Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2000-02-01
2001-08-07
McElheny, Jr., Donald E. (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C702S011000
Reexamination Certificate
active
06272434
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to drilling systems and more particularly to a system of drilling boreholes having a measurement-while-drilling (“MWD”) system wherein drilling and formation data and parameters determined from various downhole measuring devices are transformed downhole into selected parameters of interest or “answers” which are telemetered to the surface or stored downhole for subsequent retrieval or both. In an alternate embodiment, measurements are depth-correlated, utilizing depth measurements made downhole for improving accuracy of the measurements and the parameters of interest. The measurements and/or parameters are also correlated with stored reference data for providing additional information pertaining to the drilling operations and the formation characteristics. The system also is adapted to determine the drill bit location relative to the desired drilling path and to adjust the drilling activity downhole based on such determination.
2. Background of the Art
To obtain hydrocarbons such as oil and gas, boreholes are drilled by rotating a drill bit attached at a drill string end. A large proportion of the current drilling activity involves directional drilling, i.e., drilling deviated and horizontal boreholes to increase the hydrocarbon production and/or to withdraw additional hydrocarbons from the earth's formations. Modern directional drilling systems generally employ a drill pipe having a drill bit at the bottom that is rotated by a drill motor (commonly referred to as the “mud motor”). Pressurized drilling fluid (commonly known as the “mud” or “drilling mud”) is pumped into the drill pipe to rotate the drill motor and to provide lubrication to various members of the drill string including-the drill bit. As required the drill pipe is rotated by a prime mover, such as a motor, to facilitate directional drilling and to drill vertical boreholes.
A plurality of downhole devices are placed in close proximity to the drill bit to measure formation properties, downhole operating parameters associated with the drill string and to navigate the drill bit along a desired drill path. Downhole devices, frequently referred to as the measurement-while-drilling (“MWD”) devices, are typically coupled between the drill bit and the drill pipe along with the mud motor, kick-off device and stabilizers. For convenience, all such devices are collectively sometimes referred herein as the “downhole subassembly.” The MWD devices typically include sensors for measuring downhole temperature and pressure, an inclination measuring device for determining the inclination of a portion of the drill string, a resistivity measuring device to determine the presence of hydrocarbons against water, and devices for determining the formation porosity, density and formation fluid conditions.
Prior to drilling a borehole, substantial information about the subsurface formations is obtained from seismic surveys, offset wells, and prior drilled boreholes in the vicinity of the current borehole. The borehole is then usually drilled along a predetermined path based upon such prior information. During the borehole drilling, the downhole subassembly transmits information about the various downhole parameters, which are typically analyzed and correlated with other parameters at the surface to decide whether the drilling path needs to be adjusted. To adjust the drilling path, the drill string is usually retrieved from the borehole and then certain mechanical devices, such as kick-off subassemblies and stabilizers, are adjusted to alter the drilling direction. Stopping the drilling operation and retrieving the drill string to adjust the drilling direction results in great expense. Additionally, surface-measured downhole depth of the drill bit is typically utilized to take corrective actions. Surface-measured depth readings rely on the drill pipe length, which over several thousand feet may have an error of several feet (15 to 50 feet) from the true location, which is highly undesirable, especially for horizontal drilling through relatively narrow formations. Thus, it is desirable to have a drilling system which provides more accurate measure of the depth of the downhole subassembly and means for adjusting the drilling direction without retrieving the drill string from the borehole.
The downhole subassembly usually transmits information about the various downhole parameters to the surface by an uplink telemetry via the mud column in the drill string or electromagnetic means. The current telemetry systems such as the mud-pulse telemetry systems are capable of transmitting typically one bit per second, which greatly limits the ability to transmit a vast amount of useful information about the downhole formations and downhole conditions to the surface during the drilling operation.
To accurately determine the properties of the formations along the borehole, such as porosity, permeability, hydrocarbon saturation and other geophysical properties and the borehole profile, the drilling activity is intermittently stopped, the drill string is retrieved and wireline logs are obtained by traversing wireline tools through the borehole. The wireline tools contain a set of downhole devices such as resistivity devices, porosity and permeability measuring devices and acoustic devices. Such devices transmit a vast amount of data relating to the formations and the downhole conditions via a high transmission rate telemeter system to the surface, where the data is transformed into certain parameters of interest, which parameters are then utilized to aid in the drilling of the borehole and to determine the formation lithology, producibility of the pay zones, etc. The wireline systems provide a method for conveying the devices in the borehole and means for transmitting data at very high data rates.
Current wireline systems contain multiple sensors and complex processing algorithms to determine formation properties along the borehole. Examples include electromagnetic sensors comprising multiple transmitters and multiple receivers which measure attenuation and phase shift of the transmitted signals as they traverse the formation. Acoustic sensors which measure attenuation, phase shift and the full wave form of acoustic signals traversing the formation and borehole are also used. Nuclear sensors are used to measure the natural gamma ray energy spectrum of the formation which is indicative of shale content, shale type and other parameters of interest. Nuclear sensors comprising chemical neutron or isotopic gamma ray sources and neutron or gamma ray detectors are used to measure a plurality of geophysical parameters. Pulsed neutron sources and gamma ray accelerators are used in other types of nuclear sensors. All of the aforementioned sensors used in the wireline tools are data intensive. When such measurements are made simultaneously with a single pass of a multiple sensor wireline device along the borehole, massive amounts of raw data are generated per depth interval of borehole traversed.
With some wireline systems, raw sensor data are transmitted to the surface of the earth over the logging cable for subsequent processing to obtain the multiple parameters of interest. As examples, current wireline telemetry systems using seven conductor electrical logging cable can telemeter data to the surface at a rate of 500 kilobits to 1000 kilobits per second. Use of fiber optic cables substantially increases the data transmission rate. Such wireline telemetry systems have large telemetry bandwidths which enable the use of multiple sensors and transmission of the data to the surface for processing.
However, in boreholes in which the pressure of the well is above atmospheric pressure at the surface, the logging cable must pass through a pressure-containing device known in the art as a “lubricator.” The cross sectional area of current multiple conductor and fiber optic cables is such that the lubricator cannot contain surface well pressures of several thousand psi and still p
Beimgraben Herbert W.
Deady Ronald
Hubner Bernard G.
Leggett, III James V.
Meyer Wallace H.
Baker Hughes Incorporated
Madan Mossman & Sriram P.C.
McElheny Jr. Donald E.
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