Abstract: Artificial Barriers to Control Excessive Frac Height Growth "Bracketfrac"
Rob Arbaugh, Mike Greener
The Garfield and Beaver Creek fields produce from several dolomite layers in the Devonian Richfield formation at depths of 4200-4600 ft. The Richfield is a series of relatively thin, 4-20 ft dolomite reservoirs, which are confined above and below by anhydrites. These anhydrites are comparable to the dolomite reservoirs in fracture resistance and essentially do not present an effective stress barrier to fracture growth. The dolomite zones have a porosity range of 12-20%, and permeability ranges from 6-20 md. The dolomite reservoirs also contain significant amounts of free salt, which is apparent in the large quantities of produced salt in new wells. There are eight producing zones, oil gravity is 43° API, and viscosity is 1 cp at the reservoir with a temperature of 110°F.
Previous completions in the Richfield have been plagued by unrestricted fractured height growth because there is no control over where the frac is going. Standard practice has been to perforate and treat the zones in groups. If all zones are opened at the same time, communication usually occurs (up or down) during the fracturing of any group of zones.
Artificial barriers to control excessive frac height growth were used in the Richfield formation for the stated reasons. Because no barrier was present between producing zones, the production capabilities of each zone and each new and existing well in the field were limited. INVERTAFRAC and DIVERTAFRAC services are techniques developed and used exclusively by Dowell Oilfield Service Company to control vertical fracture height. When both services are simultaneously used, the treatment is called BRACKETFRAC. By limiting fracture height to the pay zone, several important results are achieved: diversion from barren zones, water, or other undesirable fluids; improved fracture efficiency; deeper penetrating fractures; improved proppant distribution; and consistently better stimulation resul s. This treatment can be applied to producing zones that have weak barriers or no barriers that limit the production rate and optimize the capabilities of the reservoir.
The technical contributions are (1) case histories of exiting wells fractured using the old design and case histories of wells fractured using BRACKETFRAC and (2) production levels increasing in new wells two- and three-fold for initial production and leveling off to a higher level after 90 days.
AAPG Search and Discovery Article #90984©1994 AAPG Annual Convention, East Lansing, Michigan, September 18-20, 1994