An evaluation of more than 100 Saudi Aramco wells equipped with multiple downhole valves demonstrates the technology’s effectiveness and yields valuable recommendations for optimizing field performance.
Saeed Mubarak, Naseem Dawood and Salam Salamy, Saudi Aramco
Inflow-control valves (ICVs), also called smart or intelligent completions, are multi-position active downhole valves that can be controlled from the surface. This technology was developed to optimize production by providing zonal isolation and flow control of commingled production from different laterals or segments. By varying the positions of these valves, production can be managed in real time to improve well and reservoir performance.
These valves are accessories for maximum-reservoir-contact (MRC), multilateral or multi-segmented horizontal wells to manage production where there is:
• High reservoir pressure variation among laterals or segments
• Significant variation in productivities between laterals
• Varying gas/water fractions among laterals or segments
• Presence of fractures, faults and/or high-permeability intervals.
These technologies are used as fit-for-purpose. They are custom-designed to take into account reservoir characteristics, completion architecture, operations and economics. The effectiveness of these completions depends on proper planning, design and placement of laterals or segments. The presence of an integrated system including surface panels and multiphase testing capabilities is a key factor to effectively utilize ICVs.
This article documents the evaluation of more than 100 intelligent wells equipped with multiple downhole valves in Saudi Aramco assets and provides recommendations based on that evaluation. The assessment focuses on the ICVs’ impact on well and reservoir performance and development cost. Results have demonstrated these completions to be effective in sustaining oil rates, controlling water production, minimizing or eliminating water and gas production and reducing development cost.
EVOLUTION OF ICV APPLICATION
The first implementation of these completions in Saudi Aramco took place in conjunction with multilateral MRC wells in early 2004, mainly in Shaybah and Haradh Fields. Encouraging results from these wells led to the wider adoption of ICVs to optimize and manage production from different laterals.
The leveraged knowledge has provided insight into ICVs’ capabilities and how to optimize them. Moreover, this experience set the stage for Saudi Aramco’s Haradh Increment-III crude oil project, developed exclusively using MRC wells equipped with ICVs.1
The concept has not been limited to new wells. ICV utilization has extended to enhance performance of existing weak and dead conventional wells after converting them to MRCs and multilaterals. Additionally, the technology has been extended to target single-lateral new horizontal wells where downhole valves were installed across the horizontal section.
Good results with ICVs have encouraged the incorporation of new downhole technologies such as permanent downhole multiphase flowmeters, which were first field tested in a trilateral well. In this well, every downhole valve was combined with a multiphase flowmeter and permanent downhole pressure and temperature gauges.2 Most recently, ICVs have been tailored to target existing dead wells where slimhole multilateral and single-lateral wells were drilled and equipped with downhole valves across the open hole.
OVERALL FINDINGS
Field performance of wells equipped with ICVs has indicated measurable advantages over conventional completions. These completions have been instrumental in meeting both reservoir and production objectives such as sustaining well productivity, improving sweep, controlling production of multiple laterals, managing water production and minimizing production interruptions.
These advantages were more pronounced in fields that were developed with infrastructures that allow real-time remote monitoring and control capabilities.3
Productivity variation among laterals. Several multilateral wells equipped with downhole valves are located in an area characterized by high productivity variations among different laterals. These variations are influenced by reservoir properties and wellbore and completion characteristics. In the case of homogeneous reservoir environments, field data has indicated that productivity increases with a lateral’s proximity to the heel, Fig. 1. This is due mainly to the pressure drop resulting from friction losses.
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Fig. 1. Productivity variation in a quad-lateral well equipped with four ICVs at similar vertical positions.
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Optimizing the production of these wells requires regulating the settings of downhole valves in accordance with laterals’ productivities and in alignment with the overall production strategy of the well and the area. During optimization, downhole valves and surface choke adjustments are performed to accomplish one or several objectives, which may include minimizing drawdown, maximizing total production, minimizing water production or equalizing production among the laterals.4
It is fair to say that there is no “one size fits all” approach. In any optimization scenario, options are ranked according to the possibility of accomplishing the desired target.
Prolonging well life. Effective utilization of the downhole valves can minimize the negative impact on well life of large productivity variations among laterals.
Well A, a multilateral well, has demonstrated the power of ICVs in prolonging well life and eliminating water production. The multilateral well is located in a heterogeneous area characterized by irregular water movement due to the presence of fractures and high-permeablity layers. Once the well started to produce water, managing production among the laterals became more important. The production of this well was managed and maintained by changing downhole valve positions to eliminate water production that killed the well when the downhole valves were fully open.1
Managing withdrawal and optimizing sweep. Well B, a multilateral well, is located in an area with controlled injection and uniform sweep. The well’s target was set to be 10,000 bpd, in alignment with the production strategy for the reservoir. With these objectives in mind, comprehensive rate tests with several downhole choke setting combinations were conducted.
Test results indicated that the upper lateral (L-2) dominated the flow due to its higher productivity and higher reservoir pressure in the area.
The configuration of the downhole valve settings was adjusted so that all laterals were producing at about the same rate, Fig. 2. Using the surface choke, the total withdrawal of the well was restricted to an oil rate of 10,000 bpd and 0% watercut. Since then, the well has been producing at this rate with no water production.
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Fig. 2. a) In Well B, the upper lateral dominated flow when the downhole valves were fully open. b) Adjusting the valve settings to position 10 (fully open) for the main bore and lower lateral and position 4 for the upper lateral resulted in a much more balanced inflow distribution.
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Maximizing production. Well C is a trilateral well that was producing at an oil rate of 8,600 bpd at very high drawdown with all downhole valves fully open. A comprehensive test was conducted on the well at several downhole choke setting combinations. Results indicated that the upper lateral (L-2) was dominating the flow.
Having assigned a target rate to the well and knowing the reservoir performance around its three laterals, the downhole choke settings were adjusted to maximize the rate while reducing drawdown. Table 1 indicates the valve positions before and after adjustment, where ICV position 10 reflects a fully open ICV and setting 0 represents a closed valve.
| TABLE 1. ICV settings for Well C before and after adjustment |
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The adjustment resulted in an increased oil output of 13,200 bpd and raised the bottomhole flowing pressure to 2,296 psi from a previous value of 1,927 psi, thus meeting the operator’s objectives. In this particular well, the optimization of the downhole valves was done in conjection with additional control by using the surface choke.5
Managing withdrawal in homogeneous reservoirs. The examples above indicate how downhole valves have helped manage production and improve performance in heterogeneous reservoirs. ICVs can also improve performance in homogeneous reservoirs.
Well D is a trilateral well that is located in such a reservoir. The objective was to produce the well at the lowest possible pressure drawdown from all the laterals, and thereby delay both water and gas breakthrough. A production test indicated that every lateral was produced at a rate of about 9,000 bpd at a fully open surface choke setting. The well was put on production at a rate of 10,000 bpd by adjusting the surface choke, allowing the laterals to produce at lower drawdown, Table 2.
| TABLE 2. Well D test rates and flowing wellhead pressure (FWHP) at various ICV and surface choke settings |
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Field data from a number of wells has indicated equivalent flow contribution among different laterals when wells produce mainly dry oil and there are minimal variations in reservoir quality. When water or gas breaks through in any lateral, ICVs become essential in managing withdrawal among different laterals to minimize or eliminate water or gas production.
Minimizing cross-flow among laterals in heterogeneous reservoirs. Due to heterogeneity of some reservoirs and the presence of differential pressure among laterals, the efficient utilization of inflow control valves is required to manage withdrawal.
A production log on Well E, one of the first trilateral MRC wells equipped with sliding sleeve controls, was run in order to determine each lateral’s contribution and the overall well performance as well as to detect any water presence. Logging results have indicated cross-flow among the laterals at different surface choke settings and while the well was shut-in. Even if the cross-flow is expected, it is not acceptable for good reservoir management practices, since cross-flow between a wet lateral and a dry one may damage well productivity due to rock imbibitions of water. In Well E, the cross-flow was eliminated when the well surface choke was set at 102/164, Fig. 3.6
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Fig. 3. In Well E, cross-flow was eliminated by optimizing the surface choke setting.
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Similar observations were made in a trilateral well equipped with downhole valves and a downhole multiphase flowmeter.2 These occurrences of cross-flow can be reduced or eliminated by implementing an active multi-position ICV system or similar technologies.
ICV capabilities. One of the adopted strategies when installing any of these completions is to make sure that all the ICVs are functional while the rig is on location. To date, the overall deployment success rate is close to 100%. Once a completion is set and a well is put on production, it is expected that these completions are function tested at least once every six months. These routine tests can be conducted more easily in fields where surface infrastructure allows testing and optimization by either a permanent or a portable surface control and testing unit.
Field data collected over four years has confirmed that the systems are functional in controlling inflow from laterals; thus, variations of ICV flow characteristics are due to different completion designs and the productivity indices of the producing zones.
Figure 4 illustrates the control capabilities of downhole valves across various operating conditions. Efforts to improve the design of the downhole valves have led to higher levels of control at lower flowrates, thus enabling finer adjustment of the inflow distribution among different laterals or segments and, as a result, better management of wells.7
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Fig. 4. Downhole valve capabilities vary according to reservoir rock and fluid properties.
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POTENTIAL IMPROVEMENTS
A few opportunities for improvement in Saudi Aramco’s utilization of downhole valves were identified.
Cross-flow prevention. The occurrence of cross-flow between laterals or segments is not always preventable by the current ICV designs. When laterals experience differential pressures, they are vulnerable to cross-flow. When a well is shut-in, cross-flow can be prevented either by closing all the ICVs or equipping the completion with a cross-flow preventer that is triggered whenever cross-flow occurs.
ICVs with multiple downhole gauges. Optimizing the performance from the available completions requires rigorous testing for every lateral or segment. Such intensive testing can be eliminated if each ICV is equipped with multiple downhole gauges capable of reading both the upstream and downstream pressures across the valve.
The real-time pressure measurements would facilitate production optimization of each lateral by indicating the optimal ICV position; early identification of cross-flow occurrence; calculation of the total flowrate from each ICV (given a known differential pressure and flow area); and reservoir pressure reading when the valves are closed.
ICV control room. One of the recommendations is to have centralized control over all installed ICVs. The center would require a real-time collaboration environment, expert operators and remote control over all installed ICVs in all fields. The group would benefit by having multiple members keep track of changes and detect errors before they escalate.
This environment could be facilitated by implementing uniform standards for ICVs, their surface control infrastructure and their remote control capabilities.
CONCLUSIONS
Advanced well completions have opened numerous opportunities for improving production and field performance. Early implementations of downhole valves have demonstrated their advantages over conventional completions.
It has been demonstrated that the performance of wells equipped with downhole valves has exceeded that of conventional wells. However, because each completion scheme is designed as fit-for-purpose, it is essential to evaluate available completions’ capabilities in the context of the reservoir properties, the well configuration, the location and the operator’s requirements prior to installation.
Operational experience with MRC and multilateral wells equipped with ICVs continues to mature, fostering an accelerating learning environment that leads to better understanding of the technology’s capabilities and how to optimize those capabilities. 
ACKNOWLEDGMENTS
This article was prepared from the paper SPE 126089 presented at the Society of Petroleum Engineers Intelligent Energy Conference and Exhibition held in Utrecht, the Netherlands, March 23–25, 2010. The authors would like to thank Saudi Aramco for granting permission to publish the article. In addition, the authors extend their appreciation to the Petroelum Engineering Technology Assessment Team members.
LITERATURE CITED
1 Mubarak, S. M, Pham, T. R. and M. Shafiq, “Using down-hole control valves to sustain oil production from the first MRC, multilateral and smart well in Ghawar Field: Case study,” SPE Production & Operations, November 2008, pp. 427–430.
2 Arnaout, I. H. et al., “Optimizing production in maximum reservoir contact wells with intelligent completions and optical downhole monitoring system,” SPE 118033 presented at the Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, Nov. 3–6, 2008.
3 Mubarak, S. M. “Real-time reservoir management from data acquisition through implementation: Closed-loop approach,” SPE 111717 presented at the Society of Petroleum Engineers Intelligent Energy Conference and Exhibition, Amsterdam, Feb. 25–27, 2008.
4 Konopczynski, M. and A. Ajayi, “Design of intelligent well downhole valve for adjustable flow control,” SPE 90664 presented at the SPE Annual Technical Conference and Exhibition, Houston, Sept. 26–29, 2004.
5 Arnaout, I. H., Driweesh, S. M and R. M. Zaharani, “Production engineering experience with the first I-Field implementation in Saudi Aramco at Haradh-III: Transforming vision to reality,” SPE 112216 presented at the 2008 SPE Intelliegent Energy Conference and Exhibition, Amsterdam, Feb. 25–27, 2008
6 Mubarak, S. M, Afaleg, N. I., Pham, T. R., Zeybek M. and A. Soleimani, “Integrating advanced production logging and new wellbore modeling in a MRC well,” SPE 105700 presented at the Middle East Oil & Gas Show and Conference, Bahrain, March 11–14, 2007.
7 Mubarak, S. M., Sunbul, A. H., Hembling, D., Sukkestad. T and S. Jacob, “Improved performance of downhole active inflow control valves through enhanced design: Case study,” SPE 117634 presented at the Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, Nov. 3–6, 2008.
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THE AUTHORS
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Saeed M. Al-Mubarak is a Supervisor in Saudi Aramco’s Southern Area Reservoir Management Department and a specialist in real-time reservoir management and intelligent fields. He has more than 15 years of petroleum industry experience. Mr. Mubarak received a BS degree in chemical engineering and an MS degree in petroleum engineering from King Fahd University of Petroleum and Minerals in Dhahran, Saudi Arabia.
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Naseem J. Al-Dawood is a Supervisor in Saudi Aramco’s Southern Area Reservoir Management Department. He joined the company in 1993 and has worked in various disciplines, including reservoir management, reservoir description, and production and drilling engineering. Mr. Dawood received BS and MS degrees in petroleum engineering in 1990 and 1992, respectively, from the University of Alabama.
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Salam P. Salamy, a Petroleum Engineering Consultant for Saudi Aramco with over 25 years of industry experience, heads the Upstream Professional Development Center responsible for professional development of Saudi Aramco employees. He joined Saudi Aramco in 1996 as an Engineer in the Reservoir Management Department on the Shaybah Field project. Mr. Salamy holds BS (1982) and MS (1985) degrees in petroleum engineering from West Virginia University.
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