Schlumberger

Industry Article: Maximize Reservoir Contact

Brute frac-job force is not the solution to improved reservoir performance.

Publication: E&P
Volume: January
Issue: 2007
Publication Date: 01/01/2007

Hydraulic fracturing got its start when Stanolind (now BP) pumped its first job in Kansas’ Hugoton field in 1946, so it’s appropriate that the current expansion in hydraulic stimulation is manifesting itself in North America, where it’s estimated that approximately 70% of the world’s fracturing activity resides. It is estimated that 9 of every 10 frac jobs are performed in gas wells. But gas production is no longer limited to conventional sandstone reservoirs. Operators are pursuing production in carbonates, tight sandstones, shales, and coal beds, some with intrinsic permeabilities measured in nanoDarcies (10 to 9 Darcies). With extremely low permeability in the matrix rock, natural fracture networks can act as conduits and completion strategies seek to exploit these high conductivity paths. But producing from natural fractures alone is not enough. A natural conclusion seemed be to drill more wells. Although the number of wells drilled in US land has more than doubled over the last 6 years, average daily gas production has remained flat at about 50 Bcf (1.42 Bcm). Obviously, drilling lots of additional wells was not a feasible way to solve the problem, so the industry sought relief by creating conductivity through hydraulic fracturing. In vertical wells, hydraulic fracturing can improve reservoir contact several hundred percentages, but when applied in horizontal wells the improvement is exponential. Results have been encouraging, and the practice has evolved to multistage fracturing, whereby several levels are stimulated in rapid succession in an attempt to increase reservoir contact. Today, operators are completing multiple thin zones distributed over gross intervals of several thousands of feet. According to Schlumberger records, in a span of just 3 years the percentage of US land wells receiving multizone treatments has blossomed from 33% to 50%, with 25% receiving two treatments and 30% receiving more than two stages. And with individual zonal isolation, it is now possible to selectively re-frac underperforming zones.



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