Formation Tester Pretest Data Analysis
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Solution Overview
Problem
Formation testers require long equilibration times in low-mobility reservoirs, leading to increased rig time and risk of tool sticking, necessitating real-time assessment of pressure measurement quality to optimize operations and potentially terminate tests early.
Innovation Solution
A method for real-time processing of pressure data to determine the quality of pretest measurements by comparing pressure signals with simulated false buildup and sandface pressure estimation, allowing for immediate decisions on test continuation or termination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the formation tester waits for pressure equilibration in low-mobility reservoirs, then measurement quality is improved, but rig time and risk of tool sticking increase
Solution Approach 1:
The patent applies preliminary action by performing real-time quality assessment of pressure data during the pretest buildup phase. The system continuously monitors pressure derivatives and compares them against expected behavior patterns to predict whether full equilibration will yield useful data, allowing operators to make informed decisions before the test completes, thereby avoiding unnecessary waiting time while maintaining measurement quality standards
Solution Approach 2:
The patent implements feedback by continuously analyzing pressure data in real-time and providing quality assessments that feed back into the decision-making process. The system calculates pressure derivatives, compares them with theoretical models, and adjusts the test continuation decision based on this feedback loop, enabling dynamic optimization of measurement quality versus time consumption
2Measurement precision
If the formation tester waits for pressure equilibration, then data quality is improved, but risk of differential tool sticking increases
Solution Approach 1:
The system performs preliminary assessment of data quality potential during the buildup phase by analyzing pressure derivative behavior. By predicting whether the formation will provide measurable pressure changes before full equilibration occurs, the system enables early termination when data quality would be insufficient, thereby preventing tool sticking without compromising the ability to obtain quality data when conditions are favorable
3Productivity
If real-time assessment of pressure data quality is implemented, then rig time is reduced, but complexity of data processing increases
Solution Approach 1:
The patent replaces complex mechanical waiting and manual data evaluation with automated computational analysis. The system uses digital signal processing to calculate pressure derivatives, compare them against theoretical models, and generate quality assessments automatically, substituting the mechanical process of waiting with intelligent algorithms that provide rapid feedback with minimal operational complexity
4Speed
If the pretest piston withdraws at prescribed speed to increase flowline volume, then drawdown is achieved, but pressure signal quality may be compromised in low-mobility formations
Solution Approach 1:
The patent applies dynamics by making the assessment process adaptive to different formation conditions. The real-time analysis system adjusts its evaluation criteria based on the observed pressure response characteristics, allowing the system to accommodate variations in piston withdrawal speed and formation mobility while maintaining measurement quality through dynamic interpretation rather than fixed thresholds
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 efficient use of time by quickly assessing measurement quality and reducing waiting times, potentially saving hours in field operations while maintaining data integrity.
Implementation Method 1
The pretest itself starts when a command is given to withdraw a pretest piston at a prescribed speed, qpiston, to increase the flowline volume by a prescribed amount, ΔV. This is the drawdown period. The increase in the flowline volume causes a decrease in the flowline pressure, Pfl.
Implementation Method 2
Once the pretest piston stops, Pfl increases until it equilibrates to the formation pore-pressure. This is known as the buildup period.
Data Source
AI summary
Methods are disclosed for processing, in real-time, pressure data acquired with a formation tester during a pretest to quickly establish the quality of the measurement being conducted. The methods can optimize pressure measurement operations by assessing whether it is desirable or not to wait for the formation tester flowline pressure to equilibrate to the sandface pressure. In one embodiment, a determination is made as to whether the pretest succeeded in establishing hydraulic communication between the formation and the flowline by comparing the pressure signal with a simulation of the pressure behavior corresponding to a false buildup during a dry test. In another embodiment, a determination is made as to whether the pretest succeeded in isolating the tool flowline and the formation from the wellbore by using the pressure signal to estimate the sandface pressure during buildup over time, and to compare the estimated sandface pressure signal with the borehole pressure.