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Method of extracting formation density and pe using a pulsed accelerator based litho-density tool

a density tool and accelerator technology, applied in the field of pulsed gammagamma density tools, can solve the problems of many high-energy photons that carry density information lost, difficult to dispose and misuse, and the conventional - density tools have a significant drawback, and achieve the effect of precise determination of bulk formation density

Active Publication Date: 2011-12-15
SCHLUMBERGER TECH CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The invention is a method and tool for accurately measuring the density of a formation using a pulsed gamma-gamma density tool that compensates for interactions caused by the photoelectric effect and density variations caused by standoff. The tool includes a source of energetic particles, two detectors, and filters to match standoff influence. The method involves measuring the energy of photons recorded by the detectors and compensating for both effects simultaneously using filters and adjustments to the distance between the detectors. The invention also includes identifying total energy pulses likely to contain the energy of a single photon for useful information about the formation composition.

Problems solved by technology

Conventional γ-γ density tools have a significant drawback.
They require a chemical radioactive source, that is difficult to dispose and hazardous if misused.
Using filters to completely remove photons below a certain threshold comes with a penalty, namely, many high energy photons that carry density information are also lost.
Consequently, using filters to reduce the Pe effect does not meet the precision requirements of modern logging.
In practice, a significant amount of high energy flux is also absorbed by the low density scintillator rendering the technique less sensitive than desired.

Method used

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  • Method of extracting formation density and pe using a pulsed accelerator based litho-density tool
  • Method of extracting formation density and pe using a pulsed accelerator based litho-density tool
  • Method of extracting formation density and pe using a pulsed accelerator based litho-density tool

Examples

Experimental program
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example 1

[0092]Example 1 illustrates how equation (17) is utilized to prepare a compensated tool. A tool as illustrated in FIG. 7 was evaluated with a number of SS / LS spacing, collimation angles and filter thicknesses. Five values were calculated, ρe—coe; Pe—coe; Slope; No Standoff Accuracy; and 0.5 inch Standoff Accuracy and are listed sequentially in each box of Table 4. As shown in Table 4, the optimal configuration is with a 0.39 cm stainless steel LS filter and a 0.5 cm iron SS filter with the SS collimator at an angle of 70° relative to a longitudinal axis of the tool.

TABLE 4Long Space →IncreasingFilterThickness→→Short Space ↓Cs20Cs33Cs22Cs32Cs2590° Collimator0.96 ± 0.081.00 ± 0.051.00 ± 0.051.02 ± 0.041.03 ± 0.04Increasing Filter0.009 ± 0.0030.002 ± 0.0030.001 ± 0.002−0.002 ± 0.002 −0.003 ± 0.002 Thickness ↓0.78 ± 0.060.64 ± 0.060.63 ± 0.060.55 ± 0.070.54 ± 0.07−0.04~0.04 −0.03~0.02 −0.03~0.02 −0.03~0.01 −0.04~0.01 cs31−0.04~0.06 −0.07~0.05 −0.09~0.09 −0.09~0.06 −0.06~0.06 90° Collima...

example 2

[0098]Example 2 illustrates the inversion technique for obtaining compositional data. FIG. 15 compares two NaI detector spectra using a betatron source. The source to detector spacing was 14 inches in slab geometry. The formation was epoxy gravel. No Pe filter was used, and the electron beam end point energy was ˜1.7 MeV. The only difference between the two spectra was their cathode heater current, which affects only the intensity of the source, hence the ratio Na / Np.

[0099]A distinct feature of the higher count rate spectrum is the hump due to the P2 distribution. Table 5 lists known and derived spectral information based on preceding discussions.

TABLE 5Heater current0.481 A0.59 ANp3600024000Na483619670Np / Na0.1340.819Nt519341098Nt / Na1.0742.089Ē(keV)162.8319.3Ē1(keV)151.6152.8a192.93%33.66%a26.84%34.96%a30.23%22.04%a407.76%a501.44%a600.13%

[0100]The two curves in FIG. 15 were obtained by assuming the following single photon probability function:

P1(E)=b0×e−b1(E−b5)×[1−e−b2(E−b5)−b3(E−b...

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Abstract

A method for a pulsed gamma-gamma density tool to simultaneously compensate for interactions due to the photoelectric effect and density variations caused by standoff enables a more precise determination of bulk formation density. This method includes the steps of providing a source of energetic particles and directing those energetic particles at a formation having a known photoelectric factor and electron density and capturing one or more photons either emitted or deflected from the formation either a first detector or a second detector. The first detector is spaced a first distance from the source, the second detector is spaced a second distance from the detector and a third distance separates the first detector from the second detector. Measuring a first total energy of the photons striking the first detector during a time interval and measuring a second total energy of the photons striking the second detector as a function of the time interval and disposing a first filter between the first detector and the formation effective to cause Pe response to match standoff influence thereby compensating for both effects simultaneously. In addition to the first filter, the required compensation may include a second filter between the second detector and the formation as well as adjustments to the respective first distance, second distance and third distance.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention generally relates to a method for a pulsed gamma-gamma density tool to simultaneously compensate for interactions due to the photoelectric effect and density variations caused by standoff, thereby enabling a more precise determination of bulk formation density. Also disclosed a compensated tool utilizing a betatron as a Bremsstrahlung source.[0003]2. Background of the Invention[0004]In the oil well industry, reservoir characterization is used to predict the location of oil-bearing and gas-bearing formations, estimate the producibility of these formations, and assess the quantity of hydrocarbon in the reservoir.[0005]A basic parameter for reservoir characterization is bulk formation density. There are many methods to determine bulk formation density. One widely accepted method is gamma-gamma (γ-γ) density. Gamma rays are packets of electromagnetic radiation, also referred to as photons. A γ-γ density sonde...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): G01V5/12G06F19/00
CPCG01V5/125
Inventor ZHOU, TONGCHEN, FELIXCASE, CHARLES R.ELLIS, DARWIN V.ROSCOE, BRADLEY ALBERT
Owner SCHLUMBERGER TECH CORP
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