GB2255993A - Method for releasing a stuck pipe - Google Patents

Abstract

A method for releasing a stuck pipe in a well bore comprises the step of pumping a solids-free liquid composition comprising a halogenated organic compound down the well bore to the stuck region, optionally working the stuck pipe, and pulling the released pipe free. The liquid composition has a specific gravity in the range 0.9 to 2.3. The halogenated organic compound is preferably a brominated vegetable oil, ether or hydrocarbon, most preferably a brominated diphenyl ether. The halogenated organic compound may be used in conjunction with a conventional pipe release agent.

Description

METHOD FOR RELEASING A STUCK PIPE This invention relates to a method for facilitating the release of a stuck pipe, particularly a differentially stuck pipe, by using a novel pipe release agent.

Stuck pipe may be defined as drill pipe, drill collars, drill bits, stabilisers, reamers, casing, tubing, measurement while drilling tools, logging tools, etc, having inadvertently become immovable in a well bore. The term "stuck pipe" is used in the industry as a convenient compendious term to cover the sticking of all such equipment and is generally understood as not being restricted literally to pipes. Sticking may occur when drilling is in progress, when pipe and casing is being run in the hole or when a drill pipe is being hoisted.

There are numerous causes of stuck pipe; some occur regularly, some may be peculiar to a particular area and some may be unique.

Industry convention categorises the causes as either differential or mechanical sticking.

Differential sticking is believed to occur by the following mechanism. During most drilling operations, the hydrostatic pressure exerted by a drilling mud column is greater than the formation fluid pressure. In permeable formations, mud filtrate flows from the hole into the rock and builds up a filter cake. A pressure differential exists across the filter cake which is equal to the difference between the pressure of the mud column and the pressure of the formation.

When a pipe is central in the bore, the hydrostatic pressure due to the mud overbalance acts in all directions around it. If, however, the pipe touches the filter cake, the mud overbalance acts to push the pipe further into the cake, thus increasing the contact area between the pipe and the cake. Filtrate is still expelled from the filter cake between the pipe and the formation, thus shrinking the cake and allowing the pipe to penetrate further into it and so increasing the contact area still more. If the pressure difference is high enough and acts over a sufficiently large area, the pipe may become stuck.

Differential sticking usually occurs when the pipe has been motionless for a period of time, eg when making a connection or during surveying. -Differential sticking can be a particular problem when drilling depleted reservoirs because of the associated high overbalance.

The force required to pull differentially stuck pipe free depends, inter alia, upon the following factors: (a) The difference in pressure between the borehole and the formation. Any overbalance adds to side forces which may exist due to the deviation of the hole.

(b) The surface area of pipe embedded in the wall cake. The thicker the cake or the larger the pipe diameter, the greater this area is likely to be.

(c) The bond developed between the pipe and the wall cake is a very significant factor, being directly proportional to the sticking force. This can include frictional, cohesive and adhesive forces.

It tends to increase with time, making it harder to pull the pipe free.

Differential sticking may be distinguished from other forms of sticking, such as mechanical sticking. Mud circulation is not interrupted as there is no obstruction in the hole to stop the flow, as would be the case for pipe stuck due to hole bridging or caving. It is not possible to move or rotate the pipe in any direction.

When a pipe sticks the driller usually tries to free it by mechanical movement, eg by pulling, jarring or, if the pipe was moving immediately prior to sticking, trying to move it in the opposite direction. Frequently this fails to release the pipe and there is, of course, a limit to the force which can be applied, since too much force could fracture the pipe and make the situation worse.

If the pipe remains stuck it is then sometimes the practice to apply a pipe release agent.

Pipe release agents are chemically active mixtures, which may be oil or water based, which are placed over the stuck region in an attempt to free the pipe if working the pipe has failed to release it. These are believed to act by attacking the mud filter cake.

They are positioned by pumping them down the hole to the stuck region in the form of a slug, known as a pill. The pill generally contains sufficient material to cover the stuck zone and extend slightly beyond it over a total area of 1.5-2 times the area of the stuck zone. The pill volume necessary to achieve this is usually about 100 bbl (16,000 1) Pills are left to soak until the pipe is free or attempts to free it are abandoned.

Pipe release agents are generally sold as proprietary blends by companies trading in this area, frequently without divulging their chemical components. However, some pipe release agents are based on asphaltenic compounds and some on glycols, glycerols, alcohols and fatty acids and derivatives of such compounds.

Traditionally, pill density has been increased in a similar manner to muds, using solid, particulate weighting agents such as barite, with viscosifiers to prevent settling. In common with muds, the pill has the ability to form a filter cake. While the chemicals in the pipe release agent attack the mud cake, any additional cake formation by the pill will make it more difficult to free the pipe.

This is borne out by a recent study in the Gulf of Mexico (The EPA/API Diesel Pill Monitoring Program. R C Ayers et al. Drilling Wastes, P757, 1988. Elsevier Applied Science.) Increasing pill density reduced the success rate (pills of 1.44 SG or less were successful in 62% of cases whle pills of density greater than 1.44 SG had only a 21Z success rate). Pill densities were similar to the mud densities and therefore the original filter cakes are likely to be thicker for the higher mud weights and therefore have a greater contact area and require a greater force to free the pipe. It is also more difficult to attack the filter cake. However, a significant factor contributing to the poor performance of the pills is the increasing level of barite they may contain.

We have now discovered that a halogenated organic compound can be used both as a weighting agent and as an active constituent, ie, a cake attacking agent, in oil based pipe release agents.

Thus according to the present invention there is a provided a method for releasing a stuck pipe in a well bore which method comprises the step of pumping a solids-free liquid composition comprising a halogenated organic compound down the well bore to the stuck region, optionally working the stuck pipe, and pulling the released pipe free, the liquid having a specific gravity in the range 0.9 to 2.3, preferably 1.5 to 2.2.

Our European Patent EP 0247801B1 discloses a solids-free, non-aqueous, well bore fluid characterised in that it comprises a halogenated organic compound dissolved in a hydrocarbon solvent, the fluid having a specific gravity in the range 0.9 to 2.3, preferably 1.3 to 1.8.

This fluid is particularly suitable for use in a method according to the present invention and is subsequently termed dense oil.

The dense oil preferably has a Pensky Martens flash point of at least 66C.

Preferably the halogenated organic compound is a brominated organic compound.

The brominated organic compound may be, for example, a brominated vegetable oil, ether or hydrocarbon.

Suitable brominated compounds include brominated benzene, diphenyl, alkyl benzenes, aromatic ethers and aliphatic hydrocarbons. The preferred compound is a brominated diphenyl ether.

In the case of alkyl aromatic compounds, it is preferred that the bromine substituents should be in the aromatic nucleus only and not in the alkyl side chain. The preferred brominated alkyl benzenes are brominated ethyl benzene and cumene.

Mixtures of isomers and compounds of differing degrees of bromination resulting from bromination reactions are suitable.

The hydrocarbon solvent may be crude oil, kerosine, diesel oil or, preferably, a low toxicity drilling oil.

The specific gravity of the dense oil may be adjusted as desired by varying the proportions of the halogenated compound and the solvent.

However, the dense oil will generally be obtained from the manufacturer as a blend of solvent and halogenated hydrocarbon with a particular specific gravity. In this event, a further quantity of hydrocarbon solvent, termed base oil, can be added to modify the specific gravity of the total composition to the desired value.

If desired, the properties can be modified or enhanced by the use of other additives.

In particular, the pipe release activity may be enhanced by the addition of a conventional pipe release agent to the fluid. These are usually obtained in the form of a solution of one or more active agents in a solvent, usually a mineral oil.

Suitable active agents include asphaltenic compounds, glycols, glycerols, alcohols and fatty acids and derivatives of such compounds.

Water may be added as a viscosity control agent.

A suitable formulation for compositions to be used in the method of the present invention is dense oil 5 to 100%, preferably 50 to 75 % by volume, base oil 0 to 95%, preferably 5 to 40% by volume, other pipe release agent 0 to 40Z, preferably 5 to 20% by volume, water 0 to 40%, preferably 2 to 25Z by volume.

The use of a pill according to the present invention will generally result in a reduction in the time required to attack the filter cake sufficiently to free the pipe before pulling it.

The invention is illustrated with reference to the following examples and Figs 1-6 of the accompanying drawings which are plots of experimental results.

Example 1 The ability of a pill to attack and break down a filter cake was assessed using an API fluid loss cell and a simple screening test. This technique attempts to filter a pipe release agent through a mud filter cake. If the pill is successful in attacking the cake a large volume of filtrate will be obtained in a relatively short time.

Three mud types were studied, a clay based, a polymer based and an oil based mud; formulations are given Table 1. Two conventional oil based pipe release agents were used in this initial study and two based on dense oil; their formulations are shown in Table 2.

The filter cakes were examined at the end of each experiment for evidence of attack. For all of the traditionally formulated pills, there was evidence of additional filter cake build up from the pill itself. There was significantly more filter cake attack from the pills formulated with dense oil. For the water based muds, this was in the form of cracks breaking the cake into pieces rather like a jigsaw puzzle. For the oil based mud, the attack appeared to form a series of small holes or 'pits'.

Table 1 Mud Formulations Clay Based Mud Sea water 0.5 bbl 0.5 1 Fresh water 0.5 bbl 0.5 1 Bentonite 20 lb/bbl 57 g/l Q-Broxin 2 lb/bbl 5.7 g/l pH adjusted to 9.5 Drill solids (HMP) 10 lb/bbl 28 g/l Barite to required density (360 lb/bbl for SG 1.5) (1029 g/l for 1.5 SG) Q-Broxin is a chrome lignosulphonate ex Baroid which is added to stabilse and deflocculate the clay.

HMP is a mixture of clays which simulate drill solids, sold under the Trade Name Hymod Prima by Whitfield Chemicals Ltd Oil Based Mud Base oil (BP83HF) 0.76 bbl 0.76 1 Invermul 10 lbIbbl 28 g/l EZmul 4 lbIbbl 11.4 g/l Duratone 18.7 b/bbl 25 g/l Geltone 18 b/bbl 23 g/l Lime 18 b/bbl 23 g/l Calcium chloride 24.7 b/bbl 71 g/l Water 0.183 bbl 0.183 1 Barite to required density (200 lblbbl for 1.3 SG) (577 g/l for 1.3 SG) The base oil is a low toxicity drilling oil sold under the Trade Name BP 83HF by BP Chemicals Ltd. This also forms the base oil referred to in subsequent examples. Invermul and EZmul are emulsifiers sold under these Trade Names by Baroid.

Duratone and Geltone are a fluid loss control additive and a viscosifier respectively sold under these Trade Names by Baroid.

Lime is added to enhance the performance of the emulsifier and calcium chloride is added to increase the ionic strength of the water.

Polymer Based Mud Fresh water 1 bbl 1 1 Potassium chloride 33 lblbbl 94 g/l Sodium carbonate 0.5 lbIbbl 1.4 g/l Sodium hydroxide 0.75 lblbbl 2.1 g/l PAC R 2 lblbbl 5.7 g/l CMC LV 2 lbIbbl 5.7 g/l Drill solids (HMP) 20 lbIbbl 57 g/l Barite to required density (300 lblbbl for 1.5 SG) (857 g/l for 1.5 SG) The potassium chloride is present as a shale inhibitor and the sodium carbonate as a water softener.

PAC R is a regular grade polyanionic cellulose.

CMC LV is a low viscosity carboxy methyl cellulose.

Table 2 Pipe Release Agents Pipeloose Traditional Pill (Formulation is for a 1.5 SG pill. Other densities can be obtained by varying the barite level).

Base oil 0.675 bbl 0.675 1 Fresh water 0.036 bbl 0.036 1 Pipeloose 0.084 bbl 0.084 1 Emul Treat 3 lblbbl 8.6 g/l Emul Hivis 6 lblbbl 17 g/l Barite 298 lbIbbl 851 g/l Pipeloose is a proprietary pipe release agent sold under that Trade name by BW Mud Ltd.

Emul Treat is an oil-wetting surfactant and Emul-Hivis an organophilic clay to maintain solids in suspension. Both are manufactured by B W Mud Ltd.

Dense Oil Pill (Formulation is for a 1.5 SG pill. Other densities can be obtained by varying the base oil/dense oil ratio).

Base oil 25.6% by vol Fresh water 3.6 Pipeloose 8.4 Dense oil (1.8 SG) 62.4 The dense oil was a brominated diphenyl ether obtained from OSCA.

Milspot II Traditional Pill (Formulation is for a 1.5 SG pill. Other densities can be obtained by varying the barite level).

Base oil 0.526 bbl 0.526 1 Milspot II 0.100 bbl 0.100 1 Fresh water 0.192 bbl 0.192 1 Barite 264.5 lblbbl 756 g/l Milspot II is a proprietary pipe release agent sold under that Trade name by Milpark Drilling Fluids Ltd.

Dense Oil Pill (Formulation is for a 1.5 SG pill. Other densities can be obtained by varying the base oil/dense oil ratio).

Base Oil 9.4X by vol Milspot II 10.0 Fresh water 19.2 Dense oil 61.4 The dense oil was as before.

Figure 1 shows the results obtained when a filter cake derived from a clay based mud of the formulation given in Table 1 is treated with (a) a conventional pill based on Pipeloose and (b) a dense oil pill according to the present invention. The formulations of the pills are given in Table 2. It is clear that a larger volume of filtrate is obtained in a shorter time by using the dense oil pill.

This indicates that the dense oil pill attacks the filter cake more rapidly than a conventional pill and would therefore be more effective in releasing a stuck pipe.

Figure 2 shows the results obtained when a filter cake derived from a clay based mud of the formulation given in Table 1 is treated with (a) a conventional pill based on Milspot II and (b) a dense oil pill according to the present invention. The formulations of the pills are given in Table 2. Again it is clear that a larger volume of filtrate is obtained in a shorter time by using the dense oil pill.

Figure 3 shows the results obtained when a filter cake derived from a polymer based mud of the formulation given in Table 1 is treated with (a) a conventional pill based on Pipeloose and (b) a dense oil pill according to the present invention. The formulations of the pills are given in Table 2. It is clear that a larger volume of filtrate is obtained in a shorter time by using the dense oil pill.

Figure 4 shows the results obtained when a filter cake derived from a polymer based mud of the formulation given in Table 1 is treated with (a) a conventional pill based on Milspot II and (b) a dense oil pill according to the present invention. The formulations of the pills are given in Table 2. Again it is clear that a larger volume of filtrate is obtained in a shorter time by using the dense oil pill.

Figure 5 shows the results obtained when a filter cake derived from an oil based mud of the formulation given in Table 1 is treated with (a) a conventional pill based on Pipeloose and (b) a dense oil pill according to the present invention. The formulations of the pills are given in Table 2. It is clear that a larger volume of filtrate is obtained in a shorter time by using the dense oil pill.

Figure 6 shows the results obtained when filter cakes derived from (a) a clay based mud and (b) a polymer based mud are treated with the dense oil alone. Significant attacks are shown on both filter cakes, particularly the one derived from the clay based mud.

Example 2 Basic compatibility of the pills with the mud was assessed by mixing an equal volume of mud and pill and measuring the rheology on mixing and after standing for 2-3 days at ambient temperature and pressure.

Mixing the pills and mud together did sometimes cause an increase in rheology but this was not large (see Table 3). There was no significant change in rheology in standing for 2-3 days.

In Table 3, AV = apparent viscosity PV = plastic viscosity YP = yield point Gel = gel strength The left hand figure in the gel column represents the strength after 10 seconds and the right hand figure the strength after 10 minutes.

Table 3 Compatibility (RheoloRy Studies) (Mixtures are 50% pipe release agents (SG~1.5) 50-% mud (so1.5))

Sample AV PV YP* Gel* cP cP lb/lOOft2 lb/lOOft2 Polymer mud only A 54 34 40 6/4 B 50 30 40 6/6 Clay mud only A 26.5 10 33 29/32 B 20 10 20 15/20 Oil mud only A 29 30 0 3/3 Traditional Pipeloose A 35.5 33 5 3/3 only B 36 35 2 3/3 Dense oil Pipeloose A 41 40 2 3/4 only B 39.5 39 1 3/2 Traditional Milspot A 22.5 24 0 3/3 Polymer mud & A 81 62 38 13/14 traditional Pipeloose B 80 63 34 12/14 Polymer mud & dense A 80.5 58 45 6/7 oil Pipeloose B 80 56 48 5/5 Polymer mud & A 61 44 34 5/4 traditional Milspot B 51.5 39 25 4/3 Polymer mud & dense A 62 42 40 4/4 oil Milspot B 51 38 26 3/3 Clay mud & A 41 29 24 7/7 traditional Pipeloose B 42 29 26 8/10 Clay mud & dense oil A 22.5 18 9 10/15 Pipeloose B 21 17 8 10/15 Clay mud & traditional A 26.5 20 13 7/10 Milspot B 19.5 16 7 7/9 Clay mud & dense oil A 13.5 14 0 3/6 Milspot B 13 7 12 5/8 Oil mud & traditional A 22 23 0 2/3 Pipeloose B 19.5 18 3 3/4 Oil mud & dense oil A 32 30 4 2/3 Pipeloose B 32.5 30 5 4/5 A-rheology immediately on mixing B-rheology after standing for 2-3 days * to convert lb/100 ft2 to N/m2, multiply by 0.479 The following conclusion may be drawn from Examples 1 and 2: 1. Commercially available pipe release agents can be formulated into solids free pills covering a range of densities using dense oil.

2. Solids free pills formulated using dense oil attack filter cakes more rapidly than traditionally formulated pills.

3. Solids free (dense oil) pills will attack polymer, clay and oil based mud filter cakes.

4. Pills comprising 100% dense oil attack filter cakes.

5. The dense oil pills when mixed with either water or oil based muds do not cause changes in rheology which give rise for concern.

Claims (15)

Claims

1. A method for releasing a stuck pipe in a well bore which method comprises the step of pumping a solids-free liquid composition comprising a halogenated organic compound down the well bore to the stuck region and pulling the released pipe free, the liquid composition having a specific gravity in the range 0.9 to 2.3.

2. A method according to claim 1 wherein the liquid composition has a specific gravity in the range 1.3 to 1.8.

3. A method according to either of the preceding claims wherein the liquid composition has a Pensky-Martens flash point of at least 66"C.

4. A method according to any of the preceding claims wherein the halogenated organic compound is a brominated organic compound.

5. A method according to claim 4 wherein the brominated organic compound is a brominated vegetable oil, ether or hydrocarbon.

6. A method according to claim 5 wherein the brominated organic compound is a brominated benzene, diphenyl, alkyl benzene, aromatic ether or aliphatic hydrocarbon.

7. A method according to claim 6 wherein the brominated organic compound is a brominated diphenyl ether.

8. A method according to claim 6 wherein the brominated organic compound is a brominated ethyl benzene or cumene.

9. A method according to any of the preceding claims wherein the liquid composition additionally comprises a conventional pipe release agent.

10. A method according to any of the preceding claims wherein the conventional pipe release agent comprises at least one compound selected from the group consisting of asphaltenic compounds, glycols, glycerols, alcohols, fatty acids and derivatives of such compounds.

11. A method according to any of the preceding claims wherein the liquid composition additionally comprises water.

12. A method according to any of the preceding claims wherein the liquid composition comprising a halogenated organic compound contains: (a) 5 to 100% by volume of dense oil as hereinbefore defined (b) 0 to 95% by volume of base oil as hereinbefore defined (c) 0 to 40% by volume of an additional pipe release agent, and (d) 0 to 40% by volume of water.

13. A method according to claim 12 wherein the liquid composition comprising a halogenated organic compound contains: (a) 50 to 75% by volume of dense oil as hereinbefore defined (b) 5 to 40X by volume of base oil as hereinbefore defined (c) 5 to 20Z by volume of an additional pipe release agent, and (d) 2 to 25% by volume of water.

14. A method according to any of the preceding claims wherein the stuck pipe is worked before being pulled free.

15. A method for releasing a stuck pipe in a well bore according to claim 1 as hereinbefore described with reference to the Examples.