STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

MWD and LWD 971
Hydrostatic pressure: 6,240 psi
P inside DC: 7,032 psi
P standpipe: 2,382 psi
2. Total DP in pipe (friction plus leak): 1,436 psi
Pressure drop in DC due to leak 332 psi
New AP across nozzles: 386 psi
Q through nozzles: 366.5 gal/min
Q through drillpipes below leak: 366.5 gal/min
Q through leak: 133.5 gal/min
If leak at 3000 ft:
Pipe AP above leak: 477 psi
Pipe AP below leak: 646.5 psi
AP across leak: 312.5 psi
Leak cross-section: 0.24 in.2
If leak at 5000 ft:
Pipe AP above leak: 745 psi
Pipe AP below leak: 462 psi
AP across leak: 229 psi
Leak cross-section: 0.28 in.'
If leak at 7,000 ft:
Pipe AP above leak: 1,272 psi
Pipe AP below leak: 277 psi
Sum is more than total AP
The leak must be above 7,000 ft
LWD Technology
Logging while drilling has been attempted as early as 1939. The first commercial
logs were run in the early 1980s. First gamma ray logs were recorded
downhole and transmitted to the surface by mud pulses. Then came the resistivity
logs of various types that were also recorded downhole and/or transmitted
to the surface, Now, neutron-density and Pe logs are also available. Soon, sonic
logs will be offered commercially.
Gamma Ray Logs
Gamma rays of various energy are emitted by potassium-40, thorium, uranium,
and the daughter products of these two last elements contained in the earth
formations surrounding the borehole. These elements occur primarily in shales.
The gamma rays reaching the borehole form a spectrum typical of each formation
extending from a few keV to several MeV.
The gamma rays are detected today with sodium iodide crystals scintillation
counters. The counters, 6 to 12 in. long (15 to 30 cm) are shock mounted and
housed in the drill collars. Several types of measurements can be made: total
gamma rays, direction-focused gamma rays, spectral gamma rays.
Total Gamma Rays. Total gamma ray logs have been run on electric wireline
since 1940. The sondes are rather small in diameter (1.5 to 4 in. or 37 to 100 mm).