Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Utility Patent
1997-12-12
2001-01-02
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C523S130000, C507S118000, C507S119000
Utility Patent
active
06169134
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to oil-based drilling muds viscosified with ethylene/propylenes elastomers grafted with dicarboxylic acid anhydrides. Specifically, the invention relates to oil-based muds viscosified with maleated EPM copolymers and EPDM terpolymers.
In the field of drilling in the exploration for oil and gas, an important component is that of the formulation of drilling muds. Drilling muds are the fluids which are used to maintain pressure, cool drill bits and lift cuttings from the borehole and vary in composition over a wide spectrum. Generally, drilling muds are based on aqueous formulations or oil-based formulations.
A conventional oil-based drilling mud formulation is comprised of basically the following ingredients: oil (generally refined oil), emulsifying agents, water (e.g. brine), and viscosifying agent. The formulation may also include wetting agents, weighting agents and amine treated clays.
The above formulations perform adequately in a number of applications, primarily those where the use of oil-based drilling muds is dictated by the lack of stability of the formation in which drilling is taking place. For example, in various types of shale formation, the use of conventional water-based muds can result in a deterioration and collapse of the shale formation. The use of the oil-based drilling muds circumvents this problem.
Viscosifying agents are used in the drilling mud to impart Theological properties thereto to enhance the mud's ability to carry and suspend particle (drill cuttings and barite). Asbestos has been used as a viscosifying agent but, for obvious health reasons, it is no longer used as an oil based viscosifier. Sulfonated EPDM's (disclosed in U.S. Pat. Nos. 4,157,432 and 4,442,011) have been proposed for use as oil mud viscosifiers, but have not received extensive use because the lack of availability.
Oil mud viscosifiers presently widely used are organophilic clays treated with quaternary amine compounds to impart lipophilic properties thereto. For many wells, particularly deep hot wells, relatively large amounts of the organophilic clays must be used to be effective. Excessive solids in the mud can lead to problems such as high plastic viscosity, and resultant mud circulation problems.
As described below, the oil-based drilling mud of the present invention employs ethylene-propylene elastomers grafted with certain dicarboylic acid anhydride (specifically maleic anhydrides). U.S. Pat. No. 4,670,515 discloses ethylene-propylene rubbers grafted with maleic anhydrides (and other dicarbonylic acid anhydrides) used as low molecular weight oil VI improver and as impact modifier for polar thermoplastic resins. Other maleated polymers are disclosed in U.S. Pat. Nos. 4,661,554; 4,857,254; 4,950,541; 5,047,479; 5,047,479; 5,066,542; 5,151,083; and 5,346,963. None of these references however relate to oil-based drilling muds.
SUMMARY OF THE INVENTION
The oil-based drilling mud of the present invention comprises an oil mud viscsified with ethylene-propylene (EP) elastomers, particularly EPM copolymers and EPDM terpolymers, grafted with certain dicarboxylic acid anhydrides, preferably maleic anhydride.
The preferred grafted polymer, maleated EP elastomer, is prepared by reacting from 0.01 to 5.0 wt % of maleic anhydride with the EP elastomers.
The maleated EP elastomer is added to the oil mud at the desired level to improve key rheological properties (based on API RP-13) of the mud, such as viscosity, yield point, and gel strength.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
For purposes of describing the present invention, the following terms shall have the definitions indicated:
“Ethylene-propylene elastomers” are synthetic polymers comprising ethylene/propylene copolymers (EPM) and ethylene/propylene/diene terpolymers (EPDM).
“EPM” is a copolymer having the following general formula:
“EPDM” is a terpolymer having the following general formula:
“Oil mud emulsion” comprises a hydrocarbon liquid as the continuous phase and water as the discontinuous or dispersed phase.
The composition of the oil base mud of the present invention comprises mainly
(a) an oil phase
(b) a dispersed water phase
(c) a viscosifying agent (maleated EP elastomer)
These mud ingredients and methods of preparing and using the oil based mud are described below.
Oil and water phases (oil mud emulsion): As indicated above oil mud may comprise any hydrocarbon liquid including diesel oil, fuel oil, crude oil, refined oil and the like. Because of costs, diesel oil is generally the preferred hydrocarbon liquid.
The water dispersed in the oil may be fresh water but preferably is brine. From 1 to 40, generally 2 to 20, wt % of the water is dispersed in the oil by use of emulsifiers such as alkaline soaps of fatty acids.
The oil based muds described above are well known in the art (see for example U.S. Pat. No. 4,525,522).
Viscosifying Agent: The viscosifying agent of the present invention will be described with reference to the preferred maleated EP elastomers. It is to be understood, however, that other dicarboxylic acid anhydrides described generally below may be used instead of the maleated EP elastomers.
The preferred elastomers are EPM copolymers and EPDM terpolymers having the following formulas:
The values of m and n are selected to satisfy (a) the mole ratios of the ethylene and propylene in the copolymer and (b) the molecular weight of the copolymers, both of which are described below.
where R is selected from 5 ethyldiene-2-norbornine; 1-4-hexadiene; 5-phenyl-2-norbornene, and dicyclopentadiene. The values of x, y, and z are selected to satisfy (a) the mole ratios of the comonomers and (b) the molecular weight, both of which are described below.
The ethylene content of the EPM copolymer ranges from 20 to 90 mole %, preferably from 30 to 80 mole %, and most preferably 40 to 60 mole %, with a Mooney viscosity of from 7 to 90 (ML (1+4) at 125° C.) and 0 gel. The number average molecular weight ranges from 40,000 to 150,000, preferably 40,000 to 100,000, most preferably 50,000 to 80,000. The copolymer may be amorphous or crystalline.
The preparation of the EPM copolymers are well known in the art, as disclosed in U.S. Pat. No. 4,670,515, the disclosure of which is incorporated herein by reference.
The EPDM elastomers are terpolymers containing from 20 to 90 mole percent (preferably 40 to 90 mole %) of ethylene, from 20 to 70 mole percent of propylene, and from 1 to 20 mole percent of the diene monomer. The dienes include 5-ethylidene-2-norbornene; 1, 4-hexadiene; 5-phenyl- 2- norbornene; and dicyclopentadiene. As stated in the
ENCYCLOPEDIA OF POLYMER SCIENCE AND ENGINEERING
, Vol. 6, pp. 522-523, ethylene-propylene elastomers are made from the basic building blocks of ethylene and propylene and may be combined with a third, or even a fourth, monomer to provide the olefinic sites along the backbone. The term “EPDM elastomers” include terpolymers and tetrapolymers that include at least monomers of ethylene, propylene, and diene.
The preferred EPDM elastomers (ethylene/propylene/5-ethylidene-2-norbornene) have about 0.5 to about 12 wt % 5-ethylidene-2-norbornene monomer, about 30 to 70 wt % ethylene, with the balance of the polymer being propylene. A typical ethylene/propylene/5-ethylidene-2-norbornene terpolymer has an ethylene content of about 50 wt % and a 5-ethylidene-2-norbornene content of about 5 wt %. The terpolymers useful in the present invention have a number average molecular weight (M
n
), as measured by GPC, of about 40,000 to about 150,000, more preferably of about 40,000 to about 100,000, and most preferably of about 50,000 to about 80,000. All polymer molecular weights quoted herein are number average molecular weights unless otherwise indicated. The Mooney viscosity (ML 1+4, 125° C.) of the terpolymer is about 7 to about 90, more preferably of about 10 to about 80 and most preferably about 20 to about 70. The EPDM should have a low crystallinity ((50%) and preferably less than 30%. The degree of crystallinity and
Acker David B.
Jones Cruise K.
Breininger Thomas M.
Danison Walter C.
Mulcahy Peter D.
Nalco/Exxon Energy Chemicals L.P.
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