Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
1999-07-23
2001-05-15
Tsay, Frank (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C166S065100, C166S254200
Reexamination Certificate
active
06230800
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the management of hydrocarbon production. More particularly, the invention relates to methods and apparatus for the long term monitoring of reservoir fluids by locating instruments in wells.
2. State of the Art
In an oil field, numerous holes are drilled into the formation before and after oil production begins. Some holes are discovery, appraisal, and delineation wells to determine the location and boundaries of a petroleum reservoir. Other holes will become injection and production wells. Many of the hole sections which are not used for production (e.g., all except the injection and production wells) are usually sealed with cement. The injection and production wells are, in most parts of the world, each completed by installing a casing in the hole and surrounding the casing with cement. The casing is usually made from metal pipe sections having a diameter close to that of the well hole. The sections are lowered into the well hole and cement is poured into the annulus between the casing and the formation. The casings are then perforated at predetermined depths where it is believed that an oil reservoir is located.
Water may be naturally present in the reservoir acting on the oil to urge it out through the well bore. Often, water (or steam) is injected into the reservoir from an injection bore located near the production bore. As oil is extracted from the well, the water moves through the porous media of the formation closer to the production well. As a result, the oil-water interface changes shape. If the location of the oil-water interface is not monitored during production, it is possible that the well will produce a mixture of oil and water. In some cases, it is possible for the well to produce more water than oil. Similarly, it may be desirable to monitor the oil-gas interface should one exist.
Well logs are a primary source of information used to map the distribution of fluids in hydrocarbon reservoirs. The logs are made from various sensor measurements such as resistivity, pressure, temperature, sonic velocity, etc. It is a common practice in a producing well to interrupt production and re-enter the well with wireline logging tools in order to ascertain changes in the reservoir which occur as a result of production. This practice is undesirable because it interrupts production and it is expensive. In addition, logging tools used inside a production casing can only measure satisfactorily water saturation and can not measure satisfactorily changes in formation pressure, a measure which is very useful in determining the efficiency with which fluids are being extracted from the formation. Furthermore, in a completed sub-sea well, re-entry into the well with logging tools may be either impossible or prohibitively expensive.
U.S. Pat. No. 4,475,591 discloses a method for obtaining pressure measurements in a producing well by permanently mounting pressure sensors in the cement filling between the formation and the casing. Placement of these sensors is often difficult. When the sensors are located in the cement surrounding the casing, there is a danger that the sensors or the cables to the sensors will be damaged during installation. Damage can also occur during casing perforation or side tracking.
U.S. Pat. No. 5,214,384 discloses a method for electronic self-potential logging in a cased observation well which is located between a steam injector well and a production well. A metallic casing complicates the method and the placement of electrodes in a casing or between a casing and the formation is also difficult as mentioned above. Furthermore, this method requires the drilling of an additional well which will not produce any hydrocarbons.
Co-owned U.S. Pat. No. 5,467,823 discloses a method for long term monitoring of a reservoir by locating a pressure gauge in an observation well which traverses the reservoir. The upper portion of the observation well is cased and the remainder is left open. A measuring device is suspended from a cable and lowered into the observation well to the depth of the reservoir. The measuring device includes a pressure gauge mounted in a casing-like tube section and an explosive perforation device. Cement is injected into the observation well to a depth corresponding to the reservoir. After the cement cures, the explosive device is ignited to perforate the cement and put the reservoir in fluid communication with the pressure gauge. While this method has advantages over the previously described methods, the cable is still in danger of damage as the well is being injected with cement, and the sensor package can be damaged during the perforation explosion.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide methods and apparatus for long term monitoring of a hydrocarbon reservoir.
It is also an object of the invention to provide methods and apparatus for measuring formation characteristics of a producing reservoir without interrupting production.
It is another object of the invention to provide methods and apparatus for measuring changes in formation characteristics without interrupting production.
It is still another object of the invention to provide methods and apparatus for directly measuring changes in formation pressure.
It is also an object of the invention to provide methods and apparatus for measuring changes in water saturation in a formation without interrupting production.
It is another object of the invention to provide methods and apparatus for measuring changes in formation characteristics without drilling a special observation well.
It is still another object of the invention to provide methods and apparatus for permanently installing sensors in a well.
It is also an object of the invention to provide methods and apparatus for permanently installing sensors in a well with minimal risk of damage to the sensors or to cables coupled to the sensors.
In accord with these objects which will be discussed in detail below, the methods and apparatus of the present invention include installing sensors in one or more of the many holes which are sealed with cement. According to the invention, a sensor array is attached to the cement delivery device which is used to seal a hole section which would otherwise be abandoned. The preferred apparatus for cement delivery is a “coiled tubing”. Preferably, the sensor array is passed through the center of the tubing so that it is protected from damage or snagging while being delivered to its deployment position. However, the sensor array may be strapped to the outside of the tubing. The coiled tubing may be withdrawn or left in place after the cement is delivered into the hole. When the cement cures, the sensor array is preferably fixedly centered in the cement plug which seals the reservoir. The sensors in the array may include electrical sensors, pressure gauges, geophones, or other sensors.
According to the invention, the sensor array may be placed in any well which is to be abandoned. Such wells include exploration wells, appraisal wells, delineation wells, collapsed wells, oil wells which develop high levels of gas or water production, and gas wells which develop high levels of water production. In addition, the sensor array may be deployed in an unused portion of a production or injection well. For example, the sensor array may be located in a logging pocket (an extension of a well beyond its required depth which permits logging tools to log the entire depth of the formation). Similarly, the sensor array may be located in the pilot hole from which a horizontal well is drilled.
The invention has many advantages. In cases where the sensor array is deployed in an uncased well, resistivity measurements are not affected by the large steel mass of a casing. In all cases, utilizing the methods of the invention permits the use of a light weight cable since the weight of the array is supported by the cement delivery device. No separate logging run and no additional equipment is needed since the cement delivery
Batzer William B.
Gordon David P.
Schlumberger Technology Corporation
Tsay Frank
LandOfFree
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