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.

This paper presents the successful field implementation of a conformance polymer (CP) system used to control undesired gas production in the Cantarell field, a naturally fractured offshore carbonate reservoir in southern Mexico. Gas control is a challenge in this field because high gas-oil ratios (GORs) force the operator to prematurely abandon wells because of gas-handling facility constraints, leaving substantial oil reserves in place. Case histories are presented in which the CP system was successfully applied to reduce undesired gas production to an acceptable level. The CP treatments were tailed in with foam cement to avoid overdisplacement in these fractured, depleted formations. The CP system is based on a copolymer of acrylamide and t-butyl acrylate (PAtBA) crosslinked with polyethyleneamine (PEI). To date, more than 700 jobs have been performed with the CP system around the world, mostly to address excessive water production problems, such as coning/cresting, high-permeability streaks, gravel-pack isolation, fracture shutoff, and/or casing-leak repair. Similarly, this system provides excellent gas shutoff properties as well. The operating temperature range of this system is from 60 to 350°F. The CP system has been successfully applied to sandstone, carbonate, and shale formations requiring a conformance treatment. This system has been successfully tested to withstand a differential pressure of at least 2,500 psi and is resistant to acid, CO2, and H2S environments. One of the most demanding scenarios for this type of polymer system is stopping gas production, especially in this reservoir where the operator must deal with a combination of high matrix permeability (3 to 10 darcy) and natural fractures. These CP treatments have proven to be economical gas shutoff solutions in difficult well/reservoir environments, yielding significant reduction of gas and/or increased oil production. A detailed description of the wells treated with the CP systems is presented along with one-year production rates after the treatment.

Excessive water production can detrimentally affect the profitability of hydrocarbon-producing wells if not controlled properly. Water cut present in the oil stream from wells producing in several offshore Mexico fields is an issue of critical importance because oil production is sent to exportation. Lack of water handling facilities forces operators to monitor wells with water cut as low as 2.0%. Water production is normally controlled by decreasing the choke size, but in the worst cases can require shutting the well in completely, causing a negative impact on the production of the fields. Two main drivers of excessive water production in these mature fields are the influx of water behind the casing and/or water flowing through the natural fractures of these carbonate reservoirs. This paper describes the successful field implementation of a selective hydrocarbon-based ultrafine cement (UFC) slurry system to slow down water production in offshore Mexico.The UFC slurry consists of ultrafine cement with an average particle size of 2.5 µm, a surfactant, and a hydrocarbon carrier fluid (i.e., diesel). Because the slurry is hydrocarbon-based, it remains inactive when contacting an oil-producing zone. When the system contacts a water producing zone, the slurry will remain pumpable for an additional 20 to 30 min before beginning to set. The delayed setting of the cement slurry is ideal for placing the UFC slurry into water-bearing formation fractures some distance away from the wellbore. The slurry is designed to selectively shut off water flowing into the wellbore and is applicable up to 204°C. This paper describes the field implementation of the UFC slurry system in offshore Mexico to seal off unwanted water flowing through natural fractures and/or behind the casing. A variety of case histories are discussed in detail along with postproduction numbers after the treatment. Numerous UFC treatments have been performed in southern Mexico. 2

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We describe the situation and challenges, the implemented process and strategies, and the downhole tools used during the remedial work to successfully recover 3041 m of 1 3/4-in coiled tubing (CT) pipe lost-in-hole during an acidizing job. During an acidizing job through the CT string as a part of a workover job in a well of a mature field in offshore Mexico, after filling the pipe with acid, the CT operator was ready to spot it across the perforated interval. When the up-hole movement started, the CT weight reached approximately 36,000 lbf (normal pulling weight at that depth in the previous runs) and then the CT weight went to 0 lbf. After retrieving the pipe to surface, it was noticed that only 199 m of CT were recovered from the well, leaving +/- 3041 m of CT pipe inside the hole. After a total of 43 runs and over 20 days, the entire CT string including the Bottomhole assembly (BHA) was recovered, and the well was put back on production. The key was to conform the top of the fish with a downhole motor equipped with a milling shoe, and then exploit the versatility and fast rig up/down capabilities of slikcline to position the fishing tool on the top of the fish. After the fish was latched, a GS profile was left in hole, thus allowing the CT to latch and retrieve the entire fish. Fishing operations are considered more an art than a science because of all the variables involved, for example, type and top of the fish, restrictions along the wellbore, available fishing equipment, pulling capacities, and so on. However, following industry best practices, fishing can switch from a nightmare to a useful learning and successful experience. The authors will summarize the milestones in the operation, which serves as an example of collaborative work between the operator and service company that led to a successful outcome.