Abstract
Alengka Field has been producing for more than thirty years. Like the vast majority of oil and gas field in the world, Alengka field production is on decline. Alengka Field pay reservoirs consist of more than fifteen zones which are separated in three structures. Latest infill and workover activities reveal that the major productive zones are showing watered-out and depleted reservoir pressure. The last remaining potential reservoir is a low resistivity pay zone which not fully developed yet, called as Rama and Shinta zones.
These low resistivity pay reservoirs are member of Main Formation which deposited in shallow marine depositional environment. It is characterized by 30-60 feet of pay thickness, with resistivity ranging from 1.4 ohmm up to 2.2 ohmm, with shale background resistivity up to 1.2 ohmm. It has an effective porosity up to 22% and permeability up to 10 md. The hydrocarbon existence is emphasized by the ratio of total gas reading to the background gas which more than 10 times; with peak gas up to 830 unit and poor to fair oil shows.
It is a huge contest for the offshore company to seek mature field redevelopment strategy with aging facilities to extend the economic producing life by using cost-effective and low-risk technologies. Commingle Rama and Shinta zones have demonstrated to be productive reservoirs by hydraulic fracturing. Each well can contribute 300 up to 700 BOPD of initial rate by utilizing gas lift and add 0.5 up to 0.7 MMBO of reserves. Naturally, hydraulic fracturing reservoir has rapid decline in the beginning production period which will be followed by plateau decline. The optimum fracturing parameter and gas lift performance which is combined with low angle trajectory well is identified as the essential key to improve production rate and to add maximum reserves.
Low resistivity pay zones has become the new reservoir backbone for redevelopment of Alengka field with total of 14 wells that will be drilled and 4 workover wells from 5 existing platforms that will be executed within next 3 years to add more than 7 MMBO of reserves. It will sustain Alengka field production rate more than 4000 BOPD. The recent activities consist of one infill drilling and one workover has excellent result with more than 800 BOPD in total. The successful of this campaign could open the opportunity to develop field further to the eastern part of the Alengka Field by adding new platforms and wells with total potential reserves is more than 10 MMBO. The paper will discuss about the low resistivity pay zone, production approach, recent drilling-workover results, redevelopment strategy in mature field and its challenges.
