Petrophysical Analysis of the Mpera Well in the Exploration Block 7, Offshore Tanzania: Implication on Hydrocarbon Reservoir Rock Potential

The present study provides evaluation and estimation of petrophysical parameters and assessment of lithology and their thicknesses in order to characterize present reservoir rocks at Mpera well located in Exploration Block 7, deep offshore Tanzania. To achieve the objectives the wire-line logs, Techlog program was used for assessment, analysis, computation and interpretations of petrophysical parameters and results were integrated through interpretation of well logs. The results from wire-line logs reveal three (3) non hydrocarbon-bearing reservoir rocks i.e., Mpera splay (sandstone), Mpera deep sand 1 (sandstone and limestone) and Mpera deep sand 2 (sandstone and limestone) with gross thickness of 94.335 m, 28.905 m and 12.967 m respectively. The average permeability values of the reservoir rocks were 9.47 mD, 6.45 mD and 4.67 mD, while average porosity values were 14.57%, 17.4% and 16.75%, with average volume of shale 25.7%, 23.5% and 9.7% at Mpera splay, Mpera deep sand 1 and Mpera deep sand 2 respectively. These results signify poor permeability;good porosity and good quality reservoir in terms of volume of shale. Fluid type defined in the reservoirs was basically water. High water saturation (90.6% - 97.7%) in the reservoir zones of the Mpera well indicates that the proportion of void spaces occupied by water is high, thus, indicating less than 10% hydrocarbon saturation. The findings indicate that Mpera well reservoir rocks are of low quality with non-hydrocarbon bearing such that it is not potential for hydrocarbon production.

Petrophysical Analysis of the Mpapai Well Logs in the East Pande Exploration Block, Southern Coast of Tanzania: Geological Implication on the Hydrocarbon Potential

This study presents results of log analysis from Mpapai well, which is located in the East Pande Block, southern coast of Tanzania. The study aimed at assessing the hydrocarbon potential of lithological units encountered during drilling of Mpapai well. To achieve the general objective, suites of wire-line logs from Mpapai well were used for the analysis. Based on wire-line logs, three types of lithology were identified which include sandstone, shale and limestone. Seven sandstone bodies marked as MpapaiA, B, C, D, E, F and G were identified with their tops and bases at the depth interval from 3004 m to 4008 m. Four zones among seven sandstones bodies marked as MpapaiB, E, F and MpapaiG were identified as reservoir zones. Computed petrophysical parameters for the four reservoir zones gave an average total porosity ranging from 14% to 21% with low permeability in the range of 3.92 mD to 13.67 mD. The low permeability indicates that the reservoir sand bodies are impermeable, that might have been affected by the geology of the area where high content of clay minerals reduces permeability due to filling in open spaces. The fluid type defined in the reservoir zones is basically water with high saturation greater than 75%, which indicates that the proportion of void space occupied by water is high, consequently low hydrocarbon saturation and production. Despite of fair to good porosity, the low permeability and high-water saturation indicate that the quality of Mpapai prospect is poor.

Tectono-Sedimentary Evolution of the Offshore Hydrocarbon Exploration Block 5, East Africa: Implication for Hydrocarbon Generation and Migration

Sedimentary deposits in Block 5, offshore Tanzania basin have been imaged using two-dimensional (2D) seismic data. The seismic data and well data reveal four tectonic units representing different tectonic events in relation to structural styles, sedimentation and hydrocarbon potential evolved in Block 5. Results show that during Early to Late Jurassic, Block 5 was affected by the break-up of Gondwana and the drifting of Madagascar as evidenced by patterns of sediments and structural features. The chaotic and discontinuous reflectors are characteristics features on the sediments pattern indicating a possible transitional setting following the breakup of Gondwana. From the Late Cretaceous, Block 5 sits in more stable subsiding sag as the consequence of the high thermal subsidence. The period displayed continuous parallel reflectors with few markable faults. This was followed by the late post rift sedimentation that occurred after Middle Eocene Unconformity characterized by high wavy and sub parallel reflectors. The evolution of Block 5 through major tectonic events reveals a more complete petroleum system towards the south. Thus, Block 5 responded in both space and time to a complex interplay between tectonics and sedimentation. This indicates that structural styles and associated features are potential control for hydrocarbon generation and migration.

Delineation of Shallow Stratigraphy and Aquifer Formation at Kahe Basin, Tanzania: Implication for Potential Aquiferous Formation

Electrical resistivity method was conducted at Kahe-Mtakuja basin aimed at appraising the potential of the basin as a source of groundwater by establishing shallow stratigraphy and delineating aquifer formations. A total of fifty-eight vertical electrical sounding data (VES) were acquired using Schlumberger array and the data were analyzed to obtain apparent resistivity and layer depth. The interpretation of resistivity data revealed three main geoelectric layers. The first layer has resistivity values ranging from 40 to 230 Ωm with thickness ranging from 0.4 to 2 m. The second layer has resistivity values in the range of 2 to 10 Ωm and thickness of 2 to 25 m. The third layer has slightly high resistivity values ranging from 10 to 60 Ωm and thickness in the range of 30 to 70 m. This layer is mainly dominated with sand. The resistivity cross-sections constructed from the interpretation of VES data indicate that the Kahe-Mtakuja basin has shallow stratigraphy consisting of 3 layers. The layers are composed mainly of top red soil, clay (sometime alternating with sand) and sand formation holding the groundwater. These findings are consistent with lithological logs of the borehole drilled near Kahe-Mtakuja that indicate two to five layers composed of alluvial deposits alternating with different lithological thicknesses. The high correlation between the VES results and borehole lithological logs near Kahe-Mtakuja suggests that the area is potential for aquiferous formation. Based on constructed stratigraphy, the aquifer formation of the basin is found in alluvial deposits composed of mainly sand. The potentiality of this area for aquiferous formation is vital for providing additional baseline data on the aquifer characteristics and will assist in reducing water scarce in the area.

Petrophysical Analysis of Reservoirs Rocks at Mchungwa Well in Block 7 Offshore, Tanzania: Geological Implication on the Reservoir Quality

The present work highlights the results of the study conducted to estimate the petrophyiscal properties of the Mchungwa well with the aim of assessing the quality of reservoirs rocks. A set of well logs data from Mchungwa well were used for the analysis that involved identification of lithology, hydrocarbon and non-hydrocarbon zones and determinations of petrophysical parameters such as shale volume, porosity, permeability, fluid saturation and net pay thickness. This study was able to mark six sandstone zones with their tops and bases. Of the six zones hydrocarbon indication was observed on four zones from which estimation of petrophysical parameters was done to assess the reservoirs quality. The petrophysical parameters across the four reservoirs yield an average shale volume ranging from 0.08 to 0.15 v/v. The porosity ranges from 7% to 23%, indicating a fair to good porosity sandstone, while permeability ranges from 0.01 to 6 mD. The porosity and permeability results suggest that the quality of the sandstone reservoirs identified at Mchungwa well is poor. Fluid types defined in the reservoirs on the basis of neutron-density log signatures and resistivity indicate a mixture of water and gas. However, high water saturation (50% - 100%) indicates that the proportion of void spaces occupied by water is high, thus, indicating low hydrocarbon saturation of 2.4%, 17.9%, 19.2% and 39.3%. Generally the results show that hydrocarbon potentiality at Mchungwa well is extremely low because of small net pay thickness and very low hydrocarbon saturation. This could be attributed to the geology of the surrounding area where low hydrocarbon saturation suggest the presence of non-commercial volumes of either migrant gas or gas generated from the interbedded claystone sediments, which are dominant in the observed well.