Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2001-08-08
2003-12-09
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S131000, C507S244000, C507S261000, C507S925000, C166S305100, C166S309000
Reexamination Certificate
active
06660693
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present Invention relates to hydrocarbon production, particularly to methods of enhancing gas production from shaly formations having high water saturations, and more particularly to reducing water saturations in the formation immediately surrounding either a wellbore or a fracture face by treating the formation with surfactants having good oil-wetting characteristics in the presence of shale. Reduction of water saturation increases the flow of hydrocarbons in these formations. The methods may be used in drilling, completion, stimulation (acidizing or acid fracturing or hydraulic fracturing), remediation or workover, and in enhancing flow from natural fractures or from unstimulated formations.
BACKGROUND OF THE INVENTION
The present Invention relates generally to hydrocarbon (petroleum and natural gas) production from wells drilled in the earth. Hydrocarbons are obtained from a subterranean geologic formation (i.e., a “reservoir”) by drilling a wellbore that penetrates the hydrocarbon-bearing formation. In order for the hydrocarbons to be produced, that is, travel from the formation to the wellbore, and ultimately to the surface, at rates of flow sufficient to justify their recovery, a sufficiently unimpeded flowpath from the subterranean formation to the wellbore, and then to the surface, must exist or be provided. Obviously, it is desirable to maximize both the rate of flow and the overall amount of flow of hydrocarbon from the subsurface formation to the surface, where it can be recovered.
Hydrocarbon production is typically limited by two major reservoir factors: porosity and permeability. Even if the porosity is adequate, the effective permeability to the hydrocarbon may be limited. When more than one fluid is present in a permeable system, the flow of each is affected by the amount and distribution of the other(s); in particular the relative flows are affected by which fluid is the “wetting” phase, that is the fluid that coats the surfaces. Depending upon many factors, one fluid may flow while another does not. The result of stagnant fluid in the formation naturally diminishes the rate of hydrocarbon recovery. The reasons for this are both simple and complex. Most simply, the presence of fluid, in particular water or brine, in the formation acts as a barrier to the migration of hydrocarbon from the formation into the wellbore. More precisely, aqueous-based fluid injected during well treatments may saturate the pore spaces of the treated region, preventing the migration of hydrocarbon into and through the same pore spaces. In an analogous manner, if the well is to be produced without first stimulating, naturally occurring aqueous fluids in the formation in the flowpath or potential flowpath may hinder the production.
Indeed, diminished effective permeability caused by stagnant fluid often limits hydrocarbon production (both rate and capacity) from a given well. To achieve an increase in well productivity therefore involves removing stagnant fluid from the formation. No completely satisfactory method exists to remove these fluids, and therefore prevent them from reducing production.
In the natural state, formations may be oil-wet, water-wet or of mixed wettability, depending upon the nature of the fluids and the formation. (In this and following discussions, “oil-wet” is meant to include surfaces that are “wet” by adsorbed, condensed or compressed gas as well.) When the internal surface of an oil or gas producing formation or fracture face pore is oil-wet, the oil phase will occupy the pore surface as well as the smallest, least permeable flow paths. As such, the oil or gas will have to flow through a restricted pathway to be produced, and the water, which is non-wetting, will be able to flow through the high permeability, least restricted, flow path. Therefore, in order to maximize oil or gas flow capacity, it is generally preferred that the pore surface be water wet.
One exception to that recommendation has been the specific case of the recovery of methane from coal seams. In such types of formations, most gas in coal is adsorbed onto the very high internal surface area of the oil-wet organic constituents of the coal, and consequently, coals are described as being normally oil-wet, unlike in conventional gas reservoirs that are composed of inorganic minerals that are normally water-wet. In U.S. Pat. No. 5,229,017, Nimerick et al. teach that treating coal formations with dewatering agents to create persistent oil-wet coal surfaces enhances gas production by reducing the tendency of formation fines migration and increasing the drainage of water from the formation. More specifically, Nimerick et al. disclose the use of some organic surfactants selected from butylene oxide derivatives or polyethylene carbonates for hydraulic fracturing.
However, Nimerick et al. do not address other conventional reservoir operations such as drilling, completion, remediation, acidizing, acid fracturing, or enhancing flow in natural fractures, nor do they address treatment of conventional gas reservoirs that are normally water-wet or have become water-wet, or in which the producible hydrocarbons are in a porous mineral matrix such as shale formations like the Devonian Shale and the Barnett Shale. For those conventional formations, the common prejudice remains that water-wet surfaces are preferable.
It has been observed that when the formation is a shale that has a high water content, production of hydrocarbons, particularly if they are in the formation substantially as adsorbed, condensed gas, may be delayed and slow. The problem typically occurs in gas wells such as those in shale formations that contain high concentrations of adsorbed gas, primarily natural gas (that we will refer to as “methane” in the following discussions), as opposed to those that contain primarily compressed but not adsorbed gas. For those wells, it is imperative to remove the water as quickly and completely as possible to maximize production rate and total methane recovery. In this way the operator can apply maximum pressure drawdown in the formation rather than in the wellbore. Water in the formation impedes gas desorption and flow.
For those shaly formations containing adsorbed hydrocarbon gas, the inventors have found that it would be acceptable for the formation to be oil-wet during gas productions because this allows the water to be removed more quickly and more completely and open more of the pore to gas flow. It is also advantageous to minimize fines migration, since fines block flow paths throughout the production system, from the formation to downhole equipment to surface equipment. In general, these same factors and arguments, with appropriate modification to suit the specific situations, pertain to stimulation (acidizing or acid fracturing or hydraulic fracturing), remediation or workover, and in enhancing flow from natural fractures or from unstimulated formations.
SUMMARY OF THE INVENTION
There are many oil and gas well operations in which the formations are oil-wet or become oil-wet and the presence of significant amounts of water in pores or fractures is detrimental. The common denominator of the methods encompassed in this Invention is that they all deal with enhancing the recovery of hydrocarbons from subterranean formations that contain adsorbed and compressed hydrocarbon gases, especially methane, in shale rich matrixes and that the enhancement is accomplished by causing the formation to be or to remain oil-wet, thus promoting dewatering of the shale and maximizing flow paths for the hydrocarbons. By “causing the formation to be or to remain oil-wet”, we mean that if the formation is water-wet it becomes oil-wet and continues to be oil-wet while a sufficiently large volume of water or brine flows through and is removed from the formation to produce the results desired from the treatment method, and if the formation is oil-wet it continues to be oil-wet while a sufficiently large volume of water or brine flows through and is removed from the formation to produce th
Boney Curtis L.
England Kevin W.
Hinkel Jerald J.
Miller Matthew J.
Jeffery Brigitte
Menes Catherine
Mitchell Thomas O.
Schlumberger Technology Corporation
Tucker Philip
LandOfFree
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