Oil production in the United States (US) increased rapidly in the last decade due to the extensive development of tight-oil resources like Permian, Eagle Ford and Bakken. Most of these resources benefit from being in a source rock or in a close proximity to a source rock and they can be called here unconventional tight-oil resources. There are also conventional tight-oil resources, such as the vast tight-carbonate resources in the Middle East. In this research, definitions, classification, and characteristics of source- and conventional tight-oil plays are presented and contrasted, the North American experience with tight-oil plays is reviewed, and the development potential of the Middle Eastern tight-oil resources is demonstrated through numerical simulation and economic analysis. Most currently targeted Middle Eastern tight-oil resources are accumulations of oil in conventional, tight carbonates, which have migrated from an underlying source rock under the effect of buoyancy forces. The migration process causes lower critical water saturations and more mobile in-situ water compared to unconventional tight-oil plays, and more potential to have contact with aquifers. Although the permeabilities of the Middle Eastern tight-oil resources are more favorable (in the range of 0.01 – 10 md), the viscosity of the currently targeted resources is higher (in the range of 3-10 cp) than their counterparts in North America. Similar to unconventional tight-oil formations, horizontal wells with hydraulic fracturing are still the recommended approach for developing conventional tight-oil formations. The existence of natural fractures, especially in the form of high conductivity fracture corridors, is a major characteristic of the Middle Eastern, conventional tight-oil formations. Fracture corridors aide the movement of oil toward producer wells and increase the drainage areas of wells drilled across them. On the other hand, they also provide pathways for the convergence of the mobile water toward production wells or encroachment of nearby aquifers into the oil pay zone. Therefore, wider well spacing is recommended with smart well designs to divert the flow of unwanted fluids. The high conductivity fracture corridors could cause local fluid segregation, which leads to accumulations of gas at the top and water at the bottom. In addition, pressure depletion could alter the stress state of the formation, which alters the design and implementation of hydraulic fractures. Thus, a comprehensive modeling approach that couples flow and geomechanics is recommended to consider the stress behavior in the development plan. Low GOR, hydrostatic initial pressure, and high initial net stress pose serious development challenges for the Middle Eastern conventional tight-oil resources. The current well completion and stimulation (fracture) design experience in the unconventional tight-oil plays may not be transferred to these formations. Moreover, low initial pressures lead to short periods of accelerated initial production, which removes a favorable economic parameter from development considerations. In addition, high initial movable water saturation could significantly hinder the amount of oil that can be produced. The economic analysis shows that different outcomes can be achieved depending on the oil-price model used and the developer’s objective. It is best to develop these resources during an oil price peak cycle. Developing these resources in a high price environment is rewarding in the short-term. NOCs with diverse oil resource portfolios could leverage the cash flow from the high margin conventional oil resources to fund the expensive capital cost of the development of tight formations especially during high oil price periods. In addition, these companies have a better control on factors like operating expenses and a lower need for financing which could have a significant impact in improving the economics of tight-oil development.
Copyright of the original work is retained by the author.
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