Measuring and testing – Borehole or drilling – Downhole test
Reexamination Certificate
2000-11-01
2003-06-24
Kwok, Helen (Department: 2856)
Measuring and testing
Borehole or drilling
Downhole test
C702S009000, C175S050000
Reexamination Certificate
active
06581455
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the testing of underground formations or reservoirs. More particularly, this invention relates to a method and apparatus for isolating a downhole reservoir, and testing the reservoir formation and fluid.
2. Background
While drilling a well for commercial development of hydrocarbon reserves, several subterranean reservoirs and formations are encountered. In order to discover information about the formations, such as whether the reservoirs contain hydrocarbons, logging devices have been incorporated into drill strings to evaluate several characteristics of these reservoirs. Measurement-while-drilling systems (hereinafter MWD) have been developed that contain resistivity, nuclear and other logging devices which can constantly monitor formation and reservoir characteristics during drilling of wellbores. The MWD systems can generate data that includes information about the presence of hydrocarbon presence, saturation levels, and formation porosity. Telemetry systems have been developed for use with the MWD systems to transmit the data to the surface. A common telemetry method is the mud-pulsed system, an example of which is found in U.S. Pat. No. 4,733,233. MWD systems provide real time analysis of the subterranean reservoirs.
Commercial development of -hydrocarbon fields requires significant amounts of capital. Before field development begins, operators desire to have as much data as possible in order to evaluate the reservoir for commercial viability. Despite the advances in data acquisition during drilling, using the MWD systems, it is often necessary to conduct further testing of the hydrocarbon reservoirs in order to obtain additional data. Therefore, after the well has been drilled, the hydrocarbon zones are often tested by other test equipment.
One type of post-drilling test involves producing fluid from the reservoir, collecting samples, shutting-in the well and allowing the pressure to build-up to a static level. This sequence may be repeated several times for different reservoirs within a given borehole. This type of test is known as a “Pressure Build-up Test”. One of the important aspects of the data collected during such a test is the pressure build-up information gathered after drawing the pressure down. From this data, information can be derived as to permeability, and size of the reservoir. Further, actual samples of the reservoir fluid are obtained, and tested to gather Pressure-Volume-Temperature data relevant to the reservoir's hydrocarbon distribution.
In order to perform these important tests, it is currently necessary to retrieve the drill string from the well borehole. Thereafter, a different tool, designed for the testing, is run into the well borehole. A wireline is often used to lower a test tool into the well borehole. The test tool sometimes utilizes packers for isolating the reservoir. Numerous communication devices have been designed which provide for manipulation of the test tool, or alternatively, provide for data transmission from the test tool. Some of those designs include signaling from the surface of the Earth with pressure pulses, through the fluid in the well borehole, to or from a downhole microprocessor located within, or associated with the test tool. Alternatively, a wire line can be lowered from the surface, into a landing receptacle located within a test tool, establishing electrical signal communication between the surface and the test assembly. Regardless of the type of test tool and type of communication system used, the amount of time and money required for retrieving the drill string and running a second test tool into the borehole is significant. Further, if the borehole is highly deviated, a wire line tool is difficult to use to perform the testing.
There is also another type of problem, related to downhole pressure conditions, which can occur during drilling. The density of the drilling fluid is calculated to achieve maximum drilling efficiency while maintaining safety, and the density is dependent upon the desired relationship between the weight of the drilling mud column and the downhole pressures which will be encountered. As different formations are penetrated during drilling, the downhole pressures can change significantly. Currently available devices do not accurately sense the formation pressure as the drill bit penetrates the formation. The actual formation pressure could be lower than expected, allowing the lowering of mud density, or the formation pressure could be higher than expected, possibly even resulting in a pressure kick Consequently, since this information is not easily available to the operator, the drilling mud may be maintained at too high or too. low a density for maximum efficiency and maximum safety.
Therefore, there is a need for a method and apparatus that will allow for the pressure testing and fluid sampling of potential hydrocarbon reservoirs as soon as the borehole has been drilled into the reservoir, without removal of the drill string. Further, there is a need for a method and apparatus that will allow for adjusting drilling fluid density in response to changes in downhole pressures to achieve maximum drilling efficiency. Finally, there is a need for a method and apparatus that will allow for blow out prevention downhole, to promote drilling safety.
SUMMARY OF THE INVENTION
A formation testing method and a test apparatus are disclosed. The test apparatus is mounted on a work string for use in a well borehole filled with fluid. It can be a work string designed for drilling, re-entry work, or workover applications. As required for many of these applications, the work string may be one capable of going into highly deviated holes, horizontally, or even uphill. Therefore, in order to be fully useful to accomplish the purposes of the present invention, the work string must be one that is capable of being forced into the hole, rather than being dropped like a wireline. The work string can contain a Measurement While Drilling (MWD) system and a drill bit, or other operative elements. The formation test apparatus may include at least one expandable packer or other extendable structure that can expand or extend to contact the wall of the well borehole; device for moving fluid such as a pump, for taking in formation -fluid; a non-rotating sleeve; an extendable stabilizer blade; a coring device, and at least one sensor for measuring a characteristic of the fluid or the formation. The test apparatus will also contain a controller, for controlling the various valves or pumps which are used to control fluid flow. The sensors and other instrumentation and control equipment must be carried by the tool. The tool must have a communication system capable of communicating with the surface, and data can be telemetered to the surface or stored in a downhole memory for later retrieval.
The method involves drilling or re-entering a borehole and selecting an appropriate underground reservoir. The pressure, or some other characteristic of the fluid in the well borehole at the reservoir, the rock, or both, can then be measured. The extendable element, such as a packer or test probe, is set against the wall of the borehole to isolate a portion of the borehole or at least a portion of the borehole wall. In the non-rotatable sleeve embodiment, the drill string can continue rotating and advancing while the sleeve is held stationary during performance of the test.
If two packers are used, this will create an upper annulus, a lower annulus, and an intermediate annulus within the well borehole. The intermediate annulus corresponds to the isolated portion of the borehole, and it is positioned at the reservoir to be tested. Next, the pressure, or other property, within the intermediate annulus is measured. The well borehole fluid, primarily-drilling-mud, may then be withdrawn from the intermediate annulus with the pump. The level at which pressure within the intermediate annulus stabilizes may then be measured; it will correspond to the formation pre
Berger Per-Erik
Krueger Volker
Lee Jae-dong
Meister Matthias
Michaels John M.
Baker Hughes Incorporated
Madan Mossman & Sriram P.C.
Politzer Jay L
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