Summary The Cantarell field, a mature reservoir offshore Mexico, presents significant water-management problems because the hydrocarbon production comes from a naturally fractured carbonate reservoir. Controlling water production in the Cantarell field becomes more critical because of its limited water-handling facilities. This paper presents the field application of two systems widely used in the petroleum industry for water control:an organically crosslinked polymer (OCP) system anda rigid-setting-material (RSM) system. The OCP system is based on a copolymer of acrylamide and t-butyl acrylate (PAtBA) crosslinked with polyethyleneimine (PEI). To date, more than 100 jobs have been performed in Mexico with this system to address conformance problems such as water coning/cresting, high-permeability streaks, gravel-pack isolation, fracture shutoff, and casing-leak repair. This system can penetrate deep into the matrix of the rock or fractures to provide a more efficient water shutoff. The RSM system is a rigid "cement-like" setting material that has a right-angle set. Unlike cement, the RSM system is capable of rapidly developing highly compressive strength to avoid losing the treatment to the formation before setting and will not invade the formation. The RSM system is for near-wellbore applications. Several case histories are presented in this paper to show the application of these two water-shutoff systems together. The OCP system was used for deep matrix/fracture penetration, while the RSM system was used as a tail-in because of its fast-setting properties (to avoid overdisplacement of the OCP system) and its capability to stop gas migration. These advanced water-control technologies have extended the well life and profitability of the treated wells. In the past, many of these wells were abandoned because of the limited water-handling facilities.

Conformance-polymer systems have been successfully applied for many years 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. This paper presents the successful field implementation of an organically crosslinked polymer (OCP) for high-temperature applications in southern Mexico. The OCP system is based on a copolymer of acrylamide and t-butyl acrylate (PAtBA) crosslinked with polyethyleneimine (PEI). To date, more than 450 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 shutoff, and/or casing-leak repair. Originally, the OCP system had a limited working temperature range from 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 carbonate retarder allows 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. An overview of case histories that used OCP in southern Mexico is presented in this paper. In addition, the development results of the high-temperature conformance polymer are discussed in terms of (1) gelation-time measurement and (2) effectiveness to limit permeability to water and thermal stability in sandpack flow tests at elevated temperatures. To date, more than 70 jobs have been successfully performed worldwide with the OCP at temperatures higher than 250°F. Introduction Excessive water production from hydrocarbon reservoirs is one of the most serious problems in the oil industry. Water cut greatly affects the economic life of producing wells. Unwanted water production is estimated to cost the petroleum industry about $45 billion each year, although accurate records of water production are difficult to obtain (Conformance Technology Manual 1996; Curtice and Dalrymple 2004). The southern region of Mexico presents a major challenge with water management as well. Water production results in extra disposal costs, scale buildup, reduced oil production, and eventually well abandonment (with associated workover costs). Consequently, producing zones are often abandoned in an attempt to avoid excessive water production, even when intervals still retain large volumes of recoverable hydrocarbons. Although natural fractures have a positive effect on oil flow, they also negatively impact water and/or gas flow caused by coning effects or high-permeability streaks between the producing hydrocarbon zone and intervals above and/or below. If these zones contain high mobile-water saturation, they soon will impact the productivity of the hydrocarbon zone. Early water breakthrough caused by edge-water flowing through faults or natural fractures is another common problem in this region. In addition, many of these formations with high-water-management problems produce from intervals with bottomhole temperatures higher than 250°F, hence the need for a high-temperature, porosity-fill sealant in this temperature range.

Cantarell, which is an offshore complex of fields in the Bay of Campeche, is the most important complex in Mexico and is the second-largest producing field in the world. It is comprised of five fields, with the main pay zones consisting of highly fractured, vuggy carbonate formations from Jurassic, Cretaceous and Lower Paleocene geological ages. Matrix acidizing has always been the main stimulation process used to improve production from these carbonate reservoirs and this is especially the case now that this mature complex has reached its production peak. As with all acidizing programs, a critical factor for success of the treatments is distribution of the acid between all productive zones. Since most producing wells are not homogeneous and contain layers of varying permeability, even distribution of the acid is a difficult task. In addition, the water saturation of the various zones has a major effect on the acid distribution. Since acid is an aqueous fluid, it will tend to predominantly enter the zones with the highest water saturation, in many cases resulting in increased water production. This brings with it the multitude of problems associated with high water production. This paper will present the results of approximately 55 high permeability wells ranging from 1,000 to 6,000 md, which have been acidized using a novel acid diverter based on associative polymer technology (APT). This polymer inherently reduces the formation permeability to water with little or no effect on the permeability to hydrocarbon. Data from production logs from several of the treated wells will be presented, which show excellent oil production distribution along the perforated intervals. In addition, production logs will also be shown for wells acidized with other diverters, such as foams and in-situ crosslinked acid, which showed poorer results. Introduction Cantarell Field The Cantarell field is the second-largest oilfield in the world behind the Ghawar field in Saudi Arabia. It is located offshore in the Gulf of Mexico, 47 miles northeast of Ciudad del Carmen, Campeche. The main hydrocarbon zones in Cantarell are highly fractured carbonate formations from the Jurassic, Cretaceous and Lower Paleocene geological ages (Fig. 1). The field is made up of a number of subfields or fault blocks, with the main fields being Akal, Chac, Kutz, and Nohoch. Production started in 1979 and reached a peak of 1.1 million B/D in 1981 from 40 oil wells. By 1994 the production was down to 890,000 B/D. One year later it was producing 1 million B/D due to the addition of new platforms and wells and a nitrogen injection program. This program was capable of injecting a billion ft3/day of nitrogen to maintain reservoir pressure. By 1996 the field was producing 2.1 million B/D.

This paper presents the laboratory development and successful field implementation of an organically crosslinked polymer (OCP) system for water-and gas-shutoff applications. An overview of case histories in a naturally fractured carbonate reservoir (with BHT >250°F) in offshore Mexico where the OCP was successfully applied to reduce water production is presented. To control overdisplacement of the treatment, a modified tail-in combining the OCP system with inert particles was used to provide leakoff control, resulting in a controlled placement of the sealant.The OCP system is based on a copolymer of acrylamide and t-butyl acrylate (PAtBA) crosslinked with polyethyleneimine (PEI). To date, more than 600 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 shutoff, and/or casing-leak repair. The development results of this OCP system are discussed regarding its activation time and its effectiveness to limit permeability to water and provide thermal stability in sandpack flow tests at elevated temperatures. Lastly, the combination of the OCP system with inert particulates to provide fluid-loss control is discussed.The OCP system has been successfully applied to sandstone, carbonate, and shale formations in need of conformance treatments. This system has been successfully tested to withstand a differential pressure of at least 2,500 psi and is resistant to acid, CO 2 , and H 2 S environments. Because of the ability of the OCP system to withstand pressure, workover operations have been successfully performed in previously treated wells including acid-stimulation, sand-control, and frac-packs treatments, among others. An overview of case histories in which the OCP system was used in offshore Mexico is presented. This advanced water-control technology has extended the well life and profitability of the treated wells. In the past, many of these wells were abandoned because of the limited water-handling facilities.

Conformance-polymer systems have been successfully applied for many years 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. This paper presents the successful field implementation of an organically crosslinked polymer (OCP) for high-temperature applications in southern Mexico. The OCP system is based on a copolymer of acrylamide and t-butyl acrylate (PAtBA) crosslinked with polyethyleneamine (PEI). To date, more than 450 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 shutoff, and/or casing-leak repair. Originally, the OCP system had a limited working temperature range from 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 carbonate retarder allows 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. An overview of case histories that used OCP in southern Mexico is presented in this paper. In addition, the development results of the high-temperature conformance polymer are discussed in terms of (1) gelation-time measurement and (2) effectiveness to limit permeability to water and thermal stability in sandpack flow tests at elevated temperatures. To date, more than 70 jobs have been successfully performed worldwide with the OCP at temperatures higher than 250°F. Introduction Excessive water production from hydrocarbon reservoirs is one of the most serious problems in the oil industry. Water cut greatly affects the economic life of producing wells. Unwanted water production is estimated to cost the petroleum industry about ﹩45 billion each year, although accurate records of water production are difficult to obtain (Conformance Technology Manual 1996; Curtice and Dalrymple 2004). The southern region of Mexico presents a major challenge with water management as well. Water production results in extra disposal costs, scale buildup, reduced oil production, and eventually well abandonment (with associated workover costs). Consequently, producing zones are often abandoned in an attempt to avoid excessive water production, even when intervals still retain large volumes of recoverable hydrocarbons. Although natural fractures have a positive effect on oil flow, they also negatively impact water and/or gas flow caused by coning effects or high-permeability streaks between the producing hydrocarbon zone and intervals above and/or below. If these zones contain high mobile-water saturation, they soon will impact the productivity of the hydrocarbon zone. Early water breakthrough caused by edge-water flowing through faults or natural fractures is another common problem in this region. In addition, many of these formations with high-water-management problems produce from intervals with bottomhole temperatures higher than 250°F, hence the need for a high-temperature, porosity-fill sealant in this temperature range.