HIGH-PERMEABILITY FRACTURING - THE EVOLUTION OF A TECHNOLOGY

Since its introduction almost 50 years ago, hydraulic fracturing has b een the prime engineering tool for improving well productivity tither by bypassing near-wellbore damage or by actually stimulating performan ce. Historically (and in many instances erroneously), the emphasis for propped fracturing was on fracture length, culminating in massive tre atments for tight-gas sands with several million pounds of proppant an d design lengths in excess of 1,500 ft. More recently, the importance of fracture conductivity has become appreciated. This has led to excit ing ''new'' applications of propped fractures in better-quality reserv oirs as illustrated by North Sea wells, stimulations in Prudhoe Bay, a nd ''frac-pack'' operations in the Gulf of Mexico and Indonesia. While better understanding and new technologies are being used today, the a ctual application of fracturing to higher-permeability formations is n ot new. During early development of fracturing, nearly all application s were for moderate-to high-permeability zones (because low-permeabili ty rock was of little interest at oil prices of $3/bbl). While tremend ously successful at increasing productivity index (PI), these early hi gh-permeability treatments were doing little more than bypassing damag e. More recent development of improved, artificial proppant, cleaner f luid systems, and new technologies have changed this, making it possib le to alter reservoir flow and stimulate production from moderate- to high-permeability reservoirs. The primary new tool in the engineer's a rsenal is the development of tip-screenout (TSO) fracturing. While hig her-permeability formations provide the new applications, the actual p hilosophy shift for fracturing occurred with the massive tight-gas sti mulations. Traditionally applied to fracturing of poor quality reservo irs, these treatments represented the first engineering attempts to al ter reservoir flow in the horizontal plane. The development of TSO fra cturing to allow creation of extremely wide, highly conductive fractur es has extended this ability to alter reservoir flow to better formati ons. However, creation of artificial, highly conductive flow paths in the earth also creates an ability to alter reservoir flow in the Verti cal plane, opening the way for propped Fracturing to evolve from a sti mulation technology to a total reservoir-management tool. This paper u ses field examples to trace the history, development, and application of TSO fracturing to high-permeability formations, including fracturin g to increase PI, as well as applications aimed at improving: completi ons in unconsolidated sands. Potential applications of fracturing to b ypass the need for sand control are explored. Finally, the use of frac turing as a reservoir-management tool is examined through use of a pro pped fracture to alter the vertical Row profile of a well to maximize reserves. This particular use of fracturing leads to cases where caref ul design of both fracture length and conductivity is required; i.e., too much conductivity is as damaging to reservoir management as too li ttle.