Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2002-11-14
2004-01-06
McElheny, Jr., Donald E. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
Reexamination Certificate
active
06675101
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The invention relates generally to the field of well log data acquisition and interpretation. More specifically, the invention relates to methods and systems for supplying well log data to a customer.
2. Background Art
Well logs are measurements, typically with respect to depth, of selected physical parameters of earth formations penetrated by a wellbore. Well logs are typically recorded by inserting various types of measurement instruments into a wellbore, moving the instruments along the wellbore, and recording the measurements made by the instruments. One type of well log recording includes lowering the instruments at the end of an armored electrical cable, and recording the measurements mad e with respect to the length of the cable extended into the well bore. Depth within the wellbore is inferred from the extended length of the cable. Recordings made in this way are substantially directly correlated to measurement depth within the wellbore. Other methods for measurement include a “logging while drilling” (LWD) method, a measurement while drilling (MWD), and a memory logging method. The LWD method involves attaching the instruments to the lower portion of a drilling tool assembly used to drill the wellbore. LWD and wireline tools are typically used to measure the same sort of formation properties, such as density, resistivity, gamma ray, neutron porosity, etc. MWD tools are typically used to measure parameters closely associated with drilling, such as well deviation, well azimuth, weight-on-bit, mud flowrate, annular borehole pressure, etc.
The aforementioned well logging tools may be conveyed into and out of a well via wireline cable, drilling pipe, coiled tubing, slickline, etc. Further, LWD and MWD measurement methods allow for measurement in the drill string while the bit is cutting, or measurement while tripping down or up past a section of a borehole that had been drilled at a previous time.
Some measurement tools use a pressure modulation telemetry system, which modulates pressure of a drilling fluid (mud) flowing through the interior of the drilling tool assembly, to obtain well log data. However, a much larger quantity of well log data is stored in a recording device disposed in the log instrument, which is interrogated when the instrument is retrieved from the wellbore. This information is typically recorded with respect to time. A record of instrument position in the wellbore with respect to time made at the earth's surface is then correlated to the time/measurement record retrieved from the instrument storage device to generate a conventional “well log ” of measurements with respect to wellbore depth.
Well logs are typically presented in a graphic form including a plurality of grids or “tracks” each of which is scaled from a selected lower value to a selected upper value for each measurement type presented in the particular track. A “depth track” or scale, which indicates depth in the wellbore, is typically positioned between two of the tracks. Depending on the needs of the particular user, any number of or type of measurements may be presented in one or more of the tracks. A typical well log presentation of an individual measurement is in the form of a substantially continuous curve or trace. Curves are interpolated from discrete measurement values stored with respect to time and/or depth in a computer or computer-readable storage medium. Other presentations include gray scale or color scale interpolations of selected measurement types to produce the equivalent of a visual image of the wellbore wall. Such “image” presentations have proven useful in certain types of geologic analysis.
Interpreting well log data includes correlation or other use of a very large amount of ancillary information. Such ancillary information includes the geographic location of the wellbore, geologic and well log information from adjacent wellbores, and a priori geological/petrophysical knowledge about the formations. Other information includes the types of instruments used, their mechanical configuration and records relating to their calibration and maintenance. Still other types of information include the actual trajectory of the wellbore, which may traverse a substantial geographic distance in the horizontal plane with respect to the surface location of the wellbore. Other information of use in interpreting well log data includes data about the progress of the drilling of the wellbore, the type of drilling fluid used in the wellbore, and environmental corrections applicable to the particular log instruments used.
Much of this ancillary information is applicable to any well log recorded with a particular type of well log instrument. For example, an instrument, which measures naturally occurring gamma radiation (“gamma ray”), has environmental corrections, which correspond only to the type of instrument. As one example, each wireline type gamma ray device of a selected external diameter from a particular wireline operator has the same environmental corrections for “mud weight” (drilling fluid density). Other types of ancillary information are made available from the wellbore operator (typically an oil and gas producing entity). Examples of this type of information include the geographic location of the wellbore and any information from other wellbores in the vicinity. Still other types of ancillary information include records of initial and periodic calibration and maintenance of the particular instruments used in a particular wellbore. The foregoing is only a small subset of the types of ancillary information, which may be used in interpreting a particular well log.
FIG. 1
shows a typical manner in which well log data are acquired by “wireline,” wherein an assembly or “string” of well log instruments (including sensors or “sondes” (
8
,
5
,
6
and
3
) as will be further explained) is lowered into a wellbore (
32
) drilled through the earth (
36
) at one end of an armored electrical cable (
33
). The cable (
33
) is extended into and withdrawn from the wellbore (
32
) by means of a winch (
11
) or similar conveyance known in the art. The cable (
33
) transmits electrical power to the instruments (
8
,
5
,
6
,
3
) in the string, and communicates signals corresponding to measurements made by the instruments (
8
,
5
,
6
,
3
) in the string to a recording unit (
7
) at the earth's surface. The recording unit (
7
) includes a device (not shown) to measure the extended length of the cable (
33
). Depth of the instruments (
8
,
5
,
6
,
3
) within the wellbore (
32
) is inferred from the extended cable length. The recording unit (
7
) includes equipment (not shown separately) of types well known in the art for making a record with respect to depth of the instruments,(sensors) (
8
,
5
,
6
,
3
) within the wellbore (
32
).
The sensors (
8
,
5
,
6
, and
3
) may be of any type well known in the art for purposes of the invention. These include gamma ray sensors, neutron porosity sensors, electromagnetic induction resistivity sensors, nuclear magnetic resonance sensors, and gamma-gamma (bulk) density sensors. Some sensors, such as (
8
,
5
, and
6
) are contained in a sonde “mandrel” (axially extended cylinder) which may operate effectively near the center of the wellbore (
32
) or displaced toward the side of the wellbore (
32
). Others sensors, such as a density sensor (
3
), include a sensor pad (
17
) disposed to one side of the sensor housing (
13
) and have one or more detecting devices (
14
) therein. In some cases, the sensor (
3
) includes a radiation source (
18
) to activate the formations (
36
) proximate the wellbore (
32
). Such sensors are typically responsive to a selected zone (
9
) to one side of the wellbore (
32
). The sensor (
30
) may, also include a caliper arm (
15
), which serves both to displace the sensor (
30
) laterally to the side of the wellbore (
32
) and to measure an apparent internal diameter of the wellbore.
The instrument configuration shown in
FIG. 1
is only meant to illustrate
Heliot Denis J.
Horkowitz John P.
Neville Thomas J.
Rothnemer Pascal F.
Shray Frank P.
Jeffery Brigitte L.
McElheny Jr. Donald E.
Ryberg John J.
Schlumberger Technology Corporation
Segúra Victor H.
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