6.8 a. Develop an equation for the normal pressure trend line for the interval transit time data of Table 6.4 assuming a straight-line representation on semilogarith- mic graph paper. Answer: n = 161e - 0.000043D b. Compare results with plots obtained in Exercise 6.7. c. Compute the porosity of a normally pressured shale at 28,000 ft using the straight-line interval transit time extrapolation. Answer: negative o is predicted. For reference 6.7 Graph the function developed in Example 6.5 between average interval transit time and a depth for nor- mally pressured U.S. gulf coast sediments. Use a depth interval of 0 to 30,000 ft and (a) semilogarithmic graph paper (depth on linear scale) and (b) logarithmic graph paper. w.ww pony. Uz = YOU 6.5 A tilted gas sand encountered at 4,500 ft is known to have a pore pressure of 2,700 psig. A well is to be drilled near the top of the structure, which is expected to penetrate the sand at 3,500 ft. The gas is known to have a density of 10 bm/gal at reservoir conditions. Compare the mud density required to drill the second well safely with that of the first. Answer: p2=14.5+ lbm/gal; p=11.5+ lbm/gal. TABLE 6.4-AVERAGE INTERVAL TRANSIT TIME DATA COMPUTED FROM SEISMIC RECORDS OBTAINED IN NORMALLY PRESSURED SEDIMENTS IN UPPER MIOCENE TREND OF GULF COAST AREA Depth Interval (ft) 1,500 to 2,500 2,500 to 3,500 3,500 to 4,500 4,500 to 5,500 5,500 to 6,500 6,500 to 7,500 7,500 to 8,500 8,500 to 9,500 9,500 to 10,500 10,500 to 11,500 11,500 to 12,500 12,500 to 13,500 Average Interval Transit Time (10-6 s/ft) 153 140 132 126 118 120 112 106 102 103 93 96