In the Llanos basin of Colombia, there are shallow, highly permeable, poorly consolidated sandstone reservoirs close to oil-water contacts. The Carbonera formation is typical—several small, highly permeable (600 to 3000 mD) producing sands, with poorly defined barriers. High production rates and low bottom hole flowing pressures (BHFP) result in water coning and sand production. One solution is a stacked frac-pack completion.

In these applications, conventional cross-linked fracturing fluids have limitations. High polymer concentrations and viscosity are required to control fluid leak-off and create a sufficiently wide hydraulic fracture to admit proppant. High fluid viscosity has led to uncontrolled fracture growth into oil-water contacts, while the high polymer concentration decreases fracture conductivity and effective half-length.

A linear fluid comprised of polyacrylamide and polysaccharide polymers has proved an effective solution. The polyacrylamide greatly enhances fluid efficiency and elasticity, while reducing friction pressures and horsepower requirements. Fluid elasticity ensures adequate proppant transport. Fluid efficiency is determined by the polyacrylamide concentration and adjusted to achieve the required fracture geometry. The use of this fluid along with a geomechanical model and pseudo 3D fracturing simulator ensures that the propped fracture remains within the producing sand, with increased effective fracture half-length and conductivity. The polyacrylamide reduces the effective permeability to water and limits potential conning, when the well is produced.

Wells completed with frac-packs using the linear fluid produce an average of 1420 bbl/day of fluid with 20% water-cut. The fluid efficiency during the treatments varies between 30% and 15% as a function of permeability. Offset conventionally gravel packed wells with a lower bottom hole flowing pressure (BHFP) average 980 bbl/day of fluid with 60% water-cut.

Frac-packs, using an efficient linear fluid together with a geomechanical model and a pseudo 3D fracturing simulator have greatly improved the economics of producing these highly permeable reservoirs—maximizing production and recoverable reserves, while minimizing water production.

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