This document contains code for calculating surge and swab pressures in an oil well. It takes inputs like pipe dimensions, fluid properties, flow rates, and calculates parameters like pressure losses and optimal flow rate. The code contains sections for calculating pressures at different flow rates, plotting the well dynamics, and determining the optimum hydraulic path and flow rate that balances maximum pump pressure with nozzle area and bit pressure loss.

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% Surge/Swab Pressure Calculations Algorithm Version 1.0
%
close all
clear
clc
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Developed by Ankit Kukreja (ankit.kukreja.89@gmail.com)
% on July 3rd, 2012
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
d=2.25; % Pipe ID (inch)
d1=4; % Pipe OD (inch)
d2=6.25; % Casing ID (inch)
rho=9; % Fluid density (ppg)
L= 10000; % Depth of well (ft)
theta600=60.8; % Fann dial reading at 600 rpm
theta300=37.4; % Fann dial reading at 300 rpm
Cd=0.9697; % Discharge coefficient at nozzle
Nsize=12; % Current nozzle size
Nno=3; % Number of Nozzles currently in use
qmin = 125; % Minimum flow rate (gpm)
% Pump parameters
Ppmax=3000; % Maximum achievable pump pressure
PHP=1250; % Pump rating (Horsepower)
e=0.91; % Pump efficiency
% Enter the choice of criterion to choose
% 1 - Maximum Jet impact force
% 2 - Maximum drill bit hydraulic horsepower
% 3 - Maximum jet velocity
choice=1;
%
% Step 1 calculations
% Flow behaviour parameter, n (dimensionless)
n=3.32*log10(theta600/theta300)
% Flow behaviour parameter, K (lbf/100 ft^2)
K=510*theta300/(511^n)
% Effective area through nozzle
Aeff=(pi/4)*Nno*((Nsize/32)^2)
% Maximum possible flow (gpm)
qmax=1714*PHP*e/Ppmax
% Selection of two flow rates
q1=qmax/3 % Flow rate 1 (gpm)
q2=2*qmax/3 % Flow rate 2 (gpm)
% q1=350; % Flow rate 1 (gpm)
% q2=550; % Flow rate 2 (gpm)
%%
% Calculation of pump pressure corresponding to flow rate q1
% Average velocity of pipe, vbar_pipe (ft/sec)
vbar_pipe1=q1/(2.448*(d^2))
% Average velocity of annulus, vbar_ann (ft/sec)
vbar_ann1=q1/(2.448*((d2^2)-(d1^2)));

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% Turbulence criteria of pipe, NRe_pipe
NRe_pipe1=(89100*rho*(vbar_pipe1^(2-n))/K)*((0.0416*d/(3+(1/n)))^n);
% Turbulence criteria of annulus, NRe_ann
NRe_ann1=(109000*rho*(vbar_ann1^(2-n))/K)*((0.0208*(d2-d1)/(2+(1/n)))^n);
% Define critical Reynold number, ReC
if n<=1 && n>=0.5
ReC1=2000;
else
if n<0.5 && n>=0.2
log_ReC1=((0.5-n)*(log10(2.1))/0.3)+log10(2000);
ReC1=10^(log_ReC1);
end
end
if NRe_pipe1<ReC1
% If flow is laminar, frictional pressure loss gradient of pipe
Lam_Pgrad_pipe1=K*(vbar_pipe1^n)*(((3+(1/n))/0.0416)^n)/(144000*(d^(1+n)))
% Pump pressure, Pp
deltaPp1 = L*Lam_Pgrad_pipe1
end
if NRe_ann1<ReC1
% If flow is laminar, frictional pressure loss gradient of annulus
Lam_Pgrad_ann1=K*(vbar_ann1^n)*(((2+(1/n))/0.0208)^n)/(144000*((d2-d1)...
^(1+n)))
end
% Calculation of friction factor of pipe, f_pipe
f_pipe1 = fsolve(@(f_pipe1)(sqrt(1/f_pipe1))-((4/(n^0.75))*log10...
(NRe_pipe1*(f_pipe1^(1-(n/2)))))+(0.395/(n^1.2)),1)
% Calculation of friction factor of annulus, f_ann
f_ann1 = fsolve(@(f_ann1)(sqrt(1/f_ann1))-((4/(n^0.75))*log10...
(NRe_ann1*(f_ann1^(1-(n/2)))))+(0.395/(n^1.2)),1)
if NRe_pipe1>=ReC1
% If flow is turbulent, frictional pressure loss gradient of pipe
Tur_Pgrad_pipe1=(f_pipe1*rho*(vbar_pipe1^2))/(25.8*d)
% Pump pressure, Pp
deltaPp1 = L*Tur_Pgrad_pipe1
end
if NRe_ann1>=ReC1
% If flow is turbulent, frictional pressure loss gradient of annulus
Tur_Pgrad_ann1=(f_ann1*rho*(vbar_ann1^2))/(21.1*(d2-d1))
end
% Pressure loss at bit, deltaPb
deltaPb1=8.311*(10^(-5))*rho*(q1^2)/((Cd^2)*(Aeff^2))
%
%%
% Calculation of pump pressure corresponding to flow rate q2
% Average velocity of pipe, vbar_pipe (ft/sec)
vbar_pipe2=q2/(2.448*(d^2))
% Average velocity of annulus, vbar_ann (ft/sec)
vbar_ann2=q2/(2.448*((d2^2)-(d1^2)))
% Turbulence criteria of pipe, NRe_pipe
NRe_pipe2=(89100*rho*(vbar_pipe2^(2-n))/K)*((0.0416*d/(3+(1/n)))^n)
% Turbulence criteria of annulus, NRe_ann
NRe_ann2=(109000*rho*(vbar_ann2^(2-n))/K)*((0.0208*(d2-d1)/(2+(1/n)))^n)
% Define critical Reynold number, ReC

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if n<=1 && n>=0.5
ReC2=2000;
else
if n<0.5 && n>=0.2
log_ReC2=((0.5-n)*(log10(2.1))/0.3)+log10(2000);
ReC2=10^(log_ReC2);
end
end
if NRe_pipe2<ReC2
% If flow is laminar, frictional pressure loss gradient of pipe
Lam_Pgrad_pipe2=K*(vbar_pipe2^n)*(((3+(1/n))/0.0416)^n)/(144000*(d^(1+n)))
% Pump pressure, Pp
deltaPp2 = L*Lam_Pgrad_pipe2
end
if NRe_ann2<ReC2
% If flow is laminar, frictional pressure loss gradient of annulus
Lam_Pgrad_ann2=K*(vbar_ann2^n)*(((2+(1/n))/0.0208)^n)/(144000*...
((d2-d1)^(1+n)))
end
% Calculation of friction factor of pipe, f_pipe
f_pipe2 = fsolve(@(f_pipe2)(sqrt(1/f_pipe2))-((4/(n^0.75))*...
log10(NRe_pipe2*(f_pipe2^(1-(n/2)))))+(0.395/(n^1.2)),1)
% Calculation of friction factor of annulus, f_ann
f_ann2 = fsolve(@(f_ann2)(sqrt(1/f_ann2))-((4/(n^0.75))*...
log10(NRe_ann2*(f_ann2^(1-(n/2)))))+(0.395/(n^1.2)),1)
if NRe_pipe2>=ReC2
% If flow is turbulent, frictional pressure loss gradient of pipe
Tur_Pgrad_pipe2=(f_pipe2*rho*(vbar_pipe2^2))/(25.8*d)
% Pump pressure, Pp
deltaPp2 = L*Tur_Pgrad_pipe2
end
if NRe_ann2>=ReC2
% If flow is turbulent, frictional pressure loss gradient of annulus
Tur_Pgrad_ann2=(f_ann2*rho*(vbar_ann2^2))/(21.1*(d2-d1))
end
% Pressure loss at bit, deltaPb
deltaPb2=8.311*(10^(-5))*rho*(q2^2)/((Cd^2)*(Aeff^2))
%
%%
% Parasitic pressure loss
deltaPd1=deltaPp1-deltaPb1 % Corresponding to flow rate q1
deltaPd2=deltaPp2-deltaPb2 % Corresponding to flow rate q2
% Slope of analysis plot
m=(log10(deltaPd2/deltaPd1))/(log10(q2/q1))
%%%%%%%%%%%%%%%%% Path of optimum hydraulics %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
if choice==1
% For max jet impact force
deltaPd_choice=(2/(m+2))*Ppmax
end
if choice==2
% For max bit hydraulic horsepower
deltaPd_choice=(1/(m+1))*Ppmax
end
if choice==3

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% For max jet velocity
deltaPd_choice=100
end
% Path definition
for qline=50:0.1:qmax
deltaPdline=10^(log10(deltaPd1)+m*log10(qline/q1));
plot(log10(qline),log10(deltaPdline))
hold on
if deltaPdline<=deltaPd_choice
plot(log10(qmax),log10(deltaPdline),'r')
hold on
end
if deltaPdline>=deltaPd_choice
plot(log10(qmin),log10(deltaPdline),'r')
hold on
end
if qline<=qmax && qline>=qmin
plot(log10(qline),log10(deltaPd_choice),'r')
hold on
end
plot(log10(qmin+1),log10(deltaPdline),'g')
hold on
for i=log10(100):0.1:log10(deltaPd_choice)
if log10(deltaPdline)<=log10(i+1) && log10(deltaPdline)...
>=log10(i-1) && log10(qline)<=log10(qmax+1) && ...
log10(qline)>=log10(qmax-1)
deltaPdopt=i;
qopt=qline;
end
end
if log10(deltaPdline)<=log10(deltaPd_choice+1) && ...
log10(deltaPdline)>=log10(deltaPd_choice-1) && ...
log10(qline)<log10(qmax) && log10(qline)>log10(qmin)
deltaPdopt=deltaPd_choice;
qopt=qline;
end
for k=log10(deltaPd_choice+1):0.1:log10(Ppmax)
if log10(deltaPdline)<=k+1 && log10(deltaPdline)>=k-1 && ...
log10(qline)<=log10(qmin+1) && log10(qline)>=log10(qmin-1)
deltaPdopt=k;
qopt=qline;
end
end
end
xlabel('Flow Rate (gpm)')
ylabel('Parasitic Pressure Loss(psi)')
grid on
title('Well dynamics (in blue) and optimum hydraulic path(in red and green)')
%%
% Calculation of pump pressure corresponding to flow rate qopt
% Average velocity of pipe, vbar_pipe (ft/sec)
vbar_pipeopt=qopt/(2.448*(d^2));
% Average velocity of annulus, vbar_ann (ft/sec)

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vbar_annopt=qopt/(2.448*((d2^2)-(d1^2)));
% Turbulence criteria of pipe, NRe_pipe
NRe_pipeopt=(89100*rho*(vbar_pipeopt^(2-n))/K)*((0.0416*d/(3+(1/n)))^n)
% Turbulence criteria of annulus, NRe_ann
NRe_annopt=(109000*rho*(vbar_annopt^(2-n))/K)*((0.0208*(d2-d1)...
/(2+(1/n)))^n)
% Define critical Reynold number, ReC
if n<=1 && n>=0.5
ReCopt=2000;
else
if n<0.5 && n>=0.2
log_ReCopt=((0.5-n)*(log10(2.1))/0.3)+log10(2000);
ReCopt=10^(log_ReCopt);
end
end
if NRe_pipeopt<ReCopt
% If flow is laminar, frictional pressure loss gradient of pipe
Lam_Pgrad_pipeopt=K*(vbar_pipeopt^n)*(((3+(1/n))/0.0416)^n)...
/(144000*(d^(1+n)))
% Pump pressure, Pp
deltaPpopt = L*Lam_Pgrad_pipeopt
end
if NRe_annopt<ReCopt
% If flow is laminar, frictional pressure loss gradient of annulus
Lam_Pgrad_annopt=K*(vbar_annopt^n)*(((2+(1/n))/0.0208)^n)/...
(144000*((d2-d1)^(1+n)))
end
% Calculation of friction factor of pipe, f_pipe
f_pipeopt = fsolve(@(f_pipeopt)(sqrt(1/f_pipeopt))-((4/(n^0.75))*...
log10(NRe_pipeopt*(f_pipeopt^(1-(n/2)))))+(0.395/(n^1.2)),1)
% Calculation of friction factor of annulus, f_ann
f_annopt = fsolve(@(f_annopt)(sqrt(1/f_annopt))-((4/(n^0.75))*...
log10(NRe_annopt*(f_annopt^(1-(n/2)))))+(0.395/(n^1.2)),1)
if NRe_pipeopt>=ReCopt
% If flow is turbulent, frictional pressure loss gradient of pipe
Tur_Pgrad_pipeopt=(f_pipeopt*rho*(vbar_pipeopt^2))/(25.8*d)
% Pump pressure, Pp
deltaPpopt = L*Tur_Pgrad_pipeopt
end
if NRe_annopt>=ReCopt
% If flow is turbulent, frictional pressure loss gradient of annulus
Tur_Pgrad_annopt=(f_annopt*rho*(vbar_annopt^2))/(21.1*(d2-d1))
end
% Optimum bit pressure loss
deltaPbopt=deltaPpopt-deltaPdopt
% Proper total nozzle area
Aeffopt=sqrt(8.311*(10^-5)*rho*(qopt^2)/((Cd^2)*deltaPbopt))
% Surge/Swab Pressure calculation starts from here
% surgecp = surge with closed pipe
% surgeop = surge with open pipe
% K for closed pipe is tuned to value:

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K_cp=1.527;
% Is the pipe is moving up or down?
% Down - 1
% Up - 2
direction=2;
vp=1/3; % Tripping speed (ft/s)
if direction==1
disp('Calculating surge pressure for closed pipe..')
% For closed pipe
q_surgecp=vp*pi*(d1^2)/4;
% Average velocity of pipe, vbar_pipe (ft/sec)
vbar_pipe_surgecp=0;
% Average velocity of annulus, vbar_ann (ft/sec)
vbar_ann_surgecp=q_surgecp/(2.448*((d2^2)-(d1^2)))+(K_cp*vp);
% Turbulence criteria of pipe, NRe_pipe
NRe_pipe_surgecp=(89100*rho*(vbar_pipe_surgecp^(2-n))/K)...
*((0.0416*d/(3+(1/n)))^n)
% Turbulence criteria of annulus, NRe_ann
NRe_ann_surgecp=(109000*rho*(vbar_ann_surgecp^(2-n))/K)*((0.0208*(d2-d1)...
/(2+(1/n)))^n)
% Define critical Reynold number, ReC
if n<=1 && n>=0.5
ReC_surgecp=2000;
else
if n<0.5 && n>=0.2
log_ReC_surgecp=((0.5-n)*(log10(2.1))/0.3)+log10(2000);
ReC_surgecp=10^(log_ReC_surgecp);
end
end
if NRe_pipe_surgecp<ReC_surgecp
% If flow is laminar, frictional pressure loss gradient of pipe
Lam_Pgrad_pipe_surgecp=K*(vbar_pipe_surgecp^n)*(((3+(1/n))/0.0416)^n)...
/(144000*(d^(1+n)));
% Pump pressure, Pp
deltaPp_surgecp = L*Lam_Pgrad_pipe_surgecp
end
if NRe_ann_surgecp<ReC_surgecp
% If flow is laminar, frictional pressure loss gradient of annulus
Lam_Pgrad_ann_surgecp=K*(vbar_ann_surgecp^n)*(((2+(1/n))/0.0208)^n)/...
(144000*((d2-d1)^(1+n)));
% Annular pressure, Pa
deltaPa_surgecp = L*Lam_Pgrad_ann_surgecp
end
% Calculation of friction factor of pipe, f_pipe
f_pipe_surgecp = fsolve(@(f_pipe_surgecp)(sqrt(1/f_pipe_surgecp))...
-((4/(n^0.75))*log10(NRe_pipe_surgecp*(f_pipe_surgecp^...
(1-(n/2)))))+(0.395/(n^1.2)),1);
% Calculation of friction factor of annulus, f_ann
f_ann_surgecp = fsolve(@(f_ann_surgecp)(sqrt(1/f_ann_surgecp))-((4/(n^0.75))*...
log10(NRe_ann_surgecp*(f_ann_surgecp^(1-(n/2)))))+(0.395/(n^1.2)),1);

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if NRe_pipe_surgecp>=ReC_surgecp
% If flow is turbulent, frictional pressure loss gradient of pipe
Tur_Pgrad_pipe_surgecp=(f_pipe_surgecp*rho*(vbar_pipe_surgecp^2))/(25.8*d);
% Pump pressure, Pp
deltaPp_surgecp = L*Tur_Pgrad_pipe_surgecp
end
if NRe_ann_surgecp>=ReC_surgecp
% If flow is turbulent, frictional pressure loss gradient of annulus
Tur_Pgrad_ann_surgecp=(f_ann_surgecp*rho*(vbar_ann_surgecp^2))/(21.1*(d2-d1));
% Annular pressure, Pa
deltaPa_surgecp = L*Tur_Pgrad_ann_surgecp
end
disp('Calculating Equivalent Mud Weight for closed pipe..')
rho_c=rho+(231/(12*deltaPa_surgecp))
disp('Calculating surge pressure for open pipe..')
% For open pipe
K_op=1.2;
for fa=0:0.01:1
qa_surgeop=fa*vp*((pi*(d1^2)/4)-Aeffopt);
qp_surgeop=(1-fa)*vp*((pi*(d1^2)/4)-Aeffopt);
% Average velocity of pipe, vbar_pipe (ft/sec)
vbar_pipe_surgeop=qp_surgeop/(2.448*(d^2))+(K_op*vp);
% Average velocity of annulus, vbar_ann (ft/sec)
vbar_ann_surgeop=qa_surgeop/(2.448*((d2^2)-(d1^2)))+(K_op*vp);
% Turbulence criteria of pipe, NRe_pipe
NRe_pipe_surgeop=(89100*rho*(vbar_pipe_surgeop^(2-n))/K)*...
((0.0416*d/(3+(1/n)))^n);
% Turbulence criteria of annulus, NRe_ann
NRe_ann_surgeop=(109000*rho*(vbar_ann_surgeop^(2-n))/K)*((0.0208*(d2-d1)...
/(2+(1/n)))^n);
% Define critical Reynold number, ReC
if n<=1 && n>=0.5
ReC_surgeop=2000;
else
if n<0.5 && n>=0.2
log_ReC_surgeop=((0.5-n)*(log10(2.1))/0.3)+log10(2000);
ReC_surgeop=10^(log_ReC_surgeop);
end
end
if NRe_pipe_surgeop<ReC_surgeop
% If flow is laminar, frictional pressure loss gradient of pipe
Lam_Pgrad_pipe_surgeop=K*(vbar_pipe_surgeop^n)*(((3+(1/n))/0.0416)^n)...
/(144000*(d^(1+n)));
% Pump pressure, Pp
deltaPp_surgeop = L*Lam_Pgrad_pipe_surgeop;
end
if NRe_ann_surgeop<ReC_surgeop
% If flow is laminar, frictional pressure loss gradient of annulus
Lam_Pgrad_ann_surgeop=K*(vbar_ann_surgeop^n)*(((2+(1/n))/0.0208)^n)/...

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(144000*((d2-d1)^(1+n)));
% Annular pressure, Pa
deltaPa_surgeop = L*Lam_Pgrad_ann_surgeop;
end
% Calculation of friction factor of pipe, f_pipe
f_pipe_surgeop = fsolve(@(f_pipe_surgeop)(sqrt(1/f_pipe_surgeop))-...
((4/(n^0.75))*log10(NRe_pipe_surgeop*(f_pipe_surgeop^...
(1-(n/2)))))+(0.395/(n^1.2)),1);
% Calculation of friction factor of annulus, f_ann
f_ann_surgeop = fsolve(@(f_ann_surgeop)(sqrt(1/f_ann_surgeop))...
-((4/(n^0.75))*log10(NRe_ann_surgeop*(f_ann_surgeop^(1-(n/2)))))...
+(0.395/(n^1.2)),1);
if NRe_pipe_surgeop>=ReC_surgeop
% If flow is turbulent, frictional pressure loss gradient of pipe
Tur_Pgrad_pipe_surgeop=(f_pipe_surgeop*rho*(vbar_pipe_surgeop^2))/(25.8*d);
% Pump pressure, Pp
deltaPp_surgeop = L*Tur_Pgrad_pipe_surgeop;
end
if NRe_ann_surgeop>=ReC_surgeop
% If flow is turbulent, frictional pressure loss gradient of annulus
Tur_Pgrad_ann_surgeop=(f_ann_surgeop*rho*(vbar_ann_surgeop^2))/(21.1*(d2-d1));
% Annular pressure, Pa
deltaPa_surgeop = L*Tur_Pgrad_ann_surgeop;
end
if deltaPa_surgeop - deltaPp_surgeop <1
fa_final=fa;
end
end
qa_surgeop=fa_final*vp*((pi*(d1^2)/4)-Aeffopt);
qp_surgeop=(1-fa_final)*vp*((pi*(d1^2)/4)-Aeffopt);
% Average velocity of pipe, vbar_pipe (ft/sec)
vbar_pipe_surgeop=qp_surgeop/(2.448*(d^2))+(K_op*vp);
% Average velocity of annulus, vbar_ann (ft/sec)
vbar_ann_surgeop=qa_surgeop/(2.448*((d2^2)-(d1^2)))+(K_op*vp);
% Turbulence criteria of pipe, NRe_pipe
NRe_pipe_surgeop=(89100*rho*(vbar_pipe_surgeop^(2-n))/K)*...
((0.0416*d/(3+(1/n)))^n);
% Turbulence criteria of annulus, NRe_ann
NRe_ann_surgeop=(109000*rho*(vbar_ann_surgeop^(2-n))/K)*((0.0208*(d2-d1)...
/(2+(1/n)))^n);
% Define critical Reynold number, ReC
if n<=1 && n>=0.5
ReC_surgeop=2000;
else
if n<0.5 && n>=0.2
log_ReC_surgeop=((0.5-n)*(log10(2.1))/0.3)+log10(2000);
ReC_surgeop=10^(log_ReC_surgeop);
end
end

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if NRe_pipe_surgeop<ReC_surgeop
% If flow is laminar, frictional pressure loss gradient of pipe
Lam_Pgrad_pipe_surgeop=K*(vbar_pipe_surgeop^n)*(((3+(1/n))/0.0416)^n)...
/(144000*(d^(1+n)));
% Pump pressure, Pp
deltaPp_surgeop = L*Lam_Pgrad_pipe_surgeop
end
if NRe_ann_surgeop<ReC_surgeop
% If flow is laminar, frictional pressure loss gradient of annulus
Lam_Pgrad_ann_surgeop=K*(vbar_ann_surgeop^n)*(((2+(1/n))/0.0208)^n)/...
(144000*((d2-d1)^(1+n)));
% Annular pressure, Pa
deltaPa_surgeop = L*Lam_Pgrad_ann_surgeop
end
% Calculation of friction factor of pipe, f_pipe
f_pipe_surgeop = fsolve(@(f_pipe_surgeop)(sqrt(1/f_pipe_surgeop))-...
((4/(n^0.75))*log10(NRe_pipe_surgeop*(f_pipe_surgeop^...
(1-(n/2)))))+(0.395/(n^1.2)),1);
% Calculation of friction factor of annulus, f_ann
f_ann_surgeop = fsolve(@(f_ann_surgeop)(sqrt(1/f_ann_surgeop))...
-((4/(n^0.75))*log10(NRe_ann_surgeop*(f_ann_surgeop^...
(1-(n/2)))))+(0.395/(n^1.2)),1);
if NRe_pipe_surgeop>=ReC_surgeop
% If flow is turbulent, frictional pressure loss gradient of pipe
Tur_Pgrad_pipe_surgeop=(f_pipe_surgeop*rho*(vbar_pipe_surgeop^2))/(25.8*d);
% Pump pressure, Pp
deltaPp_surgeop = L*Tur_Pgrad_pipe_surgeop
end
if NRe_ann_surgeop>=ReC_surgeop
% If flow is turbulent, frictional pressure loss gradient of annulus
Tur_Pgrad_ann_surgeop=(f_ann_surgeop*rho*(vbar_ann_surgeop^2))/(21.1*(d2-d1));
% Annular pressure, Pa
deltaPa_surgeop = L*Tur_Pgrad_ann_surgeop
end
disp('Calculating Equivalent Mud Weight for open pipe..')
rho_o=rho+(231/(12*deltaPa_surgeop))
end
if direction==2
disp('Calculating swab pressure for closed pipe..')
% For closed pipe
q_surgecp=vp*pi*(d1^2)/4;
% Average velocity of pipe, vbar_pipe (ft/sec)
vbar_pipe_surgecp=0;
% Average velocity of annulus, vbar_ann (ft/sec)
vbar_ann_surgecp=q_surgecp/(2.448*((d2^2)-(d1^2)))+(K_cp*vp);
% Turbulence criteria of pipe, NRe_pipe
NRe_pipe_surgecp=(89100*rho*(vbar_pipe_surgecp^(2-n))/K)*...

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((0.0416*d/(3+(1/n)))^n);
% Turbulence criteria of annulus, NRe_ann
NRe_ann_surgecp=(109000*rho*(vbar_ann_surgecp^(2-n))/K)*((0.0208*(d2-d1)...
/(2+(1/n)))^n);
% Define critical Reynold number, ReC
if n<=1 && n>=0.5
ReC_surgecp=2000;
else
if n<0.5 && n>=0.2
log_ReC_surgecp=((0.5-n)*(log10(2.1))/0.3)+log10(2000);
ReC_surgecp=10^(log_ReC_surgecp);
end
end
if NRe_pipe_surgecp<ReC_surgecp
% If flow is laminar, frictional pressure loss gradient of pipe
Lam_Pgrad_pipe_surgecp=K*(vbar_pipe_surgecp^n)*(((3+(1/n))/0.0416)^n)...
/(144000*(d^(1+n)));
% Pump pressure, Pp
deltaPp_surgecp = L*Lam_Pgrad_pipe_surgecp
end
if NRe_ann_surgecp<ReC_surgecp
% If flow is laminar, frictional pressure loss gradient of annulus
Lam_Pgrad_ann_surgecp=K*(vbar_ann_surgecp^n)*(((2+(1/n))/0.0208)^n)/...
(144000*((d2-d1)^(1+n)));
% Annular pressure, Pa
deltaPa_surgecp = L*Lam_Pgrad_ann_surgecp
end
% Calculation of friction factor of pipe, f_pipe
f_pipe_surgecp = fsolve(@(f_pipe_surgecp)(sqrt(1/f_pipe_surgecp))-...
((4/(n^0.75))*log10(NRe_pipe_surgecp*(f_pipe_surgecp^...
(1-(n/2)))))+(0.395/(n^1.2)),1);
% Calculation of friction factor of annulus, f_ann
f_ann_surgecp = fsolve(@(f_ann_surgecp)(sqrt(1/f_ann_surgecp))-((4/(n^0.75))*...
log10(NRe_ann_surgecp*(f_ann_surgecp^(1-(n/2)))))+(0.395/(n^1.2)),1);
if NRe_pipe_surgecp>=ReC_surgecp
% If flow is turbulent, frictional pressure loss gradient of pipe
Tur_Pgrad_pipe_surgecp=(f_pipe_surgecp*rho*(vbar_pipe_surgecp^2))/(25.8*d);
% Pump pressure, Pp
deltaPp_surgecp = L*Tur_Pgrad_pipe_surgecp
end
if NRe_ann_surgecp>=ReC_surgecp
% If flow is turbulent, frictional pressure loss gradient of annulus
Tur_Pgrad_ann_surgecp=(f_ann_surgecp*rho*(vbar_ann_surgecp^2))...
/(21.1*(d2-d1));
% Annular pressure, Pa
deltaPa_surgecp = L*Tur_Pgrad_ann_surgecp
end
disp('Calculating Equivalent Mud Weight for closed pipe..')
rho_c=rho-(231/(12*deltaPa_surgecp))
disp('Calculating swab pressure for open pipe..')
% For open pipe
K_op1=1.2;
K_op2=1.2;
for fa=0:0.01:1

11. 7/3/12 2:53 PM C:UserskukrejankitDesktopCoursestribologys...code2.m 11 of 13
qa_surgeop=fa*vp*((pi*(d1^2)/4)-Aeffopt);
qp_surgeop=(1-fa)*vp*((pi*(d1^2)/4)-Aeffopt);
% Average velocity of pipe, vbar_pipe (ft/sec)
vbar_pipe_surgeop=qp_surgeop/(2.448*(d^2))+(K_op1*vp);
% Average velocity of annulus, vbar_ann (ft/sec)
vbar_ann_surgeop=qa_surgeop/(2.448*((d2^2)-(d1^2)))+(K_op2*vp);
% Turbulence criteria of pipe, NRe_pipe
NRe_pipe_surgeop=(89100*rho*(vbar_pipe_surgeop^(2-n))/K)*((0.0416*d...
/(3+(1/n)))^n);
% Turbulence criteria of annulus, NRe_ann
NRe_ann_surgeop=(109000*rho*(vbar_ann_surgeop^(2-n))/K)*((0.0208*(d2-d1)...
/(2+(1/n)))^n);
% Define critical Reynold number, ReC
if n<=1 && n>=0.5
ReC_surgeop=2000;
else
if n<0.5 && n>=0.2
log_ReC_surgeop=((0.5-n)*(log10(2.1))/0.3)+log10(2000);
ReC_surgeop=10^(log_ReC_surgeop);
end
end
if NRe_pipe_surgeop<ReC_surgeop
% If flow is laminar, frictional pressure loss gradient of pipe
Lam_Pgrad_pipe_surgeop=K*(vbar_pipe_surgeop^n)*(((3+(1/n))/0.0416)^n)...
/(144000*(d^(1+n)));
% Pump pressure, Pp
deltaPp_surgeop = L*Lam_Pgrad_pipe_surgeop;
end
if NRe_ann_surgeop<ReC_surgeop
% If flow is laminar, frictional pressure loss gradient of annulus
Lam_Pgrad_ann_surgeop=K*(vbar_ann_surgeop^n)*(((2+(1/n))/0.0208)^n)/...
(144000*((d2-d1)^(1+n)));
% Annular pressure, Pa
deltaPa_surgeop = L*Lam_Pgrad_ann_surgeop;
end
% Calculation of friction factor of pipe, f_pipe
f_pipe_surgeop = fsolve(@(f_pipe_surgeop)(sqrt(1/f_pipe_surgeop))-...
((4/(n^0.75))*log10(NRe_pipe_surgeop*(f_pipe_surgeop^...
(1-(n/2)))))+(0.395/(n^1.2)),1);
% Calculation of friction factor of annulus, f_ann
f_ann_surgeop = fsolve(@(f_ann_surgeop)(sqrt(1/f_ann_surgeop))-...
((4/(n^0.75))*log10(NRe_ann_surgeop*(f_ann_surgeop^...
(1-(n/2)))))+(0.395/(n^1.2)),1);
if NRe_pipe_surgeop>=ReC_surgeop
% If flow is turbulent, frictional pressure loss gradient of pipe
Tur_Pgrad_pipe_surgeop=(f_pipe_surgeop*rho*(vbar_pipe_surgeop^2))/(25.8*d);
% Pump pressure, Pp
deltaPp_surgeop = L*Tur_Pgrad_pipe_surgeop;
end
if NRe_ann_surgeop>=ReC_surgeop

12. 7/3/12 2:53 PM C:UserskukrejankitDesktopCoursestribologys...code2.m 12 of 13
% If flow is turbulent, frictional pressure loss gradient of annulus
Tur_Pgrad_ann_surgeop=(f_ann_surgeop*rho*(vbar_ann_surgeop^2))/(21.1*(d2-d1));
% Annular pressure, Pa
deltaPa_surgeop = L*Tur_Pgrad_ann_surgeop;
end
if deltaPa_surgeop - deltaPp_surgeop <1
fa_final=fa;
end
end
qa_surgeop=fa_final*vp*((pi*(d1^2)/4)-Aeffopt);
qp_surgeop=(1-fa_final)*vp*((pi*(d1^2)/4)-Aeffopt);
% Average velocity of pipe, vbar_pipe (ft/sec)
vbar_pipe_surgeop=qp_surgeop/(2.448*(d^2))+(K_op1*vp);
% Average velocity of annulus, vbar_ann (ft/sec)
vbar_ann_surgeop=qa_surgeop/(2.448*((d2^2)-(d1^2)))+(K_op2*vp);
% Turbulence criteria of pipe, NRe_pipe
NRe_pipe_surgeop=(89100*rho*(vbar_pipe_surgeop^(2-n))/K)*((0.0416*d/...
(3+(1/n)))^n);
% Turbulence criteria of annulus, NRe_ann
NRe_ann_surgeop=(109000*rho*(vbar_ann_surgeop^(2-n))/K)*((0.0208*(d2-d1)...
/(2+(1/n)))^n);
% Define critical Reynold number, ReC
if n<=1 && n>=0.5
ReC_surgeop=2000;
else
if n<0.5 && n>=0.2
log_ReC_surgeop=((0.5-n)*(log10(2.1))/0.3)+log10(2000);
ReC_surgeop=10^(log_ReC_surgeop);
end
end
if NRe_pipe_surgeop<ReC_surgeop
% If flow is laminar, frictional pressure loss gradient of pipe
Lam_Pgrad_pipe_surgeop=K*(vbar_pipe_surgeop^n)*(((3+(1/n))/0.0416)^n)...
/(144000*(d^(1+n)));
% Pump pressure, Pp
deltaPp_surgeop = L*Lam_Pgrad_pipe_surgeop
end
if NRe_ann_surgeop<ReC_surgeop
% If flow is laminar, frictional pressure loss gradient of annulus
Lam_Pgrad_ann_surgeop=K*(vbar_ann_surgeop^n)*(((2+(1/n))/0.0208)^n)/...
(144000*((d2-d1)^(1+n)));
% Annular pressure, Pa
deltaPa_surgeop = L*Lam_Pgrad_ann_surgeop
end
% Calculation of friction factor of pipe, f_pipe
f_pipe_surgeop = fsolve(@(f_pipe_surgeop)(sqrt(1/f_pipe_surgeop))-...
((4/(n^0.75))*log10(NRe_pipe_surgeop*(f_pipe_surgeop^(1-(n/2)))))...
+(0.395/(n^1.2)),1);
% Calculation of friction factor of annulus, f_ann
f_ann_surgeop = fsolve(@(f_ann_surgeop)(sqrt(1/f_ann_surgeop))-...
((4/(n^0.75))*log10(NRe_ann_surgeop*(f_ann_surgeop^(1-(n/2)))))...
+(0.395/(n^1.2)),1);

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if NRe_pipe_surgeop>=ReC_surgeop
% If flow is turbulent, frictional pressure loss gradient of pipe
Tur_Pgrad_pipe_surgeop=(f_pipe_surgeop*rho*(vbar_pipe_surgeop^2))/(25.8*d);
% Pump pressure, Pp
deltaPp_surgeop = L*Tur_Pgrad_pipe_surgeop
end
if NRe_ann_surgeop>=ReC_surgeop
% If flow is turbulent, frictional pressure loss gradient of annulus
Tur_Pgrad_ann_surgeop=(f_ann_surgeop*rho*(vbar_ann_surgeop^2))/(21.1*(d2-d1));
% Annular pressure, Pa
deltaPa_surgeop = L*Tur_Pgrad_ann_surgeop
end
disp('Calculating Equivalent Mud Weight for open pipe..')
rho_o=rho-(231/(12*deltaPa_surgeop))
end
% End of code