Apparatus and method for combined acoustic and seismoelectric logging measurements

A method of well logging, comprising:

• inserting a well logging instrument into a wellbore penetrating earth formations, said instrument including an acoustic energy source and at least one acoustic receiver axially spaced apart from said source, said instrument including electrodes at axially spaced apart locations from said source;
• activating said source to impart acoustic energy pulses into said wellbore and said earth formations;
• detecting acoustic energy at said at least one receiver and measuring a magnitude thereof;
• measuring voltages at said electrodes;
• calculating synthetic seismoelectric voltages from said measurements of said magnitude of said acoustic energy using an initial value of porosity of said earth formations;
• determining a difference between said synthetic seismoelectric voltages and said measurements of said voltages;
• and
• adjusting said initial value of said porosity, and repeating said steps of calculating said synthetic seismoelectric voltages, determining said difference and adjusting said value of porosity until said difference reaches a minimum.

A method for estimating electrical conductivity of fluid in pore spaces of an earth formation from measurements of acoustic energy traversing said formation and from measurements of seismoelectric voltages generated in said formation in response to said acoustic energy, the method comprising:

• calculating synthetic seismoelectric voltages from said measurements of said acoustic energy using an initial value of said conductivity;
• determining a difference between said synthetic seismoelectric voltages and said measurements of said seismoelectric voltages;
• and
• adjusting said initial value of said conductivity, and repeating said steps of calculating said synthetic seismoelectric voltages, determining said difference and adjusting said value of conductivity until said difference reaches a minimum.