Monthly Archives: March 2010

What are gas show, connection gas and trip gas?

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You may have heard about gas show, connection gas and trip gas. What are differences of those term?

Gas show: It is gas that appears in drilling mud and it indicates the presence of gas zones or soluble gas in oil.

Connection gas: It is relatively small amount of gas that enters well when mud pump is stopped because ECD (equivalent circulating density) decreases when stop pumping. Connection gas indicates that mud weight in hole is less than formation pressure.

The difference of gas show and connection gas:If there is connection gas, gas shown in a mud logger screen increases and decreases sharply like small gas peak; however, gas show demonstrates the smoother curve than connection gas. Lag stroke, lag time are used to  find where the location of connection gas or gas show comes from. Especially, when the connection gas presents, lag time of gas peak will be relative to the time when pumps are off.

Trip gas: It is gas entering to well bore when tripping out of hole. There are several factors as balled-up bit,  fast pulling out rate, bigger diameter BHA, etc can create swab effect that can reduce hydrostatic pressure while tripping out of hole. If too much reduction in hydrostatic pressure is present, formation gas can influx into the well bore, called “Trip gas”.

Reference book: Well Control Books

Positive Kick (Wellbore Influx) Indications

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Positive kick (wellbore influx) indications mean signs showing almost 100% kick (wellbore influx) into wellbore.

wellbore influx

Positive Kick Indicators While Drilling

1. Increase in flow show

Without any increasing in flow rate in, increase in return flow indicates something coming into wellbore while drilling. Therefore, flow show instrument provided by the rigs or service companies must be checked and calibrated frequently.

2. Increase of active pit system (Pit gain)

Because drilling fluid system on the rig is a closed system, increasing in flow show without adjusting flow rate in will cause pit gain in a pit system. Nowadays, with high technology sensors, detecting change in pit level is easily accomplished at the rig site. However, visually check the pit level is importance as well for double checking figure from the sensors. Sometimes, change in pit level may be detected after the increase in flow show because it takes more time to accumulate volume enough to be able to detect by pit sensors.

3. Continue flowing while the pumps are off

When pumps are turned off, bottom hole pressure will decrease due to loss of equivalent circulating density (ECD). If there is any flow coming after pumps off, it indicates formation influx into wellbore.

Positive Kick Indicators While Tripping

There are 2 positive kick indicators while tripping as listed below;

1. Trip log deviation such as short fill up while tripping out and excess pit gain while tripping in

For tripping operation, it is very important to have a filling system via trip tank that provides continuous hole fill all time. With utilizing that system, we can compare fluid that is filled in or returned from wellbore with steel volume of tubular (drill pipe, drill collar, BHA, tubing, casing, etc). If drilling fluid volume is less than theoretical pipe displacement while tripping out or more return fluid while running in, you need to flow check and monitor the well.

  • If flow check indicates wellbore influx, crew must quickly shut the well in.
  • If flow check does not show any influx, drill string must be run back to bottom in order to circulate at least bottom up to ensure hole condition.

2. Positive flow when pipe is static

Every time that pipe in static condition. Trip tank with correct filling system must be monitored all time by both rig personnel and mud logger. If volume in trip tank increases, personnel must confirm flow check and prepare to shut the well in.

References

Coleman, S. (2018). Well Control Quiz Online. [online] Well Control Quiz Online – Test Your Well Control Knowledge for Free. Available at: http://wellcontrolquiz.com/ [Accessed 2 Aug. 2018].

Cormack, D. (2007). An introduction to well control calculations for drilling operations. 1st ed. Texas: Springer.

Crumpton, H. (2010). Well Control for Completions and Interventions. 1st ed. Texas: Gulf Publishing.

Grace, R. (2003). Blowout and well control handbook [recurso electrónico]. 1st ed. Paises Bajos: Gulf Professional Pub.

Grace, R. and Cudd, B. (1994). Advanced blowout & well control. 1st ed. Houston: Gulf Publishing Company.

Watson, D., Brittenham, T. and Moore, P. (2003). Advanced well control. 1st ed. Richardson, Tex.: Society of Petroleum Engineers.

Ton-miles while making short trip

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The ton-miles of work performed in short trip operation is also in term of round trips.

The ton-miles of work done in making a short trip is equal to the difference between round ton-miles of end depth and starting depth. The formula for short trip ton-miles is listed below;

Tst = T6 – T5

Where; Tst = ton-miles for short trip
T6 = ton-miles for one round trip at the deeper depth
T5 = ton-miles for one round trip at the shallower depth

Example;

Please determine short trip ton-miles from 8000 ft to 8050 ft
Ton-miles @ 8050 ft = 200
Ton-miles @ 8000 ft = 190
Tst = (200 – 190)
Tst = 10 ton-miles
Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

Ton-Miles for Setting Casing

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For the setting casing operation, the ton-miles calculation of this operation is similar to round trip ton-miles calculation. Nevertheless, buoyed weight of the casing will be used into calculation instead of buoyed weight of drill pipe and with the result will be multiplied by 0.5, because setting casing is just only one-way operation (1/2 round trip).

Ton-miles for setting casing can be determined from the following formula:

Tc = {Wp x D x (Lcs + D) + D x Wb} x 0.5 ÷ (5280 x 2000)

Where; Tc = ton-miles setting casing
Wp = buoyed weight of casing in lb/ft
Lcs = length of one joint of casing in ft
Wb = weight of travelling block assembly in lb
D = depth of casing in ft
2000 = number of pounds in one ton
5280 = number of feet in one mile

Example: Ton-Miles for Setting Casing

Mud weight = 10.0 ppg
Casing weight = 25.0 lb/ft
Depth of casing = 5200 ft
Travelling block assembly = 95,000 lb
Length of one joint of casing = 42 ft

Solution:

a) Buoyancy factor:
BF = (65.5 – 10.0) ÷ 65.5
BF = 0.8473

b) Buoyed weight of casing in mud, lb/ft (Wp):
Wp = 25.0 lb/ft x 0.8473
Wp = 21.18 lb/ft

c) Casing ton-miles
Tc = {21.18 x 5,200 x (42 + 5,200) + 5,200 x 95,000} x 0.5 ÷ (5280 x 2000)
Tc = 50.73 tone-miles

Ton-Mile (TM) for Setting Casing Calculation Sheet

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

Ton-miles for coring operation

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For coring operation, the ton-miles calculation is also expressed in terms of work in round trip ton-miles. In order to determine the coring ton-miles, you need to figure out ton-miles for one round trip at the depth where coring stopped minus ton-miles for one round trip at the depth where coring began and the multiplied that value by 2.

The formula for calculating ton-mile for coring operation is shown below;

Tc = 2 x (T4 – T3)

Where;

Tc = ton-miles for coring operation
T4 = ton-miles for one round trip at depth where coring operation stopped before coming out of hole
T3 = ton-miles for one round trip at depth where coring get started

Example – Please determine coring ton-mils from 8000 ft to 8050 ft.

Ton-miles @ 8050 ft (end of coring operation) = 200
Ton-miles for trip @ 8000 ft (start of coring operation) = 190

Tc = 2 x (T4 – T3)
Tc = 2 x (200 – 190)
Tc = 20 ton-miles



Ton-Mile (TM) for Coring Operation Calculation Sheet

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition