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Mass transport in shale reservoirs: chemical osmosis and its impact on hydrocarbon recovery
Torcuk, Mehmet Ali
Torcuk, Mehmet Ali
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2019
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2020-02-19
Abstract
Hydrocarbon production from nano-Darcy shale formations has become possible because of the application of multi-stage hydraulic fracturing technology on horizontal wells. During hydraulic fracturing operations, typically, a large amount of fracturing fluid (e.g., 10,000 barrels/stage) is injected into shale formations to crack the formation and propagate a vertical hydraulic fracture. The breakup of the rock matrix by the hydraulic fracture, and the infiltration of fracturing fluid into the tight rock matrix create a large number of smaller macrofractures. The fracturing fluid used in shale hydraulic fracturing consists of 98 to 99.5 percent water plus a relatively small amount of dissolved salt and chemicals, which includes friction reducers, acids to remove formation damage, scale and corrosion inhibitors, biocides, and proppants. Field observations have indicated that flowback of the fracturing fluid is typically under 30%; thus, the bulk of the fracturing fluid stays within the rock matrix. The main mechanism for fracturing fluid retention is often explained as capillary imbibition while it is actually by capillary osmosis. In this research, I will address capillary osmosis and provide a detailed quantification of the capillary osmosis mass transport mechanisms through the shale matrix as a pseudo-membrane. The capillary osmosis causes low-salinity brine to be imbibed in the shale matrix and push the oil of the matrix. The latter phenomenon has been described by a mathematical model, which will be presented. The model is a multi-component mass transport model that includes advective and molecular transport of water molecules and dissolved brine ions. In the transport model, I use the activity-corrected molecular diffusion coefficient of the brine solution to quantify the amount of imbibing brine into the core sample. Ultimately, the same numerical model will be used in an oil-water saturated core example to determine how much oil could be displaced as a proxy to field applications. The ultimate application of the research is to determine whether chemical osmosis could be a viable enhanced oil recovery (EOR) mechanism.
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