Boring or penetrating the earth – Processes – Boring with specific fluid
Reexamination Certificate
2001-05-07
2003-10-21
Will, Thomas B. (Department: 3672)
Boring or penetrating the earth
Processes
Boring with specific fluid
C507S138000
Reexamination Certificate
active
06634442
ABSTRACT:
The present invention relates to a process for using biodegradable muds during the drilling of a well. The invention relates more particularly to a process for using several types of mud throughout the length of the well.
It is common practice to use a single drilling mud throughout the depth of the well, the specific properties of this mud being linked to the drilling temperature at the bottom of the well and the necessary ability of the mud to cool down, to lubricate, to plug the wall of the terrains passed through and to bring the cuttings up to the surface.
In order to reach terrains in which the temperatures at the bottom of the well reach 200° C. and above, drilling muds must keep their physical properties intact, i.e. their capacity for lubrication, their resistance to oxidation, their carrying power for bringing the cuttings up to the surface, their density and their activity as filtrate-reducing agents. These muds must also contain sufficient basic reserves to neutralize the acidic species encountered during the drilling and generally found in deep layers, such as carbon dioxide or hydrogen sulphide. When terrains are reached containing these acidic species and reaching temperatures above about 100° C., 70% of the volume of the mud required for the drilling has been used, since the deeper the drilling proceeds into the ground, the more the diameter of the well reduces. This results in about 70% by volume of poorly-employed mud, since in this first part of the well corresponding to the so-called surface drilling, the properties required may be less specialized than those required at the bottom of the well. In particular, since the drilling temperatures are low (below 100° C.), the drilling fluid undergoes little transformation such as oxidation, hydrolysis or even decomposition.
It is thus a case of adapting the mud to the terrain passed through, which has a direct impact on the technical, physical and chemical properties of the muds selected, and on the order in which they are used, the consequence being economical, since the purchasing cost of the drilling muds may be reduced.
To add to this first problem are the problems of treating the cuttings at the surface, recovery of the mud by screening in order to recycle it, and storage of the cuttings. These problems, which are already difficult on land, become much more difficult in the case of offshore platforms, since the constraints with regard to environmental regulation are much stricter. Economically, it is more reasonable to dump these cuttings at sea rather than to transport them onshore for treatment, all the more since the volumes of cuttings are much greater, from 60 to 80% of the total volume of the cuttings dumped from the well, in the case of surface drilling. Dumping the cuttings at sea can thus depend on more than just the toxicity of the mud used or its biodegradability in the marine environment.
Among the muds currently used are water-based muds, oil-based muds and so-called replacement muds.
Oil-based muds comprise an oil base formed of crude petroleum or a hydrocarbon-based fraction, to which are added a certain number of additives for improving their rheological properties, their filtrate-reducing power and their basicity. Mention may be made of oils of “diesel” type or mineral oils with a low content of aromatic compounds.
Thus, U.S. Pat. No. 4,481,121 proposes oil-based muds containing from 75 to 95% by volume of gas oil or of a plant oil, in particular extract of pine resin or “tall oil”, paraffins with a melting point of between 76 and 120° C. and from 5 to 25% by volume of a basic reserve consisting of diethanolamide and alkaline hydroxides.
However, such muds are highly toxic to the environment and biodegrade very slowly in aerobic and anaerobic media. Such pollution can pose a major problem if it is necessary to drill through a water table. Certain national legislations have already banned the use of these muds or the offshore dumping of drilling cuttings impregnated therewith.
Water-based muds using aqueous compositions obtained from polymers, polyols or polyglycerol, although being less polluting and biodegradable, are little used on account of their poor stability above 100° C., their insufficient lubricant properties in deflected wells and the presence of water in clay-based terrains.
Replacement muds are used especially as a replacement for oil-based muds, which are often highly aromatic. They are formulated from non-toxic and non-aromatic hydrocarbon-based synthetic products.
A first type of replacement mud is obtained from linear or branched olefins, or, from poly(&agr;-olefins) whose performance characteristics are similar to those of oil-based muds, i.e. maintenance of the lubricant and rheological properties at high temperature, maintenance of good resistance to oxidation and maintenance of their non-toxic nature. They biodegrade slowly in aerobic medium and are relatively non-biodegradable in anaerobic medium (J. Steber et al., Offshore, September 1994). This problem is all the more critical when drillings are carried out at sea, in which it is common practice to dump the mud-impregnated cuttings. Piles of cuttings accumulate under the water, close to the platform, and an accumulation of non-biodegradable chemical compounds is observed in these piles. Inside these piles, since the medium is anaerobic, there is no possible biodegradation of these compounds, while at the surface of the piles, the medium being aerobic, there is slow degradation of these compounds. It is for this reason that certain legislations make provision to greatly limit or even ban the offshore dumping of these cuttings since they are relatively non-biodegradable.
The muds currently preferred consist of readily-biodegradable hydrocarbon-based products, among which are the synthetic esters as described in U.S. Pat. Nos. 4,374,737 and 5,232,910. These highly complicated muds are expensive since they have been designed to satisfy all drilling conditions, including drilling under extreme conditions such as withstanding a temperature above 200° C., oxidation and acidic media.
Alongside these muds are reverse emulsions, which are less polluting since they are considered as being readily biodegradable, such as those described in PCT patent application WO 95/GB95/00680. These reverse emulsions consist of refined plant oils of high viscosity mixed with appropriate diluents to lower their viscosity. These muds based on reverse emulsions can be used irrespective of the temperature throughout the depth of the well. They are less toxic and more biodegradable than the previous muds, but have a very high cost price since they are fully refined and mixed with a diluent which is often expensive and various additives, in particular antioxidants, which are essential for correct behaviour of the emulsion at high drilling temperatures.
The aim of the present invention is to reduce the risks of pollution while at the same time substantially reducing the cost prices of the drilling operation as regards the total cost of the mud used. The invention is also directed towards reducing, or even eliminating, the cost of treating impregnated cuttings, since they contain a less toxic mud and are rapidly biodegradable, it being possible for these cuttings to be dumped into the sea as they are or stored on land.
A subject of the present invention is a process for using biodegradable drilling muds, characterized in that a biodegradable surface sludge which is stable up to about 100° C., which has filtrate-reducing power which is adjustable from 2 to 13 cm
3
depending on the amount of filtrate-reducing agent used, and which has an electrical stability of greater than or equal to 1000 volts, is introduced into the well at the start of drilling, and in that, when the temperature of the terrain passed through reaches 100° C., the said surface sludge is replaced with a so-called bottom sludge which is stable up to temperatures above 200° C., the volume of the said surface sludge representing from 60 to 80% by volume relative to the total volume of sl
Durrieu Josiane
Fraisse Laurent
Guillerme Michel
Rabion Alain
Zurdo Christian
Dougherty Jennifer R.
Elf Exploration Production
Kenyon & Kenyon
Will Thomas B.
LandOfFree
Process for using biodegradable drilling muds does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for using biodegradable drilling muds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for using biodegradable drilling muds will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3129696