Application of Surfactants in Shale Chemical EOR at High Temperatures

Abstract

The goal of this work is to develop surfactant systems that can improve oil flow from shale wells after fracturing or re-fracturing. Surfactants can reduce oil-water interfacial tension and wettability of the shale, which in turn can improve water imbibition, increase oil relative permeability and reduce water blockage at the matrix-fracture interface. Temperature in typical shale reservoirs are high and the surfactants need to be aqueous stable to be effective in these treatments. Mixing two surfactants often gives higher aqueous stability than those of the single surfactants. A large number of surfactants (anionic, non-ionic and cationic) and their blends were studied for aqueous stability, contact angle and spontaneous imbibition. Seven single surfactants and nine surfactant blends were found to be stable in both high and low salinity brines at 125 °C. All aqueous stable blends changed wettability of oil-wet shale to preferentially water-wet in both high and low salinity brines. Seven single surfactants and five surfactant blends were tested for imbibition. Surfactant solutions improved water imbibition to the extent of 20% PV. Surfactant blends improved imbibition more than the single surfactants. Imbibition in cores reached a plateau in about 3 days. Surfactant blends have the potential to be used in low salinity fracturing or refracturing fluids to stimulate shale wells.

A Literature Review of CO2, Natural Gas, and Water-Based Fluids for Enhanced Oil Recovery in Unconventional Reservoirs

“…Surfactant formulations should be designed for the specific formations under consideration. − There are many examples of surfactant solutions for hydraulic fracturing, ,,− ,,,− and for EOR in conventional formations. ,,,,,− ,− , Here, we will focus on publications focused on surfactant solutions for EOR in ULRs. Many papers state that their results related to EOR in ULRs could also benefit the fracturing process.…”

Huff-n-Puff Technology for Enhanced Oil Recovery in Shale/Tight Oil Reservoirs: Progress, Gaps, and Perspectives

“…Among those reported IOR strategies that were feasible for tight oil basins are miscible fluids, surfactants, and low salinity water. The application of these methods in unconventional reservoirs has received substantial attention in recent times. − …”

Introductory Chapter: Developments in the Exploitation of Unconventional Hydrocarbon Reservoirs

“…This is the process of absorption of water as the wetting phase into rock, in which saturation by the wetting phase rises while that by the non-wetting phase reduces. This phenomenon can be induced by water flooding [17] or surfactant flooding [18,19]. A shift in wettability from oil-wet to water-wet increases water imbibition.…”