I am getting this error and do not know how to fixt it.. Warning: Matrix is singular, close to singular or badly scaled. Results may be inaccurate. RCOND = NaN. > In ResHomework3 (line 84)

Question

Sarah A Alruwayi on 1 Mar 2019

0
Link

Direct link to this question

https://in.mathworks.com/matlabcentral/answers/447644-i-am-getting-this-error-and-do-not-know-how-to-fixt-it-warning-matrix-is-singular-close-to-singu

Commented: Sarah A Alruwayi on 1 Mar 2019

clear ALL
close ALL 
clc 
Area=0.1963;
L=4;
porosity=0.18;
K=61.5;
injrate=0.01;
oilvisc=4.2;
watervisc=0.85;
Boi=1.21;
Swr=0.28;
Sorw=0.35;
KrwMax=0.31;
KroMax=0.65;
Nw=2.25;
No=2.45;
CO=0.000001;
CW=0.000004;
CR=0.000003;
POi=1500;
PWF=1460;
R=3;
dt=0.2;
Vr=Area*0.2;
for i=1:10
     Swi(1,i)=Swr;
     PO(1,i)=POi;
     PCOW(1,i)=5;
     
     Krw(1,i)=KrwMax*((Swi(1,i)-Swr)/(1-Sorw-Swr))^Nw;  
     Kro(1,i)=KroMax*((1-Swi(1,i)-Sorw)/(1-Sorw-Swr))^No;
     Omob(1,i)= Kro(1,i)/oilvisc;
     Wmob(1,i)=Krw(1,i)/watervisc;
    
end
for n=1:15
        
    
    for i=1:10
         Ctot(n,:)=CR+Swi(n,:)*CW+(1-Swi(n,:))*CO;
         if i==1
             
             Ttot=2.6366*10^-4*K*(Wmob(n,i)+Omob(n,i))*(Area/0.4);
             Tw=2.6366*10^-4*K*(Wmob(n,i))*(Area/0.4);
             
             A(i,i)=-(Ttot+(Vr*porosity*Ctot(n,i))/(dt)); %E
             A(i,i+1)=Ttot; %F
             R(i,1)= (-Vr*porosity*Ctot(n,i)*PO(n,i))/(dt)+Tw*(PCOW(n,i+1)-PCOW(n,i))-injrate; %R
     
         elseif i==10
             WI(n,i)=2.6366*10^-4*K*(Wmob(n,i)+Omob(n,i))*(Area*2/0.2);
             TtotL=Ttot;
             TwL=Tw;
             Tw=0;
             Ttot=0;
             %Ttot=2.6366*10^-4*K*(Wmob(n,i)+Omob(n,i))*(A/0.4);
             %Tw=2.6366*10^-4*K*(Wmob(n,i))*(A/0.4);
   
             
              A(i,i-1)=TtotL; %D
              A(i,i)=-(TtotL+(Vr*porosity*Ctot(n,i))/(dt))+WI(n,i); %E
              R(i,1)=(-Vr*porosity*Ctot(n,i)*PO(n,i))/(dt)-TwL*(PCOW(n,i)-PCOW(n,i-1))-WI(n,i)*PWF; %R
         else 
               TtotL=Ttot;
               TwL=Tw;
               Ttot=2.6366*10^-4*K*(Wmob(n,i)+Omob(n,i))*(Area/0.4);
               Tw=2.6366*10^-4*K*(Wmob(n,i))*(Area/0.4);
               
               A(i,i)=-(TtotL+Ttot+(Vr*porosity*Ctot(n,i))/dt); %E
               A(i,i+1)=Ttot; %F
               A(i,i-1)=TtotL; %D
               R(i,1)= (-(Vr*porosity*Ctot(n,i)*PO(n,i))/(dt))+Tw*(PCOW(n,i+1)-PCOW(n,i))-TwL*(PCOW(n,i)-PCOW(n,i-1)); %R
        
         end   
      
    end
    
Line  84   PO(n+1,:)=A\R;
   
    for i=1:10
       if i==1
          q_t(n,i)=injrate;
          Tw=2.6366*10^-4*K*(Wmob(n,i))*(Area/0.4);
          Swi(n+1,i)= (1+(CR+CW)*(PO(n+1,i)-PO(n,i)))*Swi(n,i)+...
              (dt/(Vr*porosity))*(Tw*(PO(n+1,i+1)-PO(n+1,i))-...
              Tw*(PCOW(n,i+1)-PCOW(n,i))+q_t(n,i));
       elseif i==10
            TwL=Tw;
            Tw=0;
            WI(n,i)=2.6366*10^-4*K*(Wmob(n,i)+Omob(n,i))*Area*2/0.2;
            qt(n,i)= -WI(n,i)*(PO(n,i)-PWF);
            Swi(n+1,i)=(1+(CR+CW)*(PO(n+1,i)-PO(n,i)))*Swi(n,i)+dt/(Vr*porosity)-...
                (TwL*(PO(n+1,i)-PO(n+1,i-1))+TwL*(PCOW(n,i)-PCOW(n,i-1))+qt(n,i));
       else 
         
           TwL=Tw;
           Tw=2.6366*10^-4*K*(Wmob(n,i))*(Area/0.4);
           Swi(n+1,i)=(1+(CR+CW)*(PO(n+1,i)-PO(n,i)))*Swi(n,i)+ ...
               (0.2/(Vr*porosity))*Tw*(PO(n+1,i+1)-PO(n+1,i))-...
               TwL*(PO(n+1,i)-PO(n+1,i-1))-Tw*(PCOW(n,i+1)-PCOW(n,i))+TwL*(PCOW(n,i+1)-PCOW(n,i));
       end 
     
    end 
    
    for i=1:10 
        
        if   Swi(n+1,i)<=Swr
             PCOW(n+1,i)=5;
        elseif   Swi(n+1,i)>=(1-Sorw)
             PCOW(n+1,i)=-5;
        elseif Swr<Swi(n+1,i)<0.5
             PCOW(n+1,i)= min(0.8*log((Swi(n+1,i)-Swr)/(0.5-Swr)),5);
        elseif 0.5<Swi(n+1,i)<1-Sorw 
             PCOW(n+1,i)=max(0.8*log((1-Swi(n+1,i)-Sorw)/(1-0.5-Sorw)),-5); 
        end 
    end
    for i=1:10
        
         Krw(n+1,i)=KrwMax*((Swi(n+1,i)-Swr)/(1-Sorw-Swr))^Nw;  
         Kro(n+1,i)=KroMax*((1-Swi(n+1,i)-Sorw)/(1-Sorw-Swr))^No;
         Omob(n+1,i)= Krw(n+1,i)/watervisc;
         Wmob(n+1,i)=Kro(n+1,i)/oilvisc;
    end 
end 