Girasol, one of the largest heavy oil fields in Colombia, is located in the Middle Magdalena Valley basin. The field is composed of a shallow sequence of sediments of fluvial origin in which sandstone channels contain heavy oil of 11- to 13°-API gravities.

Similar fields in the country are developed using thermal recovery techniques via vertical or deviated wells. As horizontal wells have proved to offer advantages for enhanced oil recovery, from the first stages the Girasol field development plan included the execution of horizontal wells to apply cyclic steam injection techniques.

Four different stacked sandstone reservoirs, located at 1,100-ft to 1,600-ft true vertical depth (TVD) below surface, are the main targets. The project included a series of parallel horizontal wells of 1,200-ft to 2,350-ft lateral extension, with a fixed lateral spacing and vertically placed to drain one reservoir per well. The targets were geological, 10- to 20-ft thickness to maximize production.

Horizontal well placement in this scenario—shallow, thin, and friable formations— is, in general, difficult to achieve with the use of conventional geosteering techniques, as they generally fail to identify unexpected changes in the reservoir geometry, increasing the risk of poor results. This risk was minimized by using deep, directional electromagnetic measurements while drilling, enabling the reservoir geometry mapping in real time, several feet from the borehole.

Results of the use of this technology—combined with continuous inclination measurement near the bit and an advanced geosteering process— include 96% average net pay, minimization of unproductive drilling, rig time savings, and sidetracks avoidance after 24 horizontal wells drilled to date. The strategy used for horizontally placing wells in the Girasol field can be used in similar fields worldwide.

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