2003 ASME/API GAS-LIFT WORKSHOP Kuala Lumpur, Malaysia Dual Gas Lift – EMEPMI Experience By Sies Hussain ExxonMobil Exploration and Production Malaysia Inc.
BLOCK H BLOCK SB302 SKC SKA SKD PM5 THAILAND PM8 KUALA TERENGGANU SKB SABAH 125 miles PM9 & 1995 PSCs BRUNEI Kerteh 160 miles KUALA LUMPUR Kemaman Supply Base KUANTAN Straits of Malacca Port Dickson SOUTH CHINA SEA SARAWAK SINGAPORE KALIMANTAN (INDONESIA) EMEPMI UPSTREAM OPERATIONS • Largest Crude Producer In Malaysia • Contribute 47% of Total Malaysia's Production • Gas-Lift contributes about 30% of total EPMI oil production • Growing Gas Business • Supply 70% of Peninsular Malaysia's Gas Requirement
Gas lift supply Definition: Dual gas lift term should only be used when an attempt is made to gas-lift both sides of a dual completion and gas lift is supplied through same tubing-casing annulus. • Do not include: • If one side is flowing naturally and do not equipped with gas lift valves. • If one side is not liquid producer (eg: water injector, gas injector, gas producer). • If one side uses macaroni string for gas lifting.
Why dual wells? The primary reasons are: • Limited surface space in offshore platforms. • Lower drilling cost. (1 dual well is cheaper than 2 single well). • Able to produce two reservoirs from one wellbore. • Commingling of two reservoirs are not permissible for reservoir management reasons. • Most Horizontal / multilateral wells which produce exceeding the single tubing capacity.
Dual Gas lift experience: • Started drilling and completing dual wells in Tapis field in late 70’s. • In mids 80’s, first row wells(relative to water flood scheme 3:1 line drive) of Tapis field started producing water and requiring gas lift to produce remaining reserve. • Initially used orifice valves in either first or second mandrel, depending the gas lift pressure. Gas lift volume for each string was controlled by the port size of the valves. • Increasing water production and declining reservoir pressure, there was need to gas lift wells at lower most mandrel. • New techniques using either injection pressure operated(IPO) or production pressure operated (PPO) or combination of both were tried. Other types valves such as proportional response valves were also being tried. • Extensive flowing pressure gradient surveys done in early 90’s to establish the right vertical flow correlation.
Dual Gas lift experience: • Number of active dual gas lift wells peaked at 50 – 60 in mid 90’s and has currently declined to 20 –25. • The producing zones are between 0 to 1000 meters apart in terms of vertical difference. Reservoir drive mechanism can be either similar or very large difference. Example: Large gas cap expansion and water flooded reservoir. • Multiple packers ( as high as 5) have been used to separate the production from stacked reservoir. Some reservoirs were commingled into one string. • Successful in dual gas lift if the producing zones are about similar in reservoir characteristics. The gas lift efficiency can be as high as 80 – 85 % in this case. Experienced difficulties in wells with one producing zone is only about 10 –15 % of the other zones.
Gas Lift Design Practices • Used Production Pressure Operated Valves (PPO) as unloading valves and Injection Pressure Operated (IPO) as operating. • Some variation in the above design is required if one of string uses gas lift for kick-off purposes. This string uses IPO valves with the opening pressure slightly higher than the operating valve of the opposite string. This is to ensure the valves are always close under normal production. Unloading Valves Operating Valves
Surveillance and Optimization Practices: • Unloading on high producing side of the dual first. Then, continue to unload the next string. • Run flowing pressure gradient if unable to keep either string on-line. • The monthly production test taken on each string on the same day or within 1 –2 days. • Perform 4-point production test on both strings, if the total production rate within test separator capacity. • Uses GLMS (Gas lift metering/monitoring system), real-time Casing Pressure , Tubing Pressure and gas lift rate data to monitor the well performance or diagnose the well problem.
SUMMARY • Have proven the dual gas lift work in our operation. Though efficiency can be further improved. • Need to establish good vertical flow correlations to design dual gas lift. • Experienced difficulties in wells with one zone producing only about 10 –15 % of the other zone. • Range of port sizes of the valve available are limited to exactly control gas lift volume for each string.