Kicks are the result of under balance drilling operation. Time consumed to control the kicks will be different in depending on the controlling technique. Drilling fluid considered as a first barrier to control formation pressure and well kicks. Any advance in drilling fluids leads to more controlled operation in term of time. This paper will follow the general increasing profile of pressure before entering the reservoir. Both methods of well controlling technique; circulating techniques and non-circulating have been implemented in many oil blocks. The process of designing and casing selection, setting depth and many other issues is predominately dependent on the utilization of accurate values of formation pressure. Formation pressures used to design safe mud weights to overcome fracturing the formation and prevent well kicks. Hence the emphasis has been placed on the practical utilization of kicks pressure near the reservoir. The presented relationships will help the engineer to better understand lithological columns and reduce potential hole problems during the kick appearance. Selecting the best well controlling practical method can lead to not harming the reservoir and more production later. Changes in some drilling fluid properties have been proposed with increasing the depth without damaging the reservoir. Suggestions in relation to the casing setting point of the intermediate section are also proposed. Standard equations with proper modification for gases and safety margin have been proposed for the future drilling operation in oil fields above the reservoir.
A simple definition of the kicks is unscheduled entry of formation fluid(s) into the wellbore [
1) Mud weight less than formation pore pressure
2) Failure to keep the hole full while tripping
3) Swabbing while tripping
4) Lost circulation
5) Mud cut by gas, water or oil
The ability of the industry to predict formation pressures has improved in recent years and is sophisticated [
Advances in well controlling systems came to appear in term of non-circu- lating well control techniques like volumetric method (Lubricate and Bleed) and Bullheading methods [
All methods in circulating technique use the same procedures and only differ when and if a kill weight fluid will be circulated [
BHP and surface pressures may be a combination of several types of pressure like Formation Pressure (FP), Hydrostatic Pressure (HP), circulating friction pressure and choke pressure [
A “rule of thumb” of two seconds per 1000 feet of well length is typically required to transit a pressure pulse in a drilling fluid as a lag time. So, lag time will increase with the depth. This point is very important if additional adjustments are made on the choke. Accurate and proper documentation is a very important aspect during the well control [
In general they are two groups, circulating and none circulating techniques.
・ ICP = SIDPP + KRP
ICP = initial circulating pressure (psi)
SIDPP = Static Initial Drill Pipe Pressure (psi)
KRP = Killing Rate Pressure (psi)
This ICP will be the needed pressure to circulate a well at a given rate and prevent the well from flowing or kicking [
Three well control techniques have been used during the operation of the case study, which they were:
1) Driller’s Method
When there will be an indication of the kicks the driller starts to use this method as a first response. It is easy to implement and can be used to control wells with high migration rates that may result in shut-in well problems [
2) Wait and Weight (Engineer) Method
This method kills the kick faster and keeps wellbore and surface pressures lower than any other method [
3) Volumetric Method of Well Control
It is the way of allowing controlled expansion of gas during migration. It replaces volume with pressure (or vice versa) to maintain BHP is equal to, or a little higher than FP. This method will be used to control the well until a circulating method can be implemented. Volumetric methods can be used in situations like plugged string, string is out of the hole, or pumps are not working and many other situations [
P1 V1 = P2 V2 Boyle’s Law
After 2003 many oil blocks have been awarded to the oil companies to start their investments. Up to date than 50 oil blocks have been awarded to oil operators in Kurdistan, north of Iraq
Bn-1 was the first exploration oil well in Bazian block, in general the area were closed and there were no helpful offset data in relate to the FP or FG [
Beside all the above collected data there were an accurate calculations for pore pressure for different penetrated geological formations till the target which was in Qamchuqa formation as it is clear in
Here we study and discuss the drilling operation to control the well kicks in term
CASING DATA | ||||||||
---|---|---|---|---|---|---|---|---|
LOT: 15.7 ppg @ MD 1839 m/TVD 1837 m | Last BOP Test 31.Jan.2010 | Next BOP Test is Next Casing Test | 21.Feb.10 | |||||
21.Feb.10 | ||||||||
OD (in) | ID (in) | MD (m) | TVD (m) | WT (Ib/ft) | Grade | Burst (Psi) | Collapse (Psi) | Tensile (kIbs) |
30 | 27 | 17.5 | 17.5 | 453.15 | X52 | |||
20 | 18.73 | 467 | 467 | 133 | K55 | 3060 | 1493 | 2100 |
13 3/8 | 12.415 | 1196 | 1196 | 68 | L80 | 5020 | 2260 | 1556 |
9 5/8 | 8.861 | 1839 | 1837 | 47 | L80 | 6870 | 4760 | 1086 |
Formation | Depth (m) TVD RTE | Pore Pressure (ppg) EMW | Temperature (C) |
---|---|---|---|
Gercus | 137.5 - 246 | 8.3 - 8.6 | 38 - 40 |
Khurmala | 246 - 330 | 8.6 | 40 - 42 |
Sinjar | 330 - 440 | 8.6 | 42 - 45 |
Kolosh | 440 - 710 | 8.6 | 45 - 51 |
Aliji | 710 - 1673 | 8.6 | 51 - 72 |
Upper Shiranish | 1673 - 1943 | 8.6 | 72 - 78 |
Lower Shiranish | 1943 - 2279 | 8.6 | 78 - 86 |
Kometan | 2279 - 2376 | 8.6 | 86 - 88 |
Qamchuqa/Sarmord | 2376 - 3635 | 8.6 - 9.1 | 88 - 116 |
Qamchuqa/Sarmord | 3635 - 3803 | 10.2 - 10.7 | 116 - 121 |
of time in Bn-1 as a case study. During the drilling operation, there was a lot of time spend to control the BHP. The total of about 5 days with a full operation was spent to control the well. Similar scenario or worse happened in many other oil blocks in Kurdistan. There was an indication of Loss of Circulation (LOC) in the upper part of the production section after 2800 m and then kicks during the sliding drilling from 3630 m down. First pumping of Loss Circulating Materials (LCM) was at the upper part of the production section as a reaction of LOC. After that was an increase in pit volume up to 10 bbls [
Seven circulation stages with different mud properties and pumping a lot of LCM to control LOC the well was not controlled totally. The main changes were in the mud density starting from 8.6 ppg and going to reach 12.1 ppg at the seventh circulation stage during the implementation of Driller Technique. Engineer and Volumetric Techniques also have been implemented to control the well. Figures 5-7 show some stages of circulation to control the well with the first kick control technique.
As can be seen there were two problems at the same time loss of circulation and kicks. This situation has been shown in the
there is some loss.
Directly after the Driller Method, Volumetric Methods were implemented starting with increasing the mud density from 9.3 ppg to 12.1 ppg to control the well and reach the situation of SIDPP and SICP to be zero psi [
The process of well controlling took 5 days and this was a high cost and increased the Non-Production Time (NPT) also.
Driller’s Method was first implemented in the case study well. The crew proceeded immediately to displace the gas influx. The required calculations were made on the kill-weight. Circulating the kill mud was not easily displaced and the drilling operation was resumed very slowly. One of the most disadvantages of the Driller’s Method is that at least two circulations are required to control the well. In our case there were seven circulations which took a lot of time. After Driller method there were a decision to start implementing the Wait and Weight (Engineer Method) which is slightly more complicated but offers some distinct advantages. The most main advantages of the Engineer Method are the well will be killed in half the time [
Here in Bn-1 different controlling method have been used due to uncertainty about which one is the most suitable one. Within upper part of the near the Pay Zone Interval there were LOC and within the lower part there were kick problem. Any improvements on the drilling fluid properties give different results on upper and lower part of the section.
There are many well controlling methods; each has its advantages or disadvantages in a particular location or drilling operation situation. In our case study extending the setting point of the production casing pipes to deeper setting point between 2300 m to 2500 m in Shiranish formation will isolate the problematic interval more and more. Application of the Wait and Weight Method may even
Kick Control Method | Date (From) | Date (To) | Total Hours |
---|---|---|---|
Driller Method | 11, Feb. 2010 | 13, Feb. 2010 | 51 |
Wait and Wait | 13, Feb. 2010 | 15, Feb. 2010 | 47 |
Volumetric | 15, Feb. 2010 | 16, Feb. 2010 | 31 |
129 hours* |
give us higher shoe pressures if the drill pipe pressure schedule is not calculated and followed properly.
Drilling near the target zone and the liner section in Shiranish formation with new mud system of liner increase of density, viscosity and gel strength makes the drilling operation more free problematic operation. Most of the times there will be difficulty in following properly some methods like W&W. The Driller’s Method is not also a preferred method all the times. Drilling the near pay zone interval with increased mud density, viscosity and gel strength without waiting for kick indication will result in saving more time and cost. Drilling long intervals with different geological properties above the target makes the kick controlling more difficult. Any decrease in NPT means more production and optimized operation economically. Any decrease in NPT means more friendly environmental operation in the area in term of pollution.
Avoid using one fluid system in drilling loss interval and pressured interval together. Using the Driller Method with implementing the equation of hydrostatic pressure plus a safety margin of 500 psi will serve the operation of drilling in term of time above the target. This means that Pore pressure (Pp) will be:
Darwesh, A.K., Rasmussen, T.M. and Al-Ansari, N. (2017) Kicks Controlling Techniques Efficiency in Term of Time. Engineering, 9, 482-492. https://doi.org/10.4236/eng.2017.95028