An oil and gas discovery has been confirmed at a CNOOC-operated offshore licence in Congo (Brazzaville).
Elephant Testing Program and Results
On August 3, 2013, drilling of the E-1 well reached a total depth of 2,497 metres using the Jasper Explorer Drillship in 550 metres of water 80 kilometres offshore Congo (Brazzaville). The E-1 well was targeting a deeper turbiditic Tertiary play similar to the play being exploited in fields adjacent to the Haute Mer A license area, such as the Total operated Moho Bilondo producing field and the Chevron operated Block 14 in Angola. Primary targets for the E-1 well were the N5 and the N3 reservoir intervals in the Miocene Tertiary.
The E-1 well was drilled approximately 4.5 kilometres south-east of the Libonolo Marine-1 (LIBM-1) well drilled in 1997 by Elf Congo. The LIBM-1 well resulted in a discovery in the N5 interval of the Tertiary Miocene. Excellent reservoir quality was encountered with heavy oil 14° API gravity present. Based on preliminary logging and other data from the E-1 well, 30 metres of gross interval (20.3 metres net) of crude oil and 102 metres of gross interval (58.8 metres net) of natural gas were encountered in the N5 interval and 16 metres of gross interval (9.2 metres net) of crude oil were encountered in the N3 interval. Water was encountered in other secondary targeted intervals. Three cased hole drill stem tests (“DST”) were conducted in the E-1 well including one in the N3 and two in the N5.
The DST conducted in the oil bearing intervals of the N3 successfully flowed at sustained rates over a period of two and a half days using a series of different choke sizes The well flowed naturally at a maximum rate of 1,180 bbl/d of oil for a seven hour period on a 36/64” choke. The oil was measured on site at 24° API gravity with a Gas to Oil Ratio (“GOR”) of 320 scf/stb. No water was encountered and no sand production was reported at surface. The preliminary analyses of the pressure gauges indicated a sand plugging of the temporary screens due to the unconsolidated character of the sand. Higher rates would be expected with a proper completion pack. The pressure build-up analysis also confirmed the excellent porosity and permeability of the reservoirs in the channel complex previously reported.
The DST conducted in the N5 oil leg successfully flowed at sustained rates in intervals over a period of two and a half days using a progressing cavity pump. The maximum average rate achieved was approximately 515 bbl/d of heavy and viscous oil for a four hour period using a progressing cavity pump. No pressure decline was observed during the tests. Determining the API gravity, GOR and viscosity of crude oil from the N5 will require laboratory analysis. No water was encountered and no sand production was reported at surface. Analysis of the pressure gauges revealed that there was no damage or productivity impairment during the
test and confirmed the excellent porosity and permeability of the sand channel complex.
The DST conducted in the gas bearing interval of the N5 successfully flowed at sustained rates over a period of 24 hours on five different choke sizes. The well flowed at a maximum rate of 21 MMscf/d on a 44/64” choke for about five hours. The natural gas that flowed was dry which confirms biodegradation. No pressure decline was observed. No sand production was reported at surface during the production but the pressure build-up analysis indicated some sand plugging that impaired productivity during the test. With a proper completion, rates would have been higher. The pressure build-up analysis also indicated excellent permeability and porosity of the sand channel complex. The data gathered from the well and field tests should be considered preliminary until such time as a pressure transient analysis or well-test interpretation has been carried out. Test
results are not necessarily indicative of long-term performance or of ultimate recovery.
Appraisal Plans for Elephant and Further Exploration in Haute Mer A
Together with the Operator of the license area, Oryx Petroleum will further analyze the test results and other data accumulated during the drilling of the E-1 exploration well and determine next steps.