DRILLING FLUID

Abstract: Drilling fluid for drilling of wells is subterranean formations where the weight material includes particles of one or more metals and/or metal alloys, including iron and steel. The particles are preferably formed as pearls (pellets) or are ball-shaped and can be made of stainless steel. The weight material can have a small part of particles made of zinc for cathodic protection of pumps and pipe installations which the drilling fluid is transported through.

Description: Drilling fluid. The .invention concerns a drilling fluid with weight material for drilling of wells in subterranean formations. By drilling in subterranean formations it is known to add a weight material to the drilling fluid to counteract or partly counteract the great pressure that can be present in such formations, especially at great depths, and also to increase the buoyancy of the drilling equipment that is present in the drilling fluid. In this connection different minerals are today used as weight material, for example barite, ilmenite etc., which is ground to a suitable granulate consistancy and forms a part of the drilling mud. The properties of these minerals in pro¬ portion to the general functions of the drilling fluid can vary, and especially they can involve great wear and tear in the pumps and pipe installations the drilling fluid is led through on the way to and from the well. It is also known to supply iron as a weight material for later to remove it from the drilling fluid by magnetic means for reusing the iron. This is for example known from US patent No. 1663 492 and US patent No. 2276 075. Even if the recovering of iron particles is simplified by use of magnetism and the necessary equipment for such recovery is considerably less space demanding than corresponding equip¬ ment for mineralic weight material, there are still great problems with tear and wear of pumps, valves and other pipe installations. These problems are, however, avoided by the drilling fluid according to the invention, in the way it is described in the caracterizing part of the claims. By help of the weight material according to the invention, it is not only attained that this can be drawn out of the drill¬ ing mud by magnetism, but also that the tear and wear of pumps, valves and other pipe installations to a great extent is reduced because of the shape of the particles. It has also shown that the shape of the particles, according to the invention, gives the drilling mud a ball bearing-like effect by sidework of the drill string, which particularly is of great importance in deviation drilling. Experiments have shown that drilling mud with weight material according to the invention has good rheological properties, because the steel-spheres are stably suspended in the drill¬ ing mud. During the drilling process the particles, according to the invention, are exposed to minimal grinding because of the particles own strength and shape. The weight material according to the invention, can include particles of one or more metals, metal alloys or combina¬ tions. It is especially suitable that the particles are shaped as pearls (pellets) or balls. The particles can suitably be produced of stainless steel so that the particles are not exposed to corrosion and thus give the possibility for use in a longer period by regaining for example by the help of magnetism. The spheres can also, however, be produced of usual soft steel and it can then be suitable to mix corresponding par¬ ticles of zinc with the weight material, but in a less amount based on volume. These zinc particles can be pearl-shaped (pellet) and for example be produced by electronic evapora¬ tion and condensation. Pearl-shaped zinc particles can how¬ ever, also be produced by liquid automizing or by mechanical automizi.ng. Further the zinc particles can be produced with ball-shape by gas-atomizing. It is suitable that the diameter of the zinc-particles is less than 250 μm. Zinc particles can be mixed both with particles of soft steel and stainless steel to thus give cathodic protection of pipe installations in the mud system. The weight material of metal particles of soft steel or stainless steel can have pearl-shape (pellet) and ball-shape. Pearl-shaped particles can be produced by fluid-automizing or mechanical automizing, while the ball-shaped prticles can be formed by gas automizing. Particles of other alloys with pearl-shape or ball-shape or mixtures of different alloys, can also be suitable. The diameter of the pearls can be less than 1000 μm , preferably between 15 and 75 u . An improvement of the floating properties of the particles in the drilling fluid can be gained by coating the surface of the particles with chemicals. An improvement of the floating properties can also be gained for example by deforming the larger particles from ball-form respectively pearl-form to approximately ellipsoides. It has been carried out comparative experiments with par¬ ticles according to the invention, barite and ilmenite. Here the rheological properties, floating properties and tear and wear are examined for drilling fluids with different viscosi¬ ties, see table 1 and 2. In table 1 the results of measuring viscosity by 600, 300, 200 and 100 cycl./min. are set up. Values for the plastic viscosity PV and the floating limit (yield point) YP are also marked. The measurements were carried out for base mud with average viscosity, AV, of 5, 6,5, 8 and 10 cp. As weight material according to the invention there was used steel- balls produced by Uddeholm Stainless AB, Sweden, with frac¬ tions less than 150 μm and less than 20 μm. In addition ex¬ periments were carried out with a mixture of these two frac¬ tions and also a mixture with a fraction less than 20 μm and a fraction between 44 and 80 μm . These mixtures were all carried out by 50/50%. The experiments were carried out by baroid rheometer. The base mud consisted of bentonite pre- hydrated in destilled water. Table 2 shows measurements of stability during time of the before mentioned weight materials, where the percentage water at the top and percentage precipitate were measured after 72 h. From table 1 it appears that the weight material with par¬ ticles according to the invention gives rheological proper¬ ties that can be compared with barite and ilmenite. Table 2 shows that the steel-balls are stably suspended in the mud. It was further- made experiments to measure tear and wear of two fractions, less than 150 jam and 44 to 80 μm. The tear and wear for fractions less than 150 u was measured to 0,6 mg/min, and for 44 to 80 u 1.0 to 1.6 mg/ in. Earlier corresponding examinations of tear and wear have shown that ilmenite gives between 4.0 and 6.0 mg/min, while barite is in the order of 0.6 and 1.0 mg/min. On the basis of the experiments of tear and wear it is ex¬ pected that the tear and wear of pumps and other pipe in¬ stallations will be in the same order by use of barite and steel-balls as weight material. One further expect that the grinding of the steel-balls during drilling will be minimal because of the strength and shape of the balls and that the balls will have great advantages because they to a great ex¬ tent can , be regained in a simple way. TABLE 1 RHEOLOGICAL PROPERTIES Basemud • Weight material AV Remar cp - 600 300 200 100 PV YP < 150 n 5 19 10 7 5 9 1 Separ quite < 20 μm ' 5 32 16 10 7 16 0 Barite 5 31 16 10 7 15 1 Ilmenite 5 23 11 7 6 12 -1 50/50%0<20 n/<l£ >0μm 6,5 40 20 13 7 20 0 < 20 μm 6,5 41 20, 5 13 7 20,5 0 Barite 6,5 44 23 15 8 21 2 Ilmenite 6,5 39 22 15 10 17 5 < 150 μm 8 41 21 14 9 20 1 < 20 μn 8 44 23 16 9 21 2 Barite 8 44 23 16 8 21 2 Ilmenite 8 41 22 16 10 19 3 < 150 jum 10 54 31 19 13 23 8 Barite 10 62 34 25 14 28 6 TABLE 2 STABILITY DURING TIME (72 HOURS) Weight material asemud % water % AV at the top precipitation Remarks cp < 20 μm 6,r5 14 0 Worse to Barite 6,r5 10 ca.5 Worse to (bad passage) Ilmenite 6, ,5 0 0 Very easy stir 50/50%*<20;ιm/44- -80 m 8 17 5 Easy to s < 150 μm 8 2 11 Worse to < 20 μm 8 10 0 Easy to s Barite 8 7 0 Easy to s Ilmenite 8 0 0 Very easy stir < 150 μm 10 0 0 Very easy stir 50/50%=<20 / m/44- ■ 80μm 10 0 0 Very easy stir Barite 10 5 0 Easy to st

Claims: Patent Claims 1. Drilling fluid with weight material for drilling of wells in subterranean formations, c h a r a c t e r i z e d i n t h a t the weight material includes particles of one or more metals and/or metal alloys, including iron and steel. 2. Drilling fluid according to claim 1, c h a r a c t e r i z e d i n t h a t the particles are made of stainless steel. 3. Drilling fluid according to claim 1, c h a r a c t e r i z e d i n t h a t the weight material includes zinc particles and a greater part based on volume of at lest one other metal. 4. Drilling fluid according to claim 3, c h a r a c t e r i z e d i n t h a t the diameter of the zinc particles is less than 250 μ . 5. Drilling fluid according to claims 3 - 4, c h a r a c t e r i z e d i n t h a t the zinc particles are shaped as pearls (pellets) and are produced by electrostatic evaporation and con¬ densation. 6. Drilling fluid according to claim 5, c h a r a c t e r i z e d i n t h a t the zinc particles are shaped as ellipsoides and are produced by pressing together particles shaped like pearls (pellets). 7. Drilling fluid according to claims 1 - 4, c h a r a c t e r i z e d i n t h a t the particles are in the shape of pearls (pellets). 8. Drilling fluid according to claim 7, c h a r a c t e r i z e d i n t h a t the pearl-shaped particles are produced by fluid atomizing. 9. Drilling fluid according to claim 7, c h a r a c t e r i z e d i n t h a t the pearl-shaped particles are produced by mechanical atomizing. 10. Drilling fluid according to claims 7 - 9, c h a r a c t e r i z e d i n t h a t the pearl-shaped particles, after being produced, are pressed together to an ellipsoidic form. 11. Drilling fluid according to claims 1 - 4, c h a r a c t e r i z e d i n t h a t the particles are ball-shaped. 12. Drilling fluid according to claim 11, c h a r a c t e r i z e d i n t h a t the ball-shaped particles are produced by atomizing with gases, including steam. 13. Drilling fluid according to claims 11 - 12, c h a r a c t e r i z e d i n t h a t the ball-shaped particles are pressed together to an ellipsoidic shape. 14. Drilling fluid according to claim 1 - 2, c h a r a c t e r i z e d i n t h a t the diameter of the particles is less than 250 μm, preferentially between 15 and 75 μm. 15. Drilling fluid according to claims 6 - 11, c h a r a c t e r i z e d i n t h a t the surface of the metal particles is coated with chemicals to improve the floating properties of the particles.

Inventors: FARSTAD OTTO, FARSTAD, OTTO
Applicants: FARSTAD OTTO, FARSTAD, OTTO
Application year: 1985
Main classification: C09K7
IPC codes: C09K8