Pillar Fracturing a Sandstone Reservoir Shows Benefit Over Conventional Fracturing
Authors: Wilson Adam 
Published: March 2018

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 186199, “Unlocking Depleted and Low-Modulus Telisa Sandstone Reservoir With Pillar-Fracturing Technique: Well-Performance-Improvement Comparison With Conventional Fracturing,” by M. Azhari, SPE, N.F. Prakoso, and D. Ningrum, Medco E&P Indonesia, and L. Soetikno and A. Makmun, Schlumberger, prepared for the 2017 SPE/IATMI Asia Pacific Oil and Gas Conference and Exhibition, Bali, Indonesia, 17–19 October. The paper has not been peer reviewed.

The Kaji Semoga Field in South Sumatra consists of three main reservoirs—Telisa sandstone (TLS), Baturaja limestone, and Talangakar sandstone. The successful development of TLS with hydraulic fracturing led to further efforts to maximize oil recovery. After a study with suitable samples and cases, pillar fracturing was considered. This method is similar to conventional fracturing techniques where fluid and proppant are used to create conductive paths in the reservoir layer; however, pillar fracturing relies on open flow channels.

Pillar Fracturing

A major step change in the development of the Kaji Semoga Field was to use the hydraulic-fracturing technique referred to as pillar fracturing. The pillar-fracturing technique creates stable voids within the proppant pack that serve as infinite-conductivity channels for fluid flow rather than the intragranular flow of conventional fracturing techniques (Fig. 1). Hydrocarbon will flow preferentially through the channels rather than through the proppant pack. In addition, pillar fracturing allows for better fracture cleanup, longer fracture effective half-lengths, and lower pressure drops along the fracture. Consequently, production after pillar fracturing is greater than that following conventional fracturing. Another advantage of the pillar-fracturing technique is a low screenout rate compared with conventional fracturing. The prevention of screen out is related to the different bridging characteristics of conventional- and pillar-fracturing slurries.

The stable voids within the proppant pack are created through a combination of specific pumping schedules, specific equipment, and fracturing-fluid design. The voids are achieved by alternate pumping of gelled fluid in two types of pulses, proppant-laden pulses and proppant-free pulses. Fibers are added continuously during pumping to mitigate the dispersion of the proppant-laden pulses as they are conveyed throughout the surface lines and the wellbore and within the fracture. A dispersed pulse can create narrow fracture widths and a reduction in the number and quality of the channels, which leads to a reduction of fracture conductivity. The fiber also enhances the proppant-carrying capacity and prevents proppant settling within the fracture. The pulse stage is then followed by a continuous proppant tail-in stage near the end of the treatment before the flush stage. This tail-in stage ensures good connectivity between the wellbore and the channels created during the treatment. Specially engineered blending equipment was needed to ensure stable and consistent pulse delivery.