Abstract
Girasol oilfield is the first oilfield of Mansarovar Energy Colombia Ltd. (MECL) employing horizontal wells. With first well drilled in 2004 and commercial development started in 2008, this typical heavy oilfield have been produced for 10 years, but the current recovery factor is only 5.09%, and that is much lower than that of similar oilfields.
Girasol oilfield is at the medium stage of the cyclic steam stimulation (CSS) with 5.3 cycles and remaining reserves of 40.54 MMbbl. Based on characteristics of typical mid-shallow inter-bedded reservoirs with heavy oil in Girasol oilfield, by applying methodology of reservoir engineering and numerical reservoir simulation, the development status of Girasol oilfield is analyzed through full utilization of the geologic, logging and production performance data, and etc. Five potentials for production enhancement are researched including (1) Potential for well pattern improvement: except layer A12 and A9-Upper, other layers exist 30%∼70% of uncontrolled regions in transition part between vertical and horizontal wells, near-boundary, low permeability areas; (2) Potential for well infilling: the well spacing is about 150m, while heating radius is about 50m, so there exist oils hard to exploit between wells. Numerical simulation shows the average heating area is only 33.07%. (3) Potential for CSS parameter optimization: compared with other similar blocks, the steam injection parameter is unoptimized, and there is a good potential for steam injection parameters adjustment; (4) Potential for horizontal lateral optimization: the current horizontal lateral of 600m on average is too long for thermal production because it will leads to high heat loss, un-uniform steam adsorption and poor steam injection effect; (5) Potential for steam flooding.
Aiming at the development potentials of Girasol oilfield, Sector models based on numerical simulation are carried out to optimize thermal mode, well pattern type, well spacing, injection-production parameters and horizontal lateral length for vertical wells and horizontal wells separately. Full field EOR conceptual designs are conducted and 7 development schemes are simulated.
Results show increasing periodic steam injection amount for CSS to 2 times can get much better production performance; the optimized horizontal well lateral length is 300-400 meters. Steam flooding is a very promising EOR method for Girasol oilfield and it can lead to 43.73% of recovery under current well pattern to year 2030; it can get 45% more oils by only adjusting CSS injection parameters and improving well pattern with 12 new wells, so it's recomended under current production period.
This paper constructs a framework and technical route for fullfield EOR enhancement design of heavy oil reservoir from potential analysis, sector simulation to fullfield scale implementation.
