous media in high permeability zones and divert fluid into a low permeability zone, thus improving formation profiles and enhancing oil recovery

Permeability Evolution Study After Breaking of Friction Reducer in Near Fracture Matrix of Tightgas Reservoir

Hydraulic fracturing is generally required for tightgas formation with low matrix permeability to achieve economic production rate. Slickwater fracturing is one of most commonly used technology. Friction reducer is the primary component of this fluid. During fracturing, million gallons of friction reducer fluid are pumped downhole to initiate fractures, and lots of fluid would filtrate into formation matrix. Due to the small pore size of tightgas reservoir, breaking of the friction reducer fluid is required to minimize formation damage and improve the conductivity in fracture. However, this performance in tightgas is not clear. In this paper, tightsand samples were treated with a friction reducer and a breaker to simulate the filtration process during hydraulic fracturing. Three breaking scenarios were proposed and studied correspondingly. Over balance breaking resulted in higher permeability regain than balance and under balance breaking, which means less formation damage to the near fracture matrix. The short sample has a full recovery of permeability with over balance breaking and it is higher than that with balance and under balance breaking. With over balance breaking, 0.012 wt% breaker recovers 79.5% permeability, and the permeability regain increases with higher breaker concentration. The permeability regain of longer sample is improved, up to 116.3%. With under balance breaking, 0.1 vol% friction reducer shows 81.6% permeability regain. Lower concentration friction reducer achieves a higher permeability regain. The reasons can be attributed to pore blocking effect and wettability alteration introduced by the friction reducer and breaker. The emulsion particle size in the friction reducer solution is found to overlap with the pore size distribution of tightgas sandstone. Therefore, it was able to block the matrix pores in tightsand after treated with the friction reducer and breaker. The contact angle on sample surface was changed from 24.3° to 81.1° in average

Preparation of Dispersed Particle Gel (DPG) through a Simple High Speed Shearing Method

Dispersed particle gel (DPG) has been first successfully prepared using cross-linked gel systems through a simple high speed shearing method with the aid of a colloid mill at room temperature. The gel microstructure and particle size were investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), and dynamic light scattering (DLS) measurements. The results clearly show that the prepared DPG particles have highly uniformly spherical structures with an average size of 2.5 μm. A possible mechanism for the formation of DPG has been put forward and discussed in details. The high speed shearing method is considered to be the simple and rapid method for the preparation of DPG

Preparation of Dispersed Particle Gel (DPG) through a Simple High Speed Shearing Method

Dispersed particle gel (DPG) has been first successfully prepared using cross-linked gel systems through a simple high speed shearing method with the aid of a colloid mill at room temperature. The gel microstructure and particle size were investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), and dynamic light scattering (DLS) measurements. The results clearly show that the prepared DPG particles have highly uniformly spherical structures with an average size of 2.5 μm. A possible mechanism for the formation of DPG has been put forward and discussed in details. The high speed shearing method is considered to be the simple and rapid method for the preparation of DPG

Study of the formation and solution properties of worm-like micelles formed using both N-hexadecyl-N-methylpiperidinium bromide-based cationic surfactant and anionic surfactant.

The viscoelastic properties of worm-like micelles formed by mixing the cationic surfactant N-hexadecyl-N-methylpiperidinium bromide (C16MDB) with the anionic surfactant sodium laurate (SL) in aqueous solutions were investigated using rheological measurements. The effects of sodium laurate and temperature on the worm-like micelles and the mechanism of the observed shear thinning phenomenon and pseudoplastic behavior were systematically investigated. Additionally, cryogenic transmission electron microscopy images further ascertained existence of entangled worm-like micelles

Schematic illustration for the enhanced oil recovery mechanism.

<p>(a) oil distribution in the initial stage of reservoir development; (b) a high permeability zone formed after long-term water flooding; (c) injection of DPG particles for profile control; (d) DPG particles deform and pass through pores; (c) water flooding after the treatment.</p

Visual simulation results in etched glass model.

<p>(a) model; (b) saturating water; (c: saturating oil; (d) water flooding until water cut is up to 98%; (e) retention in larger pore space; (f) directly plugging the small pore throat; (g) segregated flow of oil and water pathway; (h) adsorption on the surface; (o) water flooding until water cut is up to 98% again.</p

The visual simulation experimental flow chart.

<p>The visual simulation experimental flow chart.</p

Disproportionate permeability reduction of DPG particles.

<p>Disproportionate permeability reduction of DPG particles.</p