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.

The only way to obtain an optimum production in the wells that form the Burgos basin in the north of Mexico is using the hydraulic fracturing technique. This paper describes how was the evolution of fracture fluid since 1996 till now, based mainly on each stimulated zone's depth and temperature. A new frac fluid, whose main characteristic is the low polymer load used to stimulate moderate to high temperature wells, was introduced within a process of optimization performed by Petroleos Mexicanos. The detailed information here can be useful for future hydraulic fracture treatments to be performed in this zone. On the other hand, a typical case was analyzed using a fracture simulator linked to a production simulator. A comparison of the production result using two fluids (a conventional one and a low polymer load new one) was made. The advantage of the production company when using this new technology in fracture fluid was determined. Introduction The Burgos Basin, located in the Northeast of Mexico, has many gas fields. Most of them have low permeability (0.01 to 1 md) and high temperature (180°F to 350°F). The only possible way to obtain an optimum production volume is using the hydraulic fracture technique. Since 1996, Petroleos Mexicanos started an intensive drilling program in this basin, including in the completion program of each well, the hydraulic fracturing technique (using water based fracture fluid) in the different pay zones. Figure 1 shows the development of hydraulic fracturing activities since the beginnings of 1995 till now. As the jobs were executed, more experience was acquired. For this reason an optimization program for the hydraulic jobs started to be developed. This optimization involved the different hydraulic fracture techniques, the design of the treatments and the optimization of the different fracture fluids available in the market. Historically, the criterion to optimize a fracture fluid has been based on providing an adequate proppant carrying and causing the least damage to the fracture pack. In other words, it is expected to use a fracture fluid that maintains an adequate fracture width (leak off and viscosity), that properly carries the proppant (at a desired length and concentration). Another expectation is that an effective fracture clean up can be reached after the treatment. The final goal is to get an improvement in the fracture's conductivity. Fracture Conductivity measurements have shown that the breakers pumping schedule are essential to avoid the damage and to provide the fracture pack with the maximum possible conductivity. Recent advances in this kind of additives include new enzymes1, oxidizing agents 2 and encapsulated oxidizing agents 3. Having always as a goal the idea of increasing the conductivity of the proppant pack, the polymer concentration was minimized and the amount of breaker was increased, avoiding the destruction of the rheology. In some cases the size of the proppant and its concentration was increased. The possible causes of fracture damage, that is, the embedment effect of the proppant in the fracture's faces, the crushing effect during the fracture closing and the negative effects of the existing fluid in the fracture once the treatment is over, tried to be avoided. To do so, the gel stabilizer, cross linkers and buffer load were reduced to the minimum, and the breaker concentrations were raised to the maximum. On the other hand, a new fracture fluid with low polymer load started to be used. Application of a new fracture fluid The polymer load that a fracture fluid must have for a treatment generally depends in the well's conditions. That is, depth, BHT and the kind of treatment to be performed. For example, the length of the job, maximum desired concentration, desired geometry, etc.

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.