Successful Unconventional Fracturing Tight and Highly Laminated Silicilyte Reservoir Leading to Economic Field Development

Abstract

South Oman contains several tight silicilyte reservoirs with significant locked hydrocarbon volumes. Successful hydraulic fracturing is key for unlocking commercial production. Low production rates coupled with fast declines have remained a challenge and a new economically attractive development scheme was required. Through integrated re-evaluation of the geology and reservoir, a modified frac approach was designed to create more connectivity to the reservoir height, using an unconventional frac design and frac fluids plus over-flush. Poor well productivity in tight silicilyte reservoir can be explained by low permeability of 0.001-0.1 mD and laminated texture with almost zero vertical permeability. Fit for purpose modelling was performed to assess the forecasting range for sub-surface uncertainties and frac parameters. One of the key changes for a successful development strategy was to place a higher number of fracs to overcome the extreme lamination. [1] It was observed that the "conventional" fracturing approach inaccurately assumed higher vertical fracture coverage of the reservoir and that the guar fluid used was much more damaging due to low recovery after frac clean-up. Fifteen unconventional fracs were pumped successfully with over-flush pumping technique. To understand if this new unconventional approach was effective in overcoming the extreme lamination required additional understanding of fractures geometry and orientation. To confirm fracture dimensions and flowing heights; a set of radioactive, chemical tracers and logging activities were completed. Flowback results showed that the unconventional frac [3] fluid used, was relatively easy to recover from formation and better cleaning-up of fractures can be achieved. This led to successful well clean-up compared to previous wells in the same field and confirmed better fracs clean up. Initial production results confirmed at least double well initial productivity, which should lead to better stable oil production from the field. Radioactive tracers logging, Sonic logging and Spectrum Noise Logging (SNL) confirmed mechanical and conductive fracture heights. Sonic logging also confirmed frac orientation. Oil and water dissolvable tracers confirmed fractures clean up from water and oil production intervals. Full geological and reservoir understanding, out of box thinking in frac technology allowed the asset team to come up with an unconventional development approach to improve commercial production from tight silicilyte reservoirs. The new frac approach included unconventional frac design and fluids, and execution using over flush and resulted into unlocking significant reserves. A more economic full field development is being planned and replication of the new frac approach is already ongoing in other fields.