Worldwide Field Applications of a Polymeric Gel System for Conformance Applications

Abstract

Summary Water production becomes a major problem as hydrocarbon-producing fields mature. Higher levels of water production result in increased levels of corrosion and scale, increased load on fluid-handling facilities, increased environmental concerns, and eventually well shut-in (with associated workover costs). Consequently, producing zones are often abandoned in an attempt to avoid water contact, even when the intervals still retain large volumes of recoverable hydrocarbons. Many polymer systems have been applied over the years to control undesired water production from hydrocarbon wells, with varying degrees of success. For approximately eight years, a polymer gel system based on an acrylamide/t-butyl acrylate copolymer (PAtBA) crosslinked with polyethyleneimine (PEI) has been used successfully for various water shutoff applications. This article describes results from a sampling of over 200 jobs performed throughout the world, including the average results from more than 90 jobs performed in one geographic location alone. In addition to "standard" matrix treatments, results will be shown for other types of treatment, including a design to plug annular communication and a combination of sealant and temporary gel in an openhole horizontal completion. In addition, laboratory data pertaining to work aimed at increasing the temperature limit of the system will be presented. The upper placement temperature of the system originally was ~260°F. Data presented in this article indicates the development of a retarder system that allows the upper placement temperature to be raised to at least 350°F. Introduction Controlling water production has been an objective of the oil industry almost since its inception. Produced water has a major economic impact on the profitability of a field. Producing 1 bbl of water requires as much or more energy as producing the same volume of oil. Often, each barrel of produced water represents some lesser, but significant, amount of unproduced oil. In addition, water production causes other related problems such as sand production, the need for separators, disposal and handling concerns, and the corrosion of tubulars and surface equipment. Many methods are available to mitigate water-production problems, and perhaps the most widely used chemical system has been chrome-crosslinked polyacrylamide gels. A previous publication described the advantages of the acrylamide- (PAtBA) copolymer/polyethyleneimine system (herein referred to as OCP, or organically crosslinked polymer) (Hardy et al. 1998). A brief discussion of these advantages follows, with presentations of case histories using OCP and data showing expansion of OCP technology. OCP System Description Gel systems for water and gas shutoff have many requirements, including:Low viscosity allowing easy injection deep into a formation matrix.Capability to control gelation time of the fluid.Sufficient strength to resist drawdown in the wellbore.Temperature stability of the gel for extended periods of time. As will be shown in the following discussion, the OCP system meets all these requirements. The viscosity of the system is ~25 cp as mixed. This relatively low viscosity is due to the relatively low molecular weight, ~250,000, of the PAtBA. This polymer is covalently crosslinked with PEI, which results in excellent control over gelation time. Sufficient strength and temperature stability are also obtainable. In addition, the OCP system is insensitive to formation fluids, lithology, and/or heavy metals. Another advantage of the OCP system is its predictable viscosity profile that can be used to improve diversion over long treatment intervals.

Polymer Systems for Water Shutoff and Profile Modification: A Review Over the Last Decade

“…Eoff et al (2007) extended the working temperature of the PAtBA/PEI system to 176.7 C (350 F) by the use of this retarder. The mechanism for elongating gelation time by sodium carbonate is believed to be an interaction between the positively charged sodium ion with the carboxylate groups resulting from the hydrolysis of PAtBA, thus reducing the sites available for crosslinking and consequently increasing the gelation time.…”

Influence of polymer structure on the gelation kinetics and gel strength of acrylamide‐based copolymers, bentonite and polyethylenimine systems for conformance control of oil reservoirs

“…Organically crosslinked polymer (OCP) systems based on homopolymers or copolymers of acrylamide and polyethylenimine (PEI) have been studied to control the permeability anisotropy of oil reservoirs with harsh conditions of temperature and salinity/hardness due to their: (1) good injectivity and propagation within the reservoir rock; (2) predictable and controllable gelation time; (3) adjustable gel strength, and (4) long‐term chemical and thermal stability between 60 and 150 °C …”

“…The formed hydrogel diverts the injected fluid flow from high permeability, low‐oil‐saturation reservoir flow paths to low‐permeability, high‐oil‐saturation flow paths, improving flood sweep efficiency. Moreover, by blocking high‐permeability zones or anomalies located near the wellbore, the hydrogel may also improve the injection profile and/or prevent the early breakthrough of the injected fluid in production wells (e.g., water shutoff or gas shutoff), thus reducing oil production operational costs …”

Performance evaluation and application of new fuzzy-ball micro bubble treatment fluid

“…Oilfield produced water is a common problem which brings serious damage on oil well production, and oil and gas gathering system under the process of oilfield development (Hernandez et al 2010;Abbasy et al 2008;Eoff et al 2007;Seright and Liang 1994). To solve this problem, squeezing cement to plug channeling is one conventional way.…”