Wired-Drillpipe Technology in a Deep Ultradepleted Reservoir
Results from a well recently drilled into an underpressured reservoir in southern Mexico.
Wells drilled with nitrified drilling fluids require a solution for the transmission of measurement-while-drilling (MWD) surveys, bidirectional communication with rotary-steerable systems (RSSs), and transmission of MWD and and logging-while-drilling (LWD) measurements of downhole temperature and annular pressure for surface choke adjustments. Results from a well recently drilled into an underpressured reservoir in southern Mexico provided an opportunity to demonstrate the applicability of wired drillpipe (WDP) to deliver the required measurements and maintain the proper directional control while keeping the well fluids under control.
This paper describes how WDP and managed-pressure drilling (MPD) enabled an operator to drill a severely depleted reservoir with an inverse-emulsion mud mixed with nitrogen delivered through a drillpipe-injection system.
This field has a complex structure divided by a salt intrusion into northern and southern portions. Six reverse faults oriented in different directions are involved in this structure. The reservoirs are found in the Middle and Lower Cretaceous and in the Kimmeridgian-Jurassic. Initial production was from the Lower Cretaceous interval, which is now below saturation pressure. The reservoir pressure has declined dramatically, making it necessary to provide a gasified fluid system to avoid lost-circulation problems while drilling.
The low mud weights required for the reservoir section create operational risks, such as fluid influx from the upper sections and wellbore collapse and severe mud losses in the lower sections. As a result, real-time wellbore data while drilling were mandatory to support decision making and to avoid catastrophic incidents. Conventional drilling through these formations has proved difficult. The main problems encountered are differential sticking and lost circulation because reservoirs are underpressured and present frequent intersection of wellbore with fractures. Therefore, use of conventional drilling techniques typically results in severe lost-circulation events.
To solve these drilling problems, multiphase MPD techniques were employed. The presence of high nitrogen-injection rates through the drillpipe presents a limitation for pulse-type data-transmission tools. Because of the increase in fluid compressibility and a consequential decrease in the pressure signal, the possibility of achieving full directional control in the reservoir section is reduced. Bottomhole temperatures are higher than with conventional drilling because of the presence of the high gas/liquid ratios of the mud, reducing its cooling characteristics and causing tool-temperature limits to be reached very quickly.
Initially, concentric-casing-annulus injection was proposed to solve the mud-pulse transmission of downhole information when nitrogen injection is performed through the drillpipe. This was rejected because of well-design limitations and cost. Therefore, direct nitrogen injection was proposed along with use of WDP for the transmission of the MWD/LWD data and the WDP along-string measurements (ASMs) of annular pressures and temperatures. The technology to drill the 8½-in. section consisted of an RSS tool, an LWD array-resistivity-compensated service that included an annular-pressure-while-drilling (APWD) measurement, a bottomhole-assembly (BHA) interface sub, the WDP system including the annular-pressure sensors in the WDP repeater subs, and a nitrified inverse-oil-emulsion system.
For a discussion of prejob modeling and MPD operational strategies, please see the complete paper.
WDP, Directional BHA, and LWD Measurements
WDP was used first in 2003 and was commercially launched in 2006. The network uses individual modified drilling tubulars that integrate a high-strength co-axial cable encapsulated within a pressure-sealed, stainless-steel conduit running the length of each joint to provide bi-directional, real-time, drillstring telemetry at speeds up to 57 kbps vs. 3 to 100 bps for mud-pulse telemetry, and with a temperature rating of 150°C. (For a description of the network components, please see the complete paper.)
WDP enabled the following applications for this MPD operation:
- Real-time surveys available in compressible mud without the use of mud-pulse telemetry
- Continuous direction and inclination analysis for dogleg-severity reduction from reaming operations
- MPD choke refinement from the measurements from the APWD tool and the WDP ASM pressures during connections
- Use of interval mud density during MPD nitrogen-injection operations in the presence of high bottomhole temperatures to detect lost-circulation events
- Spectral analysis of the 9-Hz collar-rev/min measurement
- Ability to measure the effect of temperature on in-situ mud density, which has never before been quantified downhole
During initial circulation of multiphase MPD operations, the LWD APWD readings showed a mismatch between the simulated conditions and the measured values acquired by the downhole tools. The WDP allowed the team to obtain this information in real time with a minimum delay time. Initial injection parameters during the biphasic drilled intervals were 1.4 m3/min of mud and 23 m3/min of nitrogen, with 1034-kPa surface backpressure (SBP) for an equivalent circulating density (ECD) of 0.90 specific gravity (SG). Simulation design needed to be reviewed and recalibrated according to the downhole data from the APWD tool [bottomhole temperature and bottomhole pressure (BHP)] and according to the real mud rheology. It appeared to take two circulation cycles before the mud properties stabilized.
The case-study well was designed as a Type-J high-inclination well, with the primary target being the Kimmeridgian-Jurassic carbonates at 5229-m true vertical depth, with a displacement to total depth of 1488 m and azimuth of 63.73°. The directional objective was to build the 8½-in.-hole section from 55.54° to 65.36° with a dogleg severity of 2.5°/30 m and then drill tangentially to the end of the section at 5405-m measured depth (MD).
The 8½-in.-hole section was initiated on 13 December 2010 with the milling of the shoe track and cement from the 9⅞-in. casing from 5115- to 5120‑m MD, with a circulation rate of 1.59 m3/min for 0.95-SG mud (ECD of 0.97 SG) at 120 rev/min without SBP.
The same parameters were kept to drill the new formation from 5120- to ±5138‑m MD, where a cleanout pill was pumped and the well was circulated to clean the hole and perform a short trip to the 9⅞‑in. shoe on 13 December at 1400 hours. No drag or torque issues were observed.
The drilling resumed with single-phase MPD with 0.95-SG mud without problems until 5138-m MD, where high torque was observed (8,500 to 14,000 lbf-ft), but no other signals of hole instability were registered, such as excessive torque and drag off-bottom. However, the liquid rate was increased to 1.7 m3/min, which increased the equivalent BHP to an ECD of approximately 0.98 SG, solving the high-torque issues. The drilling continued to 5146‑m MD, where another increment in the torque from 8,500 to 14,800 lbf‑ft was observed. A short trip to the casing shoe was carried out with normal drag values.
Once at the casing shoe, the drilling parameters were adjusted to 130 rev/min, creating 8,700 lbf-ft of torque and adding 2413 kPa of SBP, which increased the BHP ECD to approximately 1.04 SG. Drilling continued on 13 December at 1700 hours from 5146-m MD to 5150-m MD without problems.
During the job, several adjustments to the modeling were required to take into account the actual drilling parameters used. These adjustments included the following:
The density of mud was varied and adjusted manually in the simulator to conform to the actual density of the mud flowing in the drillpipe and that flowing out of the annulus as computed by the WDP ASM pressures.
- The actual annulus-temperature profile provided by the downhole APWD sensor was used.
- The actual pressure losses for the downhole tools at different flow volumes were used.
- These adjustments allowed the relatively constant BHP (CBHP) as confirmed by the downhole tool readings transmitted through the WDP network.
For a detailed discussion of the results of the drilling operations, please see the complete paper.
Importance of WDP Data During Connections
Stand connections are a critical point in multiphase MPD, where the correct SBP compensation is key to keeping the CBHP, as shown in Fig. 1, where three stand connections were performed in the interval of 5110- to 5204-m MD.
In each of them, the value for the simulation matched the ECD readings from the APWD tool, even with short periods of circulation and during the increase of SBP to raise the ECD from 0.65 SG to 0.7 SG. Fig. 1 also shows the procedure to achieve dry connections by continuing to inject nitrogen after pump shutdown to displace all liquids below the first nonreturn valve.
The injection parameters during drilling and circulation periods shown in Fig. 1 were 120 m3/min of nitrogen and 1.36 m3/min of mud, with 1034-kPa SBP for an ECD of 0.65 SG and 1931-kPa SBP for an ECD of 0.7 SG, respectively. The average gas ratio for these parameters was approximately 50%.
Observing approximately 4275 kPa of annular frictional pressure losses, only 2413-kPa SBP needed to be added to the annulus to maintain the CBHP. This amplification ratio changes over he interval shown in Fig. 1, and it is very difficult to model (and to calibrate the model) without the downhole pressures.
The availability of the APWD-tool measurements and WDP ASM annular-pressure measurements in real time during the pump-shutdown phase of the connections has proved to be invaluable in obtaining the correct choke positions and hydraulic-model parameters.
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 163501, “Using Wired-Drillpipe Technology During Managed-Pressure-Drilling Operations To Maintain Direction Control, Constant Bottomhole Pressures, and Wellbore Integrity in a Deep, Ultradepleted Reservoir,” by John Rasmus, SPE, Alain Dorel, Tony Azizi, Andre David, Ember Duran, Hector Lopez, Gare Aguiñaga, Juan Carlos Beltran, and Antonio Ospino, Schlumberger, and Eduardo Ochoa, NOV IntelliServ, prepared for the 2013 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 5–7 March.