Wettability Alteration Study of Supercritical CO₂ Fracturing Fluid on Low Permeability Oil Reservoir

Abstract

Hydraulic fracturing has become an important stimulation technique for low/ultralow permeability reservoirs. Supercritical CO 2 (SC-CO 2 ), as a no water phase material of fracturing fluid, receives wide attention. Current researches on SC-CO 2 fracturing fluid has mainly focused on its viscous properties and superiorities. However, little attention has been devoted to the interaction between SC-CO 2 fracturing fluid and the oil reservoir during the fracturing process. Besides, in a low permeability reservoir, the wettability determines the oil recovery by imbibition, which is a main way to explore oil for a matrix. Therefore, it is crucial to study the wettability alteration on a low permeability oil reservoir introduced by SC-CO 2 fracturing fluid. In this study, a contact angle goniometer was introduced to characterize the wettability alteration on low permeability cores by SC-CO 2 fracturing fluid. Meanwhile, nuclear magnetic resonance T2 spectra, a scanning electron microscope, and a energy dispersive spectrometer were used to explain the mechanisms of wettability alteration and the adsorption of fracturing fluid was analyzed. In addition, spontaneous imbibition tests were conducted to definite the impact of wettability alteration on oil production. The results showed that the thickener in SC-CO 2 fracturing fluid, fluid filter loss, and reservoir permeability were all responsible for wettability alteration on the core surface. With the increasing thickener contents and filter loss of fracturing fluid, cores turned to be intermediate and slightly water-wet from initial strongly water-wet, which was unfavorable for oil production.Comparatively low permeability cores which consist of more micro-small pores were more likely to make treated cores oleophilic, as well. Thickener adsorption was confirmed to be the main mechanism on wettability alteration by SC-CO 2 fracturing fluid, which resulted in different pore surfaces, and thus a more oleophilic cores surface. On the basis of the results of spontaneous imbibition, strong lipophilicity cores corresponded to lower oil recovery, which illustrated that wettability alteration caused by SC-CO 2 fracturing fluid was not favored for oil flow.

Study on the Wettability and Spontaneous Imbibition Characteristics of Lacustrine Shale

“…However, the reflux efficiency of fracturing fluid in some shale oil reservoirs is too low, which dramatically increases the cost of shale oil development. erefore, the problem of shale fracturing fluid loss has attracted the attention of a large number of scholars [5][6][7][8][9][10]. e academic circles generally believe that wettability is the main factor affecting the water spontaneous imbibition of shale and the primary mechanism that causes excessive water imbibition of shale.…”

Field-scale impacts of long-term wettability alteration in geological CO$_2$ storage

“…The process of wettability alteration (WA) is a dynamic process, that involves a complex interaction of surface mineralogy, fluid composition, and reservoir conditions that is percipitated by the introduction of a wettability-altering agent [Bonn et al, 2009, Buckley et al, 1988. WA has been long studied in the petroleum sector, and a variety of methods and agents, that include solvents such as supercritical CO 2 , have been applied to enhance WA in oil reservoirs to the benefits of increased recovery [Drexler et al, 2020, Sun et al, 2017. Modeling of WA often assumes an instantaneous change of wettability as a function of solvent concentration [Lashgari et al, 2016].…”

Study on Proppant Transport in Fractures of Supercritical Carbon Dioxide Fracturing

“…Supercritical carbon dioxide (SC-CO 2 ) fracturing may give a good solution in the oil and gas production industry, which combines the utilization of greenhouse gas and the development of energy resources. − As is known to all, with the consumption of conventional resources, the emphasis and difficulty in the oil and gas industry are the unconventional reservoirs. − However, the unconventional reservoirs need to use the fracturing technology during development on account of its low porosity, low permeability, low pore-throat radius, and high gas-flow resistances. − Hydraulic fracturing has been widely used and has achieved good performance in the exploitation of oil and gas resources nowadays, while the huge water consumption and formation pollution bring a lot of limitations to the technology . Supercritical carbon dioxide (SC-CO 2 ) fracturing is regarded as a promising means in the development of unconventional oil and natural gas on account of its great advantages of environmental protection and resource-saving . CO 2 with specific pressures and temperatures is injected into the well and reaches the supercritical state (above 7.38 MPa and 304.1 K) at a certain position in the wellbore with the heat transfer with formation rocks, which could result in fracturing the formation and carry proppants into the fractures to form the flow channel of oil and natural gas from the reservoir to the well. , …”

“…18 Supercritical carbon dioxide (SC-CO 2 ) fracturing is regarded as a promising means in the development of unconventional oil and natural gas on account of its great advantages of environmental protection and resource-saving. 19 CO 2 with specific pressures and temperatures is injected into the well and reaches the supercritical state (above 7.38 MPa and 304.1 K) at a certain position in the wellbore with the heat transfer with formation rocks, which could result in fracturing the formation and carry proppants into the fractures to form the flow channel of oil and natural gas from the reservoir to the well. 6,20 With the development of the shale gas, CO 2 fracturing has been tested in many wells in America, Canada, and China and achieved good performance in the field test.…”