Method and apparatus for producing unconventional oil at shallow depths

Abstract

An oil production well is drilled into a kerogenous chalk source rock comprising (i) type IIs kerogen and (ii) shallow naturally-occurring unconventional oil derived from the type IIs kerogen that is resident within pore space of the source rock. In some embodiments, the production well is drilled at a location where the geothermal gradient is at least 3 degrees C. per 100 m is present at or near the production well. It is believed that the presence of this geothermal gradient accelerated maturation of the type IIs kerogen of the source rock to convert a portion of the type IIs kerogen into the unconventional oil. In some embodiments, the shallow production well is non-vertical. In some embodiments, at depths that are shallow and within the source rock, the production well is cased and perforated. Oil from the source rock may be produced via the production well and the shallow-depth perforated locations thereof.

Description

BACKGROUND AND RELATED ART[0001]In the last few years, the oil industry in the United States has developed methods for producing unconventional gas and oil from very low permeability source rocks. In these unconventional gas and oil plays, the gas and oil is still contained within the original source rock and has not migrated to a reservoir and trap.[0002]For example, the Bakken shale in North Dakota has been extensively produced using long horizontal wells which are stimulated with multiple propped hydraulic fractures. These Bakken wells are typically at depths greater than about 3000 m in order for the Type I kerogen to have matured over geological time sufficiently to generate oil and gas. Even though the Bakken oil produced is low viscosity and rich in NGL (natural gas liquids), because of the depth of the wells and the many stages of hydraulic stimulation that are required, these unconventional wells are very expensive and only a very small percentage of the unconventional oil ...

AI Technical Summary

Benefits of technology

The present invention provides a method for accessing oil from shallow production wells, compared to conventional techniques which require deeper wells. The shallow wells are cost-effective and can access oil from locations where it is located in pore space of the source rock. The method may use thermal energy to increase the mobility of the oil and decrease its viscosity. Additionally, pressurized steam can be injected into the source rock to thermally stimulate it and increase the mobility of unconventional oil.

Problems solved by technology

Even though the Bakken oil produced is low viscosity and rich in NGL (natural gas liquids), because of the depth of the wells and the many stages of hydraulic stimulation that are required, these unconventional wells are very expensive and only a very small percentage of the unconventional oil and gas in place is actually produced.

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