Patent Application
20120003111
The subject disclosure generally relates to the field of sensors and more particularly to mechanisms used to move sensors along the length of a housing of an oilfield tool.
Oil exploration involves evaluating reservoirs to determine the movement or absence of oil, gas, or water as the reservoir fluids are produced. Understanding movement of gas in reservoirs is important to the prevention of premature breakthroughs and optimization of reservoir performance. It is known to use gravity borehole tools to measure characteristics of geologic formation, particularly in the exploitation of hydrocarbon reservoirs found in geologic formations or in the subsurface storage of carbon dioxide or water.
The process of measuring physical properties of earth formations beneath the surface of the earth is commonly referred to as “well logging”. It comprises the step of lowering sensors or testing equipment mounted on robust tool bodies into a wellbore drilled through the earth. When the tool is suspended from an armored cable the process is more specifically referred to as “wireline” well logging. Alternative conveyance techniques as known in the art include lowering the instruments mounted on drill pipe, casing or production tubing or on coiled tubing. The drill pipe conveyance technique, in particular, is known as “logging while drilling” when measurements are performed during the actual drilling of a wellbore.
Borehole gravity measurements are a direct measure of the bulk density of the formation surrounding a wellbore. Typically gravity data are taken at different vertical depths or stations along the wellbore. The basic principle of borehole gravity measurements is that the change in gravity relates directly to the bulk density contrast of the formation, the distance from the stations and the density contrast body. The bulk density in turn is directly related to grain densities and the pore fluid (gas, oil or water) densities and porosity of the formation. Several gravity measurement tools are commercially available. U.S. Pat. No. 5,970,787 to Wignall describes a tool for conducting gravimetric survey downhole in an earth formation.
One limitation to using gravity sensors is that the accuracy of the gravity measurement may be insufficient for making gravity density measurements in boreholes. Gravity sensors are extremely sensitive to vibrations and these vibrations may throw the gravity sensors out of calibration. Further, even if the sensor remains calibrated after being subjected to vibrations the sensor will take time to settle which is undesirable as it reduces the logging speed and increases the chance of having the tool stuck in the wellbore. Minimizing both noise and vibrations in the gravity measurements may increase this accuracy.
In view of the above there is a need for an improved mechanism which permits movement of sensors along the length of a tool housing with a minimum of noise and vibrations. The subject technology accomplishes these and other objectives. The subject disclosure provides a drive system without traditional mechanical contacts e.g. metal to metal via gears, therefore, minimizing noise and vibrations in the gravity measurements.
In accordance with an embodiment of the subject disclosure, an apparatus comprising an elongated, hollow vessel is disclosed. The apparatus further comprises a fluid filled housing disposed inside the vessel with the housing defining a hydraulically isolated chamber. A pump member is disposed inside the hydraulically isolated chamber and an element is attached to the pump. The pump member provides a differential pressure which moves the pump member and element inside the length of the housing.
In accordance with a further embodiment of the subject disclosure, an apparatus comprising an elongated, hollow vessel with a fluid filled housing disposed inside the vessel is disclosed. The apparatus further comprises a housing defining a hydraulically isolated chamber and a pump member disposed inside the hydraulically isolated chamber and attached to the housing. Flexible tubing connecting the pump member to a port assembly having an element attached to the port assembly is also disclosed. Finally, the pump member provides a differential pressure thus moving the port assembly and element inside the length of the housing.
In accordance with a further embodiment of the subject disclosure, a method for moving an element inside a housing is disclosed. This method comprises disposing a fluid filled housing inside an elongated, hollow vessel and defining a hydraulically isolated chamber within the fluid filled housing. The method further comprises disposing a pump member inside the hydraulically isolated chamber and attaching an element to the pump. A differential pressure is provided by the pump member thus moving the pump member and element inside the length of the housing.
Further features and advantages of the subject disclosure will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.
The present technology is directed to a mechanism for moving objects along the axis of a confining cylinder. More particularly, the present technology is directed to a mechanical system for moving sensors in a longitudinal direction in a housing of an oilfield tool. The direction of motion of the mechanism is in the longitudinal direction of the oilfield tool.
Embodiments of the present technology comprise a pump. In one non-limiting example the pump is a bidirectional pump with a first outlet for pumping fluid to operate the system in a first direction and a second outlet for pumping fluid to operate the system in a second direction. These bidirectional pumps are commercially available. In non-limiting examples, these bidirectional pumps may be positive displacement pumps for example, a progressing cavity pump. As will be apparent to one skilled in the art, any commercial available bidirectional pump may be used. Typically, electrical, hydraulic or pneumatic means are used in energizing these pumps. The pump moves an object along the axis of a housing. In one non-limiting example the housing is a confining cylinder and may be the housing of an oilfield tool e.g. wireline or drilling tool. One skilled in the art will recognize that the subject disclosure has numerous non-oilfield applications for example, pneumatic tube systems used at drive-in banks for transporting cash and documents between the customer and the teller. The housing may be a drill collar or any other type of tubular structure that may be used to package an oilfield tool for example, a wireline tool, LWD tool or a tool moving inside a cased well for example, an intelligent “plug” comprising additional measurement tools capable of moving down the well by itself, instead of being pumped down the wellbore e.g. cement plug. The element to be moved is attached to one side of the pump. The element is physically attached to the pump utilizing methods which are known to those skilled in the art which include in non-limiting examples welded, screwed or pinned. In one non-limiting example the element is a sensor, for example, a gravity sensor. The housing is filled with a fluid which may be pumped by the pump in either direction. The fluid may comprise any gas or liquid. In non-limiting examples the fluid may be one of oil or water or both oil and water. The pump moves fluid from the bottom to the top or visa versa within the housing. When the pump moves fluid from the bottom to the top the pressure on the bottom decreases and the pressure on the top increases, resulting in a net downwards force on the pump-element assembly. The assembly will move downwards until the pressure equilibrates on the top and bottom. The pump direction can be reversed therefore moving the pump-object assembly in the opposite direction.
In one non-limiting example the apparatus comprises a sensor attached to a pump. The apparatus is located in a tool housing. The first and second outlets of the pump are located above and below a seal and in one non-limiting example the seal is a dynamic seal which seals between the pump-sensor assembly and the housing. In non-limiting examples these dynamic seals comprise elastomeric materials or polymers for example Teflon. In other examples these dynamic seals may comprise a plurality of different materials. The housing is filled with a fluid and the fluid can be pumped through the pump in either direction. The pump is attached electrically to the housing via a flexible cable. The cable in one non-limiting example may be a helical electrical line. The cable is flexible to accommodate the length change when the apparatus moves from a first position to a second position. The cable also provides electrical continuity of the pump/sensor assembly with the housing which ensures power is provided into the pump/sensor assembly and a signal can be transmitted between the pump/sensor assembly and the housing. The flexible cable provides a connection to a control unit for the apparatus which controls the pump/sensor assembly within the housing. Referring now to the drawings, in which like numerals represent like elements through the several figures, aspects of the subject disclosure will be described.
Environmental changes and fluid leakage from the housing 211 may cause the first chamber 309 and second chamber 307 to have varying pressure while the pump/sensor assembly 213 is stationary. This in turn may result in a shift in the sensor position 203. The pump 215 may be utilized to correct the shift but in certain instances it may be advantageous to maintain an idle operation which will reduce mechanical or electromagnetic noise on the sensor 213. The pump/sensor assembly 213 may further comprise one or a plurality of devices which will rigidly lock the pump/sensor assembly 213 to the housing 211. The sensor position 201 will therefore not shift as a result of vibration or mechanical shock therefore providing increased accuracy. Some non-limiting examples of these devices are hydraulic energy storage devices, valves or a physical locking mechanism.
The working fluid 415 is compensated to wellbore or atmospheric fluid 407. As the fluid moves in the direction of 511, the pressure P1 in chamber 307 increases and the pressure P2 in chamber 309 decreases. This results in a net downward force on the pump/sensor assembly 213. This pump/sensor assembly 213 moves in the direction 515 which is depicted as downwards in
Frictional losses may occur between the dynamic seals and the housing or in fluid viscous losses. Reducing frictional loss requires an increase in the pressure differential. Frictional losses may be used advantageously to dampen vibrations of the pump/sensor assembly as the pump/sensor assembly may continue movement even after the pressure has equilibrated and possibly “overshot” the targeted position.
In order to obtain a position of the sensor inside the housing relative to the top or bottom of the housing a number of devices can be used. One such device is an optical encoder wheel which is held in contact with the housing. The encoder wheel provides a means for monitoring the position of the sensor inside the housing. The encoder wheel turns when the pump/sensor assembly 213 moves and this turning of the wheel is interpreted as a change in position of the pump/sensor assembly 213. A further method for monitoring the position of the sensor inside the housing comprises determining the amount of fluid displaced by the pump which in turn would determine how much the pump/sensor assembly had moved. Other methods that may be utilized to monitor the position of the sensor inside the housing include optical or acoustic methods e.g. ultrasonic which may be mounted on the housing or the pump/sensor assembly.
Embodiments of the present disclosure may be used wherever the position of an object e.g. sensor is desired to be changed along the axis of a housing, for example, the housing of a tool. A number of sensors which may utilize the present disclosure include the following: A gravity tool which measures gravity at one location and then the sensor is moved a known distance along the borehole axis and gravity is measured again. The change in gravity over the known change in position can be used to measure density. In the case of either an electromagnetic or sonic tool a variable depth of investigation can be achieved by moving the transmitter or receiver along the axis of the borehole using the subject technology. Finally, in situations where measurements are needed without stopping the movement of a toolstring the subject technology may be useful. The pump/sensor assembly 213 may move in the direction opposite the toolstring at the same speed as the toolstring. In situations where tool sticking may occur and the operator of the tool wants to avoid stopping which is common for both wireline logging and drilling measurements the subject technology may be advantageous.
While the subject disclosure is described through the above exemplary embodiments, it will be understood by those of ordinary skill in the art that modification to and variation of the illustrated embodiments may be made without departing from the inventive concepts herein disclosed. Moreover, while the preferred embodiments are described in connection with various illustrative structures, one skilled in the art will recognize that the system may be embodied using a variety of specific structures. Accordingly, the subject disclosure should not be viewed as limited except by the scope and spirit of the appended claims.
