There are several kinds of unconventional oil production and one of them is heavy oil production from sand reservoirs with initially gas cap. A gas cap near the top of a heavy oil formation is a rare occurrence; however, high gas saturation or desaturated ("air") zones may form as a result of natural depletion.
Heavy oil is increasingly being produced by steam injection, cyclic or continuous, and to a smaller extent, by in situ combustion. A gas cap would increase the tendency of the override of the injected steam or air, resulting in poor vertical sweep. These simplified pictures are complicated by the flow of heat from the gas zones, into the oil zone.
In reservoirs with initially gas cap, it is necessary to inject in the wells that produce excessive gas in order to conserve gas, maintains reservoir pressure, decrease the oil viscosity and thereby increase ultimate oil recovery. This method depends on steam flooding injection in the crest of reservoir and this will heat the reservoir through steam injection and thus decrease the oil viscosity and increase the gas cap size due to thermal vaporization of oil and increase the gravity drainage as well.
Using steam introduces more heat into the reservoir as it flows in the gas cap and helps in distributing the heat.
The field forecast does not examined cold production as there is an initially gas cap and any production without injection in this type of reservoir will consume the pressure support.
A numerical simulation study has been undertaken to explore the optimum method to develop heavy oil sandstone reservoir of 12.8 API with initially gas cap by using steam injection stimulation either by steam flooding and/or steam cycles. This is applied on a sector model of 1200 × 1200 m from the full field model (Fig. 1) utilize compositional, and thermal options. Different sensitivities have been examined such as well spacing, number of injectors and producers, various injection strategies, injection parameters, the duration of steam cyclic stimulation, and well type whether vertical or horizontal.