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SUMMARYWe performed laboratory measurements on fully saturated sand samples in the context of deriving reliable temperature from time-lapse electrical resistivity tomography (ERT). The experiment consisted in monitoring an increase of temperature in sand samples with electrical resistivity measurements. We neglected the effect of surface conductivity since experiments showed two orders of magnitude between surface and fluid conductivities. We show that using simple linear relationship between fluid electrical conductivity and temperature alone does not allow reliable temperature estimates. Indeed, chemical analyses highlight the importance of accounting chemical reactions occurring when temperature changes, including dissolution/precipitation processes. We performed two experiments based on typical in-situ conditions. We first simulated the injection of a less conductive tap water and second, the injection of heated formation water. In the second case, minerals solubility decreases and precipitation occurs, leading to an increase of bulk resistivity. This mechanism competes with dissolution of minerals when tap water is injected, since tap water is not in equilibrium with the medium. In any case, further research is needed to fully understand the mechanisms and to develop a fully integrated law to derive better temperature estimates.

Rwanda hosts million tons of peat deposits and that of western province is of great importance as it close to Kivu Lake. The discovery of methane gas in Kivu Lake has attracted investors in methane gas utilization as source of power supply and Compressed Natural Gas (CNG). Researchers identified Kivu Lake and adjacent area as an area of interest for hydrocarbon exploration. However, organic geochemical prospecting for hydrocarbon and energy content assessment is inadequate for the identified areas. The study aimed at determining the organic geochemistry of peat deposits in southwest, Rwanda. Forty (40) subsurface peat samples (1 to 10 m depth) were collected, air-dried and pulverized and screened. Five (5) samples with high organic matter content were subjected to biomarkers analysis using GC-GCMS. The n-alkanes distribution comprised mainly n-C11 to n-C 37. The Pr/Ph ratios (3.3-10.4, the waxiness index (0.09-0.87), CPI (3.6-7.8), OEP (3.5-6.0), C29 steranes (63.0–100.0%), C28 (0.0–28.0%), C27 (0.0–18.0%) and C27/ C29 sterane ratios (0.0-0.28). The ββ/ (ββ + αα) and 20S/ (20S + 20R) are 0.5 and 0.46 respectively. The C30 -moretane/ C30 -hopane ratios ranged from 1.56 to 2.42, while the oleanane index ranged from 0.07 to 0.26. The Ts/ (Ts + Tm) ratios ranged from 0.13 to 1.05. The dominance of C-29 sterols and C29/C27 sterane ratio which ranged from 3.5 to 100 indicating derivation from terrigenous higher plant material. The Pr/Ph ratio (>3) reflect the oxic to sub-oxic environmental condition during peat deposition. The peat deposits in Western Province, Rwanda are very rich in organic matter of mainly terrestrial precursor deposited in dry and cold climate.

The peat deposits in Rwanda are distributed over an area of 50,000 ha and were formed about the end of last glaciations period. However Akanyaru peat is 20,000 years old and contains peat of glacial and postglacial period. The studies show that Rwanda has 155 million tons of dry peat which can generate electrical energy and this deposit is sufficient to meet country's vast energy requirements for 30 years. Hence, it was felt necessary to map prospective locations of peat and their energy potential. The result of the study and assessment of peat to power in Rwanda show that the average in-situ ash content, in-situ moisture content and in-situ bulk density of the collected peat samples are 36 wt%, 70.8 wt% and 1112 kg/m 3 respectively. Their average thickness ranges from 0.9 to 7.8 m. In Finland, peat was used as fuel in 1996 and produced 10% of total installed capacity. Rwanda has the same operational peat power plant in Gishoma: Rusizi District generating 15 MW connected to the national electrical grid. A peat-fuelled power plant is under construction and is expected to generate 80 MW. This plant, once completed, is expected to connect 50% more households into national grid. Thus, this effort along with other projects will increase electrical power from 208 MW to 563 MW in 2024. Peat deposit is expected to generate 500 Megawatt electrical powers for 30 years. Although an effort was done to use peat as fuel, the power plant is still vulnerable to the lack of good quality of dry peat to operate and thus efforts are on to develop suitable technology for exploitation.

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