Wells – Processes – Separate steps of fracturing or attacking formation
Patent
1985-06-27
1986-11-11
Suchfield, George A.
Wells
Processes
Separate steps of fracturing or attacking formation
166278, 166292, 166297, E21B 33138, E21B 4302
Patent
active
046216928
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention pertains to a new process to minimize any decrease in permeability of the formation surrounding the perforations in a perforated well, i.e., to prevent or minimize any damage to the formation which would decrease the flow of oil or gas from the formation through the perforations and hence into the well bore for transport to the surface.
PRIOR ART
Various procedures have been developed and utilized to increase the flow of hydrocarbons from hydrocarbon-containing subterranean formations penetrated by well bores. For example, a commonly used technique involves perforating the formation to provide flow channels therein through which hydrocarbons flow from the formation to the well bore.
In such formation perforation procedures it is important to leave the formation with maximum permeability or conductivity whereby hydrocarbons contained in the formation flow to the well bore with the least possible restriction. This can best be accomplished by: (1) preventing the entry of solids into the formation: which entry results in a decrease of the permeability of the formation, (2) utilizing well completion fluids which do not tend to swell and/or disperse formation particles contacted by the completion fluid; (3) preventing the entry of formation particles into the perforations; and (4) avoiding excessive fluid invasion into the formation.
Sand production and its control is a major problem in almost all fields that produce hydrocarbons from unconsolidated sandstone formations. Sand influx into producing wells can cause reduced productivity, loss of reserves, and added expense in combating equipment erosion and sand accumulation problems. Consequently, there is a tremendous potential for increasing profits through improved sand control.
Gravel packing inside casing is the most prevalent method of sand control. A successful inside casing gravel pack require positive placement of high permeability gravel within the critical perforation tunnels through the casing and cement, and the prevention of permeability damage within the formation around the perforation cavity beyond the cement. Basic procedures for packing gravel (actually a fine graded sand) and choosing the size of gravel to be packed are well known.
Typical applications of completion fluids in sand control procedures are in underreaming, perforating, perforation washing, as carrier fluids to place gravel in perforations or behind screens and liners, and to spot and displace acids or chemical treatments. Brine based fluids ranging from low density sea waters to very expensive commercial solutions are widely used in sand control operations. Four basic fluid properties must be considered in selecting a brine fluid for a particular application. These are: brine concentration--to prevent clay swelling and dispersion; fluid density--to provide formation pressure control; viscosity--to achieve desired solids carrying capacity; and fluid loss control--to prevent excessive whole fluid loss. The first two properties are selected based on area experience and knowledge of well properties gained during drilling. Minimum brine concentration to prevent clay reactions in most formations are generally considered to be 5 to 10% for sodium chloride, and 1% to 3% for calcium and potassium chloride brines. For well control, industry commonly designs for an overbalance of 200 to 400 psi. Fluid viscosity increases with brine concentration. It can be increased further to desired levels for suspension of solids by addition of certain water soluble polymers.
Fluid loss is controlled by the addition of polymers to "solids free" brines to increase their viscosity, or by the addition of controlled-size, solid particles. In conjunction with polymer viscosifiers, such particles bridge on the formation face and form an extremely low permeability film to prevent whole fluid loss. Materials commonly used are acid soluble calcium carbonate, oil soluble resins, and water soluble salts such as sodium chloride. The water soluble salts are used when the
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Suman, Jr., "Sand Control Part 3--How to Avoid Poorly Designed or Plugged Perforations that Impair Productivity and Prevent Effective Sand Control", World Oil, Jan. 1975, pp. 83-84, 86-88, 90-91.
Mondshine, "Completion Fluid Uses Salt for Bridging, Weighting", Oil and Gas Journal, Aug. 22, 1977.
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House Roy F.
Suchfield George A.
Texas United Chemical Corp.
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