Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
1999-09-13
2001-10-16
Warden, Jill (Department: 1742)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S143000, C507S215000, C507S216000, C507S270000, C507S271000, C106S172100
Reexamination Certificate
active
06303544
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to aluminium modified cellulose products. These products can be used as drilling-, completion- and work-over fluids additives used in the drilling of subterranean oil-, gas- and water wells. In particular, the invention provides water-soluble components which provide shale inhibiting-, thermostability-, viscosifing- and fluid loss reducing properties comparable to those of an oil based drilling fluid, without the adverse effects of an oil- or pseudo-oil based mud.
BRIEF DESCRIPTION OF PRIOR ART
A rotary system is the most common form of drilling a subterranean well. This system depends upon the rotation of the column of drill pipe to the bottom of which is attached a multi prolonged drilling bit. The drill bit cuts into the earth, causing to accumulate cuttings as drilling continues. As a result, a fluid must be used to carry these cuttings to the surface for removal, thus allowing the bit to continue functioning and the bottom of the hole to be kept clean and free of cuttings at all times.
When the drilling process is on going, the drilling fluid has to protect the borehole wall from deformation and/or deterioration resulting from reactions of the sediments or formation with the liquid and other containing elements of the said fluid. These chemical and/or physical reactions are resulting from the osmotic and/or crystalline effects. These sensitive formations are classified as shales and need to be stabilised. By “shales” is meant to refer to materials from the smectic group such as bentonite and the like, claystone and “gumbo”-type colloidal-clay substances seen in subterranean formations, and related substances which posses the property of hydrodynamic volume increase when exposed to aqueous environments. Shale stabilisation is believed to at least partially be dependent upon inhibition of swelling and dispersion process of the shale by the fluid.
Shales and shale reactions are extensively described in literature like: Van Olphen, H., “An Introduction to Clay Colloid Chemistry”, second edition, John Wiley & Sons, New York, 19977, p. 30; and Darley, H. C. H. and Gray, George R., “Compositions and Properties of Drilling and Completion Fluids” 5th edition, Gulf Publishing Company, Houston, p. 140.
To transfer the cuttings to the surface, the fluid has to posses a certain rheology to carry and suspend the solids. The viscosifying components of the ingredients of the drilling fluid are designed for this purpose.
Further, the drilling fluid has to prevent or at least reduce the introduction of fluid, salts and solids into the formation.
The temperature increase, due to reaching greater depths of the well, will reduce the viscosity and causes the deterioration of the components of the drilling fluid.
As the drilling process has reached its target depth, the well has to be prepared for its function as oil- or gas producer, water- or gas- or cutting-injector or as water well. This phase is referred to as completion phase. Very often the drilling fluid will be exchanged for a so called completion fluid to bring the well to completion.
After a certain time period the well is reduced in its function and has to be repaired. The fluid used during this operation is called as a work-over fluid.
Some cellulose derivatives do posses inhibiting-, viscosifying-, fluid loss reducing- and and thermostabilizing properties but by a chemical and/or physical treatment these phenomenon can be enhanced. Cellulose polymers like carboxy methyl cellulose (CMC), poly anionic cellulose, hydroxy ethyl cellulose and all other cellulose derivatives can be modified by cross- and block linking in the process of the synthesis.
In Russian patent RU 2001936 the application of so-called carboalumilon is reported. The ligand in this case is Trilon B (ethylene-di-amin-tetra acetic acid), a commercial product from BASF in Germany. The preparation of carboalumilon is not mentioned in RU 2001936 nor any detail of the synthesis is given nor physical or chemical properties.
DESCRIPTION OF THE INVENTION
We have discovered that certain colloids based on cellulose derivatives are acting as inhibitors-, viscosifying and fluid loss reducing and thermostability improving agents in water based drilling-, completion- and work-over fluid and are from synthesis of cellulose with chemicals to be described below.
The products can be used in technical or purified form.
The invention and some of its preferable embodiments are presented in the claims.
In the search for improved inhibiting-, viscosifying-, fluid loss reducing- and thermostabilizing properties of cellulose derivatives, a modifying ability of certain ligands and cations was utilised. The positive effect here is achieved by means of cross linking of cellulose macromolecules the cations and ligands. Further, as the drilling process is continued, the temperature of the sediment will increase depending on the nature of the formation properties. Specially when applied in a horizontal well profile the duration of higher temperature exposure is extended. The mentioned additives will provide a protection against deterioration caused by the elevated temperature of the formation.
The cellulose product may be a cellulose ether, such as carboxymethyl cellulose (CMC), hydroxyethyl cellullose (HEC), carboxymethyl hydroxyethyl cellulose (CMHEC), methyl cellulose (MC), hydroxyethyl methyl cellulose (HMEC) or ethyl hydroxyethyl cellulose (EHEC), or a xanthan gum product.
Molecules of the complex formers link cellulose molecules via aluminium-, ferro-, ferri-, zinc-, nickel-, tin(2)- and tin(4)-cations.
The amount of the salt used counted as percent based on dry cellulose may be in the range 0.1-20 wt %, preferably 0.5-5 wt %. The amount of the ligand used may be in the range 0.1-20 wt %, preferably 0.5-5 wt %.
The products have the ability to improve the interaction of drilling fluids, containing this product, and the clays/shales of the formation to be drilled through, and afterwards, exposed drilled formation to the said drilling fluid.
Especially the products have the ability to improve temperature stability of the mud system added to a water based drilling fluid, and the ability to reduce fluid loss when applied in drilling fluids for the payzone.
The products are also applicable in brines, like NaCl, KCl, NaBr, Na-formate, K-formate and Ce-formate for drilling purposes, completion and work-over fluids.
Increasing thermostability of drilling fluids treated with cellulose derivatives like CMC was obtained especially by addition of water soluble aluminium salts like Al
2
(SO
4
)
3
resulting in more stability to high temperatures.
The especially advantageous effect of the added aluminium salts can be explained by the inhibiting action of aluminium cations increasing the alkali nature of the water solution of the drilling fluid due to the formed complex compositions. In these formed complex compositions a role of linking agents (ligands) can be performed by hydroxyls, water molecules and the cellulose macro molecules, which form multi valence- and co-ordinating links with the aluminium cations by means of carboxyl and hydroxyls. In this case the positive effect of cross linking of cellulose macromolecules by three valence aluminium cations is utilised.
In the process of synthesis of aluminium modified cellulose derivatives, partial substitution of sodium ions of cellulose macro molecules for aluminium ions takes place. The introduction of aluminium cations can decrease to a certain degree the solubility of the finished product.
Besides the increased thermostability and stability to salts aluminium modified cellulose derivatives have inhibiting effects on clays.
In this case the main linking agent (ligand) of the formed complexes are CMC molecules, but beside them there can be molecules of other compounds, which are able to form complexes with polyvalent cations. By introduction of certain ligands in the complex it is possible to influence on purpose the properties of the complex.
E.g. nitrilo-tri-acetic acid (NTA) or its sodium salt; or 1,2-cyc
Kloow Goeran Einar
Maas Antonius Franciscus
Ruppert Oliver
Cross LaToya I.
Metsa Specialty Chemicals OY
Millen White Zelano & Branigan P.C.
Warden Jill
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