Water shutoff followed by selective oil stimulation

Excessive water production, a problem in most oil- producing areas, can be curtailed and then the oil production selectively stimulated by a new system that has been recently developed and field tested. Reduction of water production is accomplished with a new formula, field proven cement-oil slurry. The formula includes chemicals that cause the new slurry to thicken upon contacting oil and to thin upon contacting water. The slurry preferentially enters and sets in the water zone. Selective oil stimulation is achieved with a follow-up treatment of a unique preflush of treated oil ahead of a conventional acid treatment. The oil preflush forms an oil soluble precipitate upon contacting water in the water zone. This precipitate diverts the subsequent acid treatment into the oil-producing zone. Since the acid preferentially enters the oil zone, only the oil production will be stimulated. A description of the technique and a summary of field case histories using one or both of these water-control systems is presented.