Patent Application
20230105939
The present invention relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides for the planar propagation of multiple inclusions of differing azimuths for increased permeability planes in weakly cemented formations.
Recent advancements have been made in the art of forming increased permeability drainage planes in weakly cemented formations. These advancements are particularly useful for enhancing and maximizing injection and production flow rates of supercritical carbon dioxide in depleted petroleum reservoirs for subsurface carbon energy storage to enable the carbon electric grid to meet supply and demand needs both daily and seasonal, achieving a zero carbon grid, whilst utilizing renewable energy to its maximum potential, and assisted by gravity drainage to produce additional hydrocarbons from the pressure depleted petroleum reservoirs, etc., and also assist hydrocarbon recovery from heavy oil and oil sand formations; although the advancements have other uses, as well.
In many circumstances, it is desirable to complete such wells “open hole,” i.e., without using a cemented casing to install the high permeable inclusions at multiple azimuths and coalesce the respective inclusions at differing depths. Following installation of the multiple azimuth permeable inclusions, the well is completed with a production tubing to inject and produce fluids from the wells.
Therefore, it will be appreciated that improvements are needed in the art of improving injection and production flow rate control in wells.
In carrying out the principles of the present invention, well systems and associated devices and methods are provided which solve at least one problem in the art. One example is described below in which multiple azimuth permeable inclusions are installed in a formation from a downhole tool device in an “open hole” wellbore configuration with the multiple azimuth inclusions coalesced with their respective azimuth inclusions at differing depths, enabling high injection and production flow rates of fluids into and from the well. The downhole device seals against the formation, and at particular azimuths the device circumferentially opens and an initial slot is created by various means; explosive shape charges, mechanical slotting, fluid jetting, a combination of mechanical and fluid insertion of a wedge into the formation, etc. or by additional expansion of the downhole tool to exceed the passive Rankine effective pressure of the formation, all of which initial methods are individually followed by the injection of a highly viscous non-penetrating fluid enabling the planar propagation of an inclusion in the formation and it being maintained on azimuth during propagation. The device is particularly well suited for use in conjunction with anelastic weakly cemented formations.
In one aspect, a well system is provided which includes a downhole tool expansion device interconnected to a tubular string for initiating and propagating of at least one inclusion into a formation. The expansion tool device has at least one opening in a sidewall for fluid communication between the inclusion and an interior of the tool and tubular string. A flow control device controls the flow of highly viscous non-penetrating fluid into the formation from the tubular string.
These and other features, advantages, benefits and objects will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings, in which similar elements are indicated in the various figures using the same reference numbers.
It is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present invention. The embodiments are described merely as examples of useful applications of the principles of the invention, which is not limited to any specific details of these embodiments.
In the following description of the representative embodiments of the invention, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. In general, “above”, “upper”, “upward” and similar terms refer to a direction toward the earth's surface along a wellbore, and “below”, “lower”, “downward” and similar terms refer to a direction away from the earth's surface along the wellbore.
Representatively illustrated in
The formation 1 includes several zones penetrated by the wellbore 2, and, one or more of these zones could be in separate formations, part of other reservoirs, etc.
An open hole tool device 3 is inserted in the wellbore 2 as depicted in
The system and method could be used to install inclusion on azimuth in formations comprised of relatively strong rock, but the system and method find especially beneficial application in ductile rock formations made up of weakly cemented sediments, in which it is typically very difficult to obtain directional or geometric control over inclusions as they are being formed. In particular, the system and method are applicable to anelastic formations, having a formation Quality factor of less than 20, in which pressurizing a wellbore with a non-penetrating fluid in such formations has a poor to low efficiency in generating circumferential tensile stresses in such formations.
Weakly cemented sediments are primarily frictional materials since they have minimal cohesive strength. An uncemented sand having no inherent cohesive strength (i.e., no cement bonding holding the sand grains together) cannot contain a stable crack within its structure and cannot undergo brittle fracture. Such materials are categorized as frictional materials which fail under shear stress, whereas brittle cohesive materials, such as strong rocks, fail under normal stress.
The term “cohesion” is used in the art to describe the strength of a material at zero effective mean stress. Weakly cemented materials may appear to have some apparent cohesion due to suction or negative pore pressures created by capillary attraction in fine grained sediment, with the sediment being only partially saturated. These suction pressures hold the grains together at low effective stresses and, thus, are often called apparent cohesion.
The suction pressures are not true bonding of the sediment's grains, since the suction pressures would dissipate due to complete saturation of the sediment. Apparent cohesion is generally such a small component of strength that it cannot be effectively measured for strong rocks, and only becomes apparent when testing very weakly cemented sediments.
Geological strong materials, such as relatively strong rock, behave as brittle materials at normal petroleum reservoir depths, but at great depth (i.e. at very high confining stress) or at highly elevated temperatures, these rocks can behave like ductile frictional materials. Weakly cemented sands and weakly cemented formations behave as ductile frictional materials from shallow to deep depths, and the behavior of such materials are fundamentally different from rocks that exhibit brittle fracture behavior. Ductile frictional materials fail under shear stress and consume energy due to frictional sliding, rotation and displacement.
Conventional hydraulic dilation of weakly cemented sediments is conducted extensively on petroleum reservoirs as a means of sand control. The procedure is commonly referred to as “Frac-and-Pack.” In a typical operation, the casing is perforated over the formation interval intended to be fractured and the formation is injected with a treatment fluid of low gel loading without proppant, in order to form the desired two winged structure of a fracture. Then, the proppant loading in the treatment fluid is increased substantially to yield tip screen-out of the fracture. In this manner, the fracture tip does not extend further, and the fracture and perforations are backfilled with proppant.
The process assumes a two winged fracture is formed as in conventional brittle hydraulic fracturing. However, such a process has not been duplicated in the laboratory or in shallow field trials. In laboratory experiments and shallow field trials what has been observed is chaotic geometries of the injected fluid, with many cases evidencing cavity expansion growth of the treatment fluid around the well and with deformation or compaction of the host formation.
Weakly cemented sediments behave like a ductile frictional material in yield due to the predominantly frictional behavior and the low cohesion between the grains of the sediment. Such materials do not “fracture” and, therefore, there is no inherent fracturing process in these materials as compared to conventional hydraulic fracturing of strong brittle rocks.
Linear elastic fracture mechanics is not applicable to the behavior of anelastic formations either weakly or strongly cemented sediments. The knowledge base of propagating viscous planar inclusions in anelastic formations is primarily from recent experience over the past twenty years and much is still not known regarding the process of viscous fluid propagation in these formations.
However, the present disclosure provides information to enable those skilled in the art of hydraulic fracturing, soil and rock mechanics to practice a method and system to initiate and control the propagation of a viscous fluid in weakly cemented sediments. The viscous fluid propagation process in these sediments involves the unloading of the formation 1 in the vicinity of the tip of the propagating viscous fluid, causing dilation of the formation, which generates pore pressure gradients towards this dilating zone. As the formation 1 dilates at the tips of the advancing viscous dilation fluid, the pore pressure decreases dramatically at the tips, resulting in increased pore pressure gradients surrounding the tips.
The pore pressure gradients at the tips of the inclusions result in the liquefaction, cavitation (degassing) or fluidization of the formation 1 immediately surrounding the propagating tips. That is, the formation 1 in the dilating zone about the tips acts like a fluid since its strength, fabric and in situ stresses have been destroyed by the fluidizing process, and this fluidized zone in the formation immediately ahead of the viscous fluid propagating tip is a planar path of least resistance for the viscous fluid to propagate further. In at least this manner, the system and associated method provide for directional and geometric control over the advancing propagating inclusions 10, 11 and 12.
The behavioral characteristics of the viscous fluid are preferably controlled to ensure the propagating viscous fluid does not overrun the fluidized zone and lead to a loss of control of the propagating process. Thus, the viscosity of the fluid and the volumetric rate of injection of the fluid should be controlled to ensure that the conditions described above persist while the inclusions are being propagated through the formation 1.
For example, the viscosity of the fluid to propagate the inclusions is preferably greater than approximately 100 centipoise at the respective shear rate of inclusion propagation. However, if a foamed propagated fluid is used in the system and method, a greater range of viscosity and injection rate may be permitted while still maintaining directional and geometric control over the inclusions.
The system and associated method are applicable to formations of weakly cemented sediments with low cohesive strength compared to the vertical overburden stress prevailing at the depth of interest. Low cohesive strength is defined herein as no greater than 400 pounds per square inch (psi) plus 0.4 times the mean effective stress (p′) at the depth of propagation.
c<400 psi+0.4 p′ (1)
where c is cohesive strength and p′ is mean effective stress in the formation 1.
Examples of such weakly cemented sediments are sand and sandstone formations, mudstones, shales, and siltstones, all of which have inherent low cohesive strength. Critical state soil mechanics assists in defining when a material is behaving as a cohesive material capable of brittle fracture or when it behaves predominantly as a ductile frictional material.
Weakly cemented sediments are also characterized as having a soft skeleton structure at low effective mean stress due to the lack of cohesive bonding between the grains. On the other hand, hard strong stiff rocks will not substantially decrease in volume under an increment of load due to an increase in mean stress.
In the art of poroelasticity, the Skempton B parameter is a measure of a sediment's characteristic stiffness compared to the fluid contained within the sediment's pores. The Skempton B parameter is a measure of the rise in pore pressure in the material for an incremental rise in mean stress under undrained conditions.
In stiff rocks, the rock skeleton takes on the increment of mean stress and thus the pore pressure does not rise, i.e., corresponding to a Skempton B parameter value of at or about 0. But in a soft soil, the soil skeleton deforms easily under the increment of mean stress and, thus, the increment of mean stress is supported by the pore fluid under undrained conditions (corresponding to a Skempton B parameter of at or about 1).
The following equations illustrate the relationships between these parameters:
Δu=B Δp (2)
B=(Ku−K)/(αKu) (3)
α=1−(K/Ks) (4)
where Δu is the increment of pore pressure, B the Skempton B parameter, Δp the increment of mean stress, Ku is the undrained formation bulk modulus, K the drained formation bulk modulus, α is the Biot-Willis poroelastic parameter, and Ks is the bulk modulus of the formation grains. In the system and associated method, the bulk modulus K of the formation 14 is preferably less than approximately 750,000 psi.
For use of the system and method in weakly cemented sediments, preferably the Skempton B parameter is as follows:
B>0.95 exp(−0.04 p′)+0.008 p′ (5)
The system and associated method are applicable to formations of weakly cemented sediments (such as tight gas sands, turbidite reservoirs, mudstones and shales) where large extensive propped vertical permeable drainage planes are desired to intersect thin sand lenses and provide drainage paths for greater gas production from the formations. In weakly cemented formations containing heavy oil (viscosity >100 centipoise) or bitumen (extremely high viscosity >100,000 centipoise), generally known as oil sands, propped vertical permeable drainage planes provide drainage paths for cold production from these formations, and access for steam, solvents, oils, and heat to increase the mobility of the petroleum hydrocarbons and thus aid in the extraction of the hydrocarbons from the formation. In highly permeable weak sand formations, permeable drainage planes of large lateral length result in lower drawdown of the pressure in the reservoir, which reduces the fluid gradients acting towards the wellbore, resulting in less drag on fines in the formation, resulting in reduced flow of formation fines into the wellbore.
Although the present invention contemplates the formation of permeable drainage paths which generally extend laterally away from a vertical or near vertical wellbore penetrating an earth formation 1 and generally in a vertical plane in opposite directions from the wellbore, those skilled in the art will recognize that the invention may be carried out in earth formations wherein the permeable drainage paths can extend in directions other than vertical, such as in inclined or horizontal directions. Furthermore, it is not necessary for the planar inclusions to be used for drainage, since in some circumstances it may be desirable to use the planar inclusions exclusively for injecting fluids into the formation 1, or for forming an impermeable barrier in the formation, etc.
Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to these specific embodiments, and such changes are within the scope of the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents.
The following U.S. patent documents are incorporated by reference in their entirety as background and to assist in the understanding of the foregoing disclosure of the invention.
This invention claims priority from U.S. Provisional Patent Application No. 63/252,400, filed Oct. 5, 2021, which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63252400 | Oct 2021 | US |
