New Interactive Simulator to Mimic Kick Behavior in Wells of Southern Iraqi fields

An unprepared drilling team or an inexperienced group in dealing with bottom hole drilling problems can cause serious injury, health troubles, environmental damage and rigorous financial losses for any contingency hole troubles that might be faced during the drilling progress. For that reason, drilling simulators have been developed and used in teaching and training, usually in well control, focusing on how to handle the most dangerous and expensive problems such as kicks, mud losses, and stuck pipes. It is believed that the practice preferred to be related to real cases for best results, so modern techniques have been introduced in this research to build anew drilling simulator software under the name “KickSim100”. The main programming language used is C# language and Unity3D editor used as a No.19 Journal of Petroleum Research & Studies (JPR&S) E 50 programming environment, together used to connect, exhibit and implement field experiences and field data that gathered and analyzed from southern Iraqi fields. Kick-Sim100 imitates the behavior of the kick for both types: gas and water kick. It also mimics two of the most common well control methods, namely the “Driller” method and the “wait and weight” method. This simulator deals with southern Iraqi formations also manages the possibilities of kick occurrence and problems solving steps by involving all the potential odds that might arise during well killing procedures automatically, in which It does not need any instructor involvement. Kick-Sim100 is expected to have a great impact on the improvement of the drilling staff abilities in handling kick detection while drilling and well-killing methods. It is also planned to participate in Iraqi petroleum engineering educational systems in the future if developed.


Introduction
A Simulator is defined as a device or a software that is used to reproduce a physical behavior in some degree of exactness. In petroleum industry simulators are widely used in many aspects especially in drilling operations and reservoir modeling. Drilling operation is one of the most expensive operations in the petroleum industry. Kick is one of the most dangerous problems in drilling operation that may escalate to a blowout. Drilling staff experience is one of the most important factors that directly affects the ability of the staff to handle any of the down hole problems especially dangerous problems such as kick.
In this paper, anew drilling simulator software that concerns with kick problem and kick solving procedures has been developed under the name (Kick-Sim100) to simulate the kick behavior and well killing procedures in vertical wells. (Kick-Sim100) built based on data and information that are collected and gathered from Iraqi fields. Using drilling simulators have been proven to be one of the best ways that used for training and have a great impact on the experience and handling ability of drilling teams. This paper is based on data and information that gathered from southern Iraqi fields that distributed mainly in Basra, Missan, and Nasiriya. The fields that covered are the following: 3. West Qurna 1 Oil Field: It is an oil field, located 50 km northwest of the city of Basra, and overlaps the northern edge of the Rumaila field. . [3] 4. West Qurna 2 Oil Field: It is situated in the southern Iraqi part, 65 kilometers north-west of Basra, and it is one of the world's largest fields. [4] 5. Nasiriya Oil Field: It is located in the southern of Iraq, in Thi-Qar province (close to Nasiriya city). [5] 6. Gharraf Oil Field: This field is situated in southern Iraq, in Thi-Qar governorate. It has a dimension that is aligned in NW-SE direction of 10 km in width and 31 km in length. [6] 7. Halfaya Oil Field: is a giant oil field, located east of Amarah, Iraq. It is located at some 400 km south east of Baghdad. [7] 8. Buzurgan Oil Field: is located in the South -Eastern part of the Republic of Iraq, close to the Iran boundary, 40 Km North East of Amara. [8] 9. Noor Oil Field: is one of the smallest fields in Missan province discovered in late of 1973, the direction of Noor oil field's axis is similar to the axes of neighboring structures, north westsouth east. [9] 10. Fauqi Oil Field: Fauqi Oil Field has an axial length about 26 km and its width is about 6 km with these coordinates (3554000-3565000) northing lines and (737000-743000) easting lines. [10]

Kick analysis
The kick is one of the most dangerous downhole problems because of its relation to staff safety. To mimic the behavior of the kick during the occurrence and the solving procedures accurately, the physical forces in the downhole should be fully understood. This problem will be discussed in many parts and as follows:

Kick occurrence
When a certain amount of formation fluid enters the well, a kick is formed. The kick could occur only in permeable formations with a fluid (gas or water) in it. The kick occurs if the driller failed to maintain proper hydrostatic pressure (due to human error or some other external circumstances).
Formation fluids have densities less than drilling mud. If a kick takes place, the hydrostatic pressure will decrease as a result of the kick entering which occupies a portion in the mud column, and as the amount of the kick increases, the hydrostatic pressure will decrease simultaneously. This continuous decrease in the hydrostatic pressure will increase the severity of the kick and the chances to escalate to a blowout.
The amount of the hydrostatic pressure drop due to kick entrance depends on the density of the fluid that formed the kick and the amount of the kick (the kick amount will affect the height of the kick column in the annulus).
The Hydrostatic pressure of the fluid column in the annulus can be represented by the following equation: ...… (1) As ρ influx is always less than ρ mud, Term A will always be greater than Term B. as the parameters (ρ influx, ρ mud and TVD) are constant for each problem case when the problem occurs, the main affected factor is the influx height. Term A is a negative value and the Term B is a positive value, and from the mathematical point of view, any increase in the influx height has a greater impact on Term A than Term B because the density of the mud is always higher than influx density. As a result of these two points, any increase in the influx height decreases the hydrostatic pressure.

Kick treatment
The Driller's method and the Engineer's method are the most common well control methods used in Iraqi fields, so they will be analyzed in details to be inserted to the software. The correct solving steps will be studied to match them with the steps in the simulator. The most important part of the kick analysis is the effect of the incorrect decisions that might happen during solving the problem.

Driller's method
The main feature of the driller's method is killing the well with two steps. Each step requires certain parameters and a united procedure. If the driller failed to supply the right values of the required parameters, the problem may escalate and add more complexity to the case.

A. First circulation
This step concerns with circulating the kick with the original mud. To proceed correctly through the first circulation, correct (ICP) value is needed to control the formation pressure through the process. As long as the initial circulating pressure is higher than the KRP, the circulation can take place. SIDPP value is equivalent to the pressure difference between formation pressure and hydrostatic pressure. As a result, if a circulation needs to be established, the circulating pressure should be equal or higher than KRP and to make a balance between the well and the formation pressure, the SIDPP value should be added to the KRP to make the circulation and make a balance in the well.
Using pump pressure less than KRP instead of ICP, the circulating will be impossible to take place as the pump pressure is less than the minimum pressure required to overcome the friction in the well. And in this case another kick will enter the well because of the lack of the pressure in the well to balance the pressure in the downhole while circulating.
If the used pump pressure is higher than KRP and lower than ICP, the circulation will be initiated as the minimum pressure required to circulating the mud is met but the pump pressure won't be enough to maintain the balance in the downhole and a new kick is expected to enter the well.
If the used pump pressure is higher than ICP, the circulation will be initiated as the pressure is higher than the KRP. The formation fluids will be blocked as the Pressure in the downhole is higher than the correct ICP, but if the pressure in the downhole exceeds the formation fracture pressure, a fracture will occur and the well might be lost.
To understand the choke principles in the first circulation, the first circulation will be divided into two stages to be understood fully. The pump enters a new pressure to the system (bottom hole), so the pressure will be increased and that may form a fracture, and in order to maintain the pressure stable in the downhole, the choke should be adjusted carefully.
In In the second stage, if the kick type is water, the casing pressure will be constant as the driller control the choke correctly keeping the drill pipe pressure at (ICP). If the kick type is gas, the casing pressure The casing pressure will drop after the kick leaves of the annulus. This drop is caused as the result of the hydrostatic pressure increase in the annulus (the force downward is increased) because the hydrostatic pressure of the mud only is higher than the hydrostatic pressure of the summation of the gas and mud columns, and this leads to reduction in the summation of the forces in the upward direction.
After the kick exits the well, If the recorded SICP and SIDPP are unequal, then there is something went wrong in the first circulation. Either a new kick enters the well or some portion of the original kick remains sealed in the annulus, and makes the hydrostatic pressure in the annulus lower than the hydrostatic pressure in the drill string due to the existence of some of the gas kick with low density in the annulus. As the upper direction forces caused by the formation are equal in the annulus and in the drill string, the summation of the forces in the upper direction in the annulus will be higher.

B. Second circulation
In this circulation, KMW should be prepared, also FCP and STB should be calculated to be used in this circulation. To describe the physical behavior of the second circulation, it is divided into two stages.
In the first stage, the new mud is initially pumped by raising the pump pressure to ICP, then the driller

The engineer's method
This method uses only one circulation to get rid of the kick and kill the well using the new mud directly. This well control method requires the new mud to be prepared and the ICP, FCP, and STB to be calculated before the operation is started. To understand the behavior of the pressures in the drill string and in the annulus, the circulation will be divided into two stages.
In the first stage of the circulation, the driller raises the pressure of the pump to ICP in order to implement enough pressure to combine with the hydrostatic pressure of the old mud for circulation and control the formation pressure. For mud circulation, the driller directly uses the new mud and this new mud will add a new hydrostatic pressure in the drill string (the new mud is heavier than the old mud), thus implement an additional hydrostatic pressure in the drill string, and to prevent any underground blowouts or generate a new kick, the driller must adjust the choke to decrease the pressure in the drill string gradually from ICP to FCP. This stage ends when the new mud reaches the bit.
In the second stage, the new mud begins to rise in the annulus leading to an increase in the hydrostatic pressure in the annulus. If kick type is water, as the hydrostatic pressure increases in the annulus, the summation of the forces of the pump pressure against the hydrostatic pressure will be decreased in the upward direction as described in the driller's method when the new mud raises in the annulus.
If the kick type is gas, the second stage will be divided into two parts. The first part begins when the mud begins to rise in the annulus and ends when the kick gets out of the well. In this part, the casing pressure begins to increase as the kick rises in the annulus because of the gas expansion in the annulus and cause a decrease in the hydrostatic pressure which control the formation pressure. It should be noted that the effect of the gas expansion lowering the total hydrostatic pressure is greater than the effect of the new mud. At the end of this part, the kick begins to get out of the well. As the low-density kick gets out of the well, the total hydrostatic pressure will depend only on the densities of the old mud and new mud and as a result, the total hydrostatic pressure will be raised. This increase the total hydrostatic pressure and affects the summation of the forces in the annulus negatively in the upward direction, thus the casing pressure reading will be dropped.
The second part begins when all of the gas kick gets out of the annulus. As the new mud with high density goes up in the annulus, the total hydrostatic pressure in the annulus will be increased, leading to decrease the casing pressure readings.

The result
In this section, different kick problems will be simulated in the software during the normal drilling of real vertical wells case and different solving scenarios will be taken. For each case, the required calculations will be made to solve the problem and check whether our calculations solve the problem or not. Correct calculations with correct implementation can solve the problem properly, so using correct calculations and implement these calculations correctly in the software should also solve the simulated kick properly.

Driller's method
For this case the driller's method will be used. Table (1) lists the affected parameters before and after kick incidence that recorded using the program directly. Mud tank 79% 84% After kick incidence and BOP closing, the following parameters will be recorded: SIDDP is 481 psi, SICP is 546 psi, KRP is 476 psi and SPM at kill rate pressure is 33 spm. Then calculate ICP:

Fig. (1) Pressure profiles (WQ2-372)
Despite of the differences between the theoretical solution and the implemented solution by the user, the implemented solution is considered as a correct solution as it is within the acceptable range.
Then we will go to the next step and make the required calculations: Based on the pressure profile in the annular in figure (1), the type of kick is gas. Water type kick can be solved using the same calculations and procedures used with gas kick.

Engineer's method
For this case, a kick will be made and then the engineer's method will be implemented. Table (2) lists the affected parameters before and after kick incidence that recorded using the program directly. Figure (3) shows the pressure profiles in the drill string and in the annulus, and shows a comparison between the theoretical accurate solution and the solution implemented by the user.

Fig. (3) Pressure profiles (WQ2-372)
The implemented solution is within the acceptable range and the operation is considered as a successful solution. The type of kick is gas and can be noted from the pressure profiles in figure (3). Water type kick can be solved using the same calculations and procedures used with gas kick, but during the first circulation a difference pressure behavior in the annulus will be noted. Figure (4) will be used to show the pressure profile in the annulus for the water kick type.

Incorrect calculation and incorrect implementation
After we see how the simulation process goes using the correct calculations and the right procedures for driller's method and engineer's method, we will test how incorrect calculations and wrong procedures can be simulated through the solution procedures.
Two aspects of wrong decision will be tested in the program, using wrong solving inputs and improper use of choke equipment.
Wrong solving inputs with random values will be implement. The results of these inputs are presented in table (3).

1.
A new software has been built successfully to simulate kick problems in vertical wells based on data and information that gathered from southern Iraqi fields.
2. The software includes both the driller's method and the engineer's method for well control.
3. The choke is the most difficult part in the simulation process and should be handled carefully.
4. The simulator include real cases of wells drilled in Basra, Nasiriya and Missan governorates.