2. 3 Causes of Kicks and Influxes 6
2. 4 Extracts From API RP59 15
2. 5 Workshop 2 22
2.0 OBJECTIVES
The objectives of this section are to Highlight the Causes of Kicks and Influxes.
2.1 INTRODUCTION
Primary control is defined as using the drilling fluid to control formation fluid pressure. The drilling fluid has to have a density that will provide sufficient pressure to overbalance pore pressure. If this overbalance is lost, even temporarily then formation fluids can enter the wellbore. Preventing the loss of primary
control is of the utmost importance.
Definition of Kick
A kick is an intrusion of unwanted fluids into the wellbore such that the effective hydrostatic pressure of the wellbore fluid is exceeded by the formation pressure.
Definition of Influx
An influx is an intrusion of formation fluids into the wellbore which does not immediately cause formation pressure to exceed the hydrostatic pressure of the fluid in the wellbore, but may do, if not immediately recognised as an influx, particularly if the formation fluid is gas.
2.2 PRIMARY WELL CONTROL - HOW IT IS EFFECTED
To ensure primary well control is in place the following procedures and precautions must be observed.
Mud Weight
Mud into and out of the well must be weighted to ensure the correct weight is being maintained to control the well. This task is normally carried out by the shaker man at least every thirty minutes or less, depending upon the nature of the drilling operation and/or company policy. The mud weight can be increased by increasing the solid content and decreased either by dilution or the use of solids control equipment.
Tripping Procedures
Tripping in or out of the well must be maintained using an accurate log called a trip sheet. A trip sheet is used to record the volume of mud put into the well or displaced from the well when tripping.
A calibrated trip tank is normally used for the accurate measurement of mud volumes and changes to mud volumes while tripping.
Figure 2.1
Number of Stands
DISPLACEMENT
Per ___ Std. Total
Theoretical Last Trip This Trip Comments
Per ___ Std. Total Per ___ Std. Total
Well Name Date Depth
Time Trip Started
Mud Weight D.P. Size D.C. Size
Trip No.
Fluid Loss
D.P. Displacement D.C. Displacement
When tripping pipe or drill collars out of the hole, a given volume of mud is put into the well for the volume of steel removed. If the volume required to fill the hole is significantly less than the volume of steel removed, then tripping must be stopped to ensure the well is stable, and consideration given to going back to bottom to condition the mud and investigate the cause of the problem.
THE HOLE MUST BE KEPT FULL AT ALL TIMES
A full opening or safety valve should be available at all times on the drill floor together with the required crossover subs. A non-return (i.e. grey) valve should also be readily available.
Figure 2.3 Figure 2.2
Trip Margin (Safety Factor)
Trip Margin (Safety Factor) is an overbalance to compensate for the loss of ECD and to overcome the effects of swab pressures during a trip out of the hole.
Upper Seat
Ball
Lower Seat Crank
Body
FULL BORE OPENING SAFETY VALVE
NON RETURN SAFETY VALVE (GREY VALVE)
RELEASE TOOL
VALVE SEAT VALVE
RELEASE ROD
VALVE SPRING
Flow Checks
Flow checks are performed to ensure that the well is stable. Flow checks should be carried out with the pumps off to check the well with ECD effects removed. Flow checks are usually performed when a trip is going to take place at the following minimum places:
• on bottom
• at the casing shoe
• before the BHA is pulled into the BOP's Short Trips/Wiper Trips
In some circumstances prior to pulling out of the hole a short trip, 5 or 10 stands should be considered. The well is then circulated and mud returns carefully monitored.
Pumping a Slug of Heavy Mud
This is a practice often carried out to enable the pipe to be pulled dry and the hole to be more accurately monitored during the trip. The following equation is used to calculate the dry pipe volume for the slug pumped:
Dry Pipe Volume = Slug Volume x (Slug Weight ÷ Mud Weight - 1)
This dry pipe volume can be converted to Dry Pipe Length by dividing this
volume by the internal capacity of the pipe as illustrated in the following equation:
Dry Pipe Length = Dry Pipe Volume (bbls) ÷ Drill Pipe Capacity (bbls/ft) Mud Logging
A logging unit if available is extremely important particularly with respect to well control. The unit carries out some of the following services:
• Gas detection in the mud
• Gas analysis
• Cuttings density analysis
• Recording mud densities in and out
• Recording flow line temperatures
• Recording penetration rates
A typical mud logging system is illustrated in Figure 2.4 below.
KELLY POSITION ROP WOB DEPTH
STANDPIPE PRESSURE
PUMP RATE
PIT LEVELS
STAND PIPE
KELLY HOSE
SWIVEL
KELLY PUMP
SUCTION SUCTION PIT
FLOWLINE SHAKER
SHALE SLIDE
GAS QUANTITY GAS TYPE MUD TEMPERATURE RETURN MUD WEIGHT
• ROTARY SPEED
• TORQUE
VDU IN COMPANY REP'S OFFICE MUD LOGGINGUNIT
PROCESSING ANDEVALUA TION
CUTTINGS DENSITY