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Many of the mature oil fields in the world produce commingled water. Water production increases the lift cost of a barrel of oil, as it needs surface handling when it is to be disposed, re-injected into other wells, or used for a different purpose. Several techniques and chemistries have evolved over the past decades to address reduction of unwanted produced water. These different approaches to minimize water production are grouped under the name of water conformance. Selecting the proper water conformance method for a well depends on the correct understanding of the reservoir. Economics remains the main decision driver as to which technique and chemistry to use. A quite effective technique among the different water conformance methods is conformance fracturing, a combination of hydraulic fracturing and water control. Among several operating companies, hydraulic fracturing still is the preferred technology to increase well productivity. The development of a family of lightweight proppants for hydraulic fracturing has allowed a more uniform fracture height and width, due to a lesser degree of proppant settling inside the fracture, resulting in a better connectivity with the wellbore and lower chance of breaching nearby water zones. On the other hand, chemistry of relative permeability modifiers (RPM) has been greatly improved over the past decade, and one can observe longer life on water control treatments done using RPMs. In Brazil, we have conducted over 100 conformance fracturing operations to date, using conventional as well as lightweight proppants, and relative permeability modifiers, to meet the different targets they were deployed for. This paper will summarize these treatments (design, logistics, materials, equipment), with obtained results (oil and water production over time), showing the improvements made over time.

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.

In mature fields, operators are often seeking ways to increase the hydrocarbon recovery, with the help of reputable service companies. Well stimulation continues to be, by far, the preferred method of achieving such goal. Operators and service companies are continually screening out technologies which will deliver the highest benefit/cost ratio for a particular stimulation well treatment, maintaining focus on operational and health, safety and environment excellencies. This paper addresses the rebirth of a past hydraulic fracturing technique, born in the 50's, and how it is being successfully applied on onshore mature fields in Brazil: batch fracturing. It is effective due to several technological advancements on proppant density, becoming lighter than conventional frac sand and yet with sufficient mechanical properties to withstand bottom-hole environments. Batch fracturing is now contributing to equally efficient, and more economical well stimulation treatments, providing good economical returns to operating companies. Batch-Fracturing had limited success in the past. This was due to the available frac fluid and proppant technologies at that time. It is desirable that proppants have low settling when carried by a fracturing fluid, from the time they are added into such fluid, until the end of the pumping process. Batch fracturing applications are on the rise, due to the new families of ultra lightweight proppants, with specific gravities ranging from 1.05 to 1.75. In batch fracturing, the proppant is added to the carrier fluid prepared in standard oilfield mixing tanks, eliminating the need of specialized mixing equipment such as blenders. Less sophisticated equipment on location implies in lower operational and logistical costs. The carrier fluid ("frac fluid") does not need to yield high levels of viscosity, and, by consequence, does not have a high load of chemicals (gelling agents, cross-linkers, related breakers…). With batch fracs it is possible to perform common but effective types of fracturing treatments, such as "skin-by-pass" (a fracture that by-passes the damaged zone), and "partial mono layer' fracturing, both exemplified in this paper, through case histories. Introduction Today, most of the producing oil and gas fields are considered mature. Although continually being redefined, a field is considered mature when its current level of hydrocarbon production has passed its past production peak. Associated with the reservoir's production depletion, there are other hydrocarbon recovery issues inducing operators to continually seek ways to overcome these natural effects. They look, with their subcontracted service companies, for cost effective techniques and technologies able to increase production and oil recovery.

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