Maurel & Prom IDs Areas of Interest at Mafia Deep Prospect
Drilling of the Mafia Deep prospect, located on the Bigwa Rufiji Mafia exploration license in Tanzania, began August 4, 2008. The initial target depth was 4,600 m. While drilling was underway, interpretation of well data led to the reinterpretation of the seismic data and the target was changed to approximately 5,600 m depth. The gas targets represented 5 TCF or 830 MBOE at 100%, or 436 MBOE as Maurel & Prom share net of royalties.
Technical and Drilling Conditions
A depth of 3,050 m was reached on November 22, 2008. The Group then drilled a series of sidetracks to reach a final depth of 5,632 m on August 30, 2009.
During drilling, the depth of the wellbore forced the teams to very frequently cope with temperatures that are exceptional for the oil industry (over 255 degrees C or 500 degrees F) and pressures of 10,000 psi, imposing long delays for each operation. Drilling and testing equipment could not operate in a normal manner in these conditions, and the Maurel & Prom teams were challenged to create the necessary innovative techniques to complete the drilling successfully, while respecting safety standards.
Areas of Interest and Tests
Three areas of interest were highlighted during drilling:
- The deep zone (from 5,519 m) was first reached on May 5, 2009. Drilling conditions made well control difficult. Thus, a number of plugging agents were injected to creating an impenetrable barrier, fracturing and acidizing being ineffective at such temperatures. It was therefore impossible to test this zone and its potential remains intact and unknown.
- The logs of the intermediate zone confirmed the existence of a gas column 600 m thick in a fractured formation, and the existence of a column with a total thickness of 110 m in low porosity sandstone reservoirs. As this gas appeared through a fault system, that was not the objective, it was always sealed with large quantities of suitable products and barytes during the drilling phase. That is why perforations produced insignificant quantities of gas -- less than 1 MCFPD.
Nevertheless, by adding up the volumes at the various impregnated heights, the recoverable gas for this zone could be quantified at about 4 TCF. To confirm the quality of these resources, the Group is going to instruct an independent expert to assess the quantities of recoverable gas under satisfactory economic conditions.
- Tests carried out in the upper zone showed a good-quality reservoir, with low flow potential (100 to 160 boepd of filtrate) due to the formation being penetrated during drilling. This low flow rate, coupled with the time that would be needed to install a pump, led to the decision to demobilise the Caroil 14 rig and test this zone using a crane. Given the losses noted, the quantity of filtrate entering and permeating the formation has not been very precisely determined, and it may take several weeks to determine the nature of the fluid in this formation (water or hydrocarbons). At this stage, the Group has not yet evaluated the extent of the possible reservoir.
The presence of oil would allow for rapid cash flow generation.
The Mafia Deep well is today considered to be a stratigraphic well drilled in a new basin that could be transformed into a commercial well (oil or gas).
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