Intelligent choking improves production, economics in Ecuador completions
An advanced intelligent completion system that combines remotely operated, hydraulic adjustable chokes, downhole sensors, and semiautomated surface control has accelerated production, increased ultimate recovery, and reduced interventions in conventional electric submersible pump (ESP) completions.
For Occidental Exploration & Production Co. (Oxy), a subsidiary of Occidental Petroleum Corp., the installation of such a system with ESPs during well workovers in Ecuador's Eden-Yuturi field proved effective in increasing revenues by maximizing incremental production while lowering expenses because fewer wells needed to be drilled to meet the accelerated production goals.
The intelligent wells also eliminated interventions previously required to shift sliding sleeves and decreased water handling costs by reducing water production.
This type of intelligent completion can significantly economize mature field production.
Multizone commingling
Oxy operates Block 15 in the Oriente Basin in Ecuador pursuant to a participation contract with Petroecuador, the Ecuadorian state oil company. Block 15 includes Eden-Yuturi, Indillana, Yanaquincha, Paka, and Limoncocha fields, having currently 90 producing wells. Most of these fields are mature and use ESPs for enhancing recovery.
In early 2002, Oxy began reviewing the benefits of installing intelligent completions in some ESP wells to commingle zones and accelerate production.
The company decided to prove out the intelligent completion concept by retrofitting the EY-D11 well in Eden-Yuturi field with a system based on remotely operated, hydraulically adjustable chokes and a full complement of downhole electronic instrumentation.
Eden-Yuturi, discovered in 1996, has about 100 million bbl of oil reserves. Since 2000, 39 wells have been drilled in the field from five separate well pads. Currently, 32 wells are producing at an average rate of 2,750 b/d/well.
Well EY-D11, perforated and completed in December 2002, began producing in February 2003 from the T sand, the deepest reservoir in the field. The Upper U sand, above the T sand, also was perforated but remained isolated until tested in October 2003 in preparation for the intelligent completion. As with all wells in the field, the EY-D11 well never flowed naturally and required an ESP immediately after drilling.
Oxy wanted to commingle production in order to satisfy production goals with fewer wells. However, the DNH, en entity of Ecuador's Ministry of Energy, provides certain criteria for producing simultaneously from multiple zones in the same well. These criteria require the operator to "guarantee the separate and independent production of the reservoirs and the performance of maintenance work" and that "wells must be completed, maintained, and operated according to the characteristics of each particular deposit."
Previous completion techniques could not meet these requirements; therefore, operators in Ecuador have not commingled multiple zones in the same well.
Oxy decided to install an intelligent system based on hydraulic adjustable chokes and real-time data acquisition that would meet the government's criteria for commingling zones. These completions also would eliminate interventions and their associated costs and risk.
The company selected Baker Oil Tools as lead contractor for the project, with responsibility for ensuring successful implementation of the intelligent well system and for coordinating all equipment supplied from other contractors.
Overcoming production limitations
Most previous ESP completions with selective production from two or more zones have a Y-tool to offset the ESP. For intervention purposes, this type of completion provides a reduced section of the production tubing for bypassing the ESP.
Cost and risk associated with intervention pose drawbacks to this method, as does the fact that the ESP must be downsized to accommodate the side string. Downsizing the ESP reduces pump horsepower and productivity. Intervention is not possible below the ESP when a well profile is too small to accommodate a Y-tool.
Although the 95/8-in. casing in Well EY-D11 would allow installation of a Y-tool, a slightly modified version of the selected intelligent well system also can be installed with an ESP in smaller wellbore diameters that preclude the use of a Y-tool.
Intelligent well options for selectively producing and monitoring from individual zones below the ESP include:
- Dual-zone and single-valve (used when the operator knows beforehand which zone will water out first and desires to isolate or choke the zone without intervention).
- Dual-zone and dual-valve.
- Multizone and multivalve.
Production from the intelligent completion enhanced ESP wells can be commingled for accelerated recovery. The completion permits individual zones to be remotely shut off or choked in the event of water coning or breakthrough to reduce workovers and potentially increase ultimate recovery. Also the completions allow for remotely shutting in individual zones and using permanent downhole monitoring to obtain real-time and on-demand production tests without well intervention.
For these completions, the operator has minimal incremental investment because the intelligent completion equipment cost is small compared to the overall cost of the well and production system. The systems provide a significant return on the capital investment.
Intelligent completion design
The intelligent completion design in Well EY-D11 centered on a shrouded ESP and an InForce hydraulic intelligent well system with remotely operated, multiposition hydraulic chokes to control flow from each zone via a semiautomated surface control system (Fig. 1).
To complement the hydraulic system, QuantX Wellbore Instrumentation LLC provided a suite of downhole sensors that included a low cost, venturi-type flow meter, and pressure and temperature gauges, all controlled via a single surface data-acquisition unit.
Other integral parts of the completion included control-line flatpacks, cross coupling protectors, and a mechanical zonal isolation sleeve for shutting off the lower zone during a workover. This isolation sleeve was attached below a simple retrievable seal-bore packer separating the two zones. A pair of basic chemical injection mandrels comprised the remaining completion components.
The completion had two HCM-A multiposition hydraulic chokes. One controlled the flow from the upper zone (Upper U sand) and one for the lower zone (T sand). Alternating applied pressure to each side of a balanced hydraulic piston cycles each choke position.
A tungsten carbide choke assembly and J-mechanism selectively adjusts the choke position without the need for complex downhole electronics. A dual-stage choke configuration with the seal assembly completely independent of the choke provides superior erosion resistance so that any minor erosion imparted to the choke will not jeopardize the ability to isolate a zone.
Only the lower zone choke had a shroud. The shroud enabled tubing-to-tubing flow of the produced fluid. This concept of stacking a nonshrouded sleeve or choke above a shrouded sleeve or choke is common for two-zone intelligent completions and makes it possible to keep all completion equipment above the production packer and well above the upper zone perforations.
The shrouded and nonshrouded concept also eliminated the need for a feed-through packer, allowed for easy ESP retrieval if necessary, and greatly simplified the overall completion design and installation.
Electronic permanent monitoring equipment installed below the shrouded choke provides valuable real-time pressure, temperature, and flow data. Gauges monitor pressure and temperature for each zone. A venturi-type flowmeter measures flow only from the lower zone, with upper zone production calculated from surface after measuring total fluid from the well.
During commingled production, the surface data-acquisition system shows the flow rate from the lower zone, thus providing the production allocation required by the government. Although initially selected for convenience, the venturi flowmeter ultimately provided critical, real-time, at-the-well indication of flow that was vital to the government agency.
The installation also included two chemical-injection mandrels because of concerns with scale buildup on the completion equipment. One mandrel was installed immediately below the non-shrouded adjustable choke, and the second mandrel was installed with the permanent monitoring equipment to ensure proper protection of all tools in the completion.
The EY-D11 intelligent completion included six downhole control lines in addition to the ESP cable. The lines, separated into two encapsulated flatpacks, were for the hydraulic chokes, instrumentation, and chemical injection.
All lines are made of 316 stainless steel and this material is used also for the armor of the tubing-encased conductor (TEC) line.
Although each hydraulic choke required two control lines for operation, the chokes can share a common line for closing and choking. This results in the completion needing only three lines from surface: one line for opening the upper zone choke, one line for opening the lower zone choke, and one common line for choking or closing each choke.
The permanent monitoring system required two downhole conductors for operation. Each of these conductors was in a single 1/4-in. OD twisted-pair TEC that utilized only one wellhead penetration. Elimination of the extra hydraulic and extra electric lines helped reduce the overall cost and complexity of the system.
Cross-coupling protector clamps protected the two flatpacks and the ESP cable at every tubing coupling. The 7-in. shrouds on the lower zone choke and the ESP required special clamps.
Surface control system
Original specifications for Well EY-D11 called for a manually operated hydraulic surface-control system (SCS) that required manual tracking and recording of downhole choke positions.
After attending a 1-week customer training session during which Oxy operators worked with the SCS, the operator realized the value of an SCS that could track and record choke positions automatically and reduce the potential for human error. Upon Oxy's request, Baker Oil Tools upgraded the manual SCS to a semiautomated SCS that easily interfaces with Oxy's supervisory control and data acquisition (SCADA) system.
The SCS remotely operates the chokes and records the position of the chokes at each shift.
The semiautomated SCS has the capability to control two wells, and therefore was used for the second Eden-Yuturi intelligent well, EY-D15, in addition to EY-D11.
Upgraded versions of the system will be fully automated, with built-in programming for simple interactive control of all functions required to operate the chokes.
The electronic well monitoring package required that pressure, temperature, and flow were monitored and displayed on surface in real time. The data acquisition system selected can monitor the downhole sensors, display the data in real time, and provide backup storage for up to 6 months of data. The data acquisition system has the capability to interface directly with Oxy's current field SCADA system.
Reservoir studies, nodal analysis play key role
The HCM-A hydraulic chokes are infinitely variable, although six intermediate choke settings between fully open and fully closed must be selected by machining a profile prior to tool installation.
Nodal analysis helps the operator and intelligent completion provider determine whether chokes are needed for the well and, if so, the optimum settings for the chokes. Input parameters for the nodal analysis includes completion configuration, fluid properties, productivity indexes (PI), wellhead pressures, formation pressures, and ESP size and type.
Factors that affect choke size selection, based on reservoir studies and nodal analysis, include maximizing attainable oil production, reducing water cut at surface, improving final oil blend quality, controlling sand, avoiding cross flow and its consequent production loss, complying with regulatory production restrictions, and producing above the bubblepoint to avoid gas at the pump intake.
The base case for the EY-D11 nodal analysis assumed two zones commingled with no intelligent well system. The objective was to determine uncontrolled commingled production capability and flowing pressure at a given ESP operating frequency, as well as any potential for cross flow between zones.
The base case also considered various water cuts to simulate increases in water production over time. The operator provided a requirement for maximum pressure drawdown in each zone to ensure pressure maintenance above the bubblepoint as well as a requirement for maximum production rate from the lower zone to avoid water breakout. The analysis showed that cross flow was not a concern when producing commingled, but that the ESP alone could not achieve maximum drawdowns for each zone.
The second nodal analysis, with the intelligent well system in place, simulated production rates and pressures at various choke settings in each zone to optimize production at current water cuts. By increasing the water cuts, the analysis could simulate how choke size could reduce water production. Because decreasing water production also means lower oil production, the analysis provided a way to balance the gain in incremental commingled oil production with the decrease in overall water production.
The ideal choke setting regulated drawdown and production from the lower zone in order for the ESP to produce more oil from the more prolific upper zone. Well data indicated that the lower zone required choking but not the upper zone.
Based on some uncertainties with the upper zone data, Oxy however opted to install chokes in both zones for added flexibility. The analysis determined that the ideal setting was 1% of the full-open flow area of the choke. This setting was expanded to determine the other five settings on the multiposition choke as 2%, 3%, 6%, 9%, and 12% of the full-open flow area.
The adjustable hydraulic choke only requires one component of the tool to configure the choke settings. This component can be machined quickly after the choke has been manufactured, so that the nodal analysis for selecting the choke can include the latest reservoir data.
The proper size of the venturi in the downhole flowmeter was based on the flow rates calculated from the nodal analysis. Conversely, the permanent monitoring equipment installed in the intelligent completion provides instantaneous reservoir data that assists in validating the nodal analysis and helps determine the optimum of the six selected choke settings at any given time in the life of the well.
In the case of Well EY-D11, the ESP provider used the nodal analysis data to size the pump. Relevant data included commingled flowing pressures and production rates.
Well EY-D11 currently produces commingled with an ESP from the upper and lower zones. Production is an incremental 3,500 b/d greater than the previous single-zone ESP completion (Fig. 2).
Based on the successful installation and results from this well, Oxy in April 2004 installed a second identical intelligent completion system in Well EY-D15 and has scheduled three additional such completions in the field for 2004.
Based on its ability to accelerate production and increase ultimate recovery from ESP completions while reducing interventions, the intelligent completion system with hydraulic adjustable chokes offers an economically viable method of optimizing production and recovery from mature fields throughout the world.
The authors
J. Michael McCelvey ([email protected]) is field manager of Eden Yuturi field in the Amazon Basin for Occidental Exploration & Production Co, Ecuador. He has more than 27 years of experience in production and drilling operations both overseas and in the US.McCelvey holds BS in geology and forestry from SF Austin State University.
Robert E. Puckett is an applications engineer in Baker Oil Tools' intelligent well systems project management group, inHouston. Puckett has coordinated IWS installations in Ecuador and Argentina. Prior to joining Baker Oil Tools in 2001, Puckett worked in theartificial lift systems groupofanother service company. Puckett holds a BSin mechanical engineering from Louisiana State University.
