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Evaluation of a wettability modifier additive for improving oil recovery in naturally fractured reservoirs
Siddique, Afrah Khalid Ahmed
Siddique, Afrah Khalid Ahmed
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2023
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Abstract
Injection of water-soluble chemical additives (e.g., surfactants) have potential for increasing oil recovery from tight fractured reservoirs. The main factors that affect oil recovery from fractured reservoirs are rock wettability, reservoir heterogeneity, capillary trapping forces, and preferential flow of injected fluid through fractures. Instead of surfactants, this research work evaluates a wettability modifying agent, a mutual solvent in water and oil phases, that when injected in fractured reservoirs, promotes water imbibition into the rock matrix while enhancing oil recovery. The injection of this wettability-modifying agent reduces the interfacial tension (IFT) between oil and water, alters the rock wettability, and dissolves in oil and water to enhance oil recovery. While wettability-altering experiments have been conducted in non-fractured cores, this study focuses on the application of a mutual solvent injection in fractured cores.
Preliminary evaluations included measurements of IFT, rock wettability, and numerical simulations at the laboratory scale using a black-oil simulator to design the core flooding experiments. Then, core flooding experiments were conducted to measure the incremental oil recovery by a mutual solvent in an unfractured core and in a fractured core. An unfractured core of 1.5 inches in diameter was divided into two pieces, 2-inch and 10-inch in length portions. Similarly, the fractured core was divided into two portions, an unfractured 2-inch and a fractured 10-inch core cut-split into two halves to mimic the induced fracture. We used 3-pentanone as the dissolution agent, an efficient wettability modifier, and a mutual solvent for oleic and water phases. The effects of changing concentration of 3-pentanone and huff-puff strategy were also investigated. The experiments were performed using samples of the Colton sandstone formation from Central Utah.
The results showed that overall oil recovery from unfractured core and fractured core at the end of the flooding tests were 59.85% and 64.28%, respectively. The incremental oil recoveries, using the dissolution agent 3-pentanone in low saline brine, from unfractured and fractured cores were 7% and 22%, respectively. The incremental oil recovery using 3-pentanone (a ketone) can be explained by the combination of various mechanisms that include reduction in IFT, wettability modification from water-wet to strongly water-wet by decrease in contact angle from 38° to 18°, and the solubility of such ketones in oil that reduces the oil viscosity and increases oil mobility.
Ketones enhance the sweep efficiency in fractured reservoirs and promote mass transfer from fractures to the rock matrix by reducing capillary forces. Evaluation of the 3-pentanone additive provides an avenue to engineer the waterflooding treatment for fractured reservoirs which is environmentally friendly, cost-effective, and has the potential to significantly reduce the environmental footprint associated with tight reservoir production.
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