Inverted-Convection Proppant Transport for Effective Conformance Fracturing

Abstract

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.