Although multiple-zone, downhole sand-control-tool systems have been in use since the early 1990s, these systems have been designed for jobs that require only low pump rates with low pressure differentials. Multiple-zone systems capable of high fracturing pump rates and the associated differentials only recently have been introduced to the oil field, but most of these completions have been limited to four or five treated zones. This paper presents a case history from Indonesia in which six discrete zones in an offshore deployment were treated successfully in a single trip.
Field History
The Bawal field is located in Block B, 1000 km north of Jakarta, in the South China Sea. The average water depth across the field is 280 ft. The Bawal field was discovered in 1979; the field is approximately 5 km long and 2 km wide. The Bawal reservoirs consist of subangular-to-rounded, well-sorted silt to extremely fine quartz sand. The initial development concept was to drill and complete two to three subsea wells and tie them back to a nearby production facility, Hangtuah, 43 km away. The first-gas-production target was 2012. The reservoirs all require sand control, varying degrees of stimulation, high-rate water packing at rates of 8 to 20 bbl/min, and fracture treatments at rates of 22 to 35 bbl/min.
The operator has completed multiple fields with two dominant completion methods: openhole standalone screen (OHSAS) and cased-hole frac pack (CHFP). The OHSAS completions typically are installed in horizontal wells or very-high-angle wells. The OHSAS requires special reservoir-drill-in fluid with calcium carbonate to drill the reservoir section, run the premium screen, wash the pipe, and conduct mudcake cleanout. Typically, a CHFP is conducted with tubing-conveyed perforation and alternative-flow-path sand screen being run in one trip; then, a frac pack is pumped with viscoelastic fracturing fluid.
Historically, the operator has completed subsea wells with downhole sand control using the OHSAS method for single-zone completions and single-trip frac-pack/high-rate water packs for multizone commingled production. For frac-pack completions, the completion system used previously was capable of treating only up to three zones; therefore, the treatment rate per zone became lower, and there was always an issue with slurry distribution. If more than two to three zones were required per well, a stacked frac-pack completion was implemented.
Completing these wells with conventional stacked sand-control methods meant spending many rig days tripping pipe in and out of each well. The single-trip multizone methods previously used in the area typically would provide only a limited pump rate of up to 10 bbl/min per zone and pressure ratings of 6,000 psi. For the new wells, the fracture treatments would require a more-robust system that would include a pressure rating of 10,000 psi because of sandout conditions.
Another challenge was that commingling these zones into one well has historically resulted in 50% less recovery compared with single-zone completions. Early water breakthrough coming in from one of the zones would cause the well to load up and die. Therefore, the operator also wanted to include installation of an intelligent-completion system that would allow zonal isolation without intervention, to optimize reserves recovery. The multizone frac-pack completion not only would have to be capable of completing up to six zones in one run but also would have to be compatible with the planned intelligent-system equipment.
For the Bawal project, two further challenges existed. The first concerned the fact that the reservoir has more than 10 sand layers in more than 2,000 ft of gross reservoir section; some zones also have bottom-drive water. The second challenge was that some of these zones can water out fairly quickly and thus need zonal isolation and a water-control device.
After performing an evaluation process, the development team determined that using two subsea wells to develop the field would deliver the best economic results. During the early planning stage, two subsea slant wells with OHSAS completions were planned. With further equipment trials, the well design was changed to one horizontal OHSAS completion; the second subsea well would be completed with a single-trip multizone CHFP with six zonal isolations and 2⅞‑in. interval-control valves.
On the basis of the economic and risk evaluations, the enhanced single-trip multizone CHFP tool plus the six-zone intelligent-well-system control valve was chosen as the method to develop the Bawal field subsea wells.
Generation IV Multizone Completion
The requirements for the sandface completions for field development located both offshore Indonesia and in the ultradeepwater Gulf of Mexico actually provided the stimulus for development of an improved single-trip multiple-zone gravel-pack system. The operators had specified a number of system requirements that the currently available systems could not provide. These criteria included the following:
- 10,000-psi system pressure rating.
- No atmospheric traps.
- Positive isolation. With the possibility of charging formations and the need to prevent losses, the system had to be capable of holding pressure from both directions as well as isolate all other zones when each zone is being completed. This would be accomplished with the use of an unperforated inner base pipe for the screen joints. Access to each zone for treatment would be provided by mechanical sliding sleeves that would be closed after each zone was treated. These sleeves are reopened along with additional midzone sleeves for production access for all the zones.
- High-rate reverse outs.
- Floating-rig capability.
- Weight-down circulate and squeeze positions.
- High fracture rating (45 bbl/min, 2,000,000 lbm of 16/30 bauxite proppant for five zones).
- Production setup must allow for fracture-closing-sleeve isolation to ensure sand control.
- System must be testable before tripping into the hole.
Typically, a single-trip, multizone sand-control system will accommodate between two and four distinct zones. As many as eight zones have been completed with Generation II and III systems. (For a detailed discussion of the development of the Generation I through III systems, please see the complete paper.) Before this six-zone completion, the selected Generation IV system had completed only up to four zones.
Planning and Preparation
The Generation IV single-trip multizone sandface-completion system was selected for the Bawal, Tembang, and South Belut completions. All the well designs in this project would use a 9⅝-in., 47-lbm/ft production-casing string set and be cemented across all zones. Zone-perforation selection was limited by a minimum distance requirement of 45 ft between zones. All zones in a given wellbore would be perforated simultaneously by overbalanced tubing-conveyed perforating methods.
As mentioned previously, the production sleeves in the Generation IV multizone sandface system are mechanically opened for production. For these completions, this was accomplished by running shifters on the lower end of the upper-completion production tubing (Fig. 1). As the intelligent upper-completion system is run through the sandface system, the sleeves are opened. The distance between the uppermost sleeve and the lowermost sleeve was slightly more than 1,800 ft. The distance between the rig floor and the subsea tree was slightly more than 300 ft. That meant that most of the production sleeves would be open when the rig installed the subsea tubing hanger. Because this is an intelligent upper completion, several hydraulic and electrical connections had to be made to the subsea tree, a process that takes several hours. With open production sleeves in the sandface completion, fluid losses will occur while installing and connecting the subsea tree. To remedy this problem, a special sealbore extension was placed strategically in the sandface system to allow a mating seal assembly to land while making up and connecting the subsea tree.
The Generation IV sandface-completion system has been tested extensively for erosion at maximum pump rates of 45 bbl/min. This testing simulated five discrete proppant-concentration ramp-up schedules to properly test the erosive effects of treating five zones. The system is rated to 3,750,000 lbm of high-strength proppant at up to 45 bbl/min for all zones combined, with a maximum of 750,000 lbm per zone. For the Bawal well, six zones were treated; initially, the plan was to treat as many as eight zones (Fig. 2). However, the total amount of proppant expected to be pumped through the system would be less than 200,000 lbm.
Other aspects of performing six to eight sand-control treatments with the same service-tool assembly are seal wear and the potential for leaks. The Generation IV multizone sandface-completion system was designed to include a test procedure that had to be followed at the end of each treatment. This testing protocol was documented in the procedure and executed successfully every time. As a contingency, a full backup set of service tools was kept on location. Thus, in the event of an unsuccessful pressure test, the service tools could be removed from the well, all sleeves could be closed, and the service seals would be replaced with a new set. The replacement service tools would be run back into the system, the appropriate sleeves opened, and the treatments continued.
Because of the short manufacturing lead times involved, the sandface-completion design was kept as simple as possible while meeting all of the system and installation requirements. For details about this design, please see the complete paper.
Tests performed in preparation for the first installation included burst-and-collapse testing of samples of the actual screen jackets to be used in the system. A successful drift test was performed, with sample components representing the multizone sand-control system and the intelligent upper completion.
Job Execution
The completion equipment was shipped to the location, and the Bawal well’s completion began in mid-July 2012. After perforating the well and performing deburring operations, the sandface-completion system was made up, tested, and run into the well. During the installation of the enhanced single-trip multizone system, most of the issues encountered were related to the actual makeup of the various components. Because many mating components were constructed of materials with different yield strengths, there were different torque values for each. Determining which torque value to use caused some confusion and some thread damages until a chart was created to assist the tong operator and equipment descriptions and torque values were entered into the torque-turn computer before continuing to run into the hole.
Another unique challenge faced during this job was the running of the single-trip multizone system on a semisubmersible drilling rig for the first time. The service specialists identified and tracked their tool positions in the presence of an ever-changing tide and motion compensator. To work around this, the tool men had to establish a procedure to mark positions consistently in the same manner. The floating rig made it very difficult to identify positions within close proximity of each other; the 1 ft of movement between the treating position and the initial cleanout position was especially difficult to note. To maintain functionality and prevent any delays in reversing out the work string, the tool was moved through the initial cleanout position and directly to the full reverse out following sand-control treatments while pumping on the annulus and taking returns on the work string.
The final upper zone was treated in early August 2012. The six-zone intelligent completion was installed successfully. Subsequent well-productivity tests were performed on each zone, and these tests were concluded by 3 September 2012. The total completion time, starting when the sump packer was installed on 23 July 2012, was 42 days.
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 24879, “Enhanced Multizone Single-Trip Sand-Control System Successfully Treats Six Zones in Offshore Indonesia Well,” by Leon Zhou and Indra Gunawan, ConocoPhillips, and Ricki Jannise, Casey Suire, and Tyson Eiman, Halliburton, prepared for the 2014 Offshore Technology Conference Asia, Kuala Lumpur, 25–28 March. The paper has not been peer reviewed. Copyright 2014 Offshore Technology Conference. Reproduced by permission.