Over 100 Confomance Fracturing Operations in Brazil: Results and Improvements

Abstract

Abstract 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. Introduction A water conformance fracture treatment 1 is required to provide a return on investment over its treatment life. If the well is marginal or damaged, it must be stimulated to at least attempt to restore its undamaged state. And if there is a water zone nearby, the fracturing fluid is the effective carrier for the conformance material. The industry chemicals used in conformance treatments and injected under high-shear conditions (pressure and rate), are Relative Permeability Modifiers (RPMs). Typically they are compatible with selected fracturing fluids. Adding an RPM to the fracturing fluid will create a resistance to water flow in the fracture fluid filtrate-invaded region on either side of the fracture faces, and also (even though not so important), inside the proppant pack itself. This resistance will act against the high water mobility. Assuming the RPM achieves a high NFRR2 (normalized fluid resistance ratio), the net effect on oil productivity would be an increase. As a consequence, a conformance-fracture technique is a method of selectively stimulating a well. Oil productivity is selectively increased, while water productivity is selectively decreased or maintained at a constant level. An additional feature of the conformance-fracture technique is that the RPM material also restricts filtrate flow 11 into the reservoir (leak-off) because the fracturing fluid in these cases is commonly water-based. Some consequences are reduced fracture leak-off, improved fracture efficiency and reduced treatment volume. Figure 1 illustrates the conformance-fracture concept.