TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractActual worldwide oil production averages some 75 million barrels per day and, while estimates vary, this is associated with the production of 300 -400 million barrels of water per day. These values of approximately 5 -6 barrels of water for every barrel of oil are quite conservative. In some areas around the world, fields remain on production when the ratio is as high as 50 to 1.Water production causes several problems to oil wells such as scaling, fines migration or sandface failure, corrosion of tubular, and kills wells by hydrostatic loading, amongst other things. Thus, while water production is an inevitable consequence of oil production, it is usually desirable to defer its onset, or its rise, for as long as possible.Numerous strategies, both mechanical and chemical, have been employed over the years in attempts to achieve this. Simple shut-off techniques using cement, mechanical plugs and cross-linked gels have been widely used. Exotic materials such as DPR (disproportionate permeability reducers) and the new generation of relative permeability modifiers (RPM) have been applied in matrix treatments with varying degrees of success. Most recently, Conformance Fracturing operations have increased substantially in mature fields as the synergistic effect obtained by adding a RPM to a fracturing fluid have produced increased oil production with reduced water cut in one step, consequently eliminating the cost of additional water shut off treatment later on.This paper is an evaluation of various RPM materials commonly used on Conformance Fracturing treatments performed in the northeast of Brazil and other South American countries, rather than the usual laboratory testing methods and theoretical estimations. The paper also describes the technical design and operational methodology to treat single zone to laminated reservoirs with different mobility ratios. We believe conformance fracture techniques could significantly impact the development strategies of many fields worldwide.

Summary In mature fields, a continuous challenge for operators is to maximize hydrocarbon recovery while minimizing associated water production. Water production causes several problems, including scaling, fines migration or sand-face failure, tubular corrosion, and increased hydrostatic loadings. Thus, although water production is almost an inevitable consequence of oil production, it is usually desirable to defer its onset, or its rise, as long as possible. Proper stimulation is required to prove many reservoirs commercially, including dirty sandstones and lower-permeability layered formations in waterdrive reservoirs and/or with nearby water zones. The focus on water avoidance has made conformance fracturing an interesting prospect in mature fields because it combines synergistically a relative permeability modifier (RPM) with a fracturing fluid to enhance production and reduce water cut in one step. However, if a water zone is below the zone being fractured, fracture invasion may create a conductive path for water production. For example, proppant convection and settling can result in heavier treatment stages displacing rapidly downward from the perforations to the bottom of the fracture. This may occur when treatments call for large pad volumes, high proppant concentrations, or stage density contrasts. An important technique used to avoid this problem is known locally as inverted proppant convection. It requires proppant buoyancy in the selected fracturing fluid, as is possible when using ultralightweight proppants (ULWPs) with specific gravities (SG) from 1.054 to 1.75. The technique involves pumping a high-density fluid pad with SG higher than the proppant carrier fluid, which in turn has SG slightly higher than the selected ULWP. This paper describes the design approach, operational procedures, and evaluation of field case histories demonstrating the synergism of conformance fracture and inverted proppant convection as applied in northeast Brazil, with the potential to impact field-development strategies worldwide.