Potential of Improving Oil Recovery with Surfactant Additives to Completion Fluids for the Bakken

Abstract

Fracture treatment performance in Bakken liquid-rich shale reservoirs can be improved by altering rock wettability from oil-wet to water-wet. The use of surfactant additives for altering wettability also results in alteration of the interfacial tension (IFT). The Young−Laplace equation relates the capillary pressure to IFT and contact angle. Thus, it follows that capillarity is significant in nanopores associated with unconventional liquid reservoirs (ULRs) and complex as the contact angle (CA) and IFT varies simultaneously. This study carefully evaluates these interactive variables and compares the performance of anionic, nonionic, blended, and complex nanofluid (CnF) surfactants in recovering liquid hydrocarbon from siliceous and carbonate Bakken shale cores through spontaneous imbibition experiments. In addition, we also analyze the effect of wettability, surfactant adsorption, and IFT alteration on the process. CA measurement is used in determining the original wettability of Bakken cores, as well as the wettability alteration effectiveness of each surfactant. The results show Bakken ULR original wettability in the oilwet region, but most importantly, all surfactants are capable of shifting the wettability of the core to the water-wet region at fieldused concentrations. However, we observed that the extent of wettability alteration strongly depends on rock lithology and surfactant type. These results were also corroborated by zeta potential measurements. In addition, IFT measurement of Bakken crude oil shows that all surfactants cause a reduction in IFT value. Surfactant dynamic adsorption measurements also show the dependence of rock lithology on surfactant performance giving higher adsorption values on carbonate rocks to negatively charged surfactants and higher adsorption values on siliceous surfaces to more positively charged surfactants. Last, the surfactant potential of improving oil recovery in ultralow permeability Bakken cores is investigated by spontaneous imbibition experiments. Through the experiment, oil recovery is recorded and the system is scanned using computed tomography (CT) in order to analyze the movement of fluid in the core and to compare the performance between surfactants and slickwater without an additive. The results suggest that surfactants are better on recovering oil from a shale core, displacing more oil, and having higher imbibition than slickwater with no additive. However, oil recovery depends on surfactant type and rock mineral composition. These findings are consistent with CA, zeta potential, surfactant adsorption, and IFT measurements. From the results obtained, it can be concluded that altering wettability and moderately reducing IFT when surfactant additives are added to aqueous solutions can improve oil recovery in Bakken cores. These findings give an important understanding for designing completion fluid treatments and flowback schedules for these ULRs.

Enhancing Imbibition Oil Recovery from Tight Rocks by Mixing Nonionic Surfactants

“…The IFT values measured for single and mixed OPE surfactants with different EO chain lengths show that both single and mixed OPE solutions similarly have low IFT values and can effectively wet the rock surface, similar to previous results reported for ionic surfactants. ,,, However, the spontaneous imbibition results show that the oil recovery factor for single OPE solutions is not significantly different from the reference case without surfactants. In contrast, mixing OPE15 (oil-soluble with a short EO chain) with OPE70 (water-soluble with a long EO chain) leads to improved oil recovery from the oil-saturated tight core plugs.…”

“…Recent studies ,, showed that synergistically favorable mixed nonionic–cationic and cationic–anionic surfactants can improve the oil recovery from tight carbonate rocks and shales, respectively. We studied the concept of mixing weakly interacting nonionic surfactants to enhance imbibition oil recovery from submicron pores.…”

“…Recent studies show how different types of surfactants (anionic, cationic, nonionic, and amphoteric) are utilized to improve imbibition oil recovery from tight rocks on a laboratory scale. ,− Alvarez and Schechter , suggested that anionic and nonionic–cationic mixed surfactants work better for tight siliceous and carbonate rocks, respectively. Although mixed ionic surfactants show proper synergism (β), their use should be with caution as they are prone to cause precipitation. , However, nonionic surfactants are preferred over ionic surfactants on a field scale.…”

Surfactant Adsorption on Shale Samples: Experiments and an Additive Model

“…28 Alvarez et al showed that AS adsorption onto different Bakken shale samples has capacities ranging from 6.2 to 8.9 mg/g at 0.2 wt % concentration. 29 Missing in these studies is an understanding of how different shale components contribute to surfactant adsorption.…”

Evaluation of Imbibition Oil Recovery in the Duvernay Formation

“…The distribution of different fluid phases in the pores affects rock/fluid properties including capillary pressure, waterflood behavior, relative permeability, and electrical characteristics of rock. Among the common techniques for evaluation of wettability (Anderson 1986), contact-angle measurement (Wang et al 2017), spontaneous imbibition (Dehghanpour et al 2012;Javaheri et al 2017), and nuclear magnetic resonance (Sulucarnain et al 2012) have been used for characterizing the wettability of tight and shale rocks with ultralow permeability.…”