Invert emulsion gravel pack fluid and method

Abstract

A gravel packing fluid and method for brine-sensitive formations. The fluid comprises an invert oil emulsion compatible with oil based drilling fluids and having a suspension agent comprising polyurea and dimer diamine. The fluid is capable of carrying gravel yet has a viscosity less than 100 cp, often eliminating the need for an emulsion breaker during flow-back of the fluid to the well surface after deposition of gravel in the well.

Claims

1. A gravel pack carrier fluid comprising: an invert emulsion comprising an oleaginous external phase, an aqueous internal phase, and a type and quantity of emulsifier effective to produce a stable invert emulsion; and a suspension agent comprising a polyurea compound and a dimer diamine compound, such that the carrier fluid is able to suspend and deposit gravel in a wellbore and flowback to the surface.

2. The carrier fluid of claim 1 wherein the dimer diamine compound is a C36 dimer diamine.

3. The carrier fluid of claim 1 having a viscosity less than 100 cp.

4. The carrier fluid of claim 1 having a viscosity less than 40 cp.

5. The carrier fluid of claim 1 wherein the polyurea compound has a concentration in the carrier fluid of from about 1 ppb to about 20 ppb.

6. The carrier fluid of claim 1 wherein the dimer diamine compound has a concentration in the carrier fluid of from about 1 ppb to about 20 ppb.

7. The carrier fluid of claim 1 wherein the aqueous internal phase of the invert emulsion comprises a brine comprising salt selected from the group consisting of: potassium chloride, ammonium chloride, tetramethyl ammonium chloride, and any combination thereof.

8. The carrier fluid of claim 1 wherein the oleaginous external phase of the invert emulsion is compatible with oil-based drilling fluids.

9. The carrier fluid of claim 1 having a density of from about 8.8 ppg to about 19.2 ppg.

10. The carrier fluid of clam 1 further comprising a solid particulate.

11. The carrier fluid of claim 10 wherein the solid particulate has an average particle size of from about 200 U.S. mesh to about 4 U.S. mesh.

12. The carrier fluid of claim 10 wherein the solid particulate has a density of from about 0.5 g/cc to about 4.5 g/cc.

13. A composition comprising: gravel and a carrier fluid that comprises an invert emulsion and a suspension agent comprising polyurea and dimer diamine, wherein the carrier fluid is a carrier for the gravel.

14. The composition of claim 13 wherein the carrier fluid has a viscosity of less than 100 cp.

15. The of claim 13 wherein the polyurea in the carrier fluid has a concentration in the range of about 1 to about 20 ppb.

16. The of claim 13 wherein the dimer diamine in the carrier fluid has a concentration in the range of about 1 to about 20 ppb.

17. The composition of claim 13 wherein the carrier fluid has a density in the range of about 8.8 ppg to about 19.2 ppg.

18. A composition comprising: an oleaginous continuous phase; a discontinuous phase; a suspension agent comprising polyurea and dimer diamine; and a solid particulate.

19. The composition of claim 18 wherein the solid particulate has an average particle size of from about 200 U.S. mesh to about 4 U.S. mesh.

20. The composition of claim 18 wherein the solid particulate has a density of from about 0.5 g/cc to about 4.5 g/cc.

Description

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

(1) The present disclosure provides an improved oil-based gravel packing fluid and method employing water-in-oil emulsions, also called invert emulsions, as the carrier fluid for the gravel. This fluid of the disclosure is especially useful for horizontal wells and wells penetrating brine-sensitive formations. The fluid may also be used as a carrier fluid for particulates for well treatments involving particulates other than gravel packing.

(2) The internal phase of the emulsion of the fluid of the disclosure comprises a brine and the external phase of the emulsion comprises natural or synthetic oil that is preferably compatible with oil or synthetic-based drilling fluids. An emulsifier blended with the brine and the oil facilitates formation of the emulsion. The brine portion of the emulsion dissolves salts to enhance and control the density of the fluid, while the oil portion of the emulsion allows for compatibility with oil-based drilling fluids and with brine-sensitive formations.

(3) Various quantities of natural or synthetic oil and water or brine may be used, so long as an invert (water-in-oil) emulsion is created and the rheology of the fluid is suitable for gravel packing. The oil to water ratio (OWR) of the emulsion for the disclosure is in the range of 30:70 to 90:10. In one embodiment, the ratio is skewed to more oil than water, such as for nonlimiting example, 70:30. In another embodiment, the ratio may have a higher water content, such as for nonlimiting example, 30:70. Higher water to oil content imparts higher viscosity to the fluid. The quantity of emulsifier used is an amount sufficient to facilitate formation of the emulsion. Generally, about 5 to about 20 pounds of emulsifier per barrel are sufficient.

(4) Most preferably, filtered brine or “clear brine” is used for the emulsion. The parameters used in selecting the brine also depend in part on the density that is required of the gravel pack carrier fluid in a given well as will be further discussed below. Brines that may be used in the present disclosure can comprise CaCl.sub.2, CaBr.sub.2, NaBr, NaCl, KCl, potassium formate, ZnBr or cesium formate, among others set forth in Table 1 below. Brines that comprise CaCl.sub.2, CaBr.sub.2, and potassium formate are particularly preferred in embodiments calling for high densities.

(5) Preferred oils for the emulsion are synthetic oils such as olefins, n-paraffins, iso-paraffins, n-alkanes, cyclic alkanes, branched alkanes, esters, and mixtures thereof and some natural oils such as crude oils (preferably diesels and lighter crude oils) and distilled hydrocarbons, and mixtures thereof. Preferred emulsifiers comprise polyaminated fatty acid, polyolefin amides and alkeneamides. Other oil wetting ionic surfactants might also be used for an emulsifer in some embodiments. Preferably, the emulsifier will be relatively passive, stable at temperatures as high as 400 degrees Fahrenheit, and suitable for use with a wide variety of oils, synthetics and produced crudes (or crude oils).

(6) Preferred densities of salts in the emulsions may be determined or controlled by the quantity of halide salt added to the brine and the particular halide chosen. Generally, the more salt added, the greater the density, and the heavier the salt added (depending on its composition), the greater the density. For example, preferably about 10 to 15 or more pounds of calcium chloride or calcium bromide or zinc bromide per gallon of gravel pack fluid may be used for the disclosure, while up to or about 20 or more pounds of cesium formate per gallon of gravel pack fluid may alternatively be used. Preferably the gravel pack fluids of the disclosure have a density that is sufficient to allow the fluid to control the well during well completion operations, since open-hole gravel packing is done almost exclusively in circulating position. Typical fluid densities for the gravel pack fluids are from about 8.8 ppg (pounds per gallon) up to about 19.2 ppg, more preferably about 8.8 ppg up to 14.2 ppg. The desired density of the fluid will depend on the pore pressure and fracture gradient in the formation. General density ranges for clear brine fluids are set forth in Table 1 below.

(7) TABLE-US-00001 TABLE 1 General Density Ranges for Clear Brine Fluids Density Range Clear Brine Fluid lb/gal Ammonium Chloride, NH.sub.4Cl 8.4-8.9  Potassium Chloride, KCl 8.4-9.7  Potassium-Sodium Chloride, KCl/NaCl 8.4-10.0 Sodium Chloride, NaCl 8.4-10.0 Sodium Formate, NaO.sub.2CH 8.4-11.1 Potassium-Calcium Chloride, KCl/CaCl.sub.2 8.4-11.6 Calcium Chloride, CaCl.sub.2 8.4-11.6 Sodium Bromide, NaBr 8.4-12.7 Sodium Bromide-Chloride, NaBr/NaCl 8.4-12.7 Potassium Formate, KO.sub.2CH 8.4-13.1 Calcium Bromide, CaBr.sub.2 8.4-15.1 Calcium Chloride-Bromide, CaCl.sub.2/CaBr.sub.2 11.6-15.1  Potassium-Cesium Formate, KO.sub.2CH/CsO.sub.2CH 13.1-19.2  Cesium Formate, CsO.sub.2CH 13.1-19.2  Zinc Bromide, ZnBr.sub.2 15.2-20.5  Zinc-Calcium Bromide, ZnBr.sub.2/CaBr.sub.2 15.0-20.5  Zinc-Calcium Bromide-Chloride, 15.0-19.2  ZnBr.sub.2/CaBr.sub.2/CaCl.sub.2

(8) The gravel packing fluid of the disclosure further comprises a suspension agent comprising a combination of a dimer diamine (or fatty acid dimer diamine) and polyurea. A commercially available non-limiting example polyurea compound for the disclosure is ADDITIN™ M10.411, available from Rhein Chemie. Preferred commercially available hydrophobic dimer amines suitable for use in the present disclosure include without limitation VERSAMINE® 552 hydrogenated fatty C36 dimer diamine, and VERSAMINE® 551 fatty C36 dimer diamine, both available from Cognis Corporation (functional products) of Monheim, Germany and Cincinnati, Ohio, and PRIAMINE™ 1074, available from Croda Chemicals. These fatty dimer diamines are prepared commercially from fatty dimer diacids which have been produced from dimerisation of vegetable oleic acid or tall oil fatty acid by thermal or acid catalyzed methods.

(9) In one embodiment, the dimer amine used in the present disclosure is a C36 fatty dimer diamine having the following molecular structure:

(10) ##STR00001##
In one embodiment, a preferred commercially available C36 dimer diamine contains C18 fatty monoamine and C54 fatty trimer triamine which are obtained during the commercial production of the dimer diamine. The dimerisation of C18 tall oil fatty acids produces the material leading to the C36 dimer acids. This material is a mixture of monocyclic dicarboxylic acid, acyclic dicarboxylic acid and bicyclic dicarboxylic acid along with small quantities of trimeric triacids. These diacids are converted into diamines via the reaction scheme given below:

(11) ##STR00002##
These diamines are further converted into compounds that fall under the scope of hydrophobic amine additives. These diamines are converted into cyanoethyl derivatives via cyanoethylation with acrylonitrile; these cyanoethyl derivatives are further reduced into aminopropyl amines via reduction as shown in the reaction scheme II below, as taught in U.S. Pat. No. 4,250,045, issued Feb. 10, 1981 to Coupland, et al.

(12) ##STR00003##
Dicyanoethylated dimer diamine is available commercially as Kemamine DC 3680 and 3695 and di N-aminopropylated dimer diamine is available commercially as Kemamine DD 3680 and 3695 from Chemtura Corporation USA. Different structures of the dimeric hydrophobic amine additives are given below:

(13) ##STR00004## ##STR00005##

(14) The suspension agent imparts to the gravel pack fluid the ability to suspend gravel even though the viscosity of the fluid is relatively low. The viscosity of the fluid is less than 100 cp, and preferably less than 40 cp. This suspension agent also eliminates the need to break the emulsion during flow-back since it has such lower viscosity values. The gravel will typically have a U.S. mesh size of between about 20/40 and 40/70.

(15) The invert emulsion carrier fluid of the disclosure should preferably be compatible with typical oil based mud and mud additives used in drilling, so that no thick emulsions or sludges are formed that could damage formations and decrease well production. Thus, for example, in one embodiment, the oil phase of the invert emulsion carrier fluid comprises the same type of oil as used in the oil based drilling mud. Therefore, in such embodiment for nonlimiting example, synthetic oil will be preferably used for the carrier fluid if the well was drilled with a synthetic oil based drilling mud. The oil of the emulsion as noted previously can be either synthetic oil or naturally occurring oil.

(16) In addition, the fluid of the disclosure should have an acceptable health, safety, and environmental profile. The dimer diamine (or fatty acid dimer diamine) and polyurea components comprising the suspension agent are environmentally compatible. Polyurea shows a biodegradability of 71.4% in 42 days and fatty acid dimer diamine shows a biodegradability of 66.5% in 28 days and 82.1% in 35 days. Fatty acid dimer diamine also shows low ecotoxicity to the marine juvenile fish Cyprinodont varieties often used for environmental tests.

(17) Optionally, the carrier fluid of the disclosure can further contain one or more additives such as surfactants, corrosion inhibitors, salts (e.g., potassium chloride), anti-foam agents, scale inhibitors, additional emulsifiers (at between about 0.5 and 3 wt % of the carrier fluid), organophilic clays and bactericides.

(18) For gravel packing, gravel is carried by the carrier fluid of the disclosure into the wellbore site for gravel packing. The emulsions will inevitably contact drilling mud or drilling fluid used in the well, and as noted above, the natural or synthetic oil comprising the emulsion should preferably be compatible with the natural or synthetic oil in the drilling mud. Best results are expected to be obtained when the emulsions are used in gravel packing where the gravel is being continuously deposited during the packing operation. This method may also be used for well treatments requiring deposits of particulates other than gravel. In one embodiment, such particulates may typically have an average particle size in the range of about 200 U.S. mesh to about 4 U.S. mesh and/or a density in the range of about 0.5 g/cc to about 4.5 g/cc.

(19) Specific techniques and conditions for pumping a gravel pack composition into a well are known to persons skilled in this field. The conditions which can be used for gravel-packing in the present disclosure include pressures that are above fracturing pressure, particularly in conjunction with the Alternate Path Technique, known for instance from U.S. Pat. No. 4,945,991, and according to which perforated shunts are used to provide additional pathways for the gravel pack slurry. Furthermore, certain oil based gravel pack compositions of the present disclosure with relatively low volume internal phases (e.g., discontinuous phases) can be used with alpha- and beta-wave packing mechanisms similar to water packing.

(20) In the method of the disclosure, the invert emulsion in the carrier fluid does not need to be broken after deposition of the gravel. That is, the fluid carries and deposits the gravel in the well and then, because of its low viscosity, readily flows back to the well surface. Any fluid that enters the formation readily mixes for production with oil being produced, without need for injection of an emulsion breaker into the well.

(21) Experiments

(22) The advantages of the disclosure are demonstrated by the following laboratory experiments.

(23) A brine in oil invert emulsion fluid was prepared having an OWR of 70:30, using XP07™ base oil, a paraffin alkane synthetic oil available from Halliburton Energy Services, Inc. in Houston, Tex. and Duncan, Okla., and 25% calcium chloride brine. Table 2 lists the additives to four samples of the fluid and their order of addition. Once formulated, 200 ml of each fluid sample was placed in an aging cell and pressurized to 100 psi. The fluid samples were then hot rolled in a roller oven at 250° F. for 2 hours, after which they were cooled in a water bath for 30 minutes. The fluid samples were then poured from the aging cell to mixing cups. To each of those cups, 96 gms of size 20-40 CARBO LITE® sand (available from Carbo Ceramics, Inc. in Houston, Tex. and Halliburton Energy Services, Inc. in Houston, Tex. and Duncan, Okla., were added and mixed well for 5 minutes using a multimixer. The contents of the cups were then transferred into 100 ml measuring cylinders and after 90 minutes, the extent of sand settling and oil separation in each was recorded. The fluid viscosities were also measured and are reported in Table 2. All trademarked products in Table 2 are available from Halliburton Energy Services, Inc. in Houston, Tex. and Duncan, Okla., except that XP07™ is available from ExxonMobil in Houston, Tex. and CARBO LITE® sand is also available from Carbo Ceramics, Inc. in Houston, Tex.

(24) TABLE-US-00002 TABLE 2 Mixing Order of Additives and Fluid Formulations 70:30 Mixing OWR Composition, time, Total 200 ml emulsion min Fluid 1 Fluid 2 Fluid 3 Fluid 4 XP-07 ™ oil, ml — 140 ml  140 ml  140 ml  140 ml  EZ MUL NT ™ 2 7 7 7 10 emulsifier, g Lime, g 2 1.5 1.5 1.5 1.5 BDF 566 ™ polyurea, g 5 3 — 3 3 25% CaCl.sub.2 brine, ml 5 60 ml 60 ml 60 ml 60 ml BDF 570 ™ 5 — 3 3 3 dimer diamine, g 20-40 CARBO LITE ® 5 96 gm 96 gm 96 gm 96 gm sand, g Initial fluid density 7.5 7.5 7.5 7.5 (without sand), ppg Final density, 10 10 10 10 (with 20-40 CARBO LITE ® sand), ppg Viscosity, cp@ 300 rpm 20 10 22 36 on Fann 35, i.e. 511 s.sup.−1 Oil separation 12 17 4 2 after 30 min Sand Suspended No No Yes Yes

(25) The first fluid sample, Fluid 1 in Table 2, was formulated with polyurea as a suspension agent, without any dimer diamine. The viscosity of the fluid after hot rolling at 250° F. was 20 cp when measured on a FANN 35 rheometer at 300 rpm. Sand settling was observed immediately after pouring the contents from the mixing cup into the 100 ml measuring cylinder.

(26) The second fluid sample, Fluid 2 in Table 2, was formulated using a C36 fatty acid dimer diamine as a suspension agent, in the absence of polyurea. The viscosity of the fluid after hot rolling the fluid at 250° F. was 10 cp when measured on a FANN 35 rheometer at 300 rpm. Sand settling was observed immediately after pouring the contents from the mixing cup into the 100 ml measuring cylinder.

(27) The third fluid sample, Fluid 3 in Table 2, was formulated according to the disclosure, with a suspension agent comprising both polyurea and C36 fatty acid dimer diamine. The viscosity of the fluid was 22 cp, after hot rolling the fluid at 250° F. when measured on a FANN 35 rheometer at 300 rpm. The fluid held the sand in suspension and after 90 minutes of settling time in the measuring cylinder was still able to hold the 20-40 Carbolite sand in suspension. Thus, even with a low viscosity of 22 cp, no sand settling was observed.

(28) The fourth fluid sample, Fluid 4 in Table 2, was also formulated according to the disclosure, with a suspension agent comprising both polyurea and C36 fatty acid dimer diamine, but with a higher emulsifier concentration (10 g instead of 7 g of EZ MUL® NT emulsifier, available from Halliburton Energy Services, Inc. in Houston, Tex. and Duncan, Okla.) than used with the other fluid samples. The final viscosity of the hot rolled fluid was 36 cp. Increasing the emulsifier concentration helped to stabilize the emulsion, thereby minimizing oil separation and providing good sand suspension. Even with this still relatively low viscosity for a gravel packing fluid, Fluid 4 showed good gravel suspension characteristics. This fluid sample also showed an oil separation of 2 ml after 30 minutes and that separation remained the same—did not increase—after six hours.

(29) The foregoing description of the disclosure is intended to be a description of preferred embodiments. Various changes in the details of the described fluids and methods of use can be made without departing from the intended scope of this disclosure as defined by the appended claims.