Abstract

The objective of this paper is to review the hydrofracturing experience in one of the Omani oil fields and to provide better understanding of geological and operational controls on the productivity of the fractured wells.

The methodology adopted in the study relied on the geomechanical evaluation for understanding the hydrofracture geometry. In particular a geomechanical model was built and calibrated by history matching the simulated and field data. Further, the implications of the created hydrofracture geometry in productivity have been studied based on the conceptual understanding and actual production histories. Last but not least, the influence of operational parameters on the hydrofracture success has also been studied.

The geomechanical evaluation concluded that it is likely that the hydraulic fracture’s growth is unconfined and downwards. Because of the combination of the unconstrained growth with relatively high reservoir permeability, the created fractures potentially are of limited length and of relatively good conductivity. According to a semi-analytical bi-linear production model, these parameters are nearly optimal for the particular reservoir. Preference for highly conductive and short fracture is due to reazonably high fluid mobility in the reservoir, high viscosity of hydrocarbons, and a relatively close well spacing. Horizontal well technology is an alternative to the hydraulic fracturing in the considered settings. Meanwhile the preference may be given to hydraulic fracturing if the commingling of the targeted unit with the overlying or underlying reservoirs is sought after. On the other hand, in the areas of structural deep, the unconfined downward growth poses a risk of connecting to the water zone. Production histories of the wells indicate that water inflow has a very pronounced negative effect on hydrocarbon production and thus must be avoided. The calibrated geomechanical model helps in choosing operational parameters that allow for proper hydrofracture design in the areas of structural deep. Nevertheless, horizontal wells will be beneficial in the areas where fracture connectivity to the water zone is likely.

Finally, a review of the fracturing operations has been carried out to understand the potential for improving the success rate. Because of the overall limited number of hydrofracturing jobs in the field, the results are far from being definitive. Meanwhile it is possible to hypothesize on the range of optimal operational parameters. In particular, this study recommends using limited volumes of fracturing fluids and coarser proppant mesh. The choice is based on the necessity to avoid communication with the water zone and the requirement of a highly conductive fracture for the efficient drainage. The recommendation is supported by limited trials. A viable alternative is combining deviated drilling technology with hydraulic fracturing. In such combination longitudinal small volume fractures should be targeted. The benefits of production enhancement and potentially achieving better capital efficiency are then achieved through commingling production from several units and increasing wellbore connectivity with the reservoirs.

Meanwhile, it is important to keep in mind that the economic benefits can be realized when applying each of the considered development options, i.e., i) vertical, or ii) deviated commingled fractured wells, or dedicated horizontal non-fractured wells. In the considered field the particular choice is driven by the current economic environment, thorough risk assessment, and operational efficiency.

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