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Journal Article
Wamalwa RN, WASWA AARONK, Nyamai CM, Mulwa JK, Ambuso WJ. "Evaluation of the factors controlling concentration of non-condensable gases and their possible impact on the performance of geothermal systems: Case study of Olkaria Wells in the Kenyan Rift Valley." International Journal of Geosciences. 2016;7:257-279. Abstract

The Olkaria geothermal field is located in the Kenyan Rift valley, about 120 km from Nairobi. Development of geothermal resources in the Olkaria area, a high temperature field, started in the early 1950s. In the subsequent years numerous expansions have been carried out with additional power plants being installed in Olkaria. These include a binary plant at Olkaria South West (Olkaria III) in 2000, a condensing plant at Olkaria North East (Olkaria II) in 2003, another binary plant at Olkaria North West (Oserian) in 2004 and finally condensing plants in the year 2014 within East production field (EPF) and Olkaria Domes (OD) areas. The total generation from this field is about 730 Mw. The study considered samples from 4 producing wells from 3 fields of the Olkaria geothermal area (OW-44 from the Olkaria East, OW-724A from the Olkaria North East, and OW-914 and OW-915 from the Olkaria Domes field). The chemical data were first analyzed using SOLVEQ. This helped in the determination of the equilibrium state of the system, the reservoir temperatures and the total moles to be run through CHILLER. The run CHILLER considered the processes that have been proven to be occurring in the Olkaria field i.e., boiling and condensing processes, fluid-fluid mixing rocks and titration resulting from water-rock interaction. The effects on gas evolution were evaluated based on the resulting recalculated gas pressures. The results indicate that the gas species are not in equilibrium with the mineral assemblages. The CHILLER evaluation shows boiling as the major process leading to the evolution of gases. OW-44 had the least gas concentrations, arising from the considered reservoir processes due to degassing, and near surface boiling, besides the removal of NH3 , H2 and H2S are through the reaction with steam condensate. The gas breakout is most likely in OW-914 and least in OW-44. The study proposes different reservoir management strategies for the different parts of the Olkaria geothermal field. That is by increasing hot reinjection in the eastern sector around well OW-44. The reservoir around OW-914 is to be managed by operating the wells at a minimum flow rate (or even to close them) or the use of chemical inhibitors to prevent calcite scaling.

Mulwa JK. Earth Processes Lecture series for Bachelor of Science (Geology) and Bachelor of Science (ODL). Nairobi: Nairobi University Press; 2003. Abstract

The Earth Processes course unit is one of the three core courses in Geology. The other two core courses are SGL 101 – Materials of the Earth and SGL 103 - Introduction to Paleontology. Geology is a science of the study of the earth with reference to its evolution, composition and processes that have prevailed from the time of its evolution to the present time.

The earth is a dynamic body that has undergone various changes. These changes are both of internal and external origin. The internal processes are referred to as diastrophism and they tend to elevate the earth’s surface. They are counterbalanced by the external processes that wear down the land surface. The constant interaction between these two processes determines the configuration of the earth’s surface. The external processes are as a result of solar energy and gravitational forces whereas the internal processes are as a result of the earth’s internal heat.

Weather pattern, for example, is to a large extent due to the solar energy on the one hand. Along the equator there is a substantial amount of heating because the sun is always overhead and therefore this results in the rising up of hot air. The rising hot air is replaced by cold air from the colder regions. This cyclic process is closely related to ocean waves and currents generated by solar heating. Waves are effective forces for determining the shape of the landscape along shorelines of oceans and seas.

The force of gravity on the other hand is due to mutual attraction between bodies. The greater the attracting bodies the greater the gravitational force. Because the mass of the earth is greater than any other body on its surface, materials are attracted towards the earth’s center. Rain and snow precipitate due to gravitational attraction of the earth. Water moves towards the oceans because of gravitational force. Glaciers on higher mountains are normally pulled down by the force of gravity.

Internal earth processes are due to heat energy which keeps rocks in the mantle below the earth’s crust in a molten state. This break forth as a volcanic flow during volcanic eruptions. Heat energy is also responsible for large-scale processes such as earthquakes and mountain building, and small scale processes such as geysers, hot springs, steaming ground and hydrothermal processes.

We can therefore conclude that all earth processes are manifestations of energy and these processes are responsible for sculpturing the land surface.

The Earth Processes course unit begins with an overview of the types of energy which contribute to earth processes. These are discussed in Lecture 1. The unit is thereafter subdivided into two parts. Lectures in Part I of the course unit discusses the External Earth processes where else lectures in Part II of the unit discusses the Internal Earth Processes.

The general objective of the Earth processes course unit is to introduce you to the basic concepts of geosciences. More specifically, at the end of this course unit you should be able to:

 describe the internal and external processes which shape the earth;
 explain the present configuration of the earth and attempt to reconstruct its original form;
 explain the natural processes of the earth;
 categorize hazardous and non-hazardous processes of the earth;
 outline the contribution of the earths natural fields in exploration of natural resources;
• propose measures of minimizing hazards due to earth processes.

You are required to have writing materials e.g. books or foolscaps, pens, lead pencils, coloured pencils or crayons, a scientific calculator, a ruler and a mathematical set. Although every effort has been made to provide you with an up-to-date lecture notes, you are expected to do further reading for a better understanding of Geology, Geological concepts and Processes.

Practicals are compulsory in this course unit and a separate practical manual will be availed to you.

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