Patent Application: US-201615191099-A

Abstract:
a new method of assessing wettability of a reservoir rock is provided , using a mineral oil / alkane saturated sample first , a crude oil and water saturated sample equivalent to natural reservoir rock second , and a third crude oil saturated , water free sample , measuring different wettability states and comparing the slopes of all three adjusted values to determine a wettability state for the reservoir rock .

Description:
the present invention is exemplified with respect to an outcrop rock . however , this is exemplary only , and the invention can be broadly applied to any reservoir rock or complex material . the following examples are intended to be illustrative only , and not unduly limit the scope of the appended claims . the disclosure provides a novel method of assessing wettability of reservoir rocks . the more water - wet curve was obtained by an imbibition experiment where the core was fully saturated by a mineral oil / alkane ( such as n - decane ). the more oil - wet curve was obtained by an imbibition experiment where the core was fully saturated by a crude oil . the mixed - wet curve was obtained by saturating the curve with an irreducible / connate water saturation and a crude oil . since the core samples used for the experiments here had similar core properties , a dimensionless time correlation was not used . instead , a square root of time was used to plot oil recovery as a % ooip for comparison . this is another way to correlate imbibition data . the curve should be a straight line . the equations used were : where % ooip recovered is 100 times the recovered oil divided by the initial oil in place . if core samples with different core properties / reservoir rocks are used instead , it is suggested to plot oil recovery against a dimensionless time . as noted above , there are different variations of dimensionless time correlations available in the literature . one correlation that applies to a wide range of data : where t d is the dimensionless time , t is the imbibition time , k is the permeability of the rock , φ is the porosity of the rock , σ is the interfacial tension between water and oil , μ w is the water viscosity , μ 0 is the oil viscosity , and l is the characteristic length . the most commonly used geometry and boundary condition in the laboratory studies is the cylindrical core samples with all of the faces open to flow . for core samples with similar geometry / shape and boundary condition , the characteristic core length , l , could be defined as following : where d is the diameter of the cylindrical core and l is the length of the core sample . as noted above , our data was plotted as square root of time versus oil recovery as a % ooip in fig3 . next , the intercept of each of the curves in fig3 is set to zero , as shown in fig4 , and slopes obtained for these adjusted curves . obtain the slopes of the vsww and oil - wet curves first , followed by the slopes of the other curves . divide the slope of the imbibition curve of the core sample of interest by the addition of the slopes of the curves for vsww and oil - wet core sample imbibition curves , per the following equation : where m x is the slope of the imbibition curve from the core sample of interest , m vsww is the slope of the imbibition curve of a vsww core sample and mow is the slope of the imbibition curve of an oil - wet core sample . the wettability index may be calculated by using imbibition curves . for example , using the data in fig4 , the calculated wettability index was 0 . 169 /( 8 . 81 + 0 . 097 )= 0 . 169 / 8 . 907 = 0 . 019 the index is between “ 0 ” and “ 1 ”. if the calculated value is less than 0 . 25 , the core could be considered as more oil - wet and if the value is greater than 0 . 75 , the core could be considered as more water - wet . the values in - between could be considered as mixed - wet . the rock tested herein is more oil - wet . the following references are incorporated by reference in their entirety for all purposes . abe , a . a ., relative permeability and wettability implications of dilute surfactants at reservoir conditions ( thesis 2005 ). al - mahrooqi , s . h ., et al ., 2003 , an investigation of the effect of wettability on nmr characteristics of sandstone rock and fluid systems , j . petrol . sci . eng ., vol . 39 , p . 389 - 398 . anderson , w . g ., “ wettability literature survey — part ii : wettability measurement ”, jpt , november 1986 , 38 , 12 , 1246 - 1262 . behbahani , h . s . z ., analysis , scaling and simulation of counter - current imbibition ( thesis 2004 ). bobek , j . e ., et al ., “ reservoir rock wettability — its significance and evaluation ”, trans . aime , 1958 , 213 , 155 . buckley , j . s ., “ mechanism and consequences of wettability alteration by crude oils ”, ph . d . dissertation , heriot - watt university , edinburgh , united kingdom , september 1996 . buckley , j . s ., et al ., “ mechanisms of wetting alteration by crude oils ”, spej , march 1998 , 3 , 54 - 61 . calhoun , j . c ., “ criteria for determining rock wettability ”, oil & amp ; 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