<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;"><DIV>Dear Manooch,</DIV>
<DIV> </DIV>
<DIV>Thank you very much for your help!!!</DIV>
<DIV> </DIV>
<DIV>I agree with you that for the first boundary conditions, the total radial stress should be equal to the pressure from the drilling mud. This can be easily done in the ABAQUS by impose a surface load equal to the mud weight pressure.<BR></DIV>
<DIV>As for the second boundary conditions (which actually I think should be correct for the fluid injection or borehole fracturing problem), you suggest to <FONT color=#0000ff>"impose appropriate flux rate depends on the type of your prolem, for considering effective stress zero on the borehole wall </FONT><FONT face=Arial><FONT color=#0000ff><FONT size=2>please assin<SPAN class=081044509-15012009>g</SPAN> <SPAN class=081044509-15012009>a </SPAN>surface load through Dload<SPAN class=081044509-15012009> as equal as pore pressure on the surface of the borehole then the effective pressure on the surface of borehole is zero". <FONT color=#000000>The problem is, however, how could we assign a surface load equal to the pore pressure on the borehole surface? Because the pore pressure is induced by the fluid injection and itself is unknown to be determined. This means that the pore pressure and the total
stress are coupled with each other.</FONT></SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT color=#000000 size=2><SPAN class=081044509-15012009></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT color=#000000 size=2><SPAN class=081044509-15012009>What do you think about this point? Thanks again.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT color=#000000 size=2><SPAN class=081044509-15012009></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT color=#000000 size=2><SPAN class=081044509-15012009>Best regards.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT color=#000000 size=2><SPAN class=081044509-15012009>Shengli Chen</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT color=#000000 size=2><SPAN class=081044509-15012009></SPAN></FONT></FONT></FONT> </DIV>
<DIV><BR>--- On <B>Thu, 1/15/09, Manooch Salehabadi <I><Manooch.Salehabadi@pet.hw.ac.uk></I></B> wrote:<BR></DIV>
<BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: rgb(16,16,255) 2px solid">From: Manooch Salehabadi <Manooch.Salehabadi@pet.hw.ac.uk><BR>Subject: RE: [Geoqus] borehole injection boundary conditions<BR>To: shengli_chen@yahoo.com, "Geoscientific Abaqus User Group" <geoqus@lists.ruhr-uni-bochum.de><BR>Cc: shengli.chen@yahoo.com<BR>Date: Thursday, January 15, 2009, 3:57 AM<BR><BR>
<DIV id=yiv599599191>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN class=081044509-15012009>Hi Shengli,</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN class=081044509-15012009></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN class=081044509-15012009>as you know on the surface of bore hole shear stress is zero, about your first boundary condition "<FONT color=#000000>total radial stress sigma_rr = 0, shear stress sigma_rz = 0, and flux rate q = q0" </FONT><FONT color=#0000ff>, please impose a surface load for example with Dload on the surface of borehole which normally comes from the pressure of drilling mud or injection fluid so the Sigmar=0 then asign surface flux rate or node flux rate depends on your problem,</FONT></SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN class=081044509-15012009><FONT color=#0000ff> and when it comes to your second boundary condition "<FONT color=#000000>total radial stress segma_rr = pore pressure p (which indicates zero Terzaghi effective stress), shear stress sigma_rz = 0, and flux rate q = q0" </FONT></FONT><FONT color=#0000ff>again here</FONT></SPAN></FONT></DIV>
<DIV><SPAN class=081044509-15012009></SPAN><FONT face=Arial><FONT color=#0000ff><FONT size=2>impose appropriate flux rate depends on the type of your problem, for considering effective stress zero on the borehole wall please assin<SPAN class=081044509-15012009>g</SPAN> <SPAN class=081044509-15012009>a </SPAN>surface load through Dload<SPAN class=081044509-15012009> as equal as pore pressure on the surface of the borehole then the effective pressure on the surface of borehole is zero.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN class=081044509-15012009></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN class=081044509-15012009>I hope that it helps</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN class=081044509-15012009></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN class=081044509-15012009>Regards</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN class=081044509-15012009></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN class=081044509-15012009>Manooch </SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN class=081044509-15012009></SPAN></FONT></FONT></FONT><BR> </DIV>
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<FONT face=Tahoma size=2><B>From:</B> geoqus-bounces+manooch.salehabadi=pet.hw.ac.uk@lists.ruhr-uni-bochum.de [mailto:geoqus-bounces+manooch.salehabadi=pet.hw.ac.uk@lists.ruhr-uni-bochum.de] <B>On Behalf Of </B>shengli chen<BR><B>Sent:</B> 12 January 2009 21:41<BR><B>To:</B> geoqus@lists.ruhr-uni-bochum.de<BR><B>Cc:</B> shengli.chen@yahoo.com<BR><B>Subject:</B> [Geoqus] borehole injection boundary conditions<BR></FONT><BR></DIV>
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<DIV dir=ltr><FONT face=tahoma size=2>Dear Geoqus members,</FONT></DIV>
<DIV dir=ltr><FONT face=tahoma size=2></FONT> </DIV>
<DIV dir=ltr><FONT face=tahoma size=2>I am working on the borehole prolem but recently got stuck with the specification of the boundary conditions. Consider a borehole subjected at its surface r = R (R is the borehole radius) to a uniform fluid injection rate q0, What should be the boundary condition at the borehole wall r = R looks like? (1) total radial stress sigma_rr = 0, shear stress sigma_rz = 0, and flux rate q = q0; or (2) total radial stress segma_rr = pore pressure p (which indicates zero Terzaghi effective stress), shear stress sigma_rz = 0, and flux rate q = q0???</FONT></DIV>
<DIV dir=ltr><FONT face=tahoma size=2></FONT> </DIV>
<DIV dir=ltr><FONT face=tahoma size=2>If (1) is correct then we can easily impose q = q0 in the Abaqus and just do nothing with the sigma_rr = sigma_rz = 0. However, I think the boundary condtions (2) is more reasonable as the injection of fluid will be accompanied by an induced pore pressure thus the total radial stress segma_rr should be equal to the pore pressure p. If so, how can we assign at the borehole surface sigma_rr = p (both sigma_rr and p are unknown) or Terzaghi effective stress equal to zero in additon to q = q0??? In my understanding, the applied surface stress in ABAQUS should have a meaning of total stress for porous medium.</FONT></DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>Thanks in advance for any advice!!!</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>Shengli</DIV></FONT></DIV></TD></TR></TBODY></TABLE><BR></DIV></BLOCKQUOTE></td></tr></table><br>