TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOften, the main challenge in producing hydrocarbons in north Mexico is the accompanying large associated water production. In the Cuenca de Burgos field in northern Mexico, operators typically encounter water production of over 400 BWPD following fracture-stimulation treatments. This paper discusses how water production in those fields was significantly reduced using a new conformance-whilefracturing (CWF) method that incorporates a chemical relative permeability modifier (RPM) prepad.The formations were reported to have high watersaturation levels. Fracture-stimulation treatments performed in similar intervals usually (1) intersected a stringer of water within the targeted interval, or (2) extended into the highly saturated areas above and/or below the interval. Water cuts as high as 50 to 60% had made production of such intervals uneconomical.Data gathered from the first six months of production on more than seven wells in northern Mexico illustrate the economic benefit of the stimulation treatments using the new CWF technique. In many cases, the treatment has limited water production to less than 20%, and some applications have reduced water production to negligible levels. This paper discusses the job design, field application, and results of several CWF treatments performed in this area between 2004 and 2005.

Mexico has long based its strength on the exploitation of its offshore fields to become one of the largest oil producers in the world. Although still yielding most of its production today, those mature fields have entered a downward trend for the past few years, with a gradual decline of their hydrocarbon output. This trend coincided with an increase in work over operations, most of them involving matrix acidizing interventions in carbonate formations for damage removal and stimulation purposes. Matrix stimulation of offshore Mexico fields presents several challenges, starting with the very nature of the carbonate rocks composing the reservoirs, whose properties can greatly vary within a short distance. In addition, the well conditions are also at times not well understood, with perforated intervals heterogeneously producing, and the increasing occurrence of water production. Finally, due to the location offshore, time-efficiency and operational simplicity became important workover requirements that have a direct impact on the chosen stimulation procedure, often achieved using a simple bullheading sequence, which unfortunately leaves the much needed control of zonal coverage out of the equation. This paper presents a carbonate acidizing workflow and interpretation method that have been developed and successfully implemented in offshore Mexico over the past couple of years. This technique constitutes the cornerstone to assessing and controlling matrix acidizing treatment coverage while it is pumped, in real-time, to ensure optimum treatment performance and maximum return on costs. The workflow relies on the use of a fiber-optic line enclosed inside a coiled tubing (CT) string to acquire distributed temperature sensing data, which are analyzed and translated into a zonal coverage profile using a fast interpretation algorithm. This information then allows stimulation engineers to determine the best strategy for the subsequent well stimulation treatment, including fluid volumes and placement sequence. As the case studies presented in this study will show, there is a lot to gain from this improved methodology. In particular, they show that the long-standing blind bullheading practice results in some shortcomings that may be detrimental to truly unlocking the full potential of those offshore fields.

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Burgos is the first major unassociated gas basin in Mexico. It covers an area of 50,000 km 2 and contains complex, sandstone reservoirs, which are highly compartmentalized and made up of several small, independent blocks characterized by low permeability. This basin is considered a tight-gas reservoir. Sustaining a high production level in this area requires a large number of wells to be drilled and hydraulically fracture stimulated. Historically, the initial well productivity is high, but declines quickly. This phenomenon seems as if it could be associated with the loss of fracture conductivity shortly after the well is put on production.Proppants that are factory coated with a partially cured resin, generally referred to as resin coated proppants (RCPs) have been used in the industry to reduce proppant flowback and to improve fracture conductivity. A more recent methodology is to coat proppants on location using liquid-resin systems (LRSs). This method uses a specific type of hydrophobic material to resin-coat proppants, and has often been used in the industry specifically to prevent post-frac proppant flowback. The proppant is coated on-the-fly on location with the LRS material. This technology has also proven to both initially increase and also to better sustain fracture conductivity over time. The use of liquid resins for proppant coating in the Burgos basin to enhance and maintain conductivity in several fields has shown to lead to better well performance than when using the factory-coated RCPs.Production data from a LSR treated well after almost two years of production is presented and compared to a well with similar petrophysical characteristics completed in the same productive block in the same formation using the same volume of a RCP type proppant.The similar conditions initially present in these wells will forcefully support the superior behavior of LRSs when compared to conventional RCPs when placed using identical treatment designs.