Modulated Neutron Source Drilling Fluid Activation Correction

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Solution Overview

Problem

Natural gamma ray logging measurements in the oil and gas industry are biased by drilling fluid activation induced by fast neutrons, leading to inaccurate determination of subterranean formation radioactivity.

Innovation Solution

A method involving a logging while drilling tool with a modulated electrical neutron source and a natural gamma ray sensor, where the neutron output is modulated to distinguish and correct for gamma rays induced by drilling fluid activation, allowing for accurate measurement of natural gamma rays emitted by the formation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a neutron source is used in logging while drilling operations, then formation evaluation capabilities are enhanced, but drilling fluid activation induces gamma rays that bias natural gamma ray measurements

Engineering Contradiction:

Improveformation evaluation accuracyVSAvoiddrilling fluid activation gamma rays

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The neutron source is modulated to operate in periodic pulses rather than continuously. During the 'off' periods, activated drilling fluid gamma rays decay to negligible levels, allowing the natural gamma ray sensor to measure formation radioactivity without interference. This periodic operation enables discrimination between formation gamma rays and fluid activation gamma rays based on their temporal patterns.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system measures gamma ray counts during both 'on' and 'off' periods of neutron source operation, then uses feedback algorithms to calculate and subtract the drilling fluid activation component from the total gamma ray signal. This feedback correction process isolates the formation's natural gamma ray signal, improving measurement reliability.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If continuous neutron emission is used, then drilling fluid activation is maximized for correction purposes, but natural gamma ray measurement accuracy deteriorates due to persistent activation interference

Engineering Contradiction:

Improvenatural gamma ray measurement accuracyVSAvoidactivated drilling fluid interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The neutron source operates in periodic pulses with controlled duty cycles. During the 'off' periods, activated drilling fluid gamma rays decay to negligible levels, allowing the natural gamma ray sensor to measure formation radioactivity without interference. This periodic operation enables discrimination between formation gamma rays and fluid activation gamma rays based on their temporal patterns.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system performs preliminary measurements during the 'off' periods when drilling fluid activation is minimal, establishing a baseline for formation gamma ray levels. These preliminary measurements are then used to correct the total gamma ray signal, improving the precision of natural gamma ray determination.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach significantly reduces the influence of drilling fluid activation, providing precise and accurate total natural gamma ray measurements, thereby improving formation evaluation and lithology identification.

Implementation Method 1

drilling fluids (mud) in the borehole may be activated by the generated neutrons. Such activated mud is known to emit gamma rays

Methodology Applied

Scientific EffectNeutron activation: Nuclear Fission

Implementation Method 2

The LWD tool (or tool string) includes an electrical neutron source and a natural gamma ray sensor. The neutron output of the electrical neutron source is modulated

Methodology Applied

Scientific EffectNeutron generator modulation:

Implementation Method 3

Both total gamma ray and spectral gamma ray sensors are commonly employed. Total gamma ray sensors measure the total number of detected gamma rays

Methodology Applied

Scientific EffectGamma ray detection: Photoelectric Effect

Data Source

PatentUS11675103B2Drilling fluid activation correction via neutron generator modulation

Publication Date: 2023.06.13 SCHLUMBERGER TECH CORP

AI summary

A method for making natural gamma ray measurements includes deploying a logging while drilling tool including an electrical neutron output of the electrical neutron source is modulated and the natural gamma ray sensor is used to make a corresponding gamma ray measurement during at least a portion of the modulation. The gamma ray measurement is processed to obtain a corrected total natural gamma ray measurement of the subterranean formation.