Formation Fluid Refractive Index Estimation for Brine Purity

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Solution Overview

Problem

Current methods for obtaining clean formation fluid samples from oil and gas wells are contaminated by drilling fluids, making it difficult to determine the purity or contamination levels of brine using refractive index measurements, especially when water-based mud invasion occurs, as these measurements are less sensitive to sand particles and other elements.

Innovation Solution

A method and apparatus that estimate the refractive index of connate brine using well log measurements, measure the refractive index of the fluid during withdrawal, and fit a curve to data values to determine the characteristic of the brine, allowing for real-time estimation of contamination or purity levels and predicting when clean samples can be obtained.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If refractive index measurements are used to determine brine purity, then measurement speed is improved, but measurement precision deteriorates when water-based mud invasion occurs

Engineering Contradiction:

Improvemeasurement speedVSAvoidbrine purity measurement precision

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent introduces resistivity measurements as an intermediary parameter to bridge the gap between refractive index measurements and brine purity determination. By combining refractive index data with resistivity data, the system can accurately distinguish between drilling fluid filtrate and formation brine even when water-based mud invasion occurs, thereby maintaining measurement precision while preserving the speed advantage of refractive index measurements

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent creates a composite measurement approach by combining two different measurement techniques (refractive index and resistivity) into a unified evaluation system. This composite method leverages the strengths of both techniques: refractive index provides rapid measurement capability while resistivity provides sensitivity to water-based contamination, together achieving both speed and precision

Inventive Principle:

Principle #40Composite materials

2Measurement precision

If pumping continues for a long time to obtain clean samples, then sample purity is improved, but time consumption increases

Engineering Contradiction:

Improvesample purityVSAvoidtime consumption

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent implements a real-time feedback system that continuously monitors both refractive index and resistivity measurements during the pumping process. This feedback allows the system to dynamically assess the purity of withdrawn fluid and determine the optimal stopping point for pumping, eliminating the need for prolonged pumping times while ensuring sufficient sample cleanliness

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent performs preliminary assessment of formation fluid characteristics using refractive index and resistivity measurements before initiating the pumping process. This preliminary action enables prediction of the pumping duration required to achieve clean samples, allowing for optimized pumping time determination in advance rather than through extended trial pumping

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If refractive index measurements are used alone, then device complexity is reduced, but reliability of contamination detection deteriorates

Engineering Contradiction:

Improvemeasurement device complexityVSAvoidcontamination detection reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent merges two measurement systems (refractive index measurement and resistivity measurement) into an integrated detection system. By combining these measurements, the system achieves reliable contamination detection that leverages the complementary strengths of both techniques, with refractive index providing rapid response and resistivity providing sensitivity to ionic content and water-based contamination

Inventive Principle:

Principle #5Merging (Combining)

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

Enables accurate and timely determination of brine purity or contamination levels, allowing for informed decision-making on when to collect samples, even in situations where deep invasion or continuous contamination makes sample cleanup unfeasible within a reasonable time.

Implementation Method 1

measuring a refractive index of the formation fluid to determine a contamination level of the formation fluid

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS7445934B2System and method for estimating filtrate contamination in formation fluid samples using refractive index

Publication Date: 2008.11.04 BAKER HUGHES CO

AI summary

A method and apparatus is described for estimating terminal purity or terminal contamination for a fluid during the withdrawal of the fluid from a subsurface formation. The apparatus and method provide for measuring refractive index of the fluid over a time period, fitting a curve through the refractive index measurements or data values derived therefrom and estimating a terminal refractive index or terminal value for the data values from the fitted to curve to estimate the terminal contamination or purity for the fluid.