Drilling Pressure Measurement via Mudcake Supercharging Analysis
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Solution Overview
Problem
Existing well logging devices face difficulties in accurately measuring true formation pressure, especially in low permeability formations, due to the phenomenon of supercharging caused by the finite permeability of mudcake, which leads to residual pressure differences across the mudcake interface.
Innovation Solution
A method involving a measurement device with a probe on the drill string, where the mud flow rate is controlled to obtain multiple borehole and probe pressure measurements, allowing derivation of true formation pressure by analyzing the pressure differences across the mudcake, even during drilling operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a standard wireline pressure measurement is used to measure pressure difference across the mudcake, then the measurement process is simple, but the measurement precision deteriorates because of residual finite pressure difference caused by supercharging in low permeability formations
Solution Approach 1:
The patent applies preliminary action by taking multiple pressure measurements at different times before the formation pressure fully equalizes with the borehole pressure. By measuring at multiple time points (first pressure difference at first time, second pressure difference at second time), the system captures the transient pressure behavior needed to calculate true formation pressure without waiting for complete equilibrium, thereby overcoming the supercharging effect while maintaining operational simplicity
Solution Approach 2:
The patent implements feedback by continuously monitoring pressure differences over time and using this temporal feedback to distinguish between the transient supercharging effect and the true formation pressure. The system uses the sequence of measurements (first pressure difference, second pressure difference) to iteratively determine the accurate formation pressure, effectively compensating for the mudcake permeability issue through temporal feedback analysis
2Measurement precision
If multiple probe pressure measurements are taken with different driving potentials to overcome supercharging, then the measurement precision improves, but the device complexity and measurement time increase
Solution Approach 1:
The patent applies universality by using the existing drill string and standard pressure measurement equipment to perform multiple measurements at different times. The same probe and pressure transducers used for initial measurements are reused for subsequent measurements, eliminating the need for specialized additional equipment. This multi-functional use of existing tools allows temporal sampling without increasing device complexity
Solution Approach 2:
The patent takes preliminary action by performing all necessary pressure measurements during the drilling operation itself, before the well is shut in or the drill string is removed. By capturing multiple pressure difference measurements while the drill string remains in place and mudcake is still present, the system obtains sufficient data to calculate true formation pressure without requiring subsequent complex logging operations or well shutdown procedures
3Measurement precision
If multiple pressure measurements are taken over time to determine true formation pressure, then the measurement precision improves, but the duration of the measurement process increases
Solution Approach 1:
The patent maintains continuity of useful action by taking multiple pressure measurements during the continuous drilling operation without interrupting the drilling process. The pressure measurements are taken at different times while the drill string remains in the hole and drilling continues, allowing the formation pressure to be determined without stopping drilling or requiring well shutdown. This continuous measurement approach minimizes time loss compared to methods requiring well shutdown or separate logging operations
Solution Approach 2:
The patent performs the pressure measurements preliminarily during the drilling operation itself, before any well shutdown or post-drilling analysis is required. By capturing the transient pressure behavior while the drill string is still in place and mudcake is present, the system obtains the necessary data to calculate true formation pressure during the drilling process, eliminating the need for subsequent time-consuming analysis or re-measurement operations
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 enables efficient determination of true formation pressure while drilling, effectively overcoming supercharging issues by using multiple pressure measurements to accurately calculate the formation pressure, even in low permeability formations.
Implementation Method 1
Darcy's law and Ohm's law have the same algebraic form. The pressure difference between the borehole (hydrostatic) and the virgin formation is the driving potential Vbh−Vf. The mudcake is analogous to a relatively high value resistor Rmc.
Data Source
AI summary
A drilling operation wherein a borehole can be drilled through earth formations with a drill bit at the end of a drill string, using recirculating drilling mud that flows downward through the drill string, exits through the drill bit, and returns to the earth's surface in the annulus between the drill string and the borehole wall, at least a portion of which has a mudcake thereon, and a surface pumping system for pumping the mud to recirculate. Determining true formation pressure, including the following steps: providing a measurement device, having a probe, on the drill string; controlling the mud flow rate to obtain a first measured borehole pressure and measuring, with the probe of the measurement device, as a corresponding first probe pressure, the pressure in the formation adjacent the mudcake; controlling the mud flow rate to obtain a second measured borehole pressure and measuring, with the probe of the measurement device, as a corresponding second probe pressure, the pressure in the formation adjacent the mudcake; and deriving the true formation pressure from the first and second measured borehole pressures and the first and second probe pressures.