Brunei: Noncommercial gas flows at onshore prospect

Serinus Energy Inc., Calgary, is moving the drilling rig to its Luba well location on onshore Brunei Block L after the Lukut Updip-1 well flowed at noncommercial rates estimated at less than 50 Mcfd from a secondary objective after failing to reach its primary target.

Lukut Updip-1 flowed gas continuously from two separate intervals that have not previously been penetrated by any wells onshore Brunei. The discovery of hydrocarbons in these zones indicates that further analysis and appraisal will be required to evaluate the resource potential of this play, the company said.

The LKU-1 well encountered a drilling break and an influx of gas with a total gas reading of 47% while drilling 6-in. hole starting at 2,131 m measured depth, 1,773 m true vertical depth subsea, and continuing to 2,137 m MD, the last 3 m of which is interpreted to be clean sand.

C1 gas readings peaked at 332,000 ppm, and C5 gas readings peaked at 628 ppm at TD. Pressures rose significantly, and there was material gas influx with total gas readings increasing to 47%, which resulted in gas being flared at surface for several hours. The mud weight was subsequently increased to 17.7 ppg to control the calculated formation pressure of 5,366 psi.

Due to far higher than expected formation pressures and equipment limitations, the company determined that it could no longer safely continue to drill and set a cement plug from 2,120 m to TD 2,137 m MD and set casing to 2,120 m. The initial planned depth was 2,959 m MD, 2,410 m TVD.

The first zone to be tested was 2,131-37 m, the bottom 6 m of the well. Gas flowed continuously at a low rate during the test. The formation is believed to have been damaged by heavy drilling fluid, mud system additives, and cement during drilling as the drilling team worked to control the high pressures encountered. Attempts to clean up the perforated interval by utilizing an acid treatment were not successful.

During drilling a general trend of increasing silt and-or sand content was observed from a depth of 1,890 m and continuing to 2,137 m. The sandy-silty shale encountered over this section appears to be hydrocarbon-charged, with C1 to C5 total gas readings increasing from a 10-m average of 0.49% at 1,700 m MD to a 10-m average of 8.1% at 2,110 m MD.

C1 gas readings steadily increased from a 10-m average of 3,150 ppm at 1,700 m MD to a 10-m average of 58,000 ppm at 2,110 m MD. Based upon the increased pressures and associated hydrocarbon shows, the thick silty shale zone was selected as the second zone to be tested.

A total of 60 m was selectively perforated at 1,980-2,120 m. Gas was flared at surface throughout the test, but the well did not produce at commercial rates. The entire section tested in the second test, which was open during the well control efforts, is believed to have also been damaged by drilling fluid and mud additives.

The section of the LKU-1 well below 1,100 m MD has not previously been penetrated by any well onshore Brunei. The drilling break at 2,131 m MD is interpreted to correspond to the top of a zone defined by seismic, dubbed the Green Zone, that was a secondary target of the well. The deeper primary target of the well, dubbed the Red Zone, which the company expected to encounter at 2,402 m MD, was not penetrated.

The Green Zone, the transition zone above the Green Zone (Test 2), and the Red Zone are all interpreted to be facies associated with turbiditic sandstone deposition that is likely to extend over a large area. The company believes that the tested formations may be capable of producing at commercial rates and that further analysis, evaluation, and appraisal will be required to fully assess the prospectivity and productivity of this new play.

While the well did not reach the primary target and the secondary targets appear to have been damaged, the presence of sandstone reservoirs within an interpreted deepwater-shale package suggests that the geological model of turbiditic sandstone deposition is correct, Serinus Energy said. In addition to the presence of reservoir sands, LKU-1 also demonstrated both pressure and the presence of hydrocarbons, suggesting that the elements required for a successful pool may be present within this prospect.

Serinus Energy said it will review the test results to determine if the zones tested might respond well to hydraulic fracture stimulation. In the meantime, it is suspending the initial Lukut Updip well pending further evaluation.

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