PROCESS FOR CONTROLLING WATER AND GAS CONING
BACKGROUND OF THE INVENTION
This invention relates to the production of hydrocarbons from a hydrocarbon-bearing formation. More particularly, this invention relates to controlling the ratio of fluids which are produced via a well from a subsurface formation which has a hydrocarbon-bearing portion and another fluid-bearing portion.
In the production of hydrocarbons from a hydrocarbon-bearing formation there is normally provided a well which extends from the surface of the earth into the formation. The hydrocarbon-bearing portion of the formation may be a petroleum-bearing portion that is overlain by a gas-bearing portion and may be underlain by a water-bearing portion of the formation. Also, the hydrocarbon-bearing portion of the formation may be a gas-bearing portion that is underlain by a waterbearing portion of the formation. The well may be completed by employing conventional completion practices such as running and cementing casing in the well and forming perforations through the casing and cement sheaths around the casing, thereby forming an open production interval which communicates with the formation. In the case of a petroleum-bearing formation it is normally desirable to form the open production interval such that it communicates with the petroleumbearing portion of the formation but does not extend into and communicate with the gas-bearing portion or the water-bearing portion. However, the open production interval which is formed in the well may inadvertently communicate with either or both the gas-bearing portion which overlies the petroleum-bearing portion and the water-bearing portion which underlies the petroleum-bearing portion of the formation. Even if there is no actual initial fluid communication between the open production interval and the oil- or gas-bearing portions of the formation, such communication may develop during production of petroleum from the petroleum-bearing portion of the formation. For example, in the case of a gas-bearing portion overlying the petroleum-bearing portion of the formation, gas may be drawn down from the gas-bearing portion into the petroleum-bearing portion during production of petroleum from the well. This drawing down of the gas into the petroleum-bearing formation surrounding the well is commonly referred to as gas coning. Likewise, water may be drawn upward from the water-bearing portion into the oil-bearing portion about the well. This phenomenon is known as water coning. In the case of gas coning, free gas is produced by the well, resulting in a high gas-oil ratio. This is undesirable because the reservoir energy is wasted which consequently results in a rapid decline of pressure. In the case of water coning, free water is produced in the well which results in a much higher water-to-oil ratio in the production stream than would be the case without the water coning. The higher water-to-oil ratio is undesirable and results in increased operating costs.
Various techniques have been employed to counteract the effects of gas and water coning. One such technique involves completing the production well by providing an open production interval which communicates with the petroleum-bearing portion of the formation but which does not communicate with either the gas-bearing portion of water-bearing portion which
may overlie or underlie the petroleum-bearing portion of the formation. The well may then be produced at a sufficiently low rate that coning of either the gas or water into the petroleum-bearing formation and about
5 the well is avoided. However, such production rates may be lower than are otherwise desirable.
Other methods which may be employed to reduce the effects of gas and water coning include the placing of barriers within the subsurface formations penetrated by
10 wells. One such method of preventing the flow of water or gas into oil wells involves creating a substantially horizontal barrier which extends radially outward from the well into the oil zone of the oil-bearing formation. The barrier is located between the perforations through
15 which oil flows into the well and the zone of the fluid which is to be blocked. The flow of water upwardly or of gas downwardly to the perforations through which the oil is produced is restricted by the barrier. Portland cement is commonly used as a barrier-forming mate
20 rial. For various reasons, however, substantial water may flow through or around these barriers to the perforations through which the oil is produced into the well. U.S. Pat. No. 3,237,690 to Jacy C. Karp, et al., is directed to the creation in an oil zone of a thin, substan
25 tially horizontal, highly impermeable barrier of Portland cement which is bound by strata of the formation which have had their permeability permanently destroyed by a plugging material. A method of forming a plastic pancake barrier be
30 tween an oil and water zone is described in The Oil and Gas Journal, July 11, 1960, Vol. 58, No. 28, p. 71. In accordance with this technique, a low viscosity plastic is squeezed into well perforations at the water-oil contact to form an impermeable pancake or cylinder of plastic at the water-oil contact. The low viscosity plastic was forced at less than fracturing pressure into the pores of the formation.
Still another method of decreasing the ratio of gas and/or water produced along with oil in a well is de
40 scribed in U.S. Pat. No. 3,368,624 to George J. Heuer, Jr., et al. Heuer, et al., form a foam plug in situ in the path of the gas or water. This foam plug is formed by injecting a foaming agent into a subterranean formation surrounding a wellbore and placing the well on
45 production. Heuer, et al., state that it is preferred that the foaming agent be injected such that it primarily enters the formation near the interface of the water- and oil-producing zones or the interface of the gas- and oilproducing zones, or both; and, still more preferably, that the foaming agent is injected directly into the water zone or the gas zone.
SUMMARY OF THE INVENTION
55 This invention is directed to a method of controlling the ratio of fluids produced via a well from a subsurface formation having a hydrocarbon-bearing portion and another fluid-bearing portion. A barrier which is shaped as a hollow frustum is formed about the well
6q with the small portion of the frustum being closed about the well in close proximity to the interface between the hydrocarbon-bearing portion and the other fluid-bearing portion. Hydrocarbons are produced via the well from the hydrocarbon-bearing portion of the
Another embodiment is directed to a method of controlling the water-hydrocarbon ratio of fluids produced via a cased well from a subsurface formation having a