August 31 to September 3, 1997 Rio de Janeiro, Brazil

Transcription

1 Paper # 12 Modeling the Behavior of Asphaltene-Micelle in Petroleum Fluids by J.H. Pacheco-Samchez and G.A. Mansoori PROCEEDNGS of THE SECOND NTERNATONAL SYMPOSUM ON COLLOD CHEMSTRY N OL PRODUCTON August 31 to September 3, 1997 Rio de Janeiro, Brazil

2 SCOP 97 Modeling the behavior of asphaltene-micelle in petroleum fluids Juan H. Pacheco-Sanchez a and G.Ali Mansoori b. Permanent Address: lnstitulo Mexicano de/ Petroleo, Subdireccion de Exploracion y Produccion, Eje Central Lazaro Cardenas No. 152, Col. San Bartolo Atepehuacan, Deleg. Gustavo A. Madero Mexico, DF.; mundopacheco@prodigy.net.mx b. University of llinois at Chicago, (M/C 063) Chicago, L ; mansoori@uic.edu Asphaltene particles can assume various fonns when mixed with petroleum fluids depending on the relative sizes and polarities of the particles present in such complex mixtures. Small asphaltene particles can be dissolved in a petroleum fluid. Whereas relatively large asphaltene particles can fonn steric colloids in the presence of excess amounts of resins and paraffin hydrocarbons (see Figure 1). However, asphaltene particles may fonn micelles in the presence of excess amounts of aromatic hydrocarbons (see Figure 2). Experimental observations and theoretical calculations have indicated that asphaltene monomers in the presence of aromatic (polar) solvents fonn micelles l.2_ Considering that paraffin hydrocarbons are non-polar, asphaltenes in their presence will flocculate forming steric colloids (in case of the presence of resins in the crude oil) and eventually it will deposit out of the solution 3, 4, 5. An existing micelle fonnation model, originally developed for water/amphiphile systems, is applied to predict the phase behavior of asphaltene micelle fonnation in pure aromatic hydrocarbons at various temperatures and nonnal pressure. Several mechanisms for asphaltene micelle formation are investigated. The calculations are indicative of the existence of an upper and a lower boundary for the micelle-formation region. The results are compared with limited critical micelle concentration data for asphaltenes-in-toluene systems. These experimental data cover the lower boundary of the asphaltene-micelle-formation region. Should be mentioned that there are no experimental data for the upper boundary. Based on the model for optimum composition of asphaltenes in aromatic (polar) solvents, the behaviour of phase separation for asphaltene-micelles in petroleum fluids is proposed in this report for practical field applications. n order to know the conditions of either deposition or asphaltene micellization, it is necessary to perform phase equilibrium calculation between asphaltene in micelle and asphaltene in molecular state in petroleum fluids. Such equilibrium in this model is corresponding with the following coupled system of equations 2 for the separation of the micellar solution into two coexisting phases having different total concentrations Y.. and z.. of asphaltene = (Z..-Y..)+ln ( 1-Z ) l-y: z 2 y J3rC ( aa ) 2 - ( u )2 l+(y-l)z 01 l+(y-l)y.. (1) and Page 1 of Paper # 12

3 J.H. Pacheco-Samchez and G.A. Mansoori Modeling the Behavior of Asphaltene-Micelle in Petroleum Fluids Paper # 12, Proceed. 2nd nt l Symp. on Colloidal Chem. n Oil Prod. (SCOP 97) Rio de Janeiro, Brazil, 8/31-9/03, 1997 _ (-!-./K {z:;.f[:. _) + -.jy: =./K (1-z.. ) 2 z,.-y.. +2f3C 2 (+ (y- l)z ) (1 - Y.,) 2 (2) where, K(T,P) = exp[j3(µ* 0 mic/n n " 0 mic)l, 0 (3) n0 is the minimum number of asphaltenes in the micelle. Assuming sphero-cylindrical form of the asphaltene micelles: µ 0 mici"o is the chemical potential of reference per asphaltene monomer associated to the end region and µ o mic is the chemical potential of reference per asphaltene monomer associated to the cylindrical region. n general, parameter K is responsible of the size and form of each micelle. Analysing the expression l.2, 6 (3), K can assume the following values: K =f: f µ* 0 mic/n = noµ*omic then asphaltenes are proportionally distributed in both o cylindrical and end regions of the micelles being formed, i.e., asphaltene micelles form is spherical-like. O<K<l: f µ*omic> µ 0 mic/n then asphaltenes are distributed in the cylindrical region of the 0 micelles being fonned, i.e., asphaltene micelles form is disk-like. : f µ 0 mic/ > µ o mic then asphaltenes are distributed in the end region of the micelles "o in fonnation, i.e. asphaltene micelles form is cylindrical-like. t must be mentioned that K is related to the theory of moments, M - K (a-ll/2 X (a+j/2 a - a. as a.= 0,1,2,... Finally, near of the critical point (4) where A 0 " 4{ 1 +3/[5(3y-2)Xd - (2/5)ln[4(3y..2)/3] - lnxc} Equations () and (2) must be solved simultaneously for Y,, and Z 85 To accomplish this, Equation (1) is solved by the Newton-Raphson (NR) method for one of the variables (either Y aa or Z..) assigning an initial value to the other variable. Then Equation (2) is solved by the NR method using the solution to the equation () as the initial value. This iterative procedure converges for E = 1Xi-Xi_ 1 <<. For the case when K =, y = (asphaltenes derived from tar of Kotur-Tepinski crude) and j3c = 314.5/(yT): t is important to mention that, in the absense of data for the critical point, the value of j3c=314.5/(yt) was treated as an adjustable parameter. The NR simultaneous iterative solution of Equations () and (2) for Y as and z.., is convergent, when the Page 2 of Paper # 12

4 SCOP 97 (5) (6) (7) (8) Page 3 of Paper # 12

5 J.H. Pacheco-Samchez and G.A. Mansoori Modeling the Behavior of Asphaltene-Micelle in Petroleum Fluids Paper # 12, Proceed. 2nd nt l Sym p. on Colloidal Chem. n Oil Prod. (SCOP 97) Rio de Janeiro, Brazil, 8/31-9/03, 1997 Page 4 of Paper # 12

6 SCOP p11ann n( +m(>... 2 ( ) Paraffins- Paraffinsflocculaled Rsphaltene R1phaltene Sterle Colloid Figure 1 p( ) Aromatics.. Rsphalten Figure _. T 360,,.,... - n..., 36(), i JOO,.. " ,5 O.5 0,,oo > Figure 3 r -.. r-. 1 a. 0:1 - - r-n.o., 10 JU X (Hl 3 ) Page 5 of Paper # 12

7 J.H. Pacheco-Samchez and G.A. Mansoori Modeling the Behavior of Asphaltene-Micelle in Petroleum Fluids Paper # 12, Proceed. 2nd nt l Sym p. on Colloidal Chem. n Oil Prod. (SCOP 97) Rio de Janeiro, Brazil, 8/31-9/03, T O,p,miwo T :.w._,,, - - n...., X (x!o) Figure T,,,..,._ T ,.., , E,po,_ L o.1,,,,.,,.,,.. --,,,.,., 10 J 0 X (xj0-1)., , Tl,o..,. - -., i..., o.c O X (xlo>) Figure & - T -- "* T _,._..,,.., ,l ", c,-..,!,, - "-- 1.,,... X (x!0 1 ) Figure 6 /// Page 6 of Paper # { 10 0 X (x!o>)..-" (,.-! ",. i. l,, t,, " - -- Dull:,.,,... c,mon! 0.1 X (xo)