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Atom-Interferometer-based absolute Gravimeter for oil field surface and downhole gravity mapping and recording

IP.com Disclosure Number: IPCOM000246778D
Publication Date: 2016-Jun-29
Document File: 4 page(s) / 152K

Publishing Venue

The IP.com Prior Art Database

Abstract

We propose to use atom-interferometer-based absolute Gravimeters for the measurement of variations of local absolute gravity values when producing oil and gas from reservoirs and/or when injecting gas or liquid into reservoirs from which hydrocarbons are produced. Measurements will take place on ground and downhole. The variations in absolute local gravity are in the range of some to some tens and hundreds of micro-Gal (1 Gal = 1 cm/s²) above ground and downhole, respectively. The time scale of interest is in the order of weeks, months, or years. This requires at least a gravimeter with highest stability of the full measurement duration, hence a gravimeter with constant (and known) bias, or a gravimeter with inherent absolute accuracy. Both are commonly referred to as absolute gravimeters. Above-ground reservoir monitoring based on this technique in a grid (time-resolved gravity mapping) requires a grid of sensors, or a single sensor that is easily moved from one measurement site to another with zero or constant instrument bias. This motivates the use of an absolute gravimeter with accuracy down to the micro-Gal regime which is independent of environmental conditions (ambient temperature, air pressure, humidity). Downhole measurements are realized closer to the varying mass. Therefore, they require slightly less resolution and accuracy. The measurements can be taken along the extension of a well. On the one hand, this delivers measurement data complimentary to surface measurements (depth gravity profile vs. surface gravity map). On the other hand, well position and the orientation of the gravimeter, and with this the measurement axis, are defined by the well geometry. This motivates a three-axis downhole gravity measurement enabling the full vector measurement of the gravity acceleration vector.

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Title:  Atom-Interferometer-based absolute Gravimeter for oil field surface and downhole gravity mapping and recording

Abstract:  We propose to use atom-interferometer-based absolute Gravimeters for the measurement of variations of local absolute gravity values when producing oil and gas from reservoirs and/or when injecting gas or liquid into reservoirs from which hydrocarbons are produced. Measurements will take place on ground and downhole. The variations in absolute local gravity are in the range of some to some tens and hundreds of micro-Gal (1 Gal = 1 cm/s²) above ground and downhole, respectively. The time scale of interest is in the order of weeks, months, or years. This requires at least a gravimeter with highest stability of the full measurement duration, hence a gravimeter with constant (and known) bias, or a gravimeter with inherent absolute accuracy. Both are commonly referred to as absolute gravimeters.

Above-ground reservoir monitoring based on this technique in a grid (time-resolved gravity mapping) requires a grid of sensors, or a single sensor that is easily moved from one measurement site to another with zero or constant instrument bias. This motivates the use of an absolute gravimeter with accuracy down to the micro-Gal regime which is independent of environmental conditions (ambient temperature, air pressure, humidity).

Downhole measurements are realized closer to the varying mass. Therefore, they require slightly less resolution and accuracy. The measurements can be taken along the extension of a well. On the one hand, this delivers measurement data complimentary to surface measurements (depth gravity profile vs. surface gravity map). On the other hand, well position and the orientation of the gravimeter, and with this the measurement axis, are defined by the well geometry. This motivates a three-axis downhole gravity measurement enabling the full vector measurement of the gravity acceleration vector.

Description:  Atom interferometry provides a method of absolute gravity measurement by precisely measuring the acceleration experienced by neutral atoms that freely fall in an ultra-high vacuum chamber. The measurement, realized in cycles of below 1 second duration, requires cold atomic samples (some millions to billions of atoms, mu-K-temperatures) that are provided using magneto-optical traps and optical molasses (laser-cooling). The acceleration measurement is based on the interference of each of the freely-falling atoms in the released atomic cloud, which are coherently manipulated using pulsed laser light fields with well-controlled frequency and phase. This manipulation realizes a quantum-mechanic entanglement of electronic and motional atomic states which allows for determining the atomic acceleration relative to the laser light fields by detecting the population of electronic atomic states in a fluorescence measurement of the full atomic sample (see Figure 1).

The system has two potential applications:

1.    Surfac...