Formation Pressure Testing With Drawdown-Buildup Flow Validation
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Solution Overview
Problem
Formation testing tools face challenges in low-mobility reservoirs due to long equilibration times, which increase rig time and risk of tool sticking, and are affected by pressure changes during drawdown and buildup periods due to fluid mobility and compressibility issues.
Innovation Solution
A method involving a series of pressure pre-tests with real-time data processing using statistical analysis and denoising techniques to ensure that the pressure drop during drawdown equals the total pressure increment in the buildup period, ensuring accurate measurement of formation pore pressure and mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If formation testing tools wait for pressure equilibration in low-mobility reservoirs, then measurement precision is improved, but loss of time and risk of tool sticking increase
Solution Approach 1:
The patent applies preliminary action by performing a pretest before the main pressure measurement. The pretest involves withdrawing a pretest piston to create a controlled drawdown period, establishing an initial pressure state in the flowline. This preliminary action prepares the system by removing formation fluid and creating a known initial condition, allowing the subsequent main test to start from a controlled state rather than requiring lengthy equilibration from scratch.
Solution Approach 2:
The patent utilizes parameter changes by systematically varying the pretest piston withdrawal speed (qpiston) and flowline volume increase (ΔV) to control the drawdown characteristics. By adjusting these parameters, the system can achieve different pressure drop rates and equilibration characteristics, allowing optimization of the measurement process to reduce total test time while maintaining accuracy.
2Productivity
If pretest piston is withdrawn at high speed to reduce test time, then productivity is improved, but measurement precision deteriorates due to pressure changes during drawdown
Solution Approach 1:
The patent implements feedback by continuously monitoring pressure changes during the pretest and using this information to determine when the flowline pressure has sufficiently equilibrated before initiating the main measurement. The system feedbacks on the pressure equilibrium state and adjusts the timing of the main test accordingly, ensuring measurement accuracy is not compromised by rapid piston withdrawal.
Solution Approach 2:
The patent segments the pressure test into distinct phases: a pretest phase with controlled piston withdrawal to establish initial conditions, and a main test phase for actual measurement. This segmentation allows the pretest to be optimized for speed while the main test focuses on precision, with the transition point determined by pressure equilibrium criteria.
3Measurement precision
If multiple pressure measurements are taken at several depths, then measurement precision is improved, but loss of time increases due to repeated equilibration requirements
Solution Approach 1:
The patent applies preliminary action by performing a pretest at each depth before the main measurement. This pretest establishes an initial pressure state and removes formation fluid from the flowline, creating a controlled starting condition. By doing this preliminary action at each depth, the system can reduce the equilibration time required for subsequent measurements at different depths.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the pretest piston withdrawal speed and flowline volume parameters for each depth measurement. This allows optimization of the pretest duration and intensity at each depth, enabling faster measurements while maintaining the necessary pressure equilibrium for accurate results.
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 enhances the accuracy of formation pore pressure and mobility measurements by minimizing the influence of well operations and fluid mobility, reducing the need for prolonged equilibration times and tool sticking risks.
Implementation Method 1
activating the pump, wherein a formation fluid is drawn in through the at least one probe into the at least one probe channel and the at least one fluid passageway by the pump and increasing pressure with the at least one fluid passageway
Implementation Method 2
measuring the pressure in the at least one fluid passageway by a pressure sensor
Implementation Method 3
The increase in the flowline volume causes a decrease in the flowline pressure, Pfl
Implementation Method 4
fluid mobility may be a challenge for the fluid from formation to the probe and inside the flowline of the formation testing tool
Implementation Method 5
there may be some pressure changes during the drawdown period and buildup period due to changes in the compressibility of the formation fluid from the formation to the probe to the flowline of the formation testing tool
Data Source
AI summary
Disclosed herein are systems and methods to obtain representative formation pore pressure and formation mobility from pressure measurements with a formation testing tool. One of the methods for performing a pressure test includes measuring the pressure in the fluid passageway by a pressure sensor, performing a pre-test with the pressure sensor, measuring the drawdown pressure, measuring the buildup pressure, performing another pre-test when the drawdown pressure is superior to the buildup pressure, and validating a formation flow when the drawdown pressure is equal to the buildup pressure, wherein a measured pressure obtained at an asymptote of a pressure curve after the buildup pressure corresponds to the formation pore pressure.