Managed-pressure drilling (MPD) has long held the promise of improved safety and efficiency. By precisely controlling and monitoring the annular fluid pressure drillers can avoid unwanted formation fluid influx, drilling fluid loss and formation damage, often with higher rates of penetration. The result is higher productivity from the reservoir and the drilling budget.
In deepwater applications, advanced MPD techniques, such as dual gradient drilling, reduce the fluid gradient in the riser, thereby widening the ultra-narrow margin between pore pressure and fracture gradient. As a result, wells require fewer casing strings and can have improved safety and project economics.
Much attention has been focused on machinery to manage wellbore pressure. Rotating heads, continuous circulation tools, subsea pumps and specialized annulars are all becoming established technologies that enable the drilling of wells within predefined pressure objectives.
The precision and control attainable from these systems are impressive. But how do engineers know that the selected pressure objectives are correct?
A toolbox, not a black box
Specialized equipment designed to manage wellbore pressure has been a critical development in applying MPD to offshore applications. These systems provide the machinery to precisely control wellbore hydraulics within a constricted operating window.
However, effective use of this sophisticated, computer-controlled technology requires good information about the conditions surrounding the well bore. While equipping the rig is a critical enabler of MPD, it is equally important to equip decision makers with the knowledge they need to effectively use the equipment.
In some cases, an MPD spread is regarded as a black-box solution where drillers can simply set the controls and let the system do the drilling. It is more appropriate to treat MPD as a complex toolbox that includes rig equipment, an integrated drilling team and a defined process of planning, monitoring and adapting.
The MPD process
Making MPD pay off requires new technologies, methods and practices for pore-pressure planning and real-time surveillance. Only by correctly defining and continuously tracking the required formation and fluid properties around the open hole can MPD implementation equipment be set properly.
Experience has demonstrated that using only pieces of this process results in disappointment and frustration. If process components are missing, the anticipated changes will be unrealized or depressed, and the operator will abandon the system without allowing time for goals to be realized. The process takes several wells to bear fruit, and the evaluation of this type of system on a single prospect will typically yield poor results.
Geoscience expertise
Central to the process is ensuring that actionable information gets into the decision-making process at the right time. The safe operating envelope must be delivered in a highly time-critical environment if formation fluid influx, drilling fluid loss and wellbore instability are to be minimized. By maintaining the circulating and static fluid densities in correct relation to the pore pressure, wellbore collapse pressure and minimum stress, substantial trouble and time can be avoided. This requires a dedicated geopressure analyst, using fit-for-purpose technology, to support real-time decision making.
The geopressure analyst functions as a bridge between geoscience and drilling operations by synchronizing knowledge among the drilling team. As a result, the best information relevant to trouble avoidance is available 24 hours a day, to all team members, with an expert to explain where it came from and what it means to the operation.
Integration through communication
Communication of all relevant information between drilling and geoscience assets is accomplished by managing streaming data via WITSML. WITSML allows for secure data sharing among all team members using the Internet. WITSML is a communication technology that is critical to decentralized teams making time-sensitive decisions.
This technology improves modeling efficiency by allowing use of real-time, interactive computing and customized routines with hard-coded, industry-standard methods. Geopressures,
earth stresses, compartment pressures and collapse pressures can be modeled
in three dimensions using any combination of geophysical, geological, petrophysical and drilling data. In addition, geoscience and engineering work is delivered to all stakeholders effortlessly while building a database of information for later use.
Conclusions
Because MPD succeeds by maintaining wellbore pressure within a narrow operating window, understanding pore pressure and fracture gradient is very important. Downhole and surface sensors provide important data points, but much of this information is indirectly measured, and none of it is predictive. To establish good pressure targets and proactive behavior, robust, real-time modeling capability is required.
Such models have three key parameters. First, the model should encompass the entire open-hole section (not just bottomhole pressure), to address such issues as wellbore instability. Second, the model must be updated with new data as the well is drilled. Third, the model should be capable of supplying real-time data and information sharing, to provide accurate information when tough decisions are required. With such models providing accurate guidance, equipment can be used with greater precision to yield superior drilling performance.

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