Treatment of oil and oil-containing formulations

Abstract

There is disclosed a method of separating a mixture (e.g. dispersion) of oil and water into oil-rich and water-rich phases, the method comprising the steps: (i) selecting a mixture which comprises oil recovered from a subterranean formation and a treatment formulation, wherein said treatment formulation was added to the oil in order to facilitate its recovery and/or mobility, wherein said treatment formulation has an Interfacial Tension (IFT), measured against a sample of said oil in the range 2 to 20 mN/m; (ii) directing said mixture to a separation means; and (iii) in the absence of a chemical demulsifier, heating the mixture until separation is effected at least partially under gravity. Preferably the IFT is in the range 9 to 12 mN/m. The mixture of oil and water may be formed by treating oil in a subterranean formation.

1 . A method of separating a mixture of oil and water into oil-rich and water-rich phases, the method comprising the steps of:
 (i) selecting a mixture which comprises oil recovered from a subterranean formation and a treatment formulation, wherein the treatment formulation was added to the oil in order to facilitate its recovery and/or mobility, wherein the treatment formulation has an Interfacial Tension (IFT), measured against a sample of the oil in the range 2 to 20 mN/m;   (ii) directing the mixture to a separation means; and   (iii) in the absence of a chemical demulsifier, heating the mixture until separation is effected at least partially under gravity.   
     
     
         2 . A method according to  claim 1 , wherein the treatment formulation is able to increase the mobility of the oil and has at least one of the following characteristics, measured at 25° C., when the treatment formulation is contacted with a sample of the oil, wherein the ratio of oil:treatment formulation is 70:30:
 (a) a dispersion of the oil and the treatment formulation has a viscosity, at a shear rate of 1 s −1 , of less than 5000 cP; 
 (b) a dispersion of the oil and the treatment formulation is pseudoplastic over the shear rate range 1 s −1  to 100 s −1 ; and/or 
 (c) a dispersion of the oil and the treatment formulation has a viscosity, at a shear rate of 100 s −1 , of no more than 700 cP. 
 
     
     
         3 . A method according to  claim 1 , wherein the separation means comprises a first receptacle into which the mixture is delivered, wherein the method includes the step of heating the mixture in the first receptacle into which the mixture is delivered to a temperature of at least 40° C. for at least 1 hour. 
     
     
         4 . A method according to  claim 3 , wherein during the heating, the mixture separates under gravity so that two layers of materials are defined, one being a lower layer comprising water and water-soluble materials and the other being an upper layer comprising oil, wherein the upper layer includes less than 20 wt % of water and the lower layer includes at least 70 wt % of water. 
     
     
         5 . A method according to  claim 3 , wherein the first receptacle includes vent means for removing gas from the first receptacle and the first receptacle includes a first outlet for removing fluid from an upper part of the first receptacle, the method including the step of removing fluid from an upper layer of fluid in the first receptacle. 
     
     
         6 . A method according to  claim 5 , wherein the method includes the step of removing fluid from the lower layer in the first receptacle, wherein the fluid removed from the lower layer is re-cycled. 
     
     
         7 . A method according to  claim 6 , wherein the first receptacle includes an outlet for removal of solids. 
     
     
         8 . A method according to  claim 7 , wherein the first receptacle includes a first outlet which is connected to a second receptacle and the method includes withdrawing fluid from an upper part of the first receptacle and delivering the fluid from the upper part into the second receptacle and water in the fluid is separated from oil in the fluid in the second receptacle. 
     
     
         9 . A method according to  claim 8 , wherein no chemical demulsifier is added to the second receptacle and separation in the second receptacle includes the step of heating the fluid in the second receptacle to a temperature of at least 40° C. 
     
     
         10 . A method according to  claim 8 , wherein the second receptacle is arranged for delivery of fluid from an upper part thereof into further separation means comprising a battery. 
     
     
         11 . A method according to  claim 1 , wherein the treatment formulation has a surface tension, in the absence of oil, at 25° C., in the range 40 to 65 mN/m. 
     
     
         12 . A method according to  claim 1 , wherein the IFT is in the range 8 to 14 mN/m. 
     
     
         13 . A method according to  claim 1 , wherein the treatment formulation comprises water and an active material wherein the active material affects the IFT of the treatment formulation in relation to the oil and/or modifies the water so the treatment formulation has the IFT, wherein the treatment formulation includes at least 95 wt % water. 
     
     
         14 . A method according to  claim 13 , wherein the active material is non-ionic and/or the active material is such that a 1 wt % aqueous solution has no detectable cloud point and/or the active material has a weight average molecular weight (Mw) of less than 200,000. 
     
     
         15 . A method according to  claim 13 , wherein the active material is not an optionally cross-linked hydrolysed polyvinyl alcohol. 
     
     
         16 . A method according to  claim 13 , wherein the active material comprises a polymeric material which comprises at least 50 mole % of vinylalcohol repeat units. 
     
     
         17 . A method according to  claim 16 , wherein the polymeric material includes vinylacetate repeat units. 
     
     
         18 . A method according to  claim 1 , which includes a step (a) prior to step (i) which comprises treating the oil to define the mixture selected in step (i) of the method and step (a) comprises contacting the oil to be treated with the treatment formulation. 
     
     
         19 . A method according to  claim 18 , wherein the treatment formulation has a viscosity at 25° C. and 100 s −1  of greater than 0.98 cP. 
     
     
         20 . (canceled) 
     
     
         21 . Apparatus comprising:
 a first receptacle containing fluid produced after treatment in the method of  claim 1 ;   a second receptacle downstream of the first receptacle and operatively connected to the first receptacle for transfer of fluid from an upper part in the first receptacle to the second receptacle;   a treatment formulation receptacle operatively connected to the first receptacle for transfer of fluid from a lower part in the first receptacle to the treatment formulation receptacle;   wherein the second receptacle includes a higher concentration of oil than in the treatment formulation receptacle or the first receptacle; and   the first receptacle contains more water than the second receptacle.