Pore Pressure Estimation in Unconventional Formations Using Slowness Logs

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Solution Overview

Problem

Existing methods for predicting pore pressure in unconventional formations, such as shale plays, are inadequate due to low permeability and the influence of organic matter and fluid type, which complicates the use of compressional slowness measurements.

Innovation Solution

A method using compressional slowness logs and density logs to calculate pore pressure by eliminating the effects of rock composition and fluid type, allowing for direct pore pressure estimation through a relationship-based pressure scale.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If compressional slowness logs are used to predict pore pressure in unconventional formations, then pore pressure estimation is attempted, but the measurement precision deteriorates due to the influence of organic matter and fluid type

Engineering Contradiction:

Improvepore pressure measurement precisionVSAvoidinfluence of organic matter and fluid type

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent extracts and removes the effects of organic matter and fluid type from the compressional slowness measurements through mathematical transformations and corrections. By separating these interfering factors from the raw measurements, the method isolates the pore pressure signal, thereby improving measurement precision in unconventional formations where these factors traditionally degraded accuracy.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent transforms the compressional slowness measurements by applying parameter changes that account for the specific characteristics of unconventional formations. Through calibration with density logs and application of formation-specific correction factors, the method adapts the measurements to compensate for organic matter and fluid type influences, converting the raw data into accurate pore pressure estimates.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If existing formation testing tools are used to measure pore pressure, then direct measurement is attempted, but the measurement precision deteriorates due to low permeability of unconventional formations

Engineering Contradiction:

Improvepore pressure measurement precisionVSAvoidlow permeability measurement difficulty

Core Design Contradiction:

Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The patent replaces mechanical formation testing tools with a logging-based computational method. Instead of using physical tools that attempt to directly measure pressure in low-permeability formations (where fluid flow is restricted), the method uses compressional slowness and density logs combined with mathematical models to calculate pore pressure, thereby overcoming the measurement difficulties imposed by low permeability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces density logs and computational algorithms as intermediaries between the formation and the pore pressure determination. Rather than directly measuring pressure in the low-permeability formation, the method uses density logs as an intermediary measurement that can be obtained in such formations, then applies mathematical transformations to derive the pore pressure information.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If compressional slowness logs are used in unconventional formations, then pore pressure prediction is attempted, but the reliability deteriorates due to the complex relationship between slowness and pore pressure influenced by rock composition

Engineering Contradiction:

Improvepore pressure prediction reliabilityVSAvoidrelationship complexity between slowness and pore pressure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies local quality by tailoring the pore pressure prediction method to the specific characteristics of each formation interval. By using density logs to determine local rock properties and applying formation-specific calibration factors, the method adapts the general compressional slowness approach to account for local variations in rock composition, thereby improving reliability in heterogeneous unconventional formations.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent performs preliminary calibration and characterization of the formation using density logs before applying the compressional slowness measurements for pore pressure prediction. By establishing baseline formation properties and correcting for rock composition effects in advance, the method prepares the data to account for complexity, thereby improving the reliability of subsequent pore pressure predictions.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS12504554B2Pore pressure in unconventional formations

Publication Date: 2025.12.23 SAUDI ARABIAN OIL CO

AI summary

Disclosed are methods, systems, and computer-readable medium to perform operations including: receiving a density log and a compressional slowness log measured in a wellbore located in a formation; generating, based on at least one of the density log or the compressional slowness log, a reference compressional slowness log; determining, for an interval in the formation, a relationship between the compressional slowness log and the reference compressional slowness log; generating, based on the relationship and known pressure information in the interval, a pressure scale for the formation; and using the pressure scale to calculate pressure in the interval.