LIGHTWEIGHT PARTICULATE MATERIALS
AND USES THEREFOR
The present application is a continuation-in-part of U.S. patent application Ser. No. 09/579,147, filed May 25, 2000, now U.S. Pat. No. 6,364,018, and U.S. patent application Ser. No. 09/579,146, filed May 25, 2000; each of the foregoing applications being a continuation-in-part of U.S. patent application Ser. No. 09/519,238, filed Mar. 6, 2000, which issued as U.S. Pat. No. 6,330,916; which is a continuation-in-part of U.S. patent application Ser. No. 09/085,416, filed May 27, 1998, which issued as U.S. Pat. No. 6,059,034; which is a continuation-in-part of U.S. patent application Ser. No. 08/756,414, filed Nov. 27, 1996, now abandoned, and which also claims priority to Danish patent application S/N 1333/97 filed Nov. 21, 1997; the entire disclosures of each of the foregoing applications being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to methods and compositions useful for subterranean formation treatments, such as hydraulic fracturing treatments and sand control. In particular, this invention relates to use of relatively lightweight and/or substantially neutrally buoyant particles as proppant material in hydraulic fracturing treatments and as particulate material in sand control methods such as gravel packing, frac pack treatments, etc.
2. Description of the Related Art
Hydraulic fracturing is a common stimulation technique used to enhance production of fluids from subterranean formations. In a typical hydraulic fracturing treatment, fracturing treatment fluid containing a solid proppant material is injected into the formation at a pressure sufficiently high enough to cause the formation or enlargement of fractures in the reservoir. During a typical fracturing treatment, proppant material is deposited in a fracture, where it remains after the treatment is completed. After deposition, the proppant material serves to hold the fracture open, thereby enhancing the ability of fluids to migrate from the formation to the well bore through the fracture. Because fractured well productivity depends on the ability of a fracture to conduct fluids from a formation to a wellbore, fracture conductivity is an important parameter in determining the degree of success of a hydraulic fracturing treatment.
Hydraulic fracturing treatments commonly employ proppant materials that are placed downhole with a gelled carrier fluid (e.g., aqueous-based fluid such as gelled brine). Gelling agents for proppant carrier fluids may provide a source of proppant pack and/or formation damage, and settling of proppant may interfere with proper placement downhole. Formation damage may also be caused by gelled carrier fluids used to place particulates downhole for purposes such as for sand control, e.g., gravel packs, frac packs, etc. Formulation of gelled carrier fluids usually requires equipment and mixing steps designed for this purpose.
SUMMARY OF THE INVENTION
In the disclosed method, the application of relatively lightweight and/or substantially neutrally buoyant particulate material as a fracture proppant particulate advantageously may provide for substantially improved overall system performance in hydraulic fracturing applications, or in other well treating applications such as sand control. By "relatively lightweight" it is meant that a particulate has a
density that is substantially less than a conventional particulate material employed in hydraulic fracturing or sand control operations, e.g., sand or having a density similar to these materials. By "substantially neutrally buoyant", it is
5 meant that a particulate has a density sufficiently close to the density of a selected ungelled or weakly gelled carrier fluid (e.g., ungelled or weakly gelled completion brine, other aqueous-based fluid, slick water, or other suitable fluid) to allow pumping and satisfactory placement of the proppant/
10 particulate using the selected ungelled or weakly gelled carrier fluid. For example, urethane resin-coated ground walnut hulls having a specific gravity of from about 1.25 to about 1.35 grams/cubic centimeter may be employed as a substantially neutrally buoyant proppant/particulate in
15 completion brine having a density of about 1.2. It will be understood that these values are exemplary only. As used herein, a "weakly gelled" carrier fluid is a carrier fluid having minimum sufficient polymer, viscosifier or friction reducer to achieve friction reduction when pumped down
20 hole (e.g., when pumped down tubing, work string, casing, coiled tubing, drill pipe, etc.), and/or may be characterized as having a polymer or viscosifier concentration of from greater than about 0 pounds of polymer per thousand gallons of base fluid to about 10 pounds of polymer per thousand
25 gallons of base fluid, and/or as having a viscosity of from about 1 to about 10 centipoises. An ungelled carrier fluid may be characterized as containing about 0 pounds per thousand gallons of polymer per thousand gallons of base fluid.
30 Advantageously, in one embodiment use of substantially neutral buoyant particulate material may eliminate the need for gellation of carrier fluid, thus eliminating a source of potential proppant pack and/or formation damage. Furthermore, a relatively lightweight particulate material
35 may be easier to place within a targeted zone due to lessened settling constraints, and a reduced mass of such relatively lightweight particulate material is generally required to fill an equivalent volume than is required with conventional sand control particulates, used, for example, for gravel
40 packing purposes. Elimination of the need to formulate a complex suspension gel may mean a reduction in tubing friction pressures, particularly in coiled tubing and in the amount of on-location mixing equipment and/or mixing time requirements, as well as reduced costs. Furthermore,
45 when treated to have sufficient strength (e.g., by substantially filling the permeable porosity of a porous particle with resin or hardener), the disclosed relatively lightweight proppant/particles may be employed to simplify hydraulic fracturing treatments or sand control treatments performed
50 through coil tubing, by greatly reducing fluid suspension property requirements. Downhole, a much reduced propensity to settle (as compared to conventional proppant or sand control particulates) may be achieved, particularly in highly deviated or horizontal wellbore sections. In this regard, the
55 disclosed substantially neutral buoyancy proppant/ particulate material may be advantageously employed in any deviated well having an angle of deviation of between about 0 degree and about 90 degrees with respect to the vertical. However, in one embodiment, the disclosed particulate
60 material may be advantageously employed in horizontal wells, or in deviated wells having an angle with respect to the vertical of between about 30 degrees and about 90 degrees, alternatively between about 75 degrees and about 90 degrees. Thus, use of the disclosed relatively lightweight
65 and/or substantially neutrally buoyant particulate materials disclosed herein may be employed to achieve surprising and unexpected improvements in fracturing and sand control