WO2012023074A1

WO2012023074A1 - A rapid kill and restoration system for blowout wells

Info

Publication number: WO2012023074A1
Application number: PCT/IB2011/053366
Authority: WO
Inventors: Xianhua Liu
Original assignee: Xianhua Liu
Priority date: 2010-08-18
Filing date: 2011-07-28
Publication date: 2012-02-23
Also published as: AU2011292794B2; CN103080464B; AU2011292794A1; CN103080464A

Abstract

Well blowouts, such as happened in the PTTEPAA Montara gas well in the Timor Sea in August 2009 and the BP Macondo oil well in the Gulf of Mexico in April 2010, caused colossal disasters. The existing top kill technique by pumping in kill- weight mud failed. The relief well technique worked, however it was very costly and very late due to drilling the relief well. This invention is a rapid and reliable kill and restoration technique and its implementation system for the well blowout accidents. It uses solid particles to block, suppress and greatly reduce the blowout flow to gain time for repair or replacement of the damaged blowout preventer and other devices, and connection of production pipelines; It then takes out some of the solid particles to restore well production. In such a way, environmental damage is greatly reduced and the well is kept as a valuable production asset. While any shape of solid particles may be used, the ball shape is an optimum for the kill and restoration operation; hence kill balls are the recommended solid particles. The kill procedure is to sequentially release large, medium and small density balls into the blowout well. Balls of different densities can be made of different materials such as lead, iron, stone or rubber and can have a shell cover made of iron, steel or other environmental friendly material. An implementation system for the kill procedure consists of a tubing system, a blower or a pump, a ball injection device and a cage. The transporting fluid can be air, nitrogen, carbon dioxide, oil or other fluid depending on the operation safety assessment in regarding to the specific well blowout situation. The cage mounted on the tubing and sits on top of the well will temporally contain the blown out balls at the early stage of the kill process. Balls in the cage will fall down to the well as the flow is reduced. A technique for taking out some of the balls from the well to restore production is carried out by a tubing system, a pump and a balls storage tank.

Description

A RAPID KILL AND RESTORATION SYSTEM FOR BLOWOUT WELLS

Technical Field

Well blowouts, such as happened in the PTTEPAA Montara gas well in the Timor Sea in August 2009 and the BP Macondo oil well in the Gulf of Mexico in April 2010, caused colossal disasters. This invention belongs to the field of contingency response technology for solving the oil and gas well blowout problems.

Background Art

There are currently two techniques for well blowout accidents. One is the top kill technique by pumping in kill-weight mud from the top of the blowout well; the other is the relief well technique that intercepts the blowout well and pumping kill mud from the bottom. Both techniques use kill mud for solving the problem. The top kill technique failed for the PTTEPAA Montara gas well and the BP Macondo oil well blowouts. The failure could be due to kill mud being partially lost into oil reservoir or other formation in case of there was a fracture connection and a flow between two formations through the well, but mostly it was due to the kill mud being diluted and washed out of the well. The relief well technique worked. However it was very costly and very late since it took about three months to drill the relief well. The consequence was massive oil spill into the sea and gas into the atmosphere that devastated the environment, damaged the local industry and brought huge loss to the oil companies. Although the possibility of blowout for each single well is low, there is a certainty of well blowout in the future as more and more wells are drilled, especially in offshore waters. It is only not known when, where and how the next well blowout will exactly happen. As a result, fast and reliable technology is needed for the kill of future well blowouts.

Technical Problem

As demonstrated by the above two well blowout accidents, the problems of the current mud kill technology are that either the top kill technique not reliable due to kill mud being washed out of the well, or the relief well technique being too costly and too late due to drilling of relief wells. In addition, it is much harder to kill offshore well blowout than on land well blowout.

Technical Solution

This invention provides a fast and reliable solution for the well blowout problem by using solid kill balls to do the job to avoid the disadvantages of the mud kill technology. It solves the problem in three steps: kill the blowout well to a significant extent that only a very small flow remains; allow time for repair or replacement of the damaged blowout preventer and other devices, and connection of production pipelines; restore the well to normal production. The technique achieves its goal by inserting a small diameter tubing or pipe deep into the well and releasing kill balls into the well to block and suppress the flow and later taking out some of them to increase the flow. Each ball in the well occupies some space and works as a flow suppressor; a large amount of balls work together to kill the blowout to a sufficiently small flow, for example, less than 1% of the initial blowout flow rate. The essence of the technique is to use the volume of heavy solid particles to block and the gravitational force to suppress the flow, while the ball shape is an optimum shape for the kill and restoration operation.

The technique works based on the following theorem: For a well of diameter D and a large number of balls of same size, density and surface roughness, and for certain fluid, there exists a flow rate range Q_min to Q_max that enables the balls to be distributed in the well from the bottom up to some height depending on the real flow rate Q. The density of the distribution (number of balls per unit volume) increases as the flow rate Q decreases. When the flow rate Q > Q_max the balls will all move upward to reach the top of the well; when Q < Q_min the balls will all slip downward and stack up at the bottom of the well. The flow rate Q_max corresponds to the slip velocity of a single ball in the well. This theorem provides a method for determining a desirable small flow rate Q to be achieved given the diameter of the well, property of the fluid and the size and density of balls. The relationship among these parameters can be experimentally measured and formulated.

In case of balls are blown out of the well in the early kill stage, a cage is attached to the kill tubing and sits on top of the well opening to contain the balls while allowing fluid out. As more and more balls are released and the flow is reduced, the balls in the cage will fall into the well. Most wells have several sections with reduced diameters at the bottom. For the same flow rate, the higher flow speed in the smaller diameter section is capable of floating larger density balls. The principle is to use as less heavy balls as possible to reduce stack up at the bottom and let as many lighter balls as possible to float in the fluid, so that to avoid the well from being damaged by the gravitational force of the heavy stack up balls.

Advantageous Effects

The first advantage of this technique is its reliability. Due to large size, the kill balls can not be lost by being blown out of the well. In case some balls are blown out of the well in the early kill stage, they will be contained in the cage and will fall down to the well when the flow is reduced, and even in the cage they still suppress the flow. Hence every ball is an effective kill which guarantees the reliability of the kill process. The second advantage is its rapidity. Due to the effectiveness, it takes the kill process only about one day for the blowout flow to reduce to a minimum value. The third advantage is its capability of keeping the well as a valuable asset by restoring it to normal production.

Description of Drawings

Figure 1 is an illustration of the ball kill system. It consists of a

tubing system

1 and 4, a blower or a pump 2, a ball injection device 3, a cage 5 and

different density balls

13, 14, 15, 17. The top part of the tubing is a circulating system connected with either a blower or a pump for transporting balls into the vertical part of the tubing inserted deep into the well. There can be an inclined middle part between the top part and the vertical part if necessary. The items 6 to 12 and 16 are components of the well. They are annular blowout preventer 6, blind ram 7 and shear ram 8, choke line 9 and kill line 10, wellhead 11, casing pipe 12 and liner pipe 16. If the blowout happens for a production well, the

items

12 and 16 are production tubing.

The blower 2 provides gas flow to transport balls and pressure to balance well fluid pressure. The gas is circulated back to the inlet of the blower. Balls are pushed into the tubing through the ball injection device either manually or with a purposely designed machine. The injection device has a one way valve to prevent outward flow. The cage 5 is mounted on the tubing 4 and sits on the opening of the well to contain balls blown out at the early kill stage. The blower can be substituted with a pump which pumps oil to transport balls and provide pressure to the tubing. With either blowing gas or pumping oil, the pressure only needs to be large enough to balance the fluid pressure of the well. The transporting gas can be air as long as evaluated operating safe. In case of natural gas is blown out, gases such as nitrogen or carbon dioxide can be used as the transporting fluid to assure operation safety.

Figure 2 is an illustration of the restoration system. It consists of the vertical tubing 4 (shown in figure 1) and a top horizontal tubing 18, a large diameter connector 19 mounted with a mesh 20, a pump 21 and a ball storage tank 22. After the damaged blowout preventer and associated devices are repaired or replaced, fluid in the well is pumped out fast enough to float balls up into the tubing. The production pipeline and valves can be turned on to increase the flow for floating balls up. When arriving at the large diameter connector, the balls will fall down to the storage tank. The restoration process stops when a desired number of balls are taken out of the well and the remaining balls are purposely left in the well to control the flow. The fluid flow is now under control of blowout preventer and the well is ready for oil or gas production. On the other hand, the well can be cemented and abandoned.

Best Mode for Carrying out the Invention

The ball shape is an optimum shape of solid particles for the kill and restoration operation. It is recommended that the ball size for optimum kill operation is less than 30% of the inside diameter of the blowout well.

Larger balls are better used for fast kill of oil blowout as long as the tubing size allows tubing being safely inserted deep into the well; smaller balls are better used for effective kill of gas blowout since gas is of light density and smaller balls leave smaller cavities when they stack up.

Due to very large flow rate at the start, large density balls should be first used, then medium density and large amount of small density balls. Large density balls can be made of lead with an iron shell or solid iron; medium density balls made of stone or stone with an iron shell; lighter density balls made of rubber or other material with an iron shell. Iron steel or other environmental friendly material can also be used as the shell material.

Although it is better to insert the tubing as deep as possible into the well, it is not necessary to insert over half of the vertical depth of the well.

During the restoration stage, the production pipeline and valves can be turned on to increase the flow to float balls up for taking them out by the restoration system.

Industrial Applicability

This technique and its implementation system can be used for solving any kind of well blowout problems. However it is mostly useful for solving oil and gas well blowout problem in the petroleum industry.

Claims

A technique of using solid particles to block, suppress and greatly reduce blowout flow to kill blowout wells. While any shape of solid particles can be used, the ball shape is an optimum for the kill operation hence kill balls are the recommended solid particles.
An operation procedure of sequentially releasing large, medium and small density balls into the blowout well for the kill process.
Balls of different densities can be made of different materials such as lead, iron, stone or rubber and can have a shell cover made of iron, steel or other environmental friendly material for environment protection.
An implementation system for carrying out the ball kill operation consisting of a tubing system, a blower or a pump, a ball injection device and a cage.
The top part of the tubing system is a circulating system connected with either a blower or a pump for transporting balls into the vertical part of the tubing inserted deep into the well, and the circulating fluid will then return to the inlet of the blower or pump.
The cage is for temporally containing the blown out balls at the early stage of the kill process. Balls in the cage will fall into the well as the flow is reduced.
A pumping technique for taking out some of the balls for restoration of the well to normal production.
An implementation system for the restoration process consisting of a tubing system, a pump and a balls storage tank.