Method for the Enhancement of Injection Activities and Stimulation of Oil and Gas Production

Abstract

By removing material of low permeability from within and around a perforation tunnel and creating at least one fracture at the tip of a perforation tunnel, injection parameters and effects such as outflow rate and, in the case of multiple perforation tunnels benefiting from such cleanup, distribution of injected fluids along a wellbore are enhanced. Following detonation of a charge carrier, a second explosive event is triggered within a freshly made tunnel, thereby substantially eliminating a crushed zone and improving the geometry and quality (and length) of the tunnel. In addition, this action creates substantially debris-free tunnels and relieves the residual stress cage, resulting in perforation tunnels that are highly conducive to injection under fracturing conditions for disposal and stimulation purposes, and that promote even coverage of injected fluids across the perforated interval.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority to provisional application Ser. No. 61 / 118,992, filed Dec. 1, 2008.TECHNICAL FIELD[0002]The present invention relates generally to reactive shaped charges used in the oil and gas industry to explosively perforate well casing and underground hydrocarbon bearing formations, and more particularly to an improved method for explosively perforating a well casing and its surrounding underground hydrocarbon bearing formation prior to injecting fluids or gases, enhancing the effects of the injection and the injection parameters.BACKGROUND OF THE INVENTION[0003]Injection activities are a required practice to enhance and ensure the productivity of oil and gas fields, especially in environments where the natural production potential of the reservoir is limited (e.g. low-permeability formations). Generally, injection activities use special chemical solutions to improve oil recovery, remove formation damage, clean blocke...

AI Technical Summary

Benefits of technology

[0019]While current pre-stimulation procedures do not tend to rely on the quality of the tunnel—that is, whether or not it is plugged and / or damaged-for pre-stimulation activities, it has been found that the geometry of a tunnel will determine the effectiveness and reliability of the fracture treatment. The present application provides an improved method for the perforation of a wellbore, which substantially eliminates the crushed zone and preferably fractures the end or tip of a perforation tunnel (referred to also as creating one or more tip fractures), resulting in improved perforation efficiency and effective tunnel cleanout. This method minimizes near-wellbore pressure losses during injection, improves the distribution of injected fluid across the perforated interval, reduces the pressure required to initiate an hydraulic fracture, and reduces tortuosity effects in fractures created during fracturing operations.

[0022]By fracturing the tip of a perforation tunnel, the residual stress cage caused by plastic deformation of the rock during creation of the tunnel is relieved, reducing the fluid pressure required to initiate a fracture during subsequent injection activity. By removing the crushed zone debris from a perforation tunnel, the inflow and / or outflow potential therefrom is significantly enhanced and further benefits are achieved. Without limiting the scope of the invention, the present method enhances a number of injection activities, which are further discussed below.

Problems solved by technology

However, despite these advantages shaped charges provide an imperfect solution.

Perforation is inevitably a violent event, pulverizing formation rock grains and resulting in plastic deformation of the penetrated rock, grain fracturing, and the compaction of particulate debris (fractured sand grains, cement particles, and / or metal particles from casing, shaped charge fragments or the disintegrating liner) into the tunnel and the pore throats of rock surrounding the tunnel.

This debris 38 can limit the effectiveness of the created tunnel as a conduit for flow since debris inside the perforation tunnel and embedded into the wall of the tunnel may block the ingress or egress of fluids or gases.

This may cause significant operational difficulties for the well operator and the debris may have to be cleaned out of the tunnels at significant cost.

Plugged tips 30 impair flow and obstruct the production of oil and gas from the well.

The perforating event is so fast that the associated rock deformation and compaction exceed the elastic limit of the rock and result in permanent plastic deformation.

Currently, there is no means of measuring it in the borehole.

This becomes even more significant when near-wellbore formation damage has occurred during the drilling and completion process, for example, resulting from mud filtrate invasion.

If the effective penetration is less than the depth of the invasion, fluid flow can be seriously impaired.

If the reservoir pressure and / or formation permeability is low, or the wellbore pressure cannot be lowered substantially, there may be insufficient driving force to remove the debris.

In heterogeneous formations—where rock properties such as hardness and permeability vary significantly within the perforation interval—and in formations of high-strength, high effective stress and / or low natural permeability, underbalanced techniques become increasingly less effective.

Since the maximum pressure gradient is limited by the difference between the reservoir pressure and the minimum hydrostatic pressure that can be achieved in the wellbore, perforations shot into low permeability rock may never experience sufficient surge flow to clean up.

When properly executed, a hydraulic fracture results in a “path,” connected to the well that has a much higher permeability than the surrounding formation.

However, arriving at an optimum perforation design can be difficult because essentially all perforated completions are damaged, as shown by way of example in FIGS. 2-3.

In extreme cases the altered rock cannot be broken down before surface equipment limitations are reached.

This may result in a tortuous path as depicted in FIG. 4, resulting in increased near-wellbore pressure losses, commonly known as tortuosity.

In FIG. 4, the uneven and inefficient injection and / or stimulation that results with prior art methods is seen.

As chemical solutions are introduced, debris 38 prevents their introduction through plugged tunnels, causing poor coverage across the targeted formation interval.

Furthermore, a high percentage of blocked tunnels means that only relatively few open tunnels will be aligned with the preferred fracture plan, which is determined by the prevailing stress regime in the rock.

Re-orientation of the fracture to the preferred fracture plane after initiating in the direction of the open tunnels will result in additional tortuosity.

Such tortuosity is a primary cause of excessive injection pressure, premature screen-out, and incomplete fracture stimulation treatment execution.

Thus, inadequately cleaned tunnels limit the outflow area through which injection fluids can flow; inhibit injection rates at a given injection pressure; impair fracture initiation and propagation; increase the flux rate per open perforation, causing unwanted, increased erosion; and increase the risk that solids bridging across the open perforations will eventually result in catastrophic loss of injectivity (also known as “screen out”).

Further, it becomes very difficult to accurately predict the outflow area created by a given set of perforations and the discussed prior art methods do not remedy the uncertainties associated with damaged perforation tunnels.

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