Managed Pressure Drilling is a key technique for drilling in critical areas, such as natural fractured carbonates. In this blog post, Fabio Rodrigues, Digital Twins Product Manager at ESSS Oil and Gas, explores the specific methodologies to support MPD operations, which are implemented in our real-time drilling digital twin.
The MPD (Managed Pressure Drilling) technique is an adaptive drilling process that’s used to control pressures along the wellbore. In Brazil, this technique and its variants are key for drilling in critical areas, such as natural fractured carbonates.
MPD is required for drilling formations with narrow operating windows, and thanks to technology advancements, MPD can now be used in several applications, such as pressure profile validation, increased penetration rate, improved detection and control of gains and losses, and reduction of surge and swab effects.
Pressure profiles, which delimit the minimum and maximum operational limits as a function of the vertical depth of the well, define the operational window. These profiles consist of pore, collapse, and fracture pressures. Even when they’ve been previously surveyed, these geological profiles have uncertainties and are subject to change throughout the field drilling process. Therefore, it is important to guarantee continuous updates about the operational window, providing more precise information about limits during the operation.
It is very useful for engineers to review the drilling plan in various situations. The MPD monitoring module allows companies to obtain more precise values from the DPPT (Dynamic Pore Pressure Test) and DFIT (Dynamic Formation Integrity Test) procedures in order to compose the operating window. As a consequence of applying it together with precise hydraulics, cutting transport, and torque and drag models, the developed methodology proposes the ideal operating parameters (such as choke pressure, pump flow rate, or adjustments related to drilling fluid properties) as output. The methodology always considers the best approach to meet the restrictions imposed by the operational window, avoiding drilling problems. Alternatively, if a change to the operating parameters is not sufficient, the developed methodology also simulates the best position for the anchor point.
Because optimizing the drilling process in real-time is extremely important, this blog post focuses on using specific methodologies to support MPD operations, which are implemented in our real-time drilling digital twin (PWDa) and piloted by our 24/7 team of engineers.
DPPT and DFIT Procedures
The DPPT (Dynamic Pore Pressure Test) and DFIT (Dynamic Formation Integrity Test) procedures allow a more accurate estimate of values for pore and fracture pressures, respectively. These procedures are very relevant for drilling in narrow operating window scenarios, since they take into account the current field geopressure, allowing engineers to correct previously obtained geological profiles.
Thus, the probability of gain and loss events becomes smaller in an MPD operation when compared to a conventional drilling.
During these tests, in each pressure step performed in the choke, the software calculates the volume balance due to the compression or decompression of the fluid in the well. This way, it is possible to verify if the expected volume variation follows the same magnitude of the real volume variation (decreasing or increasing) observed in the well.
The figure below illustrates a DFIT procedure. Notice that the active tank volume (brown curve) decreases in each step performed on the MPD choke pressure (blue curve). This happens due to fluid compression.
After the end of these procedures, the simulator updates the operating window (from the tests’ depths onwards) using real downhole data (ECD) in a conservative way. The logic adopted for updating is to use the largest value between the DPPT and the value of pore gradient present on the project. For the fracture gradient, the inverse logic is adopted: the lowest value between the DFIT and the fracture gradient obtained on the project is used. The figure below illustrates the pore gradient update.
MPD Optimization Module
The real-time optimization of MPD control is suggested by the software when any of the following conditions along the entire well are reached:
- The ESD or ECD profiles get close to a preset tolerance limit to the fracture or pore gradient;
- The fluid properties have changed; or
- A new point has been collected for the operating window from a DPPT or DFIT.
Once the operational data has been inserted (operating window, flow rate, fluid properties, set point, anchor point, penetration rate, among other operational limits), the software can execute the optimization module.
During the optimization module execution, the following steps are performed:
- Calculation of the ECD / ESD profiles (along the annular space) using the geometry, fluids, and operating parameters inserted;
- Calculation of proximity indices between ECD / ESD profiles and the operational window;
- Calculation of new SBP (surface backpressure) and fluid flow values for the same anchor point; and
- If necessary, calculation of new set point values and anchor point position.
Parameters are optimized in order to increase the distance between the ECD / ESD profiles with the operating window.
Within the optimization routine, a sequence of parameters will be used as primary variables, sorted according to the criteria used during the operation for the sequence of the modified parameters. Optimization processes occurs in the following order:
- Optimization of dynamic and static pressure value of the choke;
- Optimization of dynamic and static pressure value of the choke and the injection fluid flow;
- Optimization of dynamic and static pressure value of the choke, the injection fluid flow, and the mud weight; and
- If necessary, calculation of an anchor point value that best meets the conditions imposed by the operating window and by the operational parameters.
In the case illustrated by the figure above, the likely optimization suggestion to be adopted would be the one in which the ECD / ESD profiles are more centralized, but closer to the pore gradient when compared to the fracture gradient, in order to avoid fluid loss.
Several deepwater MPD drilling operations proved that a redesign on the drilling project must be performed in several situations, especially if an unexpected gain or loss event occurs. This way, the MPD monitoring module is used by the ESSS 24/7 team through PWDa, which calculates the hydraulic parameters almost instantaneously with real data. It allows for a fast project redesign and, consequently, reduces non-productive time.
This developed methodology was successfully applied to several MPD wells drilled in distinct ultra deepwater locations in Brazil. The real-time optimization procedures are a further step to ensure the reliability of MPD operations in challenging scenarios, enhancing efficiency and safety.
For more information about how ESSS Oil and Gas Real-Time Monitoring can help your company go further, contact us today.
