The block Telaga Said-Darat, located in southwestern of North Sumatra Basin, is the oldest oilfield in Indonesia, with total area of 82 km2. It was firstly discovered in 1883, with the development history of fifty years. Oil and gas exploration and development mainly depends on surface geological surveys. In the absence of any modern seismic exploration and logging techniques, oil and gas structural traps were found in the field and produced with outmoded drilling and oil extraction technology. The cumulative oil production of blocks Telaga Said and Darat reached 2335 million barrels before abandonment as the outbreak of war in 1937.Alpha Until 1960s and 1990s, the Indonesian National Oil Company (hereinafter referred to as Pertamina) and Mobil Oil Company jointly drilled two deep exploration wells; from year 1977 to 1995, Pertamina has carried out 2D seismic exploration and research , drilled four deep exploration wells, through which they basically figured out sedimentary characteristics and stratigraphic features of the field, found out Baong formation and its underlying strata with favorable reservoirs, during which period no systemetic re-exporation and development was conducted. During 2002-2012, contractor made secondary development of Telaga Said Darat oilfield. 13 development wells were drilled, among which 9 were put into production as oil well, with a total oil production of nearly 40 thousand barrels, and re exploited 12 old wells abandoned in 1937 with 18 thousand barrels of crude oil production. There were totally over 58 thousand barrels of crude oil produced from newly drilled development wells and recovery wells. 130 years of oil and gas discoveries, more than 50 years of early development, over 60 years of intermittent exploration, and 10 years of secondary recovery, all show that people have great expectation of new breakthroughs and new discoveries in this field.
1. Study Basis
All the information and data obtained during the process of the field exploration and development in last 130 years are the only basis to know this field and study it by modern technology, and what’s more, it is the origin of confidence on re-understanding, re-evaluation and re-determination of secondary development on the field. In the early period of Oil blocks selection and evaluation, three aspects of this field have been noticed as follows: （1）Before being abandoned in 1937, relying on simple basic information as surface geological survey and hydrocarbon leakage, BPM companies conducted 50 years of drilling and production work, drilling 176 wells in Telaga Said oilfield, among which146 are oil wells, accounting for 83%; 247 wells were dilled in Darat oilfield, and 161 were oil wells, accounting for 65%. From amount and success rate of BPM drilling wells, it can be seen that the drilling success rate was very high, indicating that the oil and gas reservoir-cap system is completely preserved. （2）Pertamina and Mobil drilled two exploration deep wells, Telaga A1 and Telaga B1 in 1970, and in 1977,1978,1980,1995, four exploration wells, TST-1, DUR-1, TSL-1 and PTHI-8 were drilled by Pertamina. According to 2D seismic data from 1973,1974,1975,1978, there are only a small number of seismic lines, large quantities of 2D digital seismic were intensively collected in year 1985 and 1990, which means that only PTHI-8 well is the exploration well drilled after mass of 2D digital seismic; from analysis of seismic collection and drilling time, it is thought that only PTHI-8 wells used the 2D digital seismic data, which was one of only two oil wells during this period (another well is Telaga B1). （3）During 2006-2009, 13 development wells were drilled in TSD, among which 9 were put into production as oil wells, with drilling success ratio of about 70%, while in the output of about 4 million barrels of crude oil, well ED-181A was flowing in production and the yield accounted for 50% , indicating...
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