Pressure Decay Index for Supercharging Correction

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Solution Overview

Problem

Interpreting formation pressure measurements in underground reservoirs is challenging due to the supercharging effect caused by mud filtrate invasion during drilling, which complicates the calculation of initial pressure and permeability.

Innovation Solution

A method that determines the permeability and thickness of the mud cake, hydrostatic pressure, and measures formation pressure to calculate a pressure decay index, which is used to analyze the measured pressure and derive reservoir pressure, while also estimating horizontal and vertical permeability and productivity index.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If wireline or LWD formation testers are used to make probe-based pressure measurements during drilling, then the restrictions of conventional well tests are overcome and measurements can be made in dynamic environments, but the supercharging effect from mud filtrate invasion complicates the interpretation of pressure data

Engineering Contradiction:

Improveability to make pressure measurements during drillingVSAvoiddifficulty of interpreting pressure data due to supercharging effect

Core Design Contradiction:

Adaptability or versatilityVSDifficulty of detecting and measuring

Solution Approach 1:

The method performs preliminary determination of mud cake permeability and thickness before analyzing the pressure transient data. By establishing these parameters in advance, the interpretation process can account for the supercharging effect caused by mud filtrate invasion, thereby resolving the contradiction between making measurements during drilling and interpreting the affected pressure data

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The method introduces an intermediary analysis step that uses the determined mud cake properties to calculate a supercharging correction factor. This intermediary calculation acts as a mediator between the raw pressure measurements and the final reservoir parameter interpretation, eliminating the harmful effect of supercharging on data interpretation

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If pressure transient testing is performed for a relatively long duration using DST or conventional well testing, then excellent test objectives are met for determining reservoir parameters, but environmental and cost considerations prevent use of these techniques at all times

Engineering Contradiction:

Improveprecision of reservoir parameter determinationVSAvoidtime required for long duration testing

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The method uses partial action by determining only the essential parameters (mud cake permeability and thickness) that are needed to correct for supercharging, rather than performing a complete conventional well test. This allows sufficient measurement precision for reservoir evaluation while significantly reducing the testing duration and associated costs

Inventive Principle:

Principle #16Partial or excessive action

3Loss of time

If formation pressure measurements are taken soon after drilling when supercharging is present, then early reservoir pressure data can be obtained, but any interpretation technique must account for the supercharged pressure effect

Engineering Contradiction:

Improvetime to obtain pressure measurementsVSAvoiddifficulty of interpreting supercharged pressure data

Core Design Contradiction:

Loss of timeVSDifficulty of detecting and measuring

Solution Approach 1:

The method performs preliminary determination of mud cake properties before pressure interpretation, enabling early time measurements to be corrected for supercharging. This preliminary preparation allows accurate reservoir pressure determination even when measurements are taken immediately after drilling when supercharging effects are most pronounced

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 method effectively accounts for the supercharging effect, providing accurate reservoir pressure and permeability measurements by using the pressure decay index, improving the interpretation of pressure transient data and well productivity analysis.

Implementation Method 1

When a producing zone is penetrated, the wellbore sandface (the region of the wellbore wall in the producing zone) is exposed to mud pressure and filtrate immediately invades the near wellbore region. A mud cake is formed when drilling fluid flows into the formation and solids are deposited at the surface of the wellbore.

Methodology Applied

Scientific EffectFiltration: Filter (physical)

Implementation Method 2

During these processes a pressure gradient is established in the formation.

Methodology Applied

Scientific EffectPressure gradient: Pressure Gradient

Implementation Method 3

A mud cake is formed when drilling fluid flows into the formation and solids are deposited at the surface of the wellbore.

Methodology Applied

Scientific EffectDeposition: Deposition (physical)

Data Source

PatentUS8132453B2Method for analysis of pressure response in underground formations

Publication Date: 2012.03.13 SCHLUMBERGER TECH CORP

AI summary

A reservoir pressure in an underground formation surrounding a well is analyzed based on a direct measurement of the pressure at the wall of the well using the permeability of mud cake on the wall of the well in the region in which the pressure measurement is made; determining the thickness of mud cake on the well of the well; determining the hydrostatic pressure in the well in the region in which the pressure measurement is made; calculating a pressure decay index from the mud cake permeability and thickness, the hydrostatic pressure and the measured pressure; and using the pressure decay index to analyze the measured pressure to derive the reservoir pressure.