Downhole Fluid Segregation for Representative Hydrocarbon Sampling
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Solution Overview
Problem
Challenges exist in obtaining representative formation fluid samples, particularly in low-permeability formations drilled with water-based mud, due to severe skin damage and fluid segregation issues.
Innovation Solution
A method involving a fluid tester with a straddle packer and dual pumps is used to isolate a wellbore section, allowing fluid mixture separation into phases based on gravity and immiscibility, followed by differential pumping to collect high-quality hydrocarbon samples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional single-phase pumping is used to obtain formation fluid samples, then the sampling process is simple, but the hydrocarbon content in samples is low (5%) due to fluid segregation issues and skin damage
Solution Approach 1:
The patent divides the sampling system into multiple functional segments: a fluid tester with inlet and outlet, a first pump for sampling hydrocarbon phase, a second pump for removing water-based phase, and a sample chamber. This segmentation allows separate handling of different fluid phases, enabling high-quality hydrocarbon sampling (90% hydrocarbon content) by isolating the sampling function from the fluid removal function.
Solution Approach 2:
The patent introduces a dead volume space as an intermediary between the formation and the pumps. This dead volume allows fluid mixture to separate into phases before entering the pumping system, acting as a buffer that enables phase separation without requiring complex separation equipment directly at the formation interface.
2Productivity
If high pump rate is used to obtain samples quickly, then productivity increases, but hydrocarbon phase separation is insufficient
Solution Approach 1:
The patent performs preliminary phase separation in the dead volume before the pumping stage. The fluid mixture is allowed to reside in the dead volume where gravity and density differences cause hydrocarbon and water-based phases to separate. This preliminary action ensures that when high-rate pumping begins, the phases are already separated, allowing the first pump to selectively sample hydrocarbon phase at high productivity without compromising separation quality.
Solution Approach 2:
The patent employs dynamic pump rate control with two pumps operating at different rates. The first pump operates at a lower rate to selectively sample the hydrocarbon phase, while the second pump operates at a higher rate to remove the water-based phase. This dynamic differentiation of pump rates maintains both separation quality and overall productivity.
3Measurement precision
If dual-phase pumping system is implemented to separate hydrocarbon and water phases, then sample quality improves (90% hydrocarbon content), but device complexity and operational difficulty increase
Solution Approach 1:
The patent combines multiple functions into integrated components: the fluid tester incorporates both the dead volume for separation and the inlet/outlet for pumping; the first and second pumps are coordinated to work simultaneously on the same fluid stream. This merging reduces operational complexity compared to separate separation and sampling systems, as the phase separation and selective pumping occur in an integrated flow path.
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 hydrocarbon content determination, increasing the hydrocarbon fraction in samples from 5% to 90% by providing residence time and segregation, facilitating better wellbore evaluation and production planning.
Implementation Method 1
the fluid mixture at least partially separates within the dead space into at least two phases, including a hydrocarbon-based phase and a water-based phase
Implementation Method 2
the fluid mixture enters the space and at least partially separates within the space into at least two phases. The at least two phases include a hydrocarbon-based phase and a water-based phase
Data Source
AI summary
The disclosure provides for a method for sampling fluid from a subterranean formation that is intersected by a wellbore. The method includes performing an initial draw-down at a target interval in the wellbore to pump fluid from the subterranean formation with a 3D radial probe. The method includes isolating the target interval of the wellbore with a packer and providing a residence time within a dead volume of the packer to allow fluid therein to separate into hydrocarbon and water phases. The method includes pumping a sample of the hydrocarbon into a sample chamber while pumping a remainder of the fluid into the wellbore, and testing the sample to determine a hydrocarbon content of the sample.