Abstract
One of the major challenges faced in southern Mexico is water management. Producing zones are often considered for abandonment even when the intervals still retain large volumes of recoverable hydrocarbons. For many years, conformance-polymer systems have been successfully applied to control undesired water production from hydrocarbon wells. However, currently available polymers present a number of limitations for high-temperature wells (>250°F) in terms of providing longer gelation times and acceptable thermal stability. In most of the wells in Mexico, bottomhole temperatures are above 300°F with depths around 15,000 ft. This paper presents the successful field implementation of an organically crosslinked polymer (OCP) for high-temperature applications in areas of southern Mexico that are producing hydrocarbons from naturally fractured carbonates. These treatments were performed by bullheading through the producing tubing without the need to pull the tubing out of the well.
The OCP system is based on a copolymer of acrylamide and t-butyl acrylate (PAtBA) crosslinked with polyethyleneimine (PEI). To date, about 300 jobs have been performed with the OCP system around the world to address conformance problems such as: water coning/cresting, high-permeability streaks, gravel-pack isolation, fracture shut off, and/or casing-leak repair. More than 150 of these jobs have been performed in Mexico alone. Originally, the OCP system had a limited working temperature range of 100 to 250°F. The upper-placement temperature of the system was ~250°F because above this, temperature-pumping times were too short. A recently developed polyamino-acid retarder has allowed reasonable placement times up to 350°F without the need for cooling down the formation to obtain enough pumping time. The retarder is not detrimental to the thermal stability of the system.
