Intelligent Well Technology

Hydraulic, multi-drop control redefines IC economics

When less is more – in both low-capex and high-capex situations, operators are using hydraulic, multi-dropped, intelligent completion systems to maximize output while reducing short-term and long-term production costs

Donald Ross, Schlumberger, Houston

In an area of advancing technical complexity, an intelligent completion (IC) system that simplifies control issues and reduces cost can help an otherwise high-capital investment solution migrate into low-capex environments, such as brownfields. The most recent innovation for ICs – a hydraulic, multi-dropped, intelligent completion system – has inspired marginal field development operators to deploy ICs to maximize production, and reduce initial and overall life cycle costs for wells.

This new offering is unique, in that it allows multiple-flow control valves to be independently operated from a single, hydraulic control line. When integrated with reliable measurement devices, it provides more reliability with less complexity for reservoir and production management. Additionally, technology is under development that will integrate safety valves into the same single-line, multi-dropped, hydraulic control system.

INTELLIGENT WELLS – HIGH ON THE VALUE CHAIN

An obvious challenge is how to make intelligent well costs acceptable, as well as useful, to the operator's benefit. This applies to both low-capex operating environments, like brownfields, and to high-capex operating environments, as commonly seen in the offshore (particularly subsea) sector.

In low-capex operating environments, the evolution of advanced completions is all about economics. Through Schlumberger's Eclipse near-wellbore modeling and nodal designs, a customized IC is designed to maximize reservoir and production efficiency, ultimately offering maximum recovery and sweep. The multi-drop system innovation illustrates this point. It takes into account existing infrastructure not easily modified without large capital investment, and long lead times to meet complex well architectures for IC deployments. In dual completions, the IC completely removes dual-string selectors from the capital investment/ efficiency equation with respect to artificial lift designs.

Difficulties in optimizing dual completions with gas lift are well known. Without deferring production in one of the strings to optimize the other string, minimal solutions exist. Deferring production defeats the purpose of dual producers. Deploying IC in this environment allows for optimized gas lift design, zone by zone, while maintaining control of each zone to ensure against cross-flow. Designed with integral sensors, the multi-drop system offers an ability to optimize gas lift design, as well as inflow performance from multiple zones.

The multi-drop system can also be applied in water injection (WI), dump flood, or water-alternating-gas (WAG) wells. Use of the multi-drop system turns these wells into intelligent injectors, as variable flow control now permits management of mass balance between reservoirs.

OPENING UP NEW MARKETS

Intelligent flow control brings benefits to developments once thought to not be cost-efficient. Intelligent flow control represents a key component in these wells, as innovative and integral system sensors provide hard data on which to base performance metrics. The ability to manipulate subsurface control devices has become a critical enabler of active reservoir management in every type of field.

In the short term, ICs result in a decreased variance of the production profile. Over the long term, they aid in recovery of lost reserves, shorten time needed to produce reserves, and facilitate the selective production requirements between penetrated zones.

In brownfields, various levels of IC systems are utilized to access multiple zones simultaneously. These fields can now benefit from reduced surface facilities, accelerated production, decreased operating and well expense, and increased, ultimate recovery. High-tech wells, such as multilateral completions, are also benefiting from this technology. For instance, sidetrack re-entry into existing wells is accessing reserves that at one time were not considered economic, due to differential pressures, cross-flow issues and varying permeability challenges through different pay zones. ICs remove this complexity and deliver an optimal solution to efficiently producing three or more laterals through one completion string with the use of downhole flow control valves.

IC systems for offshore fields, such as those in the North Sea, require automatic surface interaction, continuous monitoring, automatic flow control and extensive downhole communication, Fig. 1. The viable recovery of an estimated 4.0 billion bbl of compartmentalized oil and 12.0 Tcf of compartmentalized gas reserves in the UK relies on modern architecture control systems with low operating costs and minimum intervention. In these compartmentalized fields, where water production is of concern, the use of ICs for dynamic, downhole flow control has a direct impact and immediate benefit to operators.

Fig. 1. RTAC – real-time acquisition and control system for multi-drop valves.

On the middle scale, semi-intelligent wells require manual surface interaction and limited downhole communication. Whatever the environment in which IC controls are employed, the ability of operators to learn more about the reservoir, and take appropriate action sooner, facilitates faster decisions to enhance output and lower operating expenditure.

RADICAL ADVANCEMENT WITHOUT RADICAL CHANGE

Operating on a single hydraulic pressure to control the multi-dropped valves, IC system architecture is simplified and requires deployment of only one hydraulic control line while utilizing familiar running procedures (as seen with downhole safety valves). A surface hydraulic control system (SHCS) ensures that remote monitoring and supervisory system control is maintained without the need for platform access to intervene in the process system. Through a simple interface, the user can actuate any necessary changes. The SHCS tracks all valves in the multi-drop well design.

Currently, the multi-dropped IC system comprises downhole sensors and temperature measurement devices, most notably fiber-optic, distributed temperature systems (DTSs). Because fiber optics present distributed data, these systems can give precise identification of when and where production events occur, making real-time diagnosis and control possible.

Having multi-dropped flow control valves deployed in the well with a DTS gives true visibility to contribution. When three or more zones are commingled for production, the behavior of commingled versus selective will show a marked difference. Having a DTS deployed will offer true performance feedback for allocation and production management.

In platform applications, the fiber optic system can be pumped down the control line and set in the completion from the surface. In this application, the fiber is installed with the downhole production tubing or subsea flowline. DTS measurements along the intelligent, multiplexed completion evaluate inflow performance, which zone is producing, and by what quantity.

Fiber optic technology is also being integrated increasingly with sand control completions. By monitoring the inflow performance within the sand face completion, job design can be evaluated effectively against well performance.

Additionally, hurdles presented by mechanical interfaces with wellhead and hanger arrangements are eliminated, as the multiplexed completion requires only one penetration. This is ideal for existing brownfield applications, where the worked-over wellhead and tubing hangers do not require additional penetrations to equip the well with IC flow control valves.

FOREVER LINKED TO RELIABILITY

Given that the window of opportunity is short for making needed adjustments in real time, reliability is forever linked to IC control functions. Maintaining a simple, on-demand functionality through the hydraulic multi-drop system offers the operator reliable transparency to downhole, multi-zone production behavior. Because there are few opportunities for intervention to determine the source of a malfunction, the technology must work optimally at all times and deliver dependable service for decades.

Multi-drop system design minimizes splices and connections previously needed to run multiple, hydraulic control lines to three or more valves. A new generation of welded connection technology removes failure mechanisms associated with feed-through connectors, and allows more sensors and control products to be placed in the production zone.

The need for reliability of permanent downhole measurement and control systems for the life of a well is recognized. The industry standard for permanent quartz gauge qualification with the PQG sensor was set at five years and 150°C. The hydraulic, single-line, three-zone, multi-dropped flow control valve system, combined with the latest generation of proven quartz sensors, sets a new benchmark. It raises the qualification bar to meet harsh production zone demands. Having ICs installed in these harsh environment wells forces the need for sensors to be deployed below the production packer.

The NPQG proven quartz sensor has been developed with a mission profile four times greater than the previous generation of quartz sensor, which has an operational track record of 10 years at 150°C in a producing well since being introduced. A new proprietary, welded-cable NPQG design for harsh producing environments bolsters an industry drive to ensure reliable, permanent zonal measurement and control.

Representing a step-change in intelligent well control technology, the new multi-drop capability for hydraulic, downhole flow control valves supports the industry's overall objectives. These include improving reservoir recovery, and removing complexity and operating capital for future interventions. They also include delivering a simplified, optimal completion philosophy for complex, compartmentalized reservoirs, and effective monitoring and control for production management. All of this is done with reduced risk and capital investment.