Neutron logging method for quantitative wellbore fluid analysis

A method of quantifying gaseous fluid flow relative to liquid fluid flow in a portion of a wellbore having fluid flow layered according to density, said method comprising:

• (a) obtaining calibration data which relates volume fraction of pipe occupied by a liquid to a normalized neutron log count rate;
• (b) shutting in said wellbore;
• (c) measuring a neutron log count rate for gaseous fluid (M.sub.gas) in said portion of said wellbore with a neutron logging tool;
• (d) measuring a neutron log count rate for liquid fluid (M.sub.liquid) in said portion of said wellbore with said neutron logging tool;
• (e) establishing fluid flow in said wellbore;
• (f) measuring a neutron log count rate for flowing fluids (M.sub.mix) over a logging interval of interest in said portion of said wellbore;
• (g) determining a neutron log count rate ratio equal to (M.sub.gas -M.sub.mix)/(M.sub.gas - M.sub.liquid);
• and
• (h) comparing said neutron log count rate ratio to said calibration data to quantify said gaseous fluid flow relative to said liquid fluid flow in said logging interval of interest.

A method of identifying a suitable location for performing a shut-off workover in a portion of a wellbore having fluid flow layered according to density, said method comprising:

• (a) obtaining calibration data which relates volume fraction of pipe occupied by a liquid to a normalized neutron log count rate;
• (b) while said wellbore is shut in, measuring a neutron log count rate for gaseous fluid (M.sub.gas) in said portion of said wellbore;
• (c) while said wellbore is shut in, measuring a neutron log count rate for liquid fluid (M.sub.liquid) in said portion of said wellbore;
• (d) while fluids are flowing in said wellbore, measuring a neutron log count rate for flowing fluids (M.sub.mix) over a logging interval in said portion of said wellbore;
• (e) determining a neutron log count rate ratio equal to (M.sub.gas -M.sub.mix)/(M.sub.gas -M.sub.liquid);
• (f) comparing the neutron log count rate ratio to said calibration data to obtain quantification data representative of said gaseous fluid flow relative to said liquid fluid flow in said logging interval;
• and
• (g) repeating steps (d) through (f) as necessary until said quantification data indicates that said logging interval is a suitable location for performing a shut-off workover.