Most of the “easy” propects have been drilled, and access to remaining resources is complicated by very narrow margins between pore and fracture pressure gradients. This creates drilling complexities that are extremely difficult to manage. The Secure Drilling system makes previously undrillable wells drillable. It the industry’s only fully automated choke system that measures and reacts in real time to changes in wellbore pressures and flows, providing a revolutionary change in the accuracy of measurement and analysis of flow and pressure data.
Using Micro-flux control technology, the system uses proprietary algorithms to identify and measure minute downhole influxes and losses on a real-time basis. Return flow is measured using an accurate flow meter installed in line with the chokes, which enables very early detection of fluid losses or gains and a reduction in gain/loss volumes through automated response. It does not rely on predictive models, allowing for critical drilling decisions to be made based on actual wellbore data. Combining closed-loop technology with sophisticated, proprietary data acquisition and computer-controlled equipment, the system takes rig safety and drilling efficiency to a level not attainable with standard drilling systems or even other managed pressure drilling (MPD) systems.
The Secure Drilling system helps achieve drilling program goals through its ability to precisely manage wellbore pressure and overcome the substantial drilling-related barriers that have been inhibitive for years using conventional drilling practices. Drilling flexibility and safety are maximized, while risks and downtime are minimized.
Challenge and solution
Several factors make a particular Middle Eastern field exceptionally difficult to tap, including a formation consisting of hydrocarbon-rich sandstone plus a mixture of weak and vuggy limestone and interbedded shale that tends to swell. Typically, this results in costly mud losses, stuck pipe, and fishing expeditions. Pockets of high-pressure gas can require days to circulate out, resulting in excessive non-productive time.
Additionally, a narrow pore-pressure and fracture-gradient window causes kicks whenever the equivalent circulating density drops slightly during pipe makeup, leading to well-control issues and borehole instability. Using sufficient mud weight to prevent kicks tends to create fractures, lost circulation, formation damage, differential sticking, and a low rate of penetration (ROP). This narrow gradient window has proven impossible to navigate successfully using conventional drilling technology.
All of these problems were effectively solved with use of the Secure Drilling system, and the operator’s circulation device hub, which, when mounted to the top of each stand of pipe, allowed circulation to continue uninterrupted while pipe connections were made up. The Secure Drilling system’s ability to monitor annular backpressure with extreme accuracy made it possible to stay within a narrow pore-fracture window. In this well, the system proved that it can detect and control an influx of less than 1.5 bbl within 2 minutes.
Components of the MPD system included a rotating control device to maintain the closed and pressurized environment. Annular pressure and other drilling variables were monitored and controlled in real time by the Secure Drilling Micro-Flux Controller, which includes an automated choke. Back pressure was augmented as needed by an automatically controlled auxiliary mud pump.
The operator’s previous exploratory well in this field had been abandoned at 11,484 ft (3,500 m), but by maintaining continuous circulation and controlling annular and bottomhole pressure in the difficult lower part of the well (from 11,812 ft or 3,600 m to 16,405 ft or 5,000 m), the operator and Weatherford were able to use a slightly underbalanced mud, which enabled the crew to drill ahead at an average ROP of 8.2 ft/hr (2.5 m/hr). The system operated successfully with no non-productive time (NPT), no kicks, and no lost circulation. In addition, the operator was able to keep drilling ahead even while circulating out as much as 50% gas.
During the course of drilling, the Secure Drilling system detected two partial loss events followed by an influx, and later a second influx. All three influxes were detected and circulated out, without impacting drilling.
The operator was very pleased with the results: the absence of NPT during MPD, the ability to drill ahead while circulating out up to 50% gas, the prevention of kicks or any kind of well-control issues, the prevention of lost circulation and differential sticking, and, most important, the ability to reach a depth that was nearly 50% deeper than had ever before been possible.
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