PCB 2044: WELL LOGGING AND FORMATION EVALUATION 2014; ASSIGNMENT: SONIC POROSITY< MANGAR MAWUT MABENY MAWUT (PE-18582)ANSWERS1. t: known as interval transit time or slowness time is the time required for a sound wave to traverse 1 feet of formation, it is the reciprocal of the velocity of the sound wave. Depends on Litho logy Porosity2. tf: Is the transit time of the saturating fluid or simply fluid travel time. Its value is about 189 microseconds per feet (189s/ft).3. tma: Is the transit time of the matrix material4. If the formation has gas, t read too high values. This is because gas transmit sound at lower velocities (high transit times) than water. It would also be slowed down.5. Compensating porosity for gas: Since the time averaged derived porosity is too high, it is compensated by multiplying the time averaged derived porosity by 0.7 in gas bearing formation6. Compensating for oil formations: this can be done by multiplying the time averaged-derived porosity by 0.9 in oil bearing formations7. To decide if the formation is compacted, a value of 100 s in nearby shale is used.8. The compaction correction factor= 100/ tsh 9. From the figure, given sandstone matrix with the correction factor in a nearby shale as 110 s/ tsh ,

tf = 189s/ft , t = 97.5 s/ft, tma = 57 (sandstone)

97.5 57 189 - 57100110= t - tma 100

= 0.279 x 100 = 27.9 % Awns. = tf - tma tsh SONIC LOGPage 1