Earth boring – well treating – and oil field chemistry – Earth boring – Contains inorganic component other than water or clay
Reexamination Certificate
2000-07-14
2002-11-05
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains inorganic component other than water or clay
C507S904000, C516S110000, C252S184000
Reexamination Certificate
active
06475959
ABSTRACT:
The present invention relates to a method for the rheology control of fluid phases and a suitable composition for this purpose.
The thickening of water- and oil-based systems, so-called rheology control, is carried out in practice especially with the aid of finely divided swellable clays and/or other silicate compounds of natural or synthetic origin. The various fields of work make use of the possibility, existing here, of the shear-thinning and/or thixotropic thickening of the respective fluid phases.
In particular, adducts of mixed metal hydroxides and clay have been widely described in the past and are popular in practice. The individual mixed metal hydroxide types each thicken the initially introduced clay suspension, with the result that pronounced shear-thinning rheology is obtained.
Mixed metal oxides (“MMH”) or layered double hydroxides (“LDH”) are a class of substances comprising clay-like minerals of the general empirical formula
[M
II
1−x
M
III
x
(OH)
2
](A
n
)
−x
Here, M
II
and M
III
are divalent or trivalent metal cations and A is any desired anion. A further designation, namely “HTC-type minerals”, is derived from the most well-known member, hydrotalcite, an Mg—Al-carbonate-MMH.
The preparation of MMH compounds by coprecipitation and their use as thickeners are described, for example, in the patent documents European Patent 207 801 and European Patent 207 811. Accordingly, an Mg Al hydroxychloride MMH having the composition MgAl(OH)
5-x
Cl
x
is obtained, for example, by precipitation of MgCl
2
with AlCl
3
in the presence of a base.
Owing to the various disadvantages of this coprecipitated MMH product, such as, for example, high production costs and the necessity of a dispersant, an improved material in the form of the activated, hydrated mixed metal oxide (AHMMO) was made available to the user. A mixed metal oxide or mixed metal oxyhydroxide of the general empirical formula
Mg
1−x
Al
x
(O)
y
(OH)
z
is obtained by thermal activation of, for example, hydrotalcite. The activation process, optimized with respect to the thickening effect, results in the compound additionally containing smaller residual amounts of carbonate and water of hydration. The commercial product thus obtained is a highly effective MMH concentrate. If this product is added to water, it undergoes hydration with formation of Mg—Al—OH-MMH (AHMMO). This MMH species having mobile hydroxide moieties instead of carbonate is suitable, according to European Patent 539 582, as a thickener for aqueous clay suspensions. In contrast to the coprecipitated MMH, the AHMMO is chloride-free, requires no additional dispersant and can be prepared in a more economical and environmentally compatible manner.
According to European Patent 617 106, however, mixtures of, for example, sodium aluminate and magnesium oxide also act as thickeners in aqueous clay suspensions. As various analytical methods, in particular X-ray diffraction, have shown, Mg—Al—OH-MMH according to the empirical formula presented at the outset form here again in situ.
In addition to these MMH or LDH types having a layer structure, the mixed metal hydroxides having a three-dimensional network structure are also used for thickening aqueous clay suspensions. In WO 94/02 566, katoites having the basic formula
Ca
3
Al
2
(OH)
12
in which some of the OH groups are replaced by silicate radicals, are mentioned as being preferred for this purpose. Such MMH compounds are also known under the name mixed metal silicates (MMS). However, some MMS/clay drilling fluids have a substantially lower thermal stability than MMH/clay-based fluids.
The Theological properties of MMH/clay-based drilling fluids are very valuable in particular for drilling technology.
Auxiliary fluids thickened to a shear-thinning viscosity of a greater or lesser extent are preferably used in the technology of geological and other drilling operations in the earth, but also, for example, as an earth support in excavations, in particular in subterrain curtain construction, in the sinking of shafts, wells and caissons, in pipe forcing, etc. Particularly important fields of use are wells for petroleum or natural gas exploration and horizontal drilling for trenchless pipe construction.
Drilling fluid systems which are sufficiently thickened by the addition of mineral viscosifiers without losing their flowability and pumpability under shearing stress and which contain additional dissolved, emulsified and/or suspended assistants adapted to the respective situation are widely used.
The high carrying capacity of MMH/clay fluids has proven its worth especially in large-caliber wells, when milling out damaged casing, in horizontal drilling and in drilling through coarse gravel. In particular, stuck-pipe problems by the settling of drill cuttings are prevented. In addition, the drilling fluid should be of low viscosity and readily pumpable at points of higher shearing stress, such as, for example, on emergence from the drill bit. For rapid advance of the drilling, a reduction in viscosity, which is high at rest, with growing shear gradient is required. This type of flow behavior is generally referred to as shear-thinnings.
MMH/clay-based drilling fluids have such a rheology. In contrast to biopolymers having also a shear-thinning effect, such as, for example, xanthan gum, crosslinking with bentonite, a smectite clay, usually used in drilling technology takes place when MMH is used. This cooperation of MMH with bentonite in the common network results in extreme shear-thinning fluid properties at relatively low costs in comparison with the biopolymer drilling fluids. The latter must in fact generate the desired rheology completely by themselves, for which purpose substantially higher doses are required.
According to Bingham, the rheology of a drilling fluid can be described by the yield point (YP[lbs/100 ft
2
]) and the plastic viscosity (PV[cP]). These parameters can be determined by measuring the shear stress in a rotational viscometer (e.g. FANN 35 from Baroid, Houston, USA) at different shear rates. Thus, plastic viscosity PV is obtained as the difference in shear stress at 600 and 300 rounds per minute, and the yield point YP as the difference between the PV and the shear stress at 300 revolutions per minute. The respective yield point is however always proportional to the carrying capacity of a drilling fluid. However, it should be noted that a high plastic viscosity results in only a small rate of penetration. A typical shear-thinning rheology is characterized by low PV and high YP values.
According to the prior art to date, MMH/clay, MMS/clay and biopolymer drilling fluids are not suitable for high-temperature applications at >300° F. (>149° C). Biopolymers lose their activity at the latest at about 280° F. (about 138° C.). High-quality AHMMO compounds, too, are limited to temperatures of use of up to and including about 300° F. (about 149° C.).
It was thus the object of the present invention to provide a method for the rheology control of fluid phases and suitable compositions therefor, which are suitable both for water-based and for oil-based systems and cover a wide temperature range.
This object was achieved by a method in which adducts of layered mixed metal hydroxides (MMH) and smectite clays are used as rheology control compositions, a hectorite being at least partly used as the smectite clay. Hectorite is a material having the approximate composition Na
0.33
(Mg,Li)
3
[Si
4
O
10
](OH, F)
2
, optionally without Li and/or F. The hectorite structure derived from the prototype talc is described, for example, in Ullmann's Encyclopaedia of Industrial Chemistry, 5
th
Edition, Vol. A7, pages 110-111. The proportion of hectorite in the total amount of smectite clay is preferably at least 20% by weight and particularly preferably at least 50% by weight.
Surprisingly, it has been found that, with the method according to the invention, the corresponding composition, not only is the desired broad field of use as a rheology cont
Keilhofer Gregor
Lange Peter
Plank Johann
Fulbright & Jaworski L.L.P.
SKW Polymers GmbH
Tucker Philip
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