Subterranean Pressure Profile via Resistivity-Density Conversion
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Solution Overview
Problem
Existing methods for determining hydrostatic pressure in subterranean formations fail to accurately account for variations in pore fluid density along the wellbore, leading to inaccuracies in pressure measurements and misinterpretation of over- or under-pressure conditions.
Innovation Solution
The method involves drilling a wellbore, measuring resistivity values, identifying porous zones, converting resistivity data to pore fluid density, and calculating pressure based on the sum of pore fluid densities along the wellbore length to generate a depth-based pressure profile, using available data such as salinity information and pressure gradients to create a hydrostatic pressure profile tailored to the specific well location.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If hydrostatic pressure is calculated by weight of water column from measured point to reference datum, then calculation is simple, but measurement precision deteriorates due to ignoring fluid density variation
Solution Approach 1:
The wellbore is divided into multiple depth intervals, with each interval having its own fluid density value. Pressure is calculated by summing the weight of fluid segments rather than using a single average density, thereby accounting for density variations while maintaining computational feasibility
Solution Approach 2:
Different fluid density values are assigned to different depth intervals based on local conditions (salinity, temperature, hydrocarbon presence). This allows the calculation to reflect local variations in fluid properties rather than assuming uniform density throughout the wellbore
2Measurement precision
If detailed pore fluid density variation is accounted for along wellbore, then pressure determination accuracy improves, but device complexity increases due to multiple measurements and conversions
Solution Approach 1:
Resistivity measurements serve multiple functions: they directly indicate fluid type (hydrocarbon vs. water) and, through conversion using salinity information, provide pore fluid density values. This multi-functionality reduces the need for separate measurement tools
Solution Approach 2:
Resistivity data acts as an intermediary that links easily obtainable electrical measurements to the desired fluid density information. By converting resistivity values to density through established relationships and salinity data, the system obtains accurate density profiles without direct density measurements
3Measurement precision
If resistivity data is converted to pore fluid density using salinity information, then pressure profile accuracy improves, but loss of information increases due to multiple conversion steps
Solution Approach 1:
The system uses available salinity information and pressure gradient data to constrain and validate the resistivity-to-density conversion. This feedback mechanism ensures that converted density values remain physically realistic and consistent with independent measurements, minimizing information loss
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 allows for accurate characterization of pore zones, enhancing the commercial and technical analysis of pore fluid pressure information by providing precise quantification of over- or under-pressure relative to a baseline, thus improving the determination of hydrocarbon volume and commerciality.
Implementation Method 1
lowering a logging tool into the wellbore to measure resistivity values as a function of depth along the wellbore
Implementation Method 2
converting the measured resistivity values to an amount of total dissolved solids for each of the plurality of identified porous zones; converting the amount of total dissolved solids to a pore fluid density
Implementation Method 3
calculating a pressure based on a sum of the pore fluid densities derived along a length of the well
Data Source
AI summary
A method for determining a pressure profile in a subterranean formation is described. The method includes drilling a wellbore in the subterranean formation; lowering a logging tool into the wellbore to measure resistivity values as a function of depth along the wellbore; identifying a plurality of porous zones from the wellbore based on petrophysical logs; converting the measured resistivity values to an amount of total dissolved solids for each of the plurality of identified porous zones; converting the amount of total dissolved solids to a pore fluid density; calculating a pressure based on a sum of the pore fluid densities derived along a length of the well; and generating a depth-based pressure profile.