Achieving constant bottom hole pressure (BHP) by accurate control of annular pressures using a surface rotating control device (RCD) and choke manifold is the principal concept for managed-pressure drilling (MPD). The MPD technique is widely used in challenging drilling environments such as deepwater drilling with narrow pore pressure and fracture gradient windows, drilling in depleted high-pressure, high-temperature (HPHT) environment, drilling in highly fractured formations Prior to the field deployment of the MPD system, a robust, detailed operational testing on a test rig is crucial to validate the equipment operability, pressure control and hydraulic modeling.

A suite of complex MPD tests were conducted with several creative ways to manage wellbore pressures to accomplish all the test objectives. The MPD tests were conducted successfully in both a cased hole and an open hole drilling environment on a modern drilling testing rig located in Grimes County, Texas. The design and actual, surface and downhole pressure window for both the cased hole and open hole testing is presented in the paper.

The cased hole test was conducted inside a 13-3/8” casing with test string bottom located at ~2,500 ft. A combination of pressure-while-drilling (PWD) tool and an enhanced measurement system (EMS) memory sub was used to record and quality control the BHP measurement. Nine (9) joints of 11” drill collars were included in the bottomhole assembly (BHA) to artificially create annular friction drops in the well. Up to 1200 gal/min (gpm) were flowed in the cased-hole test to simulate the impact on BHP changes.

In the open hole drilling test, both a live-streaming EMS sub and a memory EMS sub were instrumented in the BHA with a mud motor, an MWD/PWD tool and an 8-1/2” PDC bit. A 69-bbl 8.9ppg pill and a 126-bbl 10.0 ppg pill were pumped down the drillpipe and into annulus to test the system's capability to maintain constant BHP with multiple fluids in the wellbore. Surge and swab were tested through various pick-up and slackoff speeds with various pump ramps-up to 850 gpm. The open hole was drilled to 4,430 ft TD for MPD testing.

In conclusion, the tested MPD equipment system is proven to be able to maintain constant bottomhole pressure by adjusting the MPD choke manifold pressures and the hydraulic model is able to simulate the downhole equivalent circulating density (ECD) for various operation phases including drilling, flowing, tripping, making connections and etc. and thereby control drilling processes from model. Model correlation allows drilling control from model of downhole conditions.

In the meantime, we are able to use the NOVOS drilling automation system to automate some of the procedures with one command. Good examples are mud pump ramp up and surge / swab testing.

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