Saudi Aramco successfully applied a natural gas lift method to sustain production in an intermittent well in Saudi Arabia’s Abqaiq field. The application of WellDynamics’ SmartWell intelligent completion technology used the energy from a gas cap to lift the oil.

Background
Abqaiq was discovered in 1940, with full-scale development beginning in 1946. Abqaiq is

The auto-gas lift SmartWell completion allows the ABBQ-A well to make the best use of the gas cap for production. (Graphic courtesy of WellDynamics)
characterized by a high-relief south dome and a low-relief north dome and produces from two reservoirs: the Jurassic Arab-D (upper) and the Hanaifa (lower), which are separated by the 450-ft (137-m) thick Jubaila formation. While the Arab-D reservoir extends throughout the entire field, the Hanaifa reservoir is located in the south dome region only. Most of the production in this field comes from the Arab-D reservoir, but the Hanaifa contains a significant oil pool that requires a specialized development approach due to poor flow characteristics. In the Jubaila formation, faults and extensive fractures allow pressure and fluid communication between the two reservoirs.

Hanaifa includes micropores and fractures that made development planning a challenge for reservoir engineers, who had to implement horizontal producers to mitigate the reservoir communication and effectively extract reserves. In addition, the permeability of the Hanaifa reservoir is low, and well productivity is controlled by wellbore fracturing.

Production of Hanaifa began in 1954, and further development and production increased in 1975 with the implementation of gravity water injection.

Natural gas lift as an option
In determining the best solution for sustaining production in the Hanaifa reservoir, Saudi Aramco evaluated performance for both gas and oil zones.

Ultimately the company selected natural gas lift (or “auto gas lift”), a process that relies on a natural source of lift gas from either the gas cap of the producing oil zone or a separate gas formation above or below the producing oil reservoir. Gas cap energy is essentially free energy. In this process, lift gas from the downhole source is commingled with the oil production in the tubing to reduce the density of the produced fluids, thereby reducing the hydrostatic head in the production conduit and increasing the inflow from the oil zone.

The ability to monitor and control the rate at which the lift gas is added is a key requirement to the success of natural gas lift applications. Intelligent completion technology provides the ability to monitor the downhole pressure, temperature and flow rates to allow the operator to optimize oil production throughout the life of the well as gas zone and oil zone pressures decline and as water production increases.

Certain well conditions must exist to justify the application of natural gas lift:
• The pressure of the gas reservoir must exceed the hydrostatic pressure of the fluid column in the production tubing (to the depth of gas entry) plus the line-pack under fixed conditions in order to “kick off” the well;
• The gas reservoir must produce sufficient gas for effective lift at moderate drawdown pressures; and
• The volume of gas reserves from the gas source must be large enough to maintain sufficient pressure and productivity under a variety of conditions as the oil zone is depleted and water cut increases.

Selecting the candidate well
The primary goal of the project was to lift the Hanaifa using the gas cap from the Arab-D reservoir. The ABQQ-A well was selected because of its location in the middle of the south dome, where the gas cap sits over the Arab-D. The well was drilled through the Arab-D gas cap and completed as a highly deviated openhole producer.

The well must be shut-in when the flowing bottom hole pressure approaches the bubble point pressure, making the well an intermittent producer.

Completion design
The intelligent completion that supported natural gas lift in the ABQQ-A well was designed to allow the entry of gas from the Arab-D gas cap into the production tubing to lift the oil from the intermittent well. A hydraulically actuated remotely operated downhole flow control valve controls the gas. The interval control valve (ICV) allows choking or shutting different zones based on well performance scenarios such as drawdown, gas-oil ratio (GOR), and water cut.
The ICV was complemented by an Accu-Pulse module, which allowed the ICV to be opened incrementally using a pre-determined amount of control fluid from the ICV piston. The module is able to recharge and exhaust the same amount of control fluid repeatedly, allowing the ICV flow trim to be accurately moved through all positions. The module can communicate with either side of the ICV piston, driving the ICV either open or closed. In this application, the control system was placed in the open side, allowing the valve to be cycled in incremental positions toward fully open. Control lines hydraulically actuate the downhole ICV from the surface.

The gas trim choke design was carefully considered to optimize the natural gas lift and also for the various reservoir uncertainties that are typical to this application, such as:
• Gas and oil zone productivity indices;
• Gas and oil zone reservoir pressures (including future depletion); and
• Gas and oil zone fluid compositions (including water cut and natural GOR).

The choke trim was designed to allow the entire system to absorb the large pressure drop that occurs as a function of flow rate. This design also permitted a “soft start” of the lift gas entry, avoiding possible slugging and inlet separator destabilization, and easing lift gas optimization for variable well flow conditions.

Two hydraulically set retrievable packers were installed to isolate the perforated interval of the Arab-D gas cap from the Hanaifa reservoir. A permanent monitoring system, including a venturi flow meter and downhole gauges, was also installed as part of the completion.

System deployment
The well was worked over in 2004 to install the intelligent completion that was designed and equipped for natural gas lift. A 40-ft (12-m) section of the gas cap was perforated to allow conversion to the new completion.

Two packers straddled the gas cap, and the downhole ICV was placed in the gas cap to control the rate of gas flowing into the production tubing. Upon deployment the ICV was successfully cycled several times through each position. The surface hydraulic control system was installed and commissioned, and more function tests were performed with the ICV. The system operated as designed.

After well tie-in was completed, the well could not flow. The ICV was opened to position five to help unload the well and bring it back to production. Initial production was at 3,700 b/d of fluids with a 36% water cut. Long-term production rates averaged 1,700 b/d of fluids with 35% water cut, and the rate was optimized after testing various ICV positions. Flowing bottomhole pressure (FBHP) was monitored to verify that the well was flowing above the bubble point pressure.

The intelligent completion continues to operate and has successfully enabled the well to sustain production at higher water cut than before installation.