화학공학소재연구정보센터
Journal of Petroleum Technology, Vol.48, No.7, 628-633, 1996
High-Permeability Fracturing - The Evolution of a Technology
Since its introduction almost 50 years ago, hydraulic fracturing has been the prime engineering tool for improving well productivity tither by bypassing near-wellbore damage or by actually stimulating performance. Historically (and in many instances erroneously), the emphasis for propped fracturing was on fracture length, culminating in massive treatments for tight-gas sands with several million pounds of proppant and design lengths in excess of 1,500 ft. More recently, the importance of fracture conductivity has become appreciated. This has led to exciting "new" applications of propped fractures in better-quality reservoirs as illustrated by North Sea wells, stimulations in Prudhoe Bay, and "frac-pack" operations in the Gulf of Mexico and Indonesia. While better understanding and new technologies are being used today, the actual application of fracturing to higher-permeability formations is not new. During early development of fracturing, nearly all applications were for moderate-to high-permeability zones (because low-permeability rock was of little interest at oil prices of $3/bbl). While tremendously successful at increasing productivity index (PI), these early high-permeability treatments were doing little more than bypassing damage. More recent development of improved, artificial proppant, cleaner fluid systems, and new technologies have changed this, making it possible to alter reservoir flow and stimulate production from moderate- to high-permeability reservoirs. The primary new tool in the engineer’s arsenal is the development of tip-screenout (TSO) fracturing. While higher-permeability formations provide the new applications, the actual philosophy shift for fracturing occurred with the massive tight-gas stimulations. Traditionally applied to fracturing of poor quality reservoirs, these treatments represented the first engineering attempts to alter reservoir flow in the horizontal plane. The development of TSO fracturing to allow creation of extremely wide, highly conductive fractures has extended this ability to alter reservoir flow to better formations. However, creation of artificial, highly conductive flow paths in the earth also creates an ability to alter reservoir flow in the Vertical plane, opening the way for propped Fracturing to evolve from a stimulation technology to a total reservoir-management tool. This paper uses field examples to trace the history, development, and application of TSO fracturing to high-permeability formations, including fracturing to increase PI, as well as applications aimed at improving : completions in unconsolidated sands. Potential applications of fracturing to bypass the need for sand control are explored. Finally, the use of fracturing as a reservoir-management tool is examined through use of a propped fracture to alter the vertical Row profile of a well to maximize reserves. This particular use of fracturing leads to cases where careful design of both fracture length and conductivity is required; i.e., too much conductivity is as damaging to reservoir management as too little.