Proppant Flowback Control in Deviated Shallow Gas Wells

Abstract

Abstract This case-history paper presents results from various proppant flowback prevention methods. The wells studied are part of a shallow gas development project near Brooks, Alberta, Canada. The wells were drilled from multi-well pads resulting in deviated wellbores that reach the gas targets. Each well penetrates two or three gas bearing geologic formations, 400 m to 800 m in depth. Each formation has multiple sand and shale layers that were typically completed by perforating six or seven 2.0 m pay intervals. Then each interval was hydraulically fractured with energized, viscosified water frac fluid that placed 12 tonne of proppant in the formation. The fracture treatments were pumped through coiled tubing and a straddle packer was used to isolate each pay interval. The occurrence of undesirable proppant flowback into the wellbore lengthened clean-out time and increased disposal cost. Three solutions to the flowback problem were tried:curable resin-coated proppant;proppant surface- modification agent; and,fibre elements. Each product was tailed into the end of the frac treatment and the amount of each product used had to stay within the economic limits of the project. This paper describes the proppant flowback control achieved by each technique. Other considerations that were required to successfully pump the flowback control products are also discussed. Introduction History The occurrence of proppant flowback from propped hydraulic fractures has long been an operational problem. Many solutions to try and prevent proppant flowback have been attempted with inconsistent results(1, 2). In most cases, the unwanted proppant is produced during cleanup operations, immediately following the fracture treatment, when the well is being flowed or is swabbed to recover frac fluid. During this time, operators can easily handle the produced proppant with the equipment that is present for well stimulation and completion operations. However, proppant disposal can be time consuming and costly as well as reducing the effectiveness of the stimulation treatment. In other situations, proppant is produced during hydrocarbon production and can be a problem for the production life of the well. Proppant flowback can cause valve and choke erosion, plugging of surface vessels, and proppant can build up in the wellbore covering perforations. During production of the well, proppant flowback increases operating costs, compromises safety and reduces hydrocarbon production. Substantial work has been conducted in the industry to explain, predict, and reduce proppant flowback(3). Uneven closure of the formation on the proppant coupled with proppant settling allows upper portions of the proppant pack to be free moving. Proppant flowback is more prevalent in soft, low closure-stress formations and in deviated wells, but can occur in almost any situation. The chance of proppant flowback from properly packed fractures is reduced but proper packing does not insure proppant free production(2). The literature does not provide a clear understanding of proppant flowback causes or flowback prevention techniques. Problem In the subject case history, proppant flowback is a problem in the field's deviated wells but is not a problem in the nearby vertical wells.