Abstract

Exploration drilling indicated that the Natih B formation in Oman may have a significant amount of oil locked in a challenging low-permeability, laminated, carbonate reservoir. The first completed vertical wells suggested that stimulation treatments were required for economic production. The operator applied acid fracturing stimulation techniques to establish baseline production. To further improve well performance, proppant fracturing stimulations were scheduled for several vertical and horizontal wells.

Mechanical earth models were constructed to help improve understanding of fracture geometry. The earth models revealed stress inversion between layers, differentiating stress regimes into strike-slip and thrust. Areas of different stresses within the same formation would lead to different hydraulic fracture shapes (e.g., regular planar fractures in the case of strike-slip mode or horizontal fractures in the case of thrust mode). Predicting these geometries would impact the fracture design and completion strategies. In addition, the pay zone was bounded by water-bearing zones at the top and bottom, introducing a risk of water production if any of the wells exhibited excessive fracture-height growth. Several measures helped survey fracture-height extension during initial diagnostic treatments.

In the formation's first horizontal well, uncertain stress regimes and lateral unconformities, such as natural fractures, complicated the hydraulic fracturing treatments. To overcome these uncertainties and optimize stimulation, we needed to accurately model natural and hydraulic fracture interaction. A mechanical earth model from vertical wells in the vicinity, and the horizontal wellbore itself, were combined with natural fracture network data and the staging and perforation design.

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