Hydraulic Fracture Initiation and Propagation Control in Unconsolidated and Weakly Cemented Sediments

Abstract

A method and apparatus for initiating and propagating a vertical hydraulic fracture in unconsolidated and weakly cemented sediments from a single bore hole to control the fracture initiation plane and propagation of the hydraulic fracture, enabling greater yield and recovery of petroleum fluids from the formation. An injection casing with multiple fracture initiation sections is inserted and grouted into a bore hole. A fracture fluid carrying a proppant is injected into the injection casing and opens the fracture initiation sections to dilate the formation in a direction orthogonal to the required fracture azimuth plane. Propagation of the fracture is controlled by limiting the fracture fluid injection rate during fracture initiation and propagation and maintaining a minimum fracture fluid viscosity. The injection casing initiation section remains open after fracturing providing direct hydraulic connection between the production well bore, the permeable proppant filled fracture and the formation.

Description

RELATED APPLICATION [0001] This application is a continuation-in-part of copending U.S. patent application Ser. No. 11 / 363,540, filed Feb. 27, 2006.TECHNICAL FIELD [0002] The present invention generally relates to enhanced recovery of petroleum fluids from the subsurface by injecting a fracture fluid to fracture underground formations, and more particularly to a method and apparatus to control the fracture initiation plane and propagation of the hydraulic fracture in a single well bore in unconsolidated and weakly cemented sediments resulting in increased production of petroleum fluids from the subsurface formation. BACKGROUND OF THE INVENTION [0003] Hydraulic fracturing of petroleum recovery wells enhances the extraction of fluids from low permeable formations due to the high permeability of the induced fracture and the size and extent of the fracture. A single hydraulic fracture from a well bore results in increased yield of extracted fluids from the formation. Hydraulic fracturin...

AI Technical Summary

Benefits of technology

[0022] The present invention is applicable to formations of unconsolidated or weakly cemented sediments with low cohesive strength compared to the vertical overburden stress prevailing at the depth of the hydraulic fracture. Low cohesive strength is defined herein as the greater of 200 pounds per square inch (psi) or 25% of the total vertical overburden stress. Examples of such unconsolidated or weakly cemented sediments are sand and sandstone formations, which have inherent high permeability but low strength that requires hydraulic fracturing to increase the yield of the petroleum fluids from such formations and simultaneously reducing the flow of formation sediments towards the well bore. Upon conventional hydraulic fracturing such formations will not yield the full production potential of the formation due to the lack of good hydraulic connection of the hydraulic fracture in the formation and the well bore, resulting in significant drawdown in the well bore causing formation sediments to flow towards the hydraulic fracture and the well bore. The flow of formation sediments towards the hydraulic fracture and the well bore, results in a decline over time of the yield of the extracted fluids from the formation for the same drawdown in the well. The present invention is applicable to formations of unconsolidated or weakly cemented sediments, such as oil sands, in which heavy oil (viscosity >100 centipoise) or bitumen (extremely high viscosity >100,000 centipoise) is contained in the pores of the sediment. Even though these sediments are inherently permeable (in the Darcy range) the fluids are immobile due to their inherently high viscosity at reservoir temperature and pressure. Propped hydraulic fracturing of these sediments provides access for steam, solvents, oils, and convective heat to increase the mobility of the petroleum hydrocarbons either by heat or solvent dilution and thus aid in the extraction of the hydrocarbons from the formation.

Problems solved by technology

Linear elastic fracture mechanics is not applicable to the hydraulic fracturing process of weakly cemented sediments like sands.

Limits on the fracturing propagation rate are needed to ensure the propagating hydraulic fracture does not over run this zone and lead to a loss of control of the propagating process.

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