Discovery opens gas play in East China Sea

Primeline Energy Holdings has completed a drillstem test program for its LS 35-3-1 discovery in East China Sea block 25/34.

Offshore staff

LONDON -- Primeline Energy Holdings has completed a drillstem test program for its LS 35-3-1 discovery in East China Sea block 25/34.

The find opens a new exploration play in the area, the company says, and could impact development of the LS 36-1 gas field, where Primeline is in partnership with CNOOC.

Electric logging at the level of the third target zone indicated over 20 m (65.6 ft) of cumulative hydrocarbon pay in two zones. These zones were further investigated by a reservoir characterization instrument. Sidewall coring and other analysis indicated the presence of hydrocarbons in low permeability sandstones.

Primeline started its DST program in mid-May to test these zones under a turnkey arrangement with contractor China Oilfield Services. The first of two DSTs was conducted over the range 2,836-2,852 m (9,304-9,357 ft) MD, with no resultant flow of hydrocarbons to surface.

DST2 was conducted over the range 2,794-2,802 m (9,166-9,193 ft) MD. For this test, nitrogen was introduced through the wellbore to optimize pressure drawdown – as a result, gas flowed naturally to the surface and was flared continuously for over seven hours.

This flow did not attain sufficient pressure to operate the separator or the flow meters. However, gas samples were collected at the wellhead and fluid samples were taken from the wellbore which will be analyzed in a laboratory.

Testing ended on May 29, and the COSL rig will be released shortly after completion of current operations.

Primeline says the discovery confirms that hydrocarbons have migrated to and are trapped in the channel systems in the west flank of the West Lishui basin, the majority being inside block 25/34.

The find also represents the first surface flow of natural gas from a low permeability reservoir in the southern East China Sea. This has significance not just for further exploration in the block, but also as a potential tieback to the new production facility at LS 36-1, 14.5 km (9 mi) distant.

The LS 36-1 gas field has over 200 m (656 ft) of gas-bearing, low-permeability reservoirs directly beneath the gas zone under development. After factoring in the new data from LS 35-3-1, Primeline will assess the potential for advanced fracing and horizontal and multi-lateral drilling to induce commercial production rates from the low permeability reservoirs.


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