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Page 45 of 59

by DONMEI WANG may keep BAKKEN WELLS The current method of oil recovery from the Bakken formation relies on the natural pres- sure in the reservoir to push the oil through the rock to the well. However, experience has shown that after producing a relatively small fraction of oil, the natural pressure in oil res- ervoirs declines and subsequent production falls, sometimes leaving behind as much as 95 percent of the oil. Fortunately, the decline has yet to appear in the Bakken region. Oil production, at roughly a million barrels per day, is high and increasing because the re- serves are huge and large-volume produc- tion has been underway for only a short time, which means it's still too soon for the natural reservoir pressure to drop off. However, even- tually, the pressure will decline and oil produc- tion will fall, if not stop. What can be done to extract all that remaining oil? A group headed by Dr. Dongmei Wang at the University of North Dakota is researching new ways to recover the vast untapped oil likely to remain beyond the reach of current extraction practices. Through funding provided under the RPSEA (Research Partnership to Secure Energy for America) program authorized by the U.S. Energy Policy Act of 2005, the re- searchers are attempting to develop a method that may increase oil recovery five-fold. How? In simple terms, they believe it's possible to take hydraulic fracturing another step by using specially treated water to drive far higher quantities of oil out of the shale and into the wells. The key word is "imbibition." Dr. Wang's group has shown that the Bakken shale is generally wet with oil — meaning the rock surfaces are coat- ed with oil. In addition, the group has researched water treatments – mix- tures of water and surfactants, which are similar to dish detergent – that will induce the rock to absorb water and expel oil. In other words, the process alters the "wettability" of the rock. Once this change is made, the rock draws in the surfactant-water — a process called imbibition. As the sur- factant formulation is absorbed by the rock, oil will be expelled. That oil would then be collected by the same fracturing systems and horizontal wells that are currently producing Bakken oil. However, the research is in its early stages. So far, the UND research group has shown that ordinary brine (salt water) can drive out small quantities of oil from shale, though not enough for commercial success. Achieving high oil recovery rates requires the right surfactant, the proper salt content, the correct pH, and effective temperature. Dr. Wang's group is seeking that optimum formu- lation. To help, oil companies have provided rock cores, as well as oil and water from their target oil reservoirs. With these cores and flu- ids, the team is studying the effects of various surfactant formulations. The laboratory measurements are then scaled up to determine whether enough oil will be produced to make the process economic. Analytical calculations and computer simula- tions are being performed to scale the pro- cess for particular field applications. However, the analysis is complicated by the relatively early stage of pro- duction in the various producing fields, the size of the Bakken formation and the substantial variation in reservoir character (degree of fracturing, pressure, oil saturation, permeability, tem- perature). Nevertheless, results suggest that imbibition of sur- factant formulations has a sub- stantial potential to improve oil recovery in certain parts of the Bakken. MIXING OIL and WATER Flowing Photo taken by Justin Voeller, Chicken Coop Photography ➤ continued 46 B A K K E N O I L B U S I N E S S J O U R N A L Feb/March 2014

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