Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
  • C09K8/02—Well-drilling compositions
  • C09K8/32—Non-aqueous well-drilling compositions, e.g. oil-based
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
  • C09K8/02—Well-drilling compositions
  • C09K8/32—Non-aqueous well-drilling compositions, e.g. oil-based
  • C09K8/36—Water-in-oil emulsions

Definitions

• the present invention relates to oil-base drilling fluids and systems and processes for drilling a borehole in a subterranean formation.
• Oil-base drilling muds and techniques for drilling boreholes in subterranean formations to recover hydrocarbons are well known to those skilled in the art.
• an oil-base drilling fluid comprising oil, a surfactant, a fluid loss control agent, and a viscosifier
• the fluid loss control agent is selected from the group consisting of polystyrene, polybutadiene, polyethylene, polypropylene, polybutylene, polyisoprene, natural rubber, butyl rubber, polymers consisting of at least two monomers selected from the group consisting of styrene, butadiene, isoprene, and vinyl carboxylic acid, and mixtures thereof and the viscosifier is a sulfonated elastomer polymer.
• an oil-base drilling fluid weighing about 7.5 to about 20 pounds per gallon and comprising: (a) about 25 to about 85 volume percent oil based on the total volume of the fluid; (b) about 1 to about 20 pounds per barrel (ppb) surfactant; (c) up to about 45 volume percent water based on the total volume of the fluid; (d) up to about 600 ppb weighting agent; (e) about 0.5 to about 30 ppb organophilic clay; (f) up to about 30 ppb auxiliary fluid loss control agent; (g) about 3 to about 12 ppb polymeric fluid loss control agent selected from the group consisting of polystyrene, polybutadiene, polyethylene, polypropylene, polybutylene, polyisoprene, natural rubber, butyl rubber, polymers consisting of at least two monomers selected from the group consisting of styrene, butadiene, isoprene, and vinyl carboxylic acid, and mixtures thereof; (h) about 25 to about 85 volume percent oil
• a drilling system comprising: (a) at least one subterranean formation; (b) a borehole penetrating a portion of at least one of the subterranean formations; (c) a drill bit suspended in the borehole; and (d) a drilling fluid located in the borehole and proximate the drill bit, wherein the drilling fluid is the oil-base drilling fluid, as described above.
• a method for drilling a borehole in a subterranean formation comprising the steps of: (a) rotating a drill bit at the bottom of the borehole and (b) introducing a drilling fluid into the borehole (i) to pick up drill cuttings and (ii) to carry at least a portion of the drilling cuttings out of the borehole, wherein the drilling fluid is the oil-base drilling fluid, as described above.
• Organophilic clays used in oil-base drilling fluids have been observed to degrade when the drilling fluid is maintained at bottomhole temperatures exceeding 400° F. This degradation lowers the yield point of the drilling fluid ⁇ rendering the drilling fluid incapable of suspending solids and resulting in expensive drilling problems such as weighting agent sagging, mud density variations, solids settling, stuck drillpipe, poor hole cleaning, excessive fluid loss to the formation, and poor cement jobs.
• the present invention provides an oil-base drilling fluid capable of being held at temperatures in excess of 400° F while maintaining its yield point.
• the oil-base fluid comprises (i) oil, (ii) a surfactant, (iii) an organophilic clay, (iv) a polymeric fluid loss control agent selected from the group consisting of polystyrene, polybutadiene, polyethylene, polypropylene, polybutylene, polyisoprene, natural rubber, butyl rubber, polymers consisting of at least two monomers selected from the group consisting of styrene, butadiene, isoprene, and vinyl carboxylic acid, and mixtures thereof, and (v) a sulfonated elastomer polymeric viscosifier.
• a drilling system and a method for drilling a borehole are also provided by the invention.
• the drilling system comprises (a) at least one subterranean formation, (b) a borehole penetrating a portion of at least one of the subterranean formations, (c) a drill bit suspended in the borehole, and (d) the above drilling fluid located in the borehole and proximate the drill bit.
• this method comprises the steps of (a) rotating a drill bit at the bottom of the borehole and (b) introducing the aforesaid drilling fluid into the borehole (i) to pick up drill cuttings and (ii) to carry at least a portion of the drill cuttings out of the borehole.
• Figure 1 is a graph depicting the plastic viscosity as a function of aging time at about 400o F of three commercially available drilling fluids alleged by their suppliers to possess good thermal stability.
• Figure 2 is a graph depicting the yield point as a function of aging time at about 400° F of the three commercially available drilling fluids shown in Figure 1.
• Figure 3 is a graph depicting the high temperature-high pressure fluid (HTHP) loss as a function of aging time at about 400° F of the three commercially available drilling fluids shown in Figure 1.
• Figure 4 is a graph depicting the top oil separation as a function of aging time at about 400° F of the three commercially available drilling fluids shown in Figure 1.
• HTHP high temperature-high pressure fluid
• Figure 5 is a graph depicting the plastic viscosity as a function of aging time at about 400° F of an exemplary drilling fluid of the present invention and another two commercially available drilling fluids alleged by their suppliers to possess better thermal stability than the drilling fluids depicted in Figures 1-4.
• Figure 6 is a graph depicting the yield point as a function of aging time at about 400° F of the exemplary drilling fluid of the present invention and the other two commercially available drilling fluids shown in Figure 5.
• Figure 7 is a graph depicting the HTHP loss as a function of aging time at about 400° F of the exemplary drilling fluid of the present invention and the other two commercially available drilling fluids shown in Figure 5.
• Figure 8 is a graph depicting the top oil separation as a function of aging time at about 400° F of the exemplary drilling fluid of the present invention and the other two commercially available drilling fluids shown in Figure 5.
• the oil-based drilling fluid of the present invention maintains it yield point upon aging at temperatures greater than about 400° F by, among other things, the unique combination of three ingredients, namely, a thermally stable organophilic clay, a polymeric fluid loss control agent, and a sulfonated elastomeric polymeric viscosifier.
• a thermally stable organophilic clay include, but are not necessarily limited to, hectorite and bentonite, with hectorite being the more preferred.
• the organophilic clays can be employed either individually or in combination.
• Illustrative polymeric fluid loss control agents include, but are not limited to, polystyrene, polybutadiene, polyethylene, polypropylene, polybutylene, polyisoprene, natural rubber, butyl rubber, polymers consisting of at least two monomers selected from the group consisting of styrene, butadiene, isoprene, and vinyl carboxylic acid.
• Individual or mixtures of polymeric fluid loss control agents can be used in the oil base drilling fluid of this invention.
• Exemplary polymeric fluid loss control agents are described in SPE 13560 (1985), this article being incorporated herein in its entirety by reference.
• the preferred polymeric fluid loss control agents are styrene-butadiene copolymers. Characteristics of exemplary styrene-butadiene copolymers are listed in the following Table I:
• All the styrene/butadiene copolymers described in above Table I also contain about 1 to about 3 weight percent copolymerized carboxylic acid (e.g., itaconic acid and acrylic acid).
• carboxylic acid e.g., itaconic acid and acrylic acid.
• the sulfonated elastomer polymeric viscosifier is preferably a neutralized sulfonated elastomer polymer having about 5 to about 100 milliequivalents of sulfonate groups per 100 grams of sulfonated polymer. More preferably, the neutralized sulfonated elastomer polymer has about 5 to about 50 milliequivalents, and most preferably about 5 to about 30 milliequivalents, of sulfonate groups per 100 grams of sulfonated polymer.
• the sulfonated elastomer polymeric viscosifier is derived from an elastomer polymer selected from the group consisting of ethylene-propylene-diene monomer (EPDM) terpolymers, copolymers of isoprene and styrene sulfonate salt, copolymers of chloroprene and styrene sulfonate salt, copolymers of isoprene and butadiene, copolymers of styrene and styrene sulfonate salt, copolymers of butadiene and styrene sulfonate salt, copolymers of butadiene and styrene, terpolymers of isoprene, styrene, and styrene sulfonate salt, terpolymers of butadiene, styrene, and styrene sulf
• oil-base drilling fluid of the present invention contains the ingredients and properties set forth in the following Table II:
• Density ppg f 7.5-20 9-16 a. Volume percent is based on the total volume of the drilling fluid.
• surfactant means a substance that, when present at low concentration in a system, has the property of adsorbing onto the surfaces or interfaces of the system and of altering to a marked degree the surface or interfacial free energies of those surfaces (or interfaces) .
• interface indicates a boundary between any two immiscible phases and the term “surface” denotes an interface where one phase is a gas, usually air.
• exemplary ingredients referred to as surfactants by those skilled in the art include emulsifiers and oil wetting agents.
• the polymeric fluid loss control agent is preferably present in the drilling fluid in a concentration of about 6 to about 9 ppb.
• the sulfonated elastomer polymeric viscosifier is preferably present in the drilling fluid in a concentration of about 0.1 to about 1 ppb.
• the term “lime” means quicklime (CaO), quicklime precursors, and hydrated quicklime (e.g., slaked lime (Ca(OH) 2 )).
• f. ppg denotes pounds per gallon.
• the parts per barrel (ppb) is based upon the final composition of the drilling fluid.
• the volumetric ratio of oil to water in the drilling fluid of the present invention ranges from about 100:0 to about 50:50.
• the weight ratio of the polymeric fluid loss control agent to the sulfonated elastomer polymeric viscosifier is about 1.5:1 to about 50:1, more preferably about 3:1 to about 20:1, and most preferably about 5:1 to about 10:1.
• Oils, surfactants, weighting agents, and shale inhibiting salts typically used in oil-base drilling fluids are suitable for use in the present invention.
• exemplary oils, surfactants, and weighting agents are described in U.S. Patent 4,447,338 and U.S. Patent 4,425,462, these patents having previously been incorporated herein in their entireties by reference.
• Typical shale inhibiting salts are alkali metal and alkaline-earth metal salts. Calcium chloride and sodium chloride are the preferred shale inhibiting salts.
• auxiliary fluid loss control agents means particles (other than the polymeric fluid loss control agent discussed above) having a size only slightly smaller than that of the pore openings in the formation.
• the auxiliary fluid loss control agent is used to form a filter cake on the surface of a wellbore to reduce the loss of drilling fluid solids and liquids to the formation.
• Exemplary auxiliary fluid loss control agents include, but are not limited to, sulfonated asphaltenes, asphaltenes, lignite, and gilsonite.
• the softening point of the auxiliary fluid loss control agent is as high as possible, preferably at least about 300° F, and more preferably at least about 350° F. Due to its high softening point, gilsonite is the most preferred auxiliary fluid loss control agent. Commercially available gilsonite has a softening point within the range of about 290° to about 400° F.
• the drilling fluid is preferably prepared by mixing the constituent ingredients in the following order: (a) oil, (b) organophilic clay, (c) surfactant, (d) lime, (e) an aqueous solution comprising water and the shale inhibiting salt, (f) auxiliary fluid loss control agent, (g) weighting agent, (h) polymeric fluid loss control agent, and (i) sulfonated elastomer polymeric viscosifier.
• the preferred plastic viscosity, yield point, high temperature-high pressure (HTHP) fluid loss, and top oil separation ranges for the drilling mud of the present invention are set forth in the following Table III.
• Plastic Viscosity cp about 25 to about 48 Yield Point, lb/100sqft about 10 to about 32 HTHP Fluid Loss, ml about 1 to about 23
• Examples 12-18 compare various properties of an exemplary drilling fluid within the scope of the present invention (Example 1) with commercially available drilling fluids (Comparative Examples 2-7).
• Examples 8-11 demonstrate that different styrene/butadiene copolymers are suitable for use in the drilling fluids of this invention.
• the effect of varying sulfonated elastomer polymeric viscosifier and polymeric fluid loss control agent concentrations on the properties of drilling fluids is shown in Examples 12-18.
• An exemplary oil-base drilling fluid or mud (about 5 lab barrels, each lab barrel containing about 350 ml) within the scope of the present invention was formulated as shown in the following Table IV. The ingredients were sequentially added in the order set forth in Table IV. After the addition of each ingredient, the resulting composition was mixed for the indicated mixing time prior to adding a subsequent ingredient to the composition.
• N/A denoted not applicable.
• E.S. denotes electrical stability and was measured according to the procedure described in Recommended Practice - Standard Procedure for Field Testing Drilling Fluids, Recommended Practice 13B (RP 13B), Twelfth Edition, September 1, 1988, American Petroleum Institute, Washington, DC (hereinafter referred to as "API"), page 28.
• Dial readings were obtained using a 115-volt motor driven viscometer described in API, pages 7-9, sections 2.4 to 2.5.
• PV was determined in accordance with the procedure and calculations discussed in API, page 9, sections 2.5 to 2.6.
• YP was determined in accordance with the procedure and calculations discussed in API, page 9, sections 2.5 to 2.6.
• HTHP was determined in accordance with the procedure discussed in API, page 12, section 3.5.
• Top oil separation was determined by decanting and measuring the oil layer above the solids in the age-tested drilling fluid present in aging bomb.
• N/A denoted not applicable.
• N/A denoted not applicable.
• N/A denoted not applicable.
• N/A denoted not applicable.
• N/A denoted not applicable.
• N/A denoted not applicable.
• N/A denoted not applicable.
• N/A denotes not available.

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• 1992
  • 1992-10-22 EP EP92923322A patent/EP0610393A1/de not_active Withdrawn
  • 1992-10-22 WO PCT/US1992/009160 patent/WO1993009201A1/en not_active Application Discontinuation
  • 1992-10-22 AU AU29232/92A patent/AU2923292A/en not_active Abandoned

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