Abstract
Developing heavy oil in complex carbonate reservoirs requires the application of effective and customized stimulation techniques. Currently in the Issaran field in Egypt heavy oil (<14 API, 1000 – 3000 cP) carbonate reservoirs are being developed by acid treatment with subsequent cyclic steam injection. Although steam injection has proven itself at the initial stage of development, poor vertical steam conformance in the complex geological conditions in the wells reduce the effectiveness of steam injection in later cycles. This requires novel methods to reach the parts of the reservoir that remain untouched by acid and steam.
The technology of Hyper-short Radius Mechanical Radial Drilling was piloted on three wells in an onshore carbonate field with heavy oil in the Eastern desert of Egypt. The technology utilises a method of mechanical radial drilling using small-sized mud motors. This approach allows the accurate drilling of multiple radially directed production channels which are ultra-short radius with a dogleg severity of 200 deg/100ft and which extend up to 80 ft long and are 2.75″ in diameter. This approach bypasses any damage zones, targets very specific intervals in the well, can be applied to any formation, and allows the re-entering of each channel to perform selective jetting of acid, survey the trajectory and for reservoir evaluation. In the Egyptian project the radial channels benefits both the acid injection and steam injection effectiveness, in addition to improved production flow, thereby resulting in the significantly increased production rates compared to the wells’ historical performance.
A three-well pilot project was executed. After drilling the channels, recording survey data in order to confirm the trajectories, and acid treatment through a special jet sub, each well was put under a cyclic steam injection. On the first well four channels were drilled, followed by jetting 210 bbl. of acid in each channel. Two target layers stratigraphically 220 ft apart were stimulated. After the radial drilling and acidizing, 23,000 bbl. of steam was injected in the well. In the second well, four channels were drilled using only a single anchor. On the second well a unique small-diameter unique GR/SP/Resistivity tool was deployed for logging the drilled channel. After jetting acid, using a special jetting gun to target specific depths, the well intervention was completed with the steam injection cycle. The third well was stimulated by four radial channels and after surveying, acid jetting, steam injection was performed. Initial results indicated a significant enhancement for the effective permeability based on steam injectivity data with very good indications of significantly improved production.
For the first time in the industry the new Mechanical Radial Drilling technique has been successfully applied to a heavy oil carbonate reservoir. The key achievements were:
directional radial channels were drilled to stimulate viscous oil deposits,
logging inside of channels has been performed,
radial drilling was performed in conditions of total fluid loss.
Due to the vertical variability in the carbonate reservoir, it is difficult to develop it by conventional means. Upon receiving significant improvements in the oil production from the pilot wells, the radial drilling technology is now being planned for a significant number of follow-up candidate wells.
