Answers

A useful and clear way of working out the lag is to draw a diagram of the well showing the different hole sizes and drill string dimensions. On this diagram the length and the depth of each section are indicated.

i)Volume of mud in the string:

a) Drillpipe: (4.276^2/1029)x 8075 = 143.5 bbls

b) Heavy-Weight: (3^2/1029) x 275 = 2.4 bbls

c) Drill collars: (2.813^2/ 1029) x 650 = 5

a+b+c = 150.9 bbls

ii)Annular section volumes:

a) Casing – Drillpipe: ((12.145^2 - 5^2)/1029) x 3500 =439.2 bbls

b) Open hole – Drillpipe: ((12.25^2 - 5^2)/ 1029)x4575= 556.0 bbls

c) Open hole - Heavy Weight: ((12.25^2 - 5^2)/ 1029) x 275= 33.4 bbls

d) Open hole - Drill collars: ((12.25^2 - 8^2)/ 1029)x 650 = 54.4 bbls

a+b+c+d = 1083.0 bbls

iii)Lag in strokes

1083.0/.123=8805 strokes

iv) Lang. in minutes

8805 /75= 117.4 min

Trip Monitoring

Trip monitoring is considered one of the most important of the duties and responsibilities of the mud logger. The mud logger should not feel relaxed during trip times as statistics indicate that the most of the serious well problems and disasters have happened while tripping.

1. TRIP-IN MONITORING PROCEDURES

1. Calculate metal displacement for each string section.

2. Check which tank should receive the displaced mud.

3. If displaced mud will return to active pit, check if the surface tanks (sand trap) are filled:-

3.a. If they are filled:

Mud should return to active pit once tripping-in starts.

3.b. If they are not filled:

Mud can not be monitored in the active pit until surface tanks get filled. Therefore you must either:-

- Inform driller and Co. Man that they should fill the surface pits prior to tripping-in; . . .OR Start the monitoring once the surface tanks gets filled and the displaced mud starts returning to active pit. In this case, estimate how many bbls would be required to fill surface tanks and how many stands should run-in to displace this required volume.

Note that surface tanks are monitored manually.

4. When displaced mud returns directly to the active system, one of the following PVT monitoring trends would be expected:

PVT	TREND	INTERPRETATION	ACTION
Steady		Mud losses due to surge action	Inform driller and Co. Man.
	Increase is equal to the metal displacement	Everything is OK	No action.
Showing	Increase is less than the metal displacement	Partial mud loss	Inform driller and Co. Man.
increase	Increase is more than	1. Well flowing	Inform driller and Co. Man.
	the metal displacement	2. Jet plugging (pipe is not filled completely)	Ask driller to fill the pipe.

What would a trip schedule tell you when running pipe in the hole:

By monitorng the trip schedule while RIH, the mud displacement will schedule will dictate if hole is standing up with the added pressure (surge caused by lowering pipe)

Stands (94 ft.)	Displacement (BBL)		Time	Measured Trend Differences (BBL)
PIH	Calculated (Cum.)	Actual (Cum.)	0600	Calcu-lated	Actual	Trend Change
1 - 4 DC	13.2	13.0	0620	13.2	13	-0.2
5 - 8	26.4	26.0	0640	13.2	13	-0.2
9 - 11	36.3	35.5	0700	9.9	9.5	-0.4
1 1 - 20	43.0	41.8	0720	6.7	6.3	-0.4
2 1 - 30	49.7	47.8	0740	6.7	6.0	-0.7
31 - 40	56.4	52.8	0700	6.7	5.0	- 1.7
41 - 50	63.1	52.8	0720	6.7	4.0	- 2.7

If a logger looks at only volume (actual vs. calculated), everything might look good after POH with 90 stands. However, the trends tell a completely different story. After pulling 40-50 stands, the logger should become suspicious of the changing trends. The well actually started coming in between 40 and 60 stands. An alert logger should closely observe the well and should have the driller returned to bottom to condition the hole. Many blowouts occur during trips because a trip schedule is not made out or is not monitored in such a way to establish trends. Trying to kill a well off bottom leads to many associated well control problems, e.g. lost circulation, differential sticking, hole bridging... etc. Side tracking and hole problems associated with unscheduled deviated holes is normally the end result.