In Colombia, hydraulic fracturing in the Cusiana and Cupiaga fields had increased rates by 100 to 1000%, reaching 15,000 to 25,000 bopd per well - better than any other stimulation technique. Measured skin factors were highly rate-dependent due to the severe non-Darcy and multiphase effects. The first attempted stimulation treatment increased the production rate of an exploration well from 1600 bopd to 12,500 bopd.
The Cusiana and Cupiagua fields are located in the Casanare region of Colombia. Current daily production (June 1997) is of the order of 185,000 stb/d, with production due to increase substantially. The reservoirs are severely compacted quartz arenites, of low porosity but with large pore throats. This makes them extremely vulnerable to formation damage by mud invasion. The extremely high compressive strength of the rock reduces perforation penetration, resulting in high skin factors. The skin factors are rate dependent due to turbulence associated with the high production rates, production of oil below the bubble point (Cusiana) and condensate banking effects (Cupiagua).
The wells are costly to drill, so in order to maximise the production rates hydraulic fracturing has been applied. Post fracture well rates of up to 21 mstbpd have been achieved. At these rates non- Darcy flow in the fractures is extremely important, all the more so as problems with fracture-wellbore communication and the initiation of multiple fractures have been experienced at modest deviations, as a direct result of an extreme contrast between the two principal horizontal stresses. Wide variations in the minimum horizontal stress have also been encountered in this tectonically active area. The high Young's modulus of the rock limits the achievable fracture width and therefore proppant coverage. The paper outlines the progress made to date, and the results achieved in these economically significant but technically challenging fields.
Author(s): M.R. Jackson, M. Rylance, L.G. Acosta, BP Exploration (Colombia) Ltd
Paper Number: SPE 38608