Wells – Processes – Distinct – separate injection and producing wells
Patent
1993-06-02
1994-11-29
Suchfield, George A.
Wells
Processes
Distinct, separate injection and producing wells
166274, 166275, 1663051, E21B 4322
Patent
active
053681010
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to a method for reducing retention of a displacement agent used in secondary recovery. This method consists principally of treating the rock matrix in a special manner by injecting a solution including, in particular, phosphate or sulfite salts.
It also relates to application of this same method to improve a secondary hydrocarbon recovery operation that affords savings in particular in the quantity of displacement agent injected while controlling the stability of particles present in the rock matrix of the oil reservoirs concerned, which particles generally come from clay compounds.
BACKGROUND OF THE INVENTION
Primary recovery by natural drainage of liquid hydrocarbon deposits may be somewhat scanty, even in the presence of an active aquifer or a free-gas cap, so it is often necessary to use an assisted recovery method, for example by injecting a flushing fluid into the formation.
Water treated to be compatible with the reservoir rock, gases not miscible with hydrocarbons, gases miscible with hydrocarbons, microemulsions, or fluids based on polymers with high viscosity in situ may be injected.
All these processes, well known in the prior art, have the goal of flushing the reservoir rock containing the hydrocarbon as efficiently as possible. This flushing consists of driving the hydrocarbon toward the producing wells.
However, to different degrees depending on their sophistication, these processes all encounter the problem of economic feasibility. Because of the extra cost represented by the injection operations and the products injected, which are often not recoverable, profitability of such a deposit may be low or even zero. Thus it is crucial not to consume a large quantity of these expensive products.
If the displacement agent is polymer-based, the polymers are additives used principally as products that increase the viscosity of the basic fluid, namely water. They can also act on the water in the deposits.
These polymers have the property of adsorbing onto the rock matrix. This adsorption is manifested by retention of product on the rock matrix and hence decreases the polymer concentration in the displacement agent. Moreover, adsorption favors retention of the agent by a trapping phenomenon in the rock matrix. Thus the ratio between the mobility of the displacement agent and that of the hydrocarbon, which depends directly on the concentration, is favorable only in a small area around the injection zone. To remedy this major drawback, large concentrations of polymers may be injected, but this represents a high consumption of injected product and the cost of the operation becomes prohibitive.
U.S. Pat. No. 4,627,494 teaches a process for injecting a chemical into an oil reservoir to limit losses of surfactants used in secondary recovery. However this process relates only to products based on lignosulfonates.
U.S. Pat. No. 3,523,581 describes a process for injecting a first and then a second fluid before injecting the displacement fluid. The second fluid contains a product that can contain polyphosphates in particular, but these are intended only for pre-desorption of the first fluid in the reservoir rock. This method is particularly suitable for reservoirs with nonuniform permeability.
SUMMARY OF THE INVENTION
The present invention is directed to a method for reducing the retention of a displacement agent in a rock matrix of an underground reservoir containing a fluid, said agent being designed to displace said fluid, said rock matrix being stabilized by the presence of cations, and said reduction being effected by treating the rock matrix with an adsorbent solution.
In the present invention, this adsorbent solution contains phosphate or sulfite salts and the adsorption of said solution is increased by the presence of cations at a given concentration.
Said adsorbent solution may comprise sodium phosphate salts (Na.sub.2 HPO.sub.4, Na.sub.3 PO.sub.4), potassium phosphate salts (K.sub.2 HPO.sub.4, K.sub.3 PO.sub.4), or sodium or potassium sulfites.
Th
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Chauveteau Guy
Lecourtier Jacqueline
Plazanet Veronique
Putz Antide
Institut Francais du Pe'trole
Suchfield George A.
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